JP6042875B2 - Glass for magnetic recording medium substrate, glass substrate for magnetic recording medium and use thereof - Google Patents

Description

  The present invention relates to a glass for a magnetic recording medium substrate suitable as a substrate material for a magnetic recording medium such as a hard disk, a glass substrate for a magnetic recording medium using the glass, a magnetic recording medium substrate blank usable for obtaining the substrate, The present invention relates to a magnetic recording medium including the substrate and a magnetic recording apparatus.

  With the progress of information-related infrastructure technologies such as the Internet, the demand for information recording media such as magnetic disks and optical disks is growing rapidly. The main components of a magnetic storage device such as a computer are a magnetic recording medium and a magnetic head for magnetic recording and reproduction. As a magnetic recording medium, a flexible disk and a hard disk are known. Among these, as substrate materials for hard disks (magnetic disks), there are, for example, aluminum substrates, glass substrates, ceramic substrates, carbon substrates and the like. Practically, depending on the size and application, mainly aluminum substrates and glass are used. A substrate is used. In hard disk drives for laptop computers, in addition to impact resistance, the demands for improving the surface smoothness of disk substrates are becoming stricter as the recording density of magnetic recording media becomes higher. There is a limit to dealing with an inferior aluminum substrate. Therefore, the development of glass substrates is currently mainstream (see, for example, Patent Documents 1 to 10).

  In recent years, magnetic materials with high magnetic anisotropy energy (high Ku magnetic materials) such as Fe—Pt and Co—Pt are used for the purpose of achieving higher density recording of magnetic recording media. (For example, refer to Patent Document 11). In order to increase the recording density, it is necessary to reduce the particle size of the magnetic particles. On the other hand, when the particle size is decreased, there is a problem of deterioration of magnetic characteristics due to thermal fluctuation. High Ku magnetic materials are less susceptible to thermal fluctuations and are expected to contribute to high density recording.

JP-T 9-507206 JP 2007-51064 A JP 2001-294441 A JP 2001-134925 A JP 2001-348246 A JP 2001-58843 A JP 2006-327935 A JP-A-2005-272212 JP 2004-43295 A JP 2005-314159 A JP 2004-362746 A

  However, the high Ku magnetic material needs to obtain a specific crystal orientation state in order to realize a high Ku. Therefore, it is necessary to perform film formation at a high temperature or heat treatment at a high temperature after film formation. Therefore, in order to form a magnetic recording layer made of these high Ku magnetic materials, the glass substrate is required to have high heat resistance that can withstand the above-described high temperature processing, that is, high glass transition temperature.

In addition, in order to increase the reliability of HDDs (hard disk drives), glass substrates for magnetic recording media that require extremely high recording density, such as energy-assisted magnetic recording media that are being studied in recent years. Excellent impact resistance is required.
As a background to this, firstly, the flying height of the magnetic head (the gap between the magnetic head and the surface of the magnetic recording medium) is significantly reduced (low flying height). By doing so, since the distance between the magnetic head and the magnetic layer of the medium becomes closer, it becomes possible to pick up signals of smaller magnetic particles, so that high recording density can be achieved. In recent years, a function called DFH (Dynamic Flying Height) has been mounted on a magnetic head in order to achieve a lower flying height than ever. This is a function of providing a heating unit such as a very small heater near the recording / reproducing element part of the magnetic head and projecting only the periphery of the element part toward the medium surface. In the future, this function is expected to make the gap between the element portion of the magnetic head and the medium surface extremely small, less than 2 nm. For this reason, the magnetic head easily collides with the medium surface even with a slight impact.
Secondly, there is an increase in the rotation speed of the medium. Thereby, first, the impact at the time of collision with the magnetic head is increased. It should be noted that since the deflection of the substrate becomes large at the outer peripheral portion, it can easily collide with the magnetic head even with a slight impact. Further, in the inner peripheral portion, due to the influence of tightening (fixing) of the medium by the spindle and the clamp, there is a high possibility that the substrate will crack when an external impact is applied to the HDD itself.

Thus, a glass substrate having both high heat resistance and excellent impact resistance is required for a magnetic recording medium compatible with high recording density.
The present invention provides a glass for a magnetic recording medium substrate and a glass substrate for a magnetic recording medium that are suitable for the material of the glass substrate for a magnetic recording medium having both high heat resistance and excellent impact resistance as described above. Another object of the present invention is to provide a magnetic recording medium including the substrate and a magnetic recording apparatus on which the magnetic recording medium is mounted.

One aspect of the present invention includes, as an essential component, one or more alkaline earth metal oxides selected from the group consisting of SiO ₂ , Li ₂ O, Na ₂ O, and MgO, CaO, SrO, and BaO,
The molar ratio of the content of CaO to the total content of MgO, CaO, SrO and BaO (CaO / (MgO + CaO + SrO + BaO)) is 0.20 or less,
Glass transition temperature of 650 ° C. or higher,
Glass for magnetic recording medium substrate,
About.

  The further aspect of this invention is related with the glass substrate for magnetic recording media which consists of chemically strengthened glass obtained by chemically strengthening the glass for magnetic recording medium substrates mentioned above.

In a further aspect of the present invention, the glass transition temperature is 650 ° C. or higher, and
In the stress profile in a virtual cross section perpendicular to the two main surfaces obtained by the Babinet method, the tensile stress distribution is a convex shape, but the convex shape is a magnetic recording made of chemically strengthened glass that does not include a concave portion recessed toward the compression stress Glass substrate for medium,
About.

In a further aspect of the present invention, the glass transition temperature is 650 ° C. or higher, and
The average value Tav of the tensile stress obtained by the Babinet method and the maximum value Tmax of the tensile stress are expressed by the following formula (1):
Tav / Tmax ≧ 0.5
A glass substrate for a magnetic recording medium comprising a chemically strengthened glass satisfying
About.

A further aspect of the present invention includes, as an essential component, one or more alkaline earth metal oxides selected from the group consisting of SiO ₂ , Li ₂ O, Na ₂ O, and MgO, CaO, SrO, and BaO,
The molar ratio of the content of CaO to the total content of MgO, CaO, SrO and BaO (CaO / (MgO + CaO + SrO + BaO)) is 0.20 or less,
Glass transition temperature of 650 ° C. or higher,
A glass substrate blank for a magnetic recording medium,
About.

A further aspect of the present invention includes, as an essential component, one or more alkaline earth metal oxides selected from the group consisting of SiO ₂ , Li ₂ O, Na ₂ O, and MgO, CaO, SrO, and BaO,
The molar ratio of the content of CaO to the total content of MgO, CaO, SrO and BaO (CaO / (MgO + CaO + SrO + BaO)) is 0.20 or less,
Glass transition temperature of 650 ° C. or higher,
Formulating the glass raw material so that a glass is obtained,
Melting the prepared glass raw material to obtain a molten glass; and
Producing a substrate blank made of glass by press-molding the obtained molten glass;
A method for producing a glass substrate blank for a magnetic recording medium, comprising:
About.

A further aspect of the present invention provides a method for producing a glass substrate for a magnetic recording medium, comprising processing the glass substrate blank for a magnetic recording medium described above,
About.

A further aspect of the present invention is to produce a glass substrate blank for a magnetic recording medium by the method described above, and
Processing the substrate blank;
A method for producing a glass substrate for a magnetic recording medium, comprising:
About.

According to a further aspect of the present invention, there is provided a magnetic recording medium having a magnetic recording layer on the above-described glass substrate for a magnetic recording medium,
About.

In a further aspect of the present invention, a magnetic material mainly composed of an alloy of Fe and / or Co and Pt is formed on the main surface of the glass substrate for a magnetic recording medium, and then an annealing treatment is performed. A method of manufacturing a magnetic recording medium comprising forming a magnetic recording layer by
About.

According to a further aspect of the present invention, there is provided a heat-assisted magnetic recording head having at least a heat source for heating a main surface of a magnetic recording medium, a recording element portion, and a reproducing element portion, and energy having the magnetic recording medium described above. Assisted magnetic recording type magnetic recording device,
About.

ADVANTAGE OF THE INVENTION According to this invention, the glass for magnetic recording media substrates suitable for the material of the magnetic recording media glass substrate which has high heat resistance and the outstanding impact resistance, and the glass substrate for magnetic recording media can be provided.
In addition, according to the present invention, it is possible to provide a magnetic recording medium provided with the substrate and a magnetic recording apparatus on which the magnetic recording medium is mounted.

It is a schematic diagram of the stress profile in a chemically strengthened glass substrate. It is a schematic diagram of the stress profile in a chemically strengthened glass substrate. It is explanatory drawing of Formula (1). It is explanatory drawing of Formula (1). It is a graph which shows the influence of molar ratio CaO / (MgO + CaO + SrO + BaO)) to the fracture toughness value after chemical strengthening.

[Glass for magnetic recording medium substrate]
The glass for a magnetic recording medium substrate of the present invention includes, as an essential component, one or more alkaline earth metal oxides selected from the group consisting of SiO ₂ , Li ₂ O, Na ₂ O, and MgO, CaO, SrO, and BaO. The molar ratio of the content of CaO to the total content of MgO, CaO, SrO and BaO (CaO / (MgO + CaO + SrO + BaO)) is 0.20 or less, and the glass transition temperature is 650 ° C. or more.

  The glass for a magnetic recording medium substrate of the present invention is an oxide glass, and the glass composition is displayed on an oxide basis. The oxide-based glass composition is a glass composition obtained by converting all glass raw materials to be decomposed during melting and existing as oxides in the glass. The glass is preferably amorphous (amorphous) glass because it does not require a heat treatment step for crystallization and has excellent workability.

The glass for magnetic recording media of the present invention is suitable for chemical strengthening. In the present invention, chemical strengthening means low temperature type chemical strengthening.
In the present invention, the “main surface” means a surface having the largest area among the surfaces of the glass substrate or the glass. In the case of a disk-shaped glass substrate, a pair of surfaces facing the front and back of the circular shape of the disk (excluding the center hole when there is a center hole) corresponds to the main surface.

  Hereinafter, unless otherwise specified, the content of glass components and the total content are expressed in mol%, and the content ratio of glass components is expressed in molar ratio.

SiO ₂ is a glass network-forming component and has an effect of improving glass stability, chemical durability, particularly acid resistance. Ingredients that reduce the thermal diffusion of the substrate and increase the heating efficiency when heating the substrate by radiation to heat-treat the film formed by the above-mentioned step or the step of forming a film such as a magnetic recording layer on a glass substrate But there is. SiO ₂ in the magnetic recording medium glass substrate of the present invention is an essential component, from the top to obtain the above effects by the introduction of SiO _2, the content of SiO ₂ preferably set to 55%, and 57% or more More preferably, it is more preferably 60% or more, still more preferably 63% or more. On the other hand, when the content of SiO ₂ is excessive, SiO ₂ is not completely melted and undissolved material is generated in the glass, or the viscosity of the glass at the time of clarification becomes too high, and there is a tendency that the bubble breakage becomes insufficient. Therefore, the content of SiO ₂ is preferably 78% or less, more preferably 75% or less, further preferably 73% or less, and even more preferably 69% or less.

Li ₂ O has an effect of improving the meltability of glass, improving the homogeneity of glass, and increasing the thermal expansion coefficient, and is an essential component that enables chemical strengthening. Further, as will be described later, by coexisting with Na ₂ O as a glass component, the stress distribution formed by chemical strengthening can be moderated, and there is an effect of preventing delayed fracture of chemically strengthened glass described later. However, if the Li ₂ O content is excessive, the glass transition temperature decreases or the chemical durability tends to deteriorate. Therefore, the Li ₂ O content should be more than 0% and not more than 5%. Is preferred. A more preferable upper limit of the content of Li ₂ O is 4%, a further preferable upper limit is 3.5%, and a more preferable upper limit is 3%. A preferable lower limit of the content of Li ₂ O is 0.1%, a more preferable lower limit is 0.3%, and a further preferable lower limit is 0.5%.

Na ₂ O has the effect of improving the meltability of glass, improving the homogeneity of glass, and increasing the thermal expansion coefficient, and is an essential component that enables chemical strengthening. However, when the content of Na ₂ O is excessive, the glass transition temperature is lowered or the chemical durability tends to deteriorate. Therefore, the content of Na ₂ O is preferably 2 to 15%. The more preferable upper limit of the Na ₂ O content is 14%, the more preferable upper limit is 12%, and the more preferable upper limit is 10%. The more preferable lower limit of the Na ₂ O content is 3%, and the more preferable lower limit is 4%. A more preferred lower limit is 5%.

When a glass containing Li ₂ O and Na ₂ O is immersed in a mixed molten salt of sodium salt and potassium salt for chemical strengthening, Li ⁺ ions in the glass and Na ⁺ ions in the molten salt are ion-exchanged, Further, Na ⁺ ions in the glass and K ⁺ ions in the molten salt are ion-exchanged to form a compressive stress layer near the surface and a tensile stress layer inside the glass.
The glass for magnetic recording medium substrate of the present invention has a glass transition temperature as high as 650 ° C. or more, has excellent heat resistance, and is used as a magnetic recording medium substrate material for forming a magnetic recording layer made of a high Ku magnetic material. Is preferred. In high temperature processing of magnetic materials, the glass substrate is exposed to high temperatures. However, if a glass material having a high glass transition temperature is used as described above, the flatness of the substrate is not impaired. From the viewpoint of providing a substrate material having high heat resistance, the preferred lower limit of the glass transition temperature in the present invention is 655 ° C., the more preferred lower limit is 660 ° C., the still more preferred lower limit is 665 ° C., and the more preferred lower limit is 670 ° C., even more preferred. The lower limit is 675 ° C. However, when the glass transition temperature is excessively increased, the chemical strengthening treatment temperature is increased, and thermal decomposition of the molten salt occurs during chemical strengthening, and the glass surface is eroded. Therefore, the upper limit of the glass transition temperature is preferably 740 ° C. . Note that the glass transition temperature is almost constant before and after chemical strengthening.
Since the diffusion rate of alkali metal ions in the glass increases as the ion radius decreases, the Na ⁺ ions in the molten salt reach the deeper layer from the glass surface to form a deep compressive stress layer, and K ⁺ in the molten salt. The ions do not reach as deep as Na ⁺ ions, and the compressive stress layer is formed in a shallow portion from the surface. The stress distribution in the depth direction of the glass chemically strengthened with the mixed salt is a combination of the stress distribution formed by ion exchange of Na ⁺ and Li ^{+ and} the stress distribution formed by ion exchange of K ⁺ and Na ^+. become. Therefore, the stress distribution in the depth direction changes slowly, and as shown in the schematic diagram of FIG. 1, the tensile stress distribution is convex in the stress profile in the virtual cross section perpendicular to the two main surfaces measured by the Babinet method. It becomes. This convex shape does not include a concave portion that is recessed toward the compressive stress as shown in FIG. In addition, a relatively deep compressive stress layer is formed. In FIG. 1, the left side of the center L line is a compressive stress region, and the right side is a tensile stress region.
Even if a crack on the glass surface grows and reaches the tensile stress layer, the chemically strengthened glass having the above stress distribution does not immediately destroy the glass.
On the other hand, when chemically strengthening a glass containing Na ₂ O and not containing Li ₂ O, the glass is immersed in potassium molten salt and exchanged between Na ⁺ ions in the glass and K ions in the molten salt. A compressive stress layer is formed near the surface. Since K ⁺ ions have a lower diffusion rate than Na ⁺ and Li ^+, they do not reach the glass deep layer, the compressive stress layer is shallow, and the stress distribution in the depth direction changes sharply, as shown in FIG. In addition, in the stress profile in the virtual cross section perpendicular to the two main surfaces measured by the Babinet method, it becomes maximum at the locations near the main surface side from the central portion between the main surfaces. That is, there are two positions where the tensile stress is maximized. Such a maximum is called uphill. In such a glass, if a crack on the glass surface grows and reaches the tensile stress layer, the crack tip reaches the maximum region of the tensile stress. cause.
Since the glass for a magnetic recording medium substrate of the present invention contains Li ₂ O and Na ₂ O as glass components, delayed fracture can be prevented by chemically strengthening with a mixed salt of Na ⁺ and K ⁺ . From the viewpoint of more effectively preventing the occurrence of delayed fracture, the Li ₂ O content is preferably 0.1 mol% or more.

  The glass for magnetic recording media of the present invention contains at least one alkaline earth metal oxide MgO, CaO, SrO, BaO. These alkaline earth metal oxides have the effect of improving the meltability of glass and the effect of increasing the thermal expansion coefficient.

By the way, when chemically strengthening a glass having a high glass transition temperature of 650 ° C. or higher, the strengthening treatment temperature also becomes high. In the case of chemically strengthening a glass having a high glass transition temperature, the reduction in ion exchange efficiency, which has not been a problem with conventional glasses having a relatively low glass transition temperature, becomes significant.
As a result of studying this point, the present inventors have obtained the following knowledge.
Table 1 shows the ionic radii of poling alkali metal ions Li ⁺ , Na ⁺ , K ⁺ , alkaline earth metal ions Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , and Ba ²⁺ .

As is clear from Table 1, the ionic radii of Li ⁺ and Mg ²⁺ , Na ⁺ and Ca ²⁺ , K ⁺ and Sr ²⁺ are close to each other. As the tempering treatment temperature is increased, in addition to ion exchange between alkali metal ions in glass and molten salt, ion exchange between alkaline earth metal ions in glass and alkali metal ions in molten salt occurs. Become. In particular, the ion exchange rate between alkali metal ions and alkaline earth metal ions having a close ion radius value is considered to increase.
When a glass containing CaO is chemically strengthened at a high temperature using a mixed molten salt of sodium salt and potassium salt, in parallel with the reaction of Na ⁺ (glass) ⇔ K ⁺ (molten salt), Ca ²⁺ (glass) ⇔ Na ⁺ (Molten salt) occurs and the exchange of alkali metal ions is considered to be hindered.
Mg ²⁺ in the glass, ion exchange that unless a lithium molten salt Mg ²⁺ (glass) ⇔Li ⁺ (molten salt) does not occur, Sr ²⁺ in the glass, ionic radius is larger diffusion rate Since it is slow, it is difficult to exchange with K ⁺ in the molten salt.
Therefore, in the present invention, the mechanical strength considered to be caused by the decrease in ion exchange efficiency peculiar to the chemical strengthening of high heat-resistant glass by limiting the content of CaO which is considered to inhibit ion exchange between alkali metal ions. To solve the decline. That is, by reducing the molar ratio of the CaO content to the total content of MgO, CaO, SrO and BaO (CaO / (MgO + CaO + SrO + BaO)) of 0.20 or less, the above-described decrease in mechanical strength was solved. From the viewpoint of maintaining ion exchange efficiency and maintaining mechanical strength, the upper limit of the molar ratio (CaO / (MgO + CaO + SrO + BaO)) is preferably 0.18, more preferably 0.16, and even more preferably 0.15.

MgO, CaO, SrO, BaO has the function of improving the rigidity of the glass and increasing the thermal expansion coefficient, and also functions to improve the meltability of the glass. However, when it is introduced excessively, the chemical durability tends to decrease. Indicates.
Therefore, the total content of MgO, CaO, SrO and BaO is preferably 10 to 25%. A more preferable upper limit of the total content of MgO, CaO, SrO and BaO is 24%, a further preferable upper limit is 22%, and a more preferable upper limit is 20%. A more preferable lower limit of the total content of MgO, CaO, SrO and BaO Is 11%, a more preferred lower limit is 13%, and a more preferred lower limit is 15%.

  MgO is a component excellent in the effect of increasing the Young's modulus and specific elastic modulus without increasing the specific gravity of glass, and does not inhibit ion exchange between alkali metal ions during chemical strengthening like CaO. Therefore, glass containing MgO is preferred. A preferred lower limit for the MgO content is 8%, a more preferred lower limit is 12%, and a still more preferred lower limit is 15%. On the other hand, the preferable upper limit of the MgO content is 25%, the more preferable upper limit is 23%, and the more preferable upper limit is 20%. The preferable range of the content of MgO can also be specified in relation to the total content of MgO, CaO, SrO, and BaO. Among MgO, CaO, SrO and BaO, MgO has a function of increasing rigidity while suppressing an increase in specific gravity, and does not inhibit ion exchange between alkali metal ions, so the total content of MgO, CaO, SrO and BaO It is preferable that the molar ratio of MgO content to MgO (MgO / (MgO + CaO + SrO + BaO)) is in the range of 0.5 to 1.0. The more preferable range of the molar ratio (MgO / (MgO + CaO + SrO + BaO)) is 0.6 to 1.0, the more preferable range is 0.7 to 1.0, the still more preferable range is 0.8 to 1.0, and the particularly preferable range is 1.0.

CaO is a component that has a function of increasing the expansion coefficient. However, since CaO is considered to have an effect of inhibiting ion exchange between alkali metal ions as described above, its content may be set to 0 to 5%. Preferably, 0 to 4% is more preferable, and 0 to 3% is more preferable. CaO may not be contained. CaO inhibits ion exchange between alkali metal ions to reduce the efficiency of chemical strengthening, whereas Na ₂ O is excellent in the function of increasing the mechanical strength of glass by chemical strengthening, and therefore excellent in chemical strengthening. From the standpoint of achieving mechanical strength, the molar ratio of the CaO content to the Na ₂ O content (CaO / Na ₂ O) is preferably in the range of 0 to 1.5, preferably in the range of 0 to 1. More preferably, it is more preferably in the range of 0 to 0.5, and even more preferably 0.

  SrO has an effect of increasing the specific gravity, and is an expensive component compared with MgO and CaO. Therefore, the content of SrO is preferably 0 to 8%, more preferably 0 to 7%. It is more preferably 0 to 5%, still more preferably 0 to 3%, still more preferably 0 to 1%, and still more preferably 0 to 0.5%. SrO may not be contained.

  BaO increases the specific gravity, lowers the Young's modulus, and lowers the chemical durability. Therefore, the content of BaO is preferably 0 to 8%, more preferably 0 to 7%. It is preferably 0 to 5%, more preferably 0 to 3%, still more preferably 0 to 1%, still more preferably 0 to 0.5%. In addition, it is not necessary to contain BaO.

  As described above, SrO is an expensive component among MgO, CaO, SrO, and BaO. Therefore, when the content of SrO is suppressed, it is a high heat-resistant glass that provides excellent chemical strengthening efficiency. Can also be specified by the molar ratio (CaO / (MgO + CaO + BaO)). From the above viewpoint, a preferable range of the molar ratio (CaO / (MgO + CaO + BaO)) is 0 to 0.20, a more preferable range is 0 to 0.18, a further preferable range is 0 to 0.16, and a more preferable range is 0 to 0. .15.

The glass for a magnetic recording medium substrate of the present invention can contain K ₂ O as an optional component, but when the content of K ₂ O increases with respect to the content of Na ₂ O, mixed melting of sodium salt and potassium salt since the ion-exchange efficiency by salt decreases, it is preferable that the molar ratio of K ₂ O content for the Na ₂ O content of the _{(K 2 O / Na 2 O} ) and 1.0 or less. A more preferable range of the molar ratio (K ₂ O / Na ₂ O) is 0.7 or less, a further preferable range is 0.3 or less, and a more preferable range is 0.1 or less, and the molar ratio may be 0. .

In order to increase the recording density, it is necessary to reduce the distance between the magnetic head and the surface of the magnetic recording medium and increase the writing / reading resolution. Therefore, in recent years, the flying height of the head has been reduced (reducing the spacing between the magnetic head and the surface of the magnetic recording medium), and as a result, the presence of slight protrusions on the surface of the magnetic recording medium has become unacceptable. ing. This is because in a recording / reproducing system with a low flying height, even a minute protrusion collides with the head and causes damage to the head element. On the other hand, BaO generates BaCO ₃ that becomes a deposit on the surface of the glass substrate by reaction with carbon dioxide in the atmosphere. In addition, BaO is a component that causes the surface of the glass to be altered (called burn) and may form microprotrusions on the substrate surface. Therefore, the content of BaO is preferably suppressed to the above range, and a glass not containing BaO, that is, a Ba-free glass is preferable. The Ba-free is preferable from the viewpoint of reducing the burden on the environment.

  In addition, in order to obtain a high glass transition temperature, from the viewpoint of mixed alkaline earth effect, alkaline earth metal oxides should not be added in plural, but only a single component of alkaline earth oxide should be added. When a plurality of types are added, the ratio of the most alkaline earth oxide is 70% or more, more preferably 80% or more, still more preferably 90% or more, particularly preferably the total amount of the alkaline earth metal oxide. It can be selected to be 95% or more.

Further, in order to improve heat resistance while maintaining the efficiency of chemical strengthening, the molar ratio of the total content of Li ₂ O, Na ₂ O and K ₂ O to the total content of MgO, CaO, SrO and BaO (( Li ₂ O + Na ₂ O + K ₂ O) / (MgO + CaO + SrO + BaO)) is preferably 2.0 or less, more preferably 1.7 or less, further preferably 1.5 or less, and 1.3 or less More preferably, it is more preferably 1.0 or less.

Al ₂ O ₃ is an optional component having an effect of improving rigidity and heat resistance and an effect of improving ion exchange efficiency. In order to obtain the effect, the content of Al ₂ O ₃ is preferably 1% or more, more preferably 2% or more, and further preferably 4% or more. However, when the content of Al ₂ O ₃ is excessive, the devitrification resistance (stability) and meltability of the glass tend to decrease. Therefore, the content of Al ₂ O ₃ is preferably 12% or less, It is more preferably 10% or less, and further preferably 7% or less.

Note that maintaining the meltability of the glass and from the top to improve acid resistance of the glass molar ratio of the content of SiO ₂ to the content of SiO ₂ of _{(Al 2 O 3 / SiO 2} ) to 0.178 or less Preferably, it is less than 0.175, more preferably less than 0.170.

K ₂ O has the effect of lowering the fracture toughness value compared to other Li ₂ O and Na ₂ O. Further, since K ₂ O has a function of reducing the efficiency of ion exchange of Na ⁺ (glass) K ⁺ (molten salt), the K ₂ O content is preferably 7% or less, and preferably 5% or less. More preferably, it is 3% or less, more preferably 1% or less, and even more preferably 0.5% or less. Furthermore, it is not necessary to contain K ₂ O.

ZrO ₂ , TiO ₂ , Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , and HfO ₂ are components that enhance rigidity and heat resistance, so at least one kind is introduced. Although it is preferable, introduction of an excessive amount reduces the meltability and thermal expansion characteristics of the glass. Therefore, the total content of ZrO ₂ , TiO ₂ , Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ and HfO ₂ is preferably 0 to 10%.
From the viewpoint of obtaining the effect of introducing the oxide, the total content of ZrO ₂ , TiO ₂ , Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ and HfO ₂ is preferable. The lower limit is 0.1%, the more preferable lower limit is 0.3%, and the more preferable lower limit is 0.5%. From the standpoint of maintaining the meltability and thermal expansion coefficient, the total content of ZrO ₂ , TiO ₂ , Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ and HfO ₂ The preferred upper limit is 8%, the more preferred upper limit is 6%, and the still more preferred upper limit is 4%.

Although ZrO ₂ is an optional component, it has a great effect of increasing the glass transition temperature and improving heat resistance, chemical durability, particularly improving alkali resistance, and increasing the Young's modulus and increasing rigidity. It also has the effect of improving ion exchange efficiency. Therefore, the ZrO ₂ content is preferably 0.1% or more, more preferably 0.3% or more, and further preferably 0.5% or more. If ZrO ₂ is introduced excessively, the meltability of the glass is lowered, the raw material remains undissolved, and it may be difficult to produce homogeneous glass. Therefore, the ZrO ₂ content is preferably 6% or less. It is more preferably 4% or less, and further preferably 3% or less.

The preferred range of the content of ZrO _{2 is} the total content of ZrO ₂ , TiO ₂ , Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ and HfO _2. Can also be specified. Since ZrO ₂ has the effect of increasing the ion exchange efficiency, the total of ZrO ₂ , TiO ₂ , Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ and HfO ₂ The molar ratio of the ZrO ₂ content to the content (ZrO ₂ / (ZrO ₂ + TiO ₂ + Y ₂ O ₃ + La ₂ O ₃ + Gd ₂ O ₃ + Nb ₂ O ₅ + Ta ₂ O ₅ + HfO ₂ )) is 0.3 to 1 It is preferable to set it in the range of 0.0. A more preferable range of the molar ratio (ZrO ₂ / (ZrO ₂ + TiO ₂ + Y ₂ O ₃ + La ₂ O ₃ + Gd ₂ O ₃ + Nb ₂ O ₅ + Ta ₂ O ₅ + HfO ₂ )) is 0.5 to 1.0, more preferably. The range is 0.7 to 1.0, particularly preferably 1.0.

From the viewpoint of improving the chemical durability of the glass, SiO ₂ , ZrO ₂ , TiO ₂ , Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Yb ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ And the total content of HfO ₂ is preferably 66% or more, more preferably 66.5% or more, and further preferably 67.0% or more. The upper limit of the total content of SiO ₂ , ZrO ₂ , TiO ₂ , Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Yb ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ and HfO ₂ is It is determined by the contents of Al ₂ O ₃ , alkali metal oxide, alkaline earth metal oxide, and other components.
When the magnetic recording medium glass substrate of the present invention contains ZrO _2, from top to improve the chemical durability of the glass, it is preferable that the total content of SiO ₂ and ZrO ₂ to 66% or more. A more preferred lower limit of the total content of SiO ₂ and ZrO ₂ is 66.5%, and a more preferred lower limit is 67.0%. The upper limit of the total content of SiO ₂ and ZrO ₂ is determined by the content of Al ₂ O ₃ , alkali metal oxide, alkaline earth metal oxide, and other components.

TiO _{2 is, ZrO 2, Y 2 O 3} , La 2 O 3, Gd 2 O 3, Nb 2 O 5, Ta 2 O 5, compared to the HfO _2, large work to suppress an increase in the specific gravity, Young's modulus, It is a component having the effect of increasing the specific modulus. However, when the glass is immersed in water due to excessive introduction, a reaction product with water adheres to the glass surface, and the smoothness of the glass surface may be impaired. Therefore, the content of TiO ₂ is 0 to 5%. The content is preferably 0 to 4%, more preferably 0 to 3%, and particularly preferably TiO ₂ is not contained.

La ₂ O ₃ , Gd ₂ O ₃ , Nb ₂ O ₅ , Y ₂ O ₃ , Ta ₂ O ₅ , and HfO ₂ are components that increase the specific gravity, so the content of each component is 0 to 7%. Preferably, 0 to 6%, more preferably 0 to 5%, and each component may not be contained.

B ₂ O ₃ is a component that improves the brittleness of the glass substrate and improves the meltability of the glass. However, since the heat resistance decreases due to the introduction of an excessive amount, the amount of introduction is set to 0 to 0 in each of the glasses. 3 mol% is preferable, 0 to 2 mol% is more preferable, 0 mol% or more and less than 1 mol% is further preferable, 0 to 0.5 mol% is more preferable, It is still more preferable to set it as 0-0.3 mol%, it is still more preferable to set it as 0-0.1 mol%, and it is not necessary to introduce | transduce substantially.

  ZnO works to improve the meltability, moldability and glass stability of glass, increase rigidity, and increase the coefficient of thermal expansion. However, when introduced excessively, the glass transition temperature is greatly reduced and the heat resistance is remarkably increased. In order to decrease or chemical durability deteriorates, it is preferable that the content of ZnO is 0 to 10%. A more preferable range of the content of ZnO is 0 to 7%, and a more preferable range is 0 to 5%, and ZnO may not be included.

  In consideration of the influence on the environment, it is preferable not to contain Pb, As, Cd, U, Th or the like.

(Additive)
In addition to the glass component, a small amount of a halide such as Sn oxide, Ce oxide, Sb ₂ O ₃ , F, or Cl may be added as a clarifier. Among them, it is preferable to use Sn oxide and Ce oxide as the fining agent. This is due to the following reason.
The Sn oxide is excellent in the function of promoting clarification by releasing oxygen gas at a high temperature during glass melting and taking in the fine bubbles contained in the glass to make it easy to float. On the other hand, Ce oxide has an excellent function of eliminating bubbles by incorporating oxygen present as a gas in glass at a low temperature as a glass component. When the size of bubbles (the size of bubbles (cavities) remaining in the solidified glass) is 0.3 mm or less, Sn oxide has a strong function of removing relatively large bubbles and extremely small bubbles. When Ce oxide is added together with Sn oxide, the density of large bubbles of about 50 μm to 0.3 mm is drastically reduced to several tenths. Thus, by allowing Sn oxide and Ce oxide to coexist, the glass refining effect can be enhanced over a wide temperature range from a high temperature range to a low temperature range, so that Sn oxide and Ce oxide can be added. preferable.
When the total amount of Sn oxide and Ce oxide added is 0.02% by mass or more, a sufficient clarification effect can be expected. When a substrate is made using glass containing unmelted material even if it is minute and small, when unmelted material appears on the surface of the glass substrate due to polishing, protrusions are generated on the surface of the glass substrate or unmelted material is missing Becomes a depression, the smoothness of the glass substrate surface is impaired, and it cannot be used as a substrate for a magnetic recording medium. On the other hand, if the total amount of Sn oxide and Ce oxide added is 3.5% by mass or less, it can be sufficiently melted in the glass, so that undissolved substances can be prevented from being mixed.
Sn and Ce serve to generate crystal nuclei when making crystallized glass. Since the glass substrate of the present invention is made of amorphous glass, it is desirable not to precipitate crystals by heating. When the amount of Sn and Ce is excessive, such crystals are likely to precipitate. Therefore, excessive addition of Sn oxide and Ce oxide should be avoided.
From the above viewpoint, it is preferable that the total amount of Sn oxide and Ce oxide added is 0.02 to 3.5% by mass. The preferable range of the total amount of the external addition of the Sn oxide and Ce oxide is 0.1 to 2.5% by mass, the more preferable range is 0.1 to 1.5% by mass, and the more preferable range is 0.5 to 1.5% by mass.
As the Sn oxide, it is preferable to use SnO ₂ from the viewpoint of effectively releasing oxygen gas at a high temperature during glass melting. By adjusting the addition amount of Sn oxide and Ce oxide, sufficient clarity can be obtained without adding Sb ₂ O ₃ .
In addition, although sulfate can be added in the range of 0 to 1% by mass as a fining agent, there is a risk that the melted material may be blown out during glass melting, and foreign substances in the glass increase dramatically. If there is concern about spillage, it is preferable not to introduce sulfate. In addition, you may use things other than the said clarifying agent, if the objective of this invention is not impaired and the clarification effect is acquired. However, as described above, addition of As, which has a large environmental load, should be avoided.
Sb ₂ O ₃ may be used alone as a fining agent, may be used in combination with Sn oxide or Ce oxide, or may be used in combination with Sn oxide and Ce oxide.

  Next, various characteristics of the glass or glass substrate according to the present invention will be described.

(Coefficient of thermal expansion)
An HDD (hard disk drive) incorporating a magnetic recording medium has a structure in which the magnetic recording medium itself is rotated by pressing the center portion with a spindle and a clamp of a spindle motor. For this reason, if there is a large difference in the thermal expansion coefficient between the magnetic recording medium substrate and the spindle material constituting the spindle portion, the thermal expansion / contraction of the spindle and the magnetic recording medium substrate Deviation occurs in expansion and contraction, resulting in a phenomenon that the magnetic recording medium is deformed. When such a phenomenon occurs, the head cannot read the written information, which causes a loss of recording / reproduction reliability. Therefore, in order to increase the reliability of the magnetic recording medium, the substrate material is required to be a glass having a thermal expansion coefficient as close as possible to the spindle material (for example, stainless steel). In particular, a magnetic recording medium having a magnetic recording layer made of a high Ku magnetic material has a very high recording density, so that the above-described trouble is likely to occur even if the magnetic recording medium is slightly deformed.
In a preferred embodiment of the glass for a magnetic recording medium substrate of the present invention, the average linear expansion coefficient in the temperature range of 100 to 300 ° C. is 50 × 10 ⁻⁷ / ° C. or higher. By making a substrate using the glass, the reliability of the HDD can be improved. Thus, a substrate material suitable for a magnetic recording medium having a magnetic recording layer made of a high Ku magnetic material can be provided. A more preferable range of the average linear expansion coefficient is 55 × 10 ⁻⁷ / ° C. or more, and a more preferable range is 60 × 10 ⁻⁷ / ° C. or more. The upper limit of the average linear expansion coefficient is, for example, preferably about 120 × 10 ⁻⁷ / ° C., more preferably 100 × 10 ⁻⁷ / ° C., considering the thermal expansion characteristics of the spindle material. The coefficient of thermal expansion becomes a substantially constant value before and after chemical strengthening.
The average linear expansion coefficient in the temperature range of 500 to 600 ° C. is preferably 60 × 10 ⁻⁷ / ° C. or more, and more preferably 70 × 10 ⁻⁷ / ° C. or more. The average linear expansion coefficient in the temperature range of 500 to 600 ° C. is, for example, preferably 100 × 10 ⁻⁷ / ° C. or less, and more preferably 90 × 10 ⁻⁷ / ° C. or less. Annealing treatment is performed when annealing is performed after forming a multilayer film such as a high Ku magnetic material by forming a substrate using glass having an average linear expansion coefficient in the temperature range of 500 to 600 ° C. within the above range. It is possible to reliably prevent the multilayer film from being peeled off from the glass substrate during and after the treatment, and the substrate from dropping from the holding member during the annealing treatment.

(Young's modulus)
In a disk-shaped magnetic recording medium, data is written and read along the rotation direction while rotating the magnetic head around the central axis and moving the magnetic head in the radial direction. In recent years, in order to increase the writing speed and the reading speed, the number of revolutions has been increasing from 5000 rpm to 7200 rpm, and further to 10000 rpm. However, in a disk-shaped magnetic recording medium, depending on the distance from the central axis in advance. Since a position for recording data is assigned, if the disk is deformed while it is rotating, the magnetic head is displaced, making accurate reading difficult. Therefore, in order to cope with the above high-speed rotation, the glass substrate is also required to have high rigidity (Young's modulus) that does not cause large deformation during high-speed rotation. In a preferred embodiment of the glass for a magnetic recording medium substrate of the present invention, since it has a Young's modulus of 75 GPa or more, the substrate is produced using the glass, thereby suppressing substrate deformation during high-speed rotation, and using a high Ku magnetic material. Even in the magnetic recording medium having a high recording density, data can be read and written accurately. A more preferable range of Young's modulus is 78 GPa or more, more preferably 80 GPa or more, and still more preferably 82 GPa or more. The upper limit of the Young's modulus is not particularly limited, but 90 GPa can be considered as a guideline for the upper limit, for example, in order to bring other characteristics into a preferable range. The Young's modulus is almost constant before and after chemical strengthening.

(Specific modulus / specific gravity)
From the viewpoint of suppressing deformation (bending of the substrate) when the magnetic recording medium is rotated at a high speed, glass having a high specific elastic modulus is preferable as the substrate material. Although the specific elastic modulus is almost constant before and after chemical strengthening, the preferable range of the specific elastic modulus in the glass for a magnetic recording medium substrate of the present invention is 25 MNm / kg or more and 27 MNm / kg or more. More preferably, it is more preferably 30 MNm / kg or more. The upper limit is, for example, about 37 MNm / kg, but is not particularly limited. The specific modulus is obtained by dividing the Young's modulus of glass by the density. Here, the density may be considered as an amount obtained by adding a unit of g / cm ³ to the specific gravity of glass. By reducing the specific gravity of the glass, the specific elastic modulus can be increased, and the weight of the substrate can be reduced. By reducing the weight of the substrate, the weight of the magnetic recording medium can be reduced, the power required for rotating the magnetic recording medium can be reduced, and the power consumption of the HDD can be suppressed. The preferred range of the specific gravity of the glass for a magnetic recording medium substrate of the present invention is 2.9 or less, more preferred range is 2.8 or less, and further preferred range is 2.7 or less. The specific gravity is almost constant before and after chemical strengthening.

(Acid and alkali resistance)
When producing a glass substrate for a magnetic recording medium, the glass is processed into a disk shape, and the main surface is processed to be extremely flat and smooth. And after the said process process, the organic substance which is the stain | pollution | contamination adhering to the surface is usually removed by acid cleaning of a glass substrate. Here, if the glass substrate is inferior in acid resistance, surface roughening occurs during the acid cleaning, flatness and smoothness are impaired, and it becomes difficult to use the glass substrate for a magnetic recording medium. In particular, the glass substrate material for a magnetic recording medium having a high recording density, which has a magnetic recording layer made of a high Ku magnetic material that requires high flatness and smoothness on the surface of the glass substrate, has excellent acid resistance. Is desirable.
Further, following the acid cleaning, foreign substances such as abrasives adhered to the surface by alkali cleaning can be removed to obtain a cleaner substrate. From the viewpoint of preventing the flatness and smoothness of the substrate surface from being deteriorated due to surface roughness even during alkali cleaning, glass having excellent alkali resistance is preferred as a material for the glass substrate. High acidity and alkali resistance and high flatness and smoothness of the substrate surface are advantageous from the viewpoint of reducing the flying height of the magnetic head. In the present invention, excellent acid resistance and alkali resistance can be realized by adjusting the glass composition described above, particularly by adjusting the composition advantageous for chemical durability.

(Liquid phase temperature)
When glass is melted and the resulting molten glass is molded, if the molding temperature falls below the liquidus temperature, the glass crystallizes, and a homogeneous glass cannot be produced. For this reason, the glass forming temperature must be equal to or higher than the liquidus temperature. However, if the forming temperature exceeds 1450 ° C., for example, the press forming mold used for press forming molten glass reacts with the high-temperature glass and is damaged. It becomes easy. Similarly, when the molten glass is cast in a mold, the mold is easily damaged. Considering these points, the liquidus temperature of the glass constituting the glass substrate of the present invention is preferably 1450 ° C. or lower. A more preferable range of the liquidus temperature is 1430 ° C. or less, and a more preferable range is 1400 ° C. or less. In the present invention, the liquid phase temperature in the above preferred range can be realized by adjusting the glass composition described above. Although a minimum is not specifically limited, What is necessary is just to consider 800 degreeC or more as a standard.

(Spectral transmittance)
A magnetic recording medium is produced through a process of forming a multilayer film including a magnetic recording layer on a glass substrate. When a multilayer film is formed on a substrate by the single-wafer type film forming method which is currently in the mainstream, for example, a glass substrate is first introduced into a substrate heating region of a film forming apparatus, and a film forming temperature by a sputtering ring or the like The glass substrate is heated to a temperature of After the temperature of the glass substrate is sufficiently raised, the glass substrate is transferred to the first film formation region, and a film corresponding to the lowermost layer of the multilayer film is formed on the glass substrate. Next, the glass substrate is transferred to the second film formation region, and film formation is performed on the lowermost layer. In this way, the glass substrate is sequentially transferred to a subsequent film formation region to form a multilayer film. Since the heating and film formation are performed under a low pressure exhausted by a vacuum pump, the glass substrate must be heated in a non-contact manner. Therefore, heating by radiation is suitable for heating the glass substrate. This film formation needs to be performed before the glass substrate falls below a temperature suitable for film formation. If the time required for forming each layer is too long, the temperature of the heated glass substrate is lowered, and there is a problem that a sufficient glass substrate temperature cannot be obtained in the subsequent film formation region. In order to maintain the temperature at which the glass substrate can be formed over a long period of time, it is conceivable to heat the glass substrate to a higher temperature, but if the heating rate of the glass substrate is low, the heating time must be longer, The time for the glass substrate to stay in the heating area must also be increased. For this reason, the residence time of the glass substrate in each film formation region also becomes long, and a sufficient glass substrate temperature cannot be maintained in the subsequent film formation region. Further, it is difficult to improve the throughput. In particular, when producing a magnetic recording medium having a magnetic recording layer made of a high Ku magnetic material, the heating efficiency by radiation of the glass substrate should be further increased in order to heat the glass substrate to a high temperature within a predetermined time.
The glass may have an absorption peak in a region including a wavelength of 2750 to 3700 nm. Further, by adding an infrared absorber described later or introducing it as a glass component, the absorption of short-wave radiation can be further increased, and absorption can be provided in the wavelength region of wavelength 700 nm to 3700 nm. In order to efficiently heat the glass substrate by radiation, that is, infrared irradiation, it is desirable to use infrared rays having a spectrum maximum in the above wavelength range. In order to increase the heating rate, it is conceivable to match the infrared spectral maximum wavelength with the absorption peak wavelength of the substrate and increase the infrared power. Taking a high-temperature carbon heater as an example of the infrared source, the input of the carbon heater may be increased to increase the infrared power. However, when the radiation from the carbon heater is considered as black body radiation, the heater temperature rises due to an increase in input, so that the maximum wavelength of the infrared spectrum shifts to the short wavelength side and deviates from the above absorption wavelength range of the glass. For this reason, in order to increase the heating rate of the substrate, the power consumption of the heater must be excessive, and problems such as shortening the life of the heater occur.
In view of such a point, by increasing the absorption of the glass in the wavelength region (wavelength 700 to 3700 nm), infrared irradiation is performed in a state where the infrared spectral maximum wavelength and the absorption peak wavelength of the substrate are close to each other. It is desirable not to overload the input. Therefore, in order to increase the infrared irradiation overheating efficiency, the glass substrate has a region where the spectral transmittance converted to a thickness of 2 mm is 50% or less in the wavelength range of 700 to 3700 nm, or over the wavelength range, What has the transmittance | permeability characteristic from which the spectral transmittance converted into thickness 2mm becomes 70% or less is preferable. For example, an oxide of at least one metal selected from iron, copper, cobalt, ytterbium, manganese, neodymium, praseodymium, niobium, cerium, vanadium, chromium, nickel, molybdenum, holmium, and erbium is used as an infrared absorber. Can work. In addition, since moisture or OH groups contained in moisture have strong absorption in the 3 μm band, moisture can also act as an infrared absorber. By introducing an appropriate amount of a component capable of acting as the infrared absorber into the glass composition, the above preferable absorption characteristics can be imparted to the glass substrate. The amount of the oxide that can act as the infrared absorber is preferably 500 ppm to 5%, more preferably 2000 ppm to 5%, and more preferably 2000 ppm to 2% as an oxide. More preferably, the range of 4000 ppm to 2% is even more preferable. In addition, the water content is preferably more than 200 ppm, more preferably 220 ppm or more, on a weight basis in terms of H ₂ O.
When Yb ₂ O ₃ or Nb ₂ O ₅ is introduced as a glass component or Ce oxide is added as a clarifier, infrared absorption by these components can be used for improving the substrate heating efficiency.

(Glass manufacturing method)
The glass for magnetic recording medium substrate of the present invention, for example, weighs and mixes raw materials such as oxide, carbonate, nitrate and hydroxide so that a glass having the above composition is obtained. Is heated and melted in the range of 1400 to 1600 ° C., clarified and stirred to produce a homogeneous molten glass that does not contain bubbles and unmelted material, and is obtained by molding this molten glass. it can. For forming molten glass, a press forming method, a cast method, a float method, an overflow down draw method, or the like can be used. For the reason described later, it is particularly preferable to use a press molding method for molding the molten glass.

(Chemical tempered glass)
The glass for a magnetic recording medium substrate of the present invention is suitable as a glass for chemical strengthening.
Since the chemical adjustment performance is imparted by the above-described composition adjustment, the ion exchange layer can be easily formed on the glass surface by the chemical strengthening treatment, and the ion exchange layer can be formed on a part or all of the surface. is there. The ion exchange layer can be formed by bringing an alkali salt into contact with the substrate surface at a high temperature and exchanging alkali metal ions in the alkali salt with alkali metal ions in the substrate.

  Normal ion exchange is performed by heating alkali nitrate to form a molten salt and immersing the substrate in the molten salt. When alkali metal ions having a large ion radius are introduced instead of alkali metal ions having a small ion radius in the substrate, a compressive stress layer is formed on the substrate surface. Thereby, the fracture toughness of the glass substrate for magnetic recording media can be improved, and its reliability can be enhanced.

The chemical strengthening can be performed by immersing the glass processed in advance as necessary in, for example, a mixed molten salt containing a sodium salt and a potassium salt. It is preferable to use sodium nitrate as the sodium salt and potassium nitrate as the potassium salt. Since the glass for a magnetic recording medium substrate of the present invention contains Li ₂ O as an essential component as described above, ion exchange is preferably performed with Na and K having a larger ion radius than Li.

  The amount of alkali elution from the chemically tempered glass surface can also be reduced by ion exchange. In addition, when chemically strengthening, it is preferable to perform ion exchange in a temperature range in which the alkali molten salt is not thermally decomposed at a temperature higher than the strain point of the glass constituting the substrate and lower than the glass transition temperature. That the substrate has an ion exchange layer is a method of observing and confirming the cross section of the glass (surface cut through the ion exchange layer) by the Babinet method, a method of measuring the concentration distribution of alkali metal ions in the depth direction from the glass surface, etc. Can be confirmed.

  The tempering temperature (temperature of the molten salt) and the tempering time (time during which the glass is immersed in the molten salt) can be adjusted as appropriate. For example, the range of the tempering treatment temperature may be adjusted to 400 to 570 ° C. The range of the tempering treatment time may be adjusted with 0.5 to 10 hours as a target, and it is preferably adjusted with 1 to 6 hours as a target.

  As described above, the glass transition temperature, thermal expansion coefficient, Young's modulus, specific elastic modulus, specific gravity, and spectral transmittance of the glass show almost constant values before and after chemical strengthening. The characteristics of thermal expansion coefficient, Young's modulus, specific elastic modulus, specific gravity, and spectral transmittance are treated as the same value. In addition, amorphous glass maintains an amorphous state after chemical strengthening.

[Glass substrate for magnetic recording media]
A first aspect of the glass substrate for a magnetic recording medium of the present invention (hereinafter referred to as glass substrate I) is a glass substrate obtained by chemically strengthening the glass for a magnetic recording medium substrate of the present invention.
The glass for a magnetic recording medium substrate of the present invention can exhibit the aforementioned stress profile by chemical strengthening, thereby preventing delayed fracture. Accordingly, the glass substrate I is a glass substrate that does not cause delayed fracture and that can have high heat resistance and excellent mechanical strength, and various glass materials obtained by chemically strengthening the glass for magnetic recording medium substrates. The features of can be shown.

The second aspect of the glass substrate for magnetic recording media of the present invention (hereinafter referred to as glass substrate II) has a glass transition temperature of 650 ° C. or higher and a virtual cross section perpendicular to the two main surfaces determined by the Babinet method. In the stress profile, the tensile stress distribution is a convex shape, but the convex shape is a glass substrate made of chemically strengthened glass that does not include a dent portion recessed toward the compressive stress side. The stress profile is as described above, and the occurrence of delayed fracture can be prevented by showing such a stress profile. For example, in the virtual section, when the depth from the main surface is x, the stress value S (x) at the depth x is referred to as a stress profile. The stress profile is usually line symmetric at the center between the two major surfaces. In order to know the stress profile, the glass substrate is broken perpendicularly to the two main surfaces, and the fracture surface is observed by the Babinet method.
As a preferred embodiment of the stress profile of the glass substrate II, the compressive stress value becomes maximum in the vicinity of both main surfaces, the compressive stress value decreases as the depth x increases, and the depth x at which the compressive stress and the tensile stress are balanced. As the depth becomes deeper than ₀ , the compressive stress is changed to the tensile stress, and the tensile stress value gradually increases so that a maximum value can be obtained at or near the center between the two main surfaces. The maximum value may be maintained in a constant region in the depth direction as shown in FIG. With a glass substrate having such a stress profile, even if the depth of cracks generated on the substrate surface is deeper than x _0, it is possible to prevent delayed fracture leading to fracture due to rapid growth of cracks due to tensile stress. it can.

The third aspect of the glass substrate for magnetic recording media of the present invention (hereinafter referred to as glass substrate III) has a glass transition temperature of 650 ° C. or higher and an average tensile stress Tav and tensile stress obtained by the Babinet method. The maximum value Tmax is the following formula (1):
Tav / Tmax ≧ 0.5
It is the glass substrate which consists of chemically strengthened glass which satisfy | fills. Hereinafter, Formula (1) is demonstrated based on FIG. 3 and FIG.
The maximum value Tmax of tensile stress is the maximum value of the tensile stress value. In FIG. 3, the L line, which is the center line between the tensile stress and the compressive stress, is determined such that the areas S ₁ , S ₂ , S ₃ are S ₁ + S ₂ = S ₃ . If the distance from the intersection of a virtual straight line parallel to the main surface on the S ₂ side and a virtual straight line perpendicular to the two main surfaces and passing through Tmax to the main surface on the S ₂ side is DOL, Tav = S ₃ / ( The average value Tav of the tensile stress is calculated as (tsub-2 × DOL).
Glass III satisfies Tav / Tmax ≧ 0.5, preferably Tav / Tmax ≧ 0.7, and more preferably Tav / Tmax ≧ 0.8. The upper limit value of Tav / Tmax is, for example, Tav / Tmax <1.0.
The Tav / Tmax defined by the equation (1) can be used as an index indicating that there is no uphill as shown in FIG. /Tmax<0.5.
On the other hand, since the glass satisfy | filling said Formula (1) does not have an uphill, generation | occurrence | production of a delayed fracture is suppressed.
Note that although the glass substrate is uphill exists as shown in FIG. 2, as shown in FIG. 4, L line area _{S 4, S 5, S 6} , S 7, S 8 _{is, S 4 + S 5 + S} 6 , = S ₇ + S ₈ . Further, Tav is calculated as Tav = (S ₇ + S ₈ −S ₆ ) / (tsub−2 × DOL). In FIG. 2, the tensile stress layer is divided into two layers S ₇ and S ₈ by S ₆ , but when the tensile stress layer is composed of one layer as shown in FIG. 1, as described above, Tav = S ₃ Tav may be calculated by / (tsub-2 × DOL).

Furthermore, since the glass substrates II and III have a glass transition temperature as high as 650 ° C. or higher, the flatness of the substrate is not impaired even if a high Ku magnetic material is formed on the substrate and heat-treated. The same applies to the glass substrate I obtained by chemically strengthening glass having a glass transition temperature of 650 ° C. or higher.
Thus, the glass substrates I, II, and III are suitable for applications that require high reliability and excellent heat resistance, such as a magnetic recording medium substrate that supports high recording density.

A more preferable embodiment as the glass substrate of the present invention is the glass substrate I and the glass substrate II or the glass III, and an even more preferable embodiment is the glass substrate I and the glass substrate II. And a glass substrate which is also a glass substrate III. The glass substrates II and III are preferably chemically strengthened glass substrates.
For example, as a preferred embodiment,
In the stress profile in the virtual cross section perpendicular to the two main surfaces obtained by the Babinet method, the tensile stress distribution is a convex shape, however, the convex shape is a glass substrate made of chemically strengthened glass that does not include a concave portion recessed toward the compressive stress side. I;
The average value Tav of the tensile stress obtained by the Babinet method and the maximum value Tmax of the tensile stress are expressed by the following formula (1):
Tav / Tmax ≧ 0.5
A glass substrate I made of chemically strengthened glass satisfying
In the stress profile in the virtual cross section perpendicular to the two main surfaces obtained by the Babinet method, the tensile stress distribution has a convex shape, however, the convex shape does not include a concave portion recessed toward the compressive stress side, and the average value of the tensile stress Tav and the maximum value Tmax of tensile stress are expressed by the following formula (1):
Tav / Tmax ≧ 0.5
A glass substrate I made of chemically strengthened glass satisfying
And so on.

  According to the glass substrate of the present invention, the amount of alkali elution from the substrate surface can be reduced. Therefore, the glass substrate of the present invention is suitable as a glass substrate for a magnetic recording medium.

  Hereinafter, the common points of the glass substrates I, II, and III will be described.

(Fracture toughness value)
In a preferred embodiment of the glass substrate of the present invention, the fracture toughness value K _1c is 0.8 MPa · m ^1/2 or more, more preferably 1.0 MPa · m ^1/2 or more, more preferably 1.1 MPa · m ^1/2. or, even more preferably 1.2 MPa · m ^1/2 or more, even more preferably 1.3 MPa · m ^1/2 or more, even more preferably 1.4 MPa · m ^1/2 or more, particularly preferably 1.5MPa A glass substrate of m ^1/2 or more, most preferably 1.6 MPa · m ^1/2 or more. As described above, with the increase in recording density of magnetic recording media, the rotational speed of the medium has increased, and the distance between the magnetic head and the medium has been decreasing. A substrate having excellent impact resistance is required in order not to damage the impact substrate hit. Since the substrate has a large fracture toughness value, it is excellent in impact resistance and suitable as a glass substrate for a magnetic recording medium having a high recording density.

The fracture toughness value is measured by the following method.
Using a device MVK-E manufactured by AKASHI, a Vickers indenter is pushed into a plate-like sample with an indentation load P [N], and indentations and cracks are introduced into the sample. When the Young's modulus of the sample is E [GPa], the diagonal length of the indentation is d [m], and the half length of the surface crack is a [m], the fracture toughness value K _1c [Pa · m ^1/2 ] is expressed by the following equation. Is done.
K _1c = [0.026 (EP / π) ^1/2 (d / 2) (a) ⁻² ] / [(πa) ^−1/2 ]
Unless otherwise specified, the fracture toughness value in the present invention means a fracture toughness value measured with a load P of 9.81 N (1000 gf). The fracture toughness value is preferably measured on a smooth surface of glass, for example, a polished surface, in order to accurately measure the indent diagonal length d and the half length a of the surface crack. The fracture toughness value varies depending on the glass composition and also varies depending on the chemical strengthening conditions. Therefore, in order to obtain the glass substrate for magnetic recording medium of the present invention composed of chemically strengthened glass, composition adjustment and chemical strengthening are required. Depending on the processing conditions, the fracture toughness value can be in a desired range.

(Surface condition)
The main surface on which the magnetic recording layer is formed preferably has one or more of the following surface properties (1) to (3).
(1) The arithmetic average Ra of the surface roughness measured at a resolution of 512 × 256 pixels in the range of 1 μm × 1 μm using an atomic force microscope is 0.15 nm or less;
(2) The arithmetic average Ra of the surface roughness measured in the range of 5 μm × 5 μm is 0.12 nm or less;
(3) The arithmetic average Wa of the surface waviness at a wavelength of 100 μm to 950 μm is 0.5 nm or less.
The grain size of the magnetic recording layer formed on the substrate is, for example, less than 10 nm in the perpendicular recording method. Even if the bit size is miniaturized for high recording density, if the surface roughness of the substrate surface is large, the improvement of the magnetic characteristics cannot be expected. On the other hand, if the arithmetic mean Ra of the two types of surface roughness (1) and (2) is in the above range, the magnetic characteristics are improved even if the bit size is reduced for higher recording density. Is possible. Further, by setting the arithmetic mean Wa of the surface waviness (3) in the above range, the flying stability of the magnetic head in the HDD can be improved.
Therefore, the glass substrate for a magnetic recording medium of the present invention preferably satisfies any of (1) to (3), more preferably satisfies (1) and (2), and (1) to (3). It is more preferable to satisfy all of the above.

(Thickness)
For HDDs for notebook computers, magnetic recording media having an outer diameter of 2.5 inches are usually used, and the thickness of the glass substrate used for them is 0.635 mm. In order to increase the rigidity and further improve the impact resistance, it is preferable to increase the plate thickness. Therefore, in the glass substrate for a magnetic recording medium of the present invention, the plate thickness is preferably 0.5 mm or more, and more preferably, for example, a plate thickness of 0.7 mm or more in order to further increase the rigidity of the substrate. More preferably, the plate thickness is 0.8 mm or more.

As described above, the glass substrate for a magnetic recording medium of the present invention can have high heat resistance and high fracture toughness. Therefore, the rotational speed for which high reliability is required is 5000 rpm or more, preferably 7200 rpm or more, more preferably 10,000 rpm. It is suitable for a glass substrate for a magnetic recording medium used in the above magnetic recording apparatus and a glass substrate for a magnetic recording medium used in a magnetic recording apparatus equipped with a DFH (Dynamic Flying Height) head.
Furthermore, it is suitable for a glass substrate for a magnetic recording medium for energy-assisted magnetic recording because of its high and low heat resistance and high reliability.
Moreover, it is effective to improve the acid resistance and alkali resistance of the glass in realizing a substrate having the above surface properties (1) to (3).

[Glass substrate blank for magnetic recording media]
Next, the glass substrate blank for magnetic recording media will be described.
The glass substrate blank for a magnetic recording medium of the present invention contains, as an essential component, one or more alkaline earth metal oxides selected from the group consisting of SiO ₂ , Li ₂ O, Na ₂ O, and MgO, CaO, SrO, and BaO. The molar ratio of the content of CaO to the total content of MgO, CaO, SrO and BaO (CaO / (MgO + CaO + SrO + BaO)) is 0.20 or less, and the glass transition temperature is 650 ° C. or more.
Here, the glass substrate blank for a magnetic recording medium (hereinafter referred to as substrate blank) means a glass base material for a substrate before being processed into a glass substrate for a magnetic recording medium. The composition and characteristics of the glass constituting the substrate blank, and the preferred range of the composition and characteristics are as described above.
The substrate blank of the present invention preferably has a disk shape since the glass substrate for magnetic recording medium has a disk shape.

In order to obtain the glass, the substrate blank is prepared by melting the glass raw material into a molten glass, and forming the molten glass into a plate shape by any one of the press molding method, the down draw method, and the float method. And it can produce by processing the obtained plate-shaped glass as needed.
In the press molding method, the molten glass flowing out is cut to obtain a required molten glass lump, which is press-molded with a press mold to produce a thin disk-shaped substrate blank.
That is, the present invention includes, as an essential component, SiO ₂ , Li ₂ O, Na ₂ O, and one or more alkaline earth metal oxides selected from the group consisting of MgO, CaO, SrO, and BaO, A glass raw material is obtained so that a glass having a molar ratio of CaO to the total content of CaO, SrO and BaO (CaO / (MgO + CaO + SrO + BaO)) of 0.20 or less and a glass transition temperature of 650 ° C. or more is obtained. A glass substrate blank for a magnetic recording medium comprising: preparing, melting a prepared glass raw material to obtain a molten glass; and press-molding the obtained molten glass to produce a substrate blank made of glass. It relates to a manufacturing method.

In the press molding method, molten glass can be pressed into a disk shape, which is suitable as a method for molding a blank for a magnetic recording medium substrate.
Among the press molding methods, a method of dropping molten glass corresponding to one substrate blank and pressing the molten glass in the air is preferable. In the method, since the molten glass in the air is pressed with a pair of press molds, the glass can be cooled uniformly from the surface in contact with each press mold, and a flat substrate blank can be manufactured. it can.

  In the down-draw method, molten glass is guided using a bowl-shaped molded body, the molten glass overflows to both sides of the molded body, and two molten glass streams flowing down along the molded body are joined below the molded body. Then, pull it downward to form a sheet. This method is also called a fusion method, and a sheet glass having no contact mark can be obtained by sticking the glass surfaces in contact with the surface of the molded body to each other. Thereafter, a thin disc-shaped substrate blank is cut out from the obtained sheet material.

  In the float process, molten glass is poured onto a float bath in which molten tin or the like is stored, and is formed into a sheet glass while being pulled. Thereafter, a thin disc-shaped substrate blank is cut out from the obtained sheet material.

  In the method of forming a sheet by applying tension to the molten glass, such as the float method or the down draw method, the molten glass is maintained at a relatively low temperature, and the tension is generated in a state where the viscosity of the glass is increased. The glass to be used is limited to those having sufficient devitrification resistance. Since the devitrification resistance and the glass transition temperature have a trade-off relationship, methods such as the float method and the downdraw method are not suitable as a method for forming a high heat resistant glass. On the other hand, the press molding method can press and quench glass in a high temperature state, so that even a high heat resistance glass that is not so excellent in devitrification resistance can produce a substrate blank with high productivity. it can.

[Method for producing glass substrate for magnetic recording medium]
The 1st aspect of the manufacturing method of the glass substrate for magnetic recording media of this invention is a method including processing the board | substrate blank of the said invention.
The 2nd aspect of the manufacturing method of the glass substrate for magnetic recording media of this invention is a method including producing a substrate blank by the manufacturing method of the said substrate blank of the said invention, and processing the said substrate blank.
In any embodiment, it is preferable to include a step of chemically strengthening glass by immersing it in a molten salt containing a sodium salt and a potassium salt.
Since the substrate blank is made using the glass, chemical strengthening is performed so that the tensile stress in the virtual cross section perpendicular to the two main surfaces of the glass substrate is maximized at the center between the two main surfaces. Is called.
Therefore, it is possible to manufacture a glass substrate that has excellent heat resistance and hardly causes delayed fracture. It is preferable to immerse the glass containing Li ₂ O in an amount of 0.1 mol% or more in the molten salt for chemical strengthening in order to obtain a glass substrate that hardly causes delayed fracture.

  When manufacturing a disk-shaped glass substrate, a disk-shaped substrate blank manufactured by a press molding method, or a disk-shaped substrate cut out from a sheet-shaped glass manufactured by either the downdraw method or the float method Using a blank, a center hole is provided in the substrate blank, inner and outer peripheral processing, lapping and polishing are performed on both main surfaces. Next, a disk-shaped glass substrate can be obtained through a cleaning process including acid cleaning and alkali cleaning.

Since the glass substrate of the present invention has been provided with good chemical strengthening performance by the above-described composition adjustment, an ion exchange layer can be easily formed on the surface by chemical strengthening treatment.
In the manufacturing process of the glass substrate for magnetic recording media, a polishing process may be further performed as long as the effect of chemical strengthening is maintained after the chemical strengthening process.

[Magnetic recording medium]
Next, the magnetic recording medium will be described.
The magnetic recording medium of the present invention is a magnetic recording medium having a magnetic recording layer on the glass substrate for a magnetic recording medium of the present invention.
The magnetic recording medium has, for example, a configuration in which at least an adhesion layer, an underlayer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer are stacked on the main surface of a glass substrate in order from the side closer to the main surface. And a disk-shaped magnetic recording medium (referred to as a magnetic disk or hard disk).
For example, a glass substrate is introduced into a vacuum-deposited film formation apparatus, and a film is sequentially formed from an adhesion layer to a magnetic layer on the main surface of the glass substrate in an Ar atmosphere by a DC magnetron sputtering method. For example, CrTi can be used as the adhesion layer, and CrRu can be used as the underlayer. After the film formation, a magnetic recording medium can be formed by forming a protective layer using, for example, C2H4 by CVD and performing nitriding treatment in which nitrogen is introduced into the surface in the same chamber. Thereafter, for example, PFPE (polyfluoropolyether) is applied on the protective layer by a dip coating method, whereby a lubricating layer can be formed.
In addition, a soft magnetic layer, a seed layer, an intermediate layer, or the like is formed between the underlayer and the magnetic layer by a known method such as sputtering (including DC magnetron sputtering, RF magnetron sputtering) or vacuum deposition. You may form using a film | membrane method.
For details of each of the above layers, reference can be made, for example, to paragraphs [0027] to [0032] of JP2009-110626A. In addition, a heat sink layer made of a material having high thermal conductivity can be formed between the glass substrate and the soft magnetic layer, details of which will be described later.

  As described above, it is preferable to form a magnetic recording layer from a high Ku magnetic material in order to achieve higher density recording of the magnetic recording medium. From this viewpoint, the magnetic recording layer is preferably a magnetic recording layer containing a magnetic material mainly composed of an alloy of Fe and / or Co and Pt, and the magnetic recording medium is a magnetic recording medium for energy-assisted magnetic recording. Preferably there is.

Examples of the magnetic material mainly composed of an alloy of Fe and / or Co and Pt include an Fe—Pt magnetic material, a Co—Pt magnetic material, and an Fe—Co—Pt magnetic material. Here, “system” means inclusion. That is, the magnetic recording medium of the present invention preferably has a magnetic recording layer containing Fe and Pt, Co and Pt, or Fe, Co and Pt as the magnetic recording layer.
In order to obtain such a magnetic recording layer, a magnetic material mainly composed of an alloy of Fe and / or Co and Pt is formed on the main surface of a glass substrate, and then an annealing process is performed. Here, the film formation temperature of the magnetic material is usually a high temperature exceeding 500 ° C. Furthermore, since these magnetic materials have the same crystal orientation after film formation, the annealing treatment is performed at a temperature exceeding the film formation temperature.
Therefore, when the magnetic recording layer is formed using the Fe—Pt magnetic material, the Co—Pt magnetic material, or the Fe—Co—Pt magnetic material, the substrate is exposed to the high temperature. If the glass constituting the substrate is poor in heat resistance, the glass is deformed at a high temperature and flatness is impaired. On the other hand, since the substrate included in the magnetic recording medium of the present invention exhibits excellent heat resistance (glass transition temperature of 650 ° C. or higher), an Fe—Pt magnetic material, a Co—Pt magnetic material, or Even after the magnetic recording layer is formed using the Fe—Co—Pt magnetic material, high flatness can be maintained.
The magnetic recording layer is formed, for example, by depositing a Fe—Pt magnetic material, a Co—Pt magnetic material, or an Fe—Co—Pt magnetic material in a Ar furnace in a DC magnetron sputtering method. It can be formed by heat treatment at a higher temperature.

By the way, Ku (crystal magnetic anisotropy energy constant) is proportional to the coercive force Hc. The coercive force Hc represents the strength of a magnetic field whose magnetization is reversed. As explained earlier, high-Ku magnetic materials are resistant to thermal fluctuations, so that even if magnetic particles are made finer, the magnetization region is less likely to deteriorate due to thermal fluctuations and is known as a material suitable for high-density recording. ing. However, since Ku and Hc are in a proportional relationship as described above, the higher the Ku is, the higher the Hc is, that is, the magnetization reversal by the magnetic head is less likely to occur, making it difficult to write information. Therefore, a recording system that assists the magnetization reversal of a high Ku magnetic material by momentarily applying energy from the head to the data writing area when the information is written by the recording head to reduce the coercive force has attracted attention in recent years. Such a recording method is called an energy-assisted recording method. Among them, a recording method that assists magnetization reversal by laser light irradiation is called a heat-assisted recording method, and a recording method that assists by microwaves is called a microwave-assisted recording method. As described above, according to the present invention, a magnetic recording layer can be formed of a high Ku magnetic material. For example, the surface recording density exceeds 1 terabyte / inch ² by combining the high Ku magnetic material and energy assist recording. High density recording can be realized. That is, the magnetic recording medium of the present invention is preferably used for an energy assist recording system. For example, IEEE TRANSACTIONSON MAGNETICS, VOL. 44, No. 1, JANUARY 2008 119 for the heat assist recording method, and IEEE TRANSACTIONS ON MAGNETICS, VOL. 44, No. 1, JANUARY for the microwave assist recording method. 2008 125, each of which is described in detail. In the present invention, energy assist recording can be performed by the methods described in these documents.

  There are no particular limitations on the dimensions of the glass substrate for magnetic recording medium and the magnetic recording medium (for example, magnetic disk). For example, since the recording density can be increased, the medium and the substrate can be miniaturized. . For example, a nominal diameter of 2.5 inches can of course be of a smaller diameter (eg, 1 inch, 1.8 inches) or 3 inches, 3.5 inches, etc.

[Magnetic recording device]
Next, the magnetic recording apparatus will be described.
The magnetic recording apparatus of the present invention comprises a heat-assisted magnetic recording head having at least a heat source for heating the main surface of a magnetic recording medium, a recording element unit, and a reproducing element unit, and the magnetic recording medium of the present invention. This is an energy-assisted magnetic recording type magnetic recording apparatus.
According to the present invention, a magnetic recording apparatus having a high recording density and high reliability can be provided by mounting the magnetic recording medium of the present invention.
In addition, since the magnetic recording apparatus includes a substrate having high fracture toughness, the magnetic recording apparatus has sufficient reliability even at a high speed rotation of 5000 rpm or higher, preferably 7200 rpm or higher, more preferably 10,000 rpm or higher.
Further, it is preferable that the magnetic recording apparatus is equipped with a DFH (Dynamic Flying Height) head from the viewpoint of increasing the recording density.
As the magnetic recording device, internal storage devices (fixed disks, etc.) of various computers such as desktop personal computers, server computers, notebook personal computers and mobile personal computers, and internal storages of portable recording / reproducing devices for recording and reproducing images and / or sounds Examples thereof include a device and an on-vehicle audio recording / reproducing device.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, this invention is not limited to the aspect shown in the Example.

(1) Production of molten glass Raw materials such as oxides, carbonates, nitrates, hydroxides and the like were weighed and mixed so as to obtain glasses having respective compositions shown in Tables 2 to 4 to prepare blended raw materials. This raw material is put into a melting vessel, heated and melted in the range of 1500 to 1600 ° C. for 3 to 6 hours, clarified and stirred to produce a homogeneous molten glass free from bubbles and unmelted materials, and molded. Eight types of glass were obtained. The obtained glass no. 1-No. In 16, bubbles, undissolved material, crystal precipitation, and contamination of refractory constituting the melting vessel were not recognized.

(2) Production of Substrate Blank Next, a disk-shaped substrate blank was produced by the following method A or B.
(Method A)
The clarified and homogenized molten glass flows out of the pipe at a constant flow rate and is received by a lower mold for press molding, and the molten glass that has flowed out is cut with a cutting blade so that a predetermined amount of molten glass lump is obtained on the lower mold. . Then, the lower mold on which the molten glass block was placed was immediately taken out from below the pipe, and was pressed into a thin disk shape having a diameter of 66 mm and a thickness of 2 mm using the upper mold and the barrel mold facing the lower mold. After the press molded product was cooled to a temperature at which it was not deformed, it was taken out of the mold and annealed to obtain a substrate blank. In the above molding, molten glass that flows out using a plurality of lower molds was formed into a disk-shaped substrate blank one after another.
(Method B)
The clarified and homogenized molten glass was continuously cast from above into a through hole of a heat resistant mold provided with a cylindrical through hole, formed into a columnar shape, and taken out from below the through hole. The annealed glass was annealed, and then the glass was sliced at regular intervals in a direction perpendicular to the cylinder axis using a multi-wire saw to produce a disk-shaped substrate blank.
In the present embodiment, the above methods A and B are employed, but the following methods C and D are also suitable as a method for manufacturing a disk-shaped substrate blank.
(Method C)
The molten glass is poured onto a float bath, formed into a sheet-like glass (formation by a float method), and then annealed, and then a disc-like glass is cut out from the sheet glass to obtain a substrate blank.
(Method D)
The molten glass can be formed into a sheet-like glass by the overflow down draw method (fusion method) and annealed, and then the disc-like glass is cut out from the sheet glass to obtain a substrate blank.

(3) Production of glass substrate A through hole is made in the center of the substrate blank obtained by each of the above methods, the outer periphery and inner periphery are ground, the main surface of the disk is lapped, and polishing (mirror polishing) is performed. A glass substrate for a magnetic disk having a diameter of 65 mm and a thickness of 0.8 mm was finished. The obtained glass substrate was washed with a 1.7% by mass aqueous solution of silicic acid (H ₂ SiF) and then with a 1% by mass aqueous potassium hydroxide solution, then rinsed with pure water and then dried. When the surface of the substrate produced from 10 kinds of glasses shown in Table 2 was magnified, surface roughness was not observed, and the surface was smooth.
Next, the disk-shaped glass substrate was immersed in a mixed molten salt of sodium nitrate and potassium nitrate, and a glass substrate having an ion exchange layer on the surface was obtained by ion exchange (chemical strengthening). Chemical strengthening conditions are shown in Tables 2-4. Applying the ion exchange treatment (chemical strengthening treatment) in this way is effective for improving the impact resistance of the glass substrate. From a plurality of glass substrates subjected to ion exchange treatment, the sample glass substrate was observed by a Babinet method for the cross section of the sampled glass substrate (the surface to cut the ion exchange layer), and it was confirmed that the ion exchange layer was formed.
The ion exchange layer may be formed on the entire surface of the glass substrate, may be formed only on the outer peripheral surface, or may be formed only on the outer peripheral surface and the inner peripheral surface.
Further, after the ion exchange treatment, a mirror polishing treatment may be performed so as to leave an ion exchange layer. In order not to significantly reduce the fracture toughness value K _1c , it is preferable to leave a sufficient ion exchange layer. In this respect, the machining allowance by the mirror polishing process is more preferably 5 μm or less.

(4) Production of magnetic disk By the following method, an adhesion layer, an underlayer, a magnetic layer, a protective layer, and a lubricating layer were formed in this order on the main surface of the glass substrate to obtain a magnetic disk.
First, an adhesion layer, a base layer, and a magnetic layer were sequentially formed in an Ar atmosphere by a DC magnetron sputtering method using a vacuum-deposited film forming apparatus.
At this time, the adhesion layer was formed using a CrTi target so as to be an amorphous CrTi layer having a thickness of 20 nm. Subsequently, a 10 nm thick layer made of CrRu was formed as a base layer by a DC magnetron sputtering method in an Ar atmosphere using a single wafer / stationary facing type film forming apparatus. Further, the magnetic layer was formed at a film forming temperature of 400 ° C. using an FePt or CoPt target so as to be an FePt or CoPt layer having a thickness of 10 nm.
The magnetic disk after film formation up to the magnetic layer was transferred from the film forming apparatus to a heating furnace, and annealed by appropriately selecting conditions in a temperature range of 650 to 700 ° C.
Subsequently, a protective layer made of hydrogenated carbon was formed to 3 nm by a CVD method using ethylene as a material gas. Thereafter, a lubricating layer using PFPE (perfluoropolyether) was formed by a dip coating method. The thickness of the lubricating layer was 1 nm.
A magnetic disk was obtained by the above manufacturing process.

1. Evaluation of glass (1) Glass transition temperature Tg, coefficient of thermal expansion The glass transition temperature Tg of the sample before the chemical strengthening treatment and the average linear expansion coefficient α at 100 to 300 ° C and 500 to 600 ° C were obtained from Rigaku Corporation. It measured using the thermomechanical analyzer (Thermo plus TMA8310). In addition, since the above characteristics hardly change before and after the chemical strengthening treatment, the glass substrate after the chemical strengthening treatment also has a glass transition temperature Tg obtained by the above measurement, and 100 to 300 ° C. and 500 to 600 ° C. Is considered to have an average coefficient of linear expansion α.
(2) Young's modulus The Young's modulus of the sample before the chemical strengthening treatment was measured by an ultrasonic method. Since the Young's modulus hardly changes before and after the chemical strengthening treatment, the glass substrate after the chemical strengthening treatment is also considered to have the Young's modulus obtained by the above measurement.
(3) Specific gravity The specific gravity of the sample before the chemical strengthening treatment was measured by the Archimedes method. Since the specific gravity hardly changes before and after the chemical strengthening treatment, the glass substrate after the chemical strengthening treatment is also considered to have the specific gravity obtained by the above measurement.
(4) Specific modulus The specific modulus was calculated from the Young's modulus obtained in (2) above and the specific gravity obtained in (3).
(5) Fracture toughness value Using a device MVK-E manufactured by AKASHI, a Vickers indenter was pushed in with a pushing load of 9.81 N into a sample processed into a plate shape and subjected to chemical strengthening treatment under the conditions described in Tables 2 to 4. Indentations and cracks were introduced into the sample.
The Young's modulus of the sample was E [GPa], the diagonal length of the indentation, and the half length of the surface crack, and the fracture toughness value K _1c was calculated from the load and the Young's modulus of the sample.
(6) Tav / Tmax
About the sample processed into a plate shape and subjected to the chemical strengthening treatment under the conditions described in Tables 2 to 4, the cross section in the plate thickness direction was observed by the Babinet method, Tmax and Tav were calculated by the above-described method, and from the calculated values Tav / Tmax was determined.

2. Substrate evaluation (surface roughness, surface waviness)
A rectangular region of 5 μm × 5 μm on the main surface (surface on which the magnetic recording layer etc. is laminated) before and after the chemical strengthening treatment is observed with an atomic force microscope (AFM) at a resolution of 512 × 256 pixels, and 1 μm × 1 μm The arithmetic average Ra of the surface roughness measured at a resolution of 512 × 256 pixels in the range, and the arithmetic average Ra of the surface roughness measured at a resolution of 512 × 256 pixels in the range of 5 μm × 5 μm. Furthermore, the main surface of each board | substrate was observed with the optical surface shape measuring apparatus, and the arithmetic mean Wa of the surface waviness in wavelength 100micrometer-950micrometer was measured.
As a result of the measurement, the arithmetic average Ra of the surface roughness measured in the range of 1 μm × 1 μm is in the range of 0.05 to 0.15 nm, and the arithmetic average Ra of the surface roughness measured in the range of 5 μm × 5 μm is 0.00. The arithmetic average Wa of the surface waviness in the range of 03 to 0.12 nm and the wavelength of 100 μm to 950 μm was 0.2 to 0.5 nm, and there was no problem as a substrate used for a high recording density magnetic recording medium.

As shown in Tables 2-4, no. 1-No. The substrate made of 16 chemically strengthened glasses has four characteristics required for a magnetic recording medium substrate, such as high heat resistance (high glass transition temperature), high rigidity (high Young's modulus), high thermal expansion coefficient, and high fracture toughness. It was a thing. Furthermore, from the results shown in Tables 2 to 4, No. 1-No. It can also be confirmed that the substrate made of 16 glass has a high specific elastic modulus that can withstand high-speed rotation, has a low specific gravity, and can reduce the weight of the substrate. In addition, it was also confirmed that the glass used in Examples for producing the glass substrate can easily form an ion exchange layer by chemical strengthening treatment, and as a result, exhibits high fracture toughness. 5 shows No. 2 shown in Tables 2 and 4. 1-No. 7, no. 11, no. It is the graph which plotted the fracture toughness value after a chemical strengthening process with respect to molar ratio (CaO / (MgO + CaO + SrO + BaO)) about 12 glasses. From this graph, it can be confirmed that as the molar ratio (CaO / (MgO + CaO + SrO + BaO)) is lowered, the fracture toughness value, that is, the mechanical strength is improved.
On the other hand, when chemical strengthening was performed at a molten salt temperature of 500 ° C. using the glass (No. 17) shown in Table 5 having a large molar ratio (CaO / (MgO + CaO + SrO + BaO)) of about 0.29, the fracture toughness value was 0. It was .74 MPa · m ^1/2 . Furthermore, when a plurality of glasses were simultaneously immersed in a molten salt at 500 ° C. and chemically strengthened, the molten salt deteriorated rapidly, and the fracture toughness value after strengthening did not reach 0.74 MPa · m ^1/2 . Similarly, even when a plurality of glasses were sequentially immersed in a molten salt at 500 ° C. and chemically strengthened, the fracture toughness value of the chemically strengthened glass after the second time decreased rapidly. As described above, this is presumed to be because Ca ²⁺ ions contained in the glass composition were dissolved in the molten salt and inhibited the ion effect between the alkali metal ions. Similar results were also observed when the molar ratio (CaO / (MgO + CaO + SrO + BaO)) was greater than 0.2.
On the other hand, No. shown in Tables 2-4. In each of the glasses 1 to 16, even when a plurality of glasses were immersed in a molten salt at the same time and chemically strengthened, the fracture toughness value of 0.80 MPa · m ^1/2 or more could be maintained. No. In each of the glasses 1 to 16, a fracture toughness value of 0.80 MPa · m ^1/2 or more could be maintained even when a plurality of glasses were sequentially immersed in a molten salt and chemically strengthened.
Thus, in a glass having a molar ratio (CaO / (MgO + CaO + SrO + BaO)) of 0.20 or less, it is difficult to cause deterioration of the molten salt due to chemical strengthening, and it is possible to stably produce chemically strengthened glass having a high fracture toughness value. it can. On the other hand, when the molar ratio (CaO / (MgO + CaO + SrO + BaO)) exceeds 0.20, the molten salt deteriorates due to chemical strengthening, and it becomes difficult to maintain a high fracture toughness value.
No. after chemical strengthening. 1-No. In the glass No. 7, a compressive stress layer having a depth of 30 to 120 μm is formed on the surface, and the magnitude of the compressive stress is 2.0 kgf / mm ² or more (19.6 MPa or more). . No. 8-No. A compression stress layer having a depth of 20 to 120 μm is formed on the surface of 16 glass, and the magnitude of the compression stress is 2.0 kgf / mm ² or more (a value of 19.6 MPa or more). .
From the above results, according to the present invention, it was confirmed that a glass having characteristics required for a magnetic recording medium substrate can be obtained.
Further, a glass substrate was produced in the same manner as described above except that mirror polishing was performed with a machining allowance within the range of 0.5 to 5 μm after the ion exchange treatment. When cross sections of the obtained plurality of glass substrates were observed by the Babinet method, an ion exchange layer was formed, and no deterioration in mechanical strength was observed. Other characteristics were the same as above.

For each example (each glass of No. 1 to 16 after chemical strengthening), in the cross-sectional photograph obtained by observation by the above-mentioned Babinet method, in the stress profile in the virtual cross section perpendicular to the two main surfaces, the tensile stress distribution Is convex and no uphill was seen. From these stress profiles, Tav / Tmax was determined by the method described with reference to FIG. The value of Tav / Tmax after chemical strengthening of glasses 1 to 13 was 0.8 or more. No. The value of Tav / Tmax after chemical strengthening of glasses 14 to 16 was 0.5 or more.
In order to demonstrate that the chemically strengthened glass substrate exhibiting the above stress profile does not exhibit delayed fracture, the following test was performed.
In the sample after the chemical strengthening treatment in which the fracture toughness value was measured in the examples, there is an indentation formed by indenting the Vickers indenter with an indentation load of 9.81N. The indented sample was placed in an environmental testing machine and left in an environment of a temperature of 80 ° C. and a relative humidity of 80% for 7 days, then taken out and indented. As a result of preparing 100 samples for each example and conducting the above test, no extension of cracks from the indentation was observed in any of the samples.
On the other hand, glass containing Na ₂ O, K ₂ O and no Li ₂ O, for example, No. The glass composition of No. 1 having a composition in which the total amount of Li ₂ O is replaced with Na ₂ O is immersed in a molten salt of potassium nitrate and chemically strengthened, as shown in FIG. Uphill was observed at Tav / Tmax <0.5. When the above-mentioned test was performed on the sample, crack extension from the indentation was recognized in 8 out of 100 sheets, and crack extension was remarkable in 3 sheets and was damaged.
From the results of the delayed fracture acceleration test described above, it was confirmed that the delayed fracture prevention effect was obtained in the chemically strengthened glass substrate of the example.

3. Evaluation of magnetic disk (1) Flatness Generally, if the flatness is 5 μm or less, highly reliable recording and reproduction can be performed. Flatness of each magnetic disk surface formed using the glass substrate of the example by the above method (distance (height difference) in the vertical direction (direction perpendicular to the surface) between the highest part and the lowest part of the disk surface) Was measured with a flatness measuring device, and the flatness of all the magnetic disks was 5 μm or less. From this result, it can be confirmed that the glass substrate of the example did not undergo major deformation even in the high-temperature treatment when forming the FePt layer or the CoPt layer.
(2) Load / unload test Each magnetic disk formed using the glass substrate of the example by the above method is mounted on a 2.5 inch hard disk drive rotating at a high speed of 10,000 rpm, and load unload (Load Unload). , Hereinafter referred to as LUL). In the hard disk drive, the spindle motor spindle was made of stainless steel. In all the magnetic disks, the LUL endurance exceeded 600,000 times. Also, if a deformation due to a difference in thermal expansion coefficient with the spindle material or a deflection due to high-speed rotation occurs during the LUL test, a crash failure or thermal asperity failure will occur during the test. I did not.
(3) Impact resistance test A glass substrate for magnetic disk (2.5 inch size, 0.8 mm thick) was prepared, and an impact test was performed using MODEL-15D manufactured by Lancemont. In this impact test, the magnetic disk glass substrate was assembled in a dedicated impact test jig made to resemble the HDD spindle and clamp, and a shock of a 1500 G sine half-wave pulse was perpendicular to the main surface in 1 msec. This was performed by observing the breakage of the glass substrate for magnetic disk. As a result, no breakage was observed in the glass substrate of the example.

  From the above results, it can be confirmed that according to the present invention, a glass substrate for a magnetic recording medium having excellent impact resistance and capable of recording and reproducing with high reliability can be obtained.

  A magnetic disk produced by using the glass substrate of the above example by the above method is mounted on a hard disk drive of a recording system (thermally assisted recording system) that assists magnetization reversal by irradiation of a laser beam, and a magnetic recording apparatus of a thermally assisted recording system is installed. Produced. The magnetic recording device includes a heat source (laser light source) for heating the main surface of a magnetic recording medium (magnetic disk), a heat-assisted magnetic recording head having a recording element unit, and a reproducing element unit, and a magnetic disk. . The magnetic head of the magnetic recording apparatus is a DFH (Dynamic Flying Height) head, and the rotational speed of the magnetic disk is 10,000 rpm. Separately, the produced magnetic disk was mounted on a recording system (microwave assisted recording system) hard disk drive assisted by microwaves to produce an information recording apparatus of microwave assisted recording system. All of these manufactured HDDs (hard disk drives) operated well. As described above, according to the information recording apparatus in which the high Ku magnetic material and the energy assist recording are combined, high-density recording can be realized.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  According to the present invention, it is possible to provide a magnetic recording medium optimum for high density recording.

Claims (38)

In mol%
The SiO ₂ 55~78%,
Li ₂ O exceeds 0% and 5% or less,
The Na ₂ O 3~15%,
10 to 25% in total of MgO, CaO, SrO and BaO,
Including
The molar ratio of the content of CaO to the total content of MgO, CaO, SrO and BaO (CaO / (MgO + CaO + SrO + BaO)) is 0.20 or less,
Glass transition temperature of 650 ° C. or higher,
A glass for a magnetic recording medium substrate. The glass for a magnetic recording medium substrate according to claim 1, wherein the B ₂ O ₃ content is 0 to 3 mol% . Al ₂ O ₃ content is 0 to 12 mol% claim 1 or 2 magnetic recording medium glass substrate according to. Na ₂ O magnetic recording medium glass substrate according to any one of claims 1 to 3 molar ratio CaO / Na ₂ O content of CaO is 1.5 or less to the content of. _{ZrO 2, TiO 2, Y 2} O 3, La 2 O 3, Gd 2 O 3, Yb 2 O 3, Nb 2 O 5, Ta 2 O 5 and claims, including one or more kinds selected from the group consisting of HfO ₂ The glass for magnetic recording medium substrates of any one of 1-4. The total content of ZrO ₂ , TiO ₂ , Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Yb ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ and HfO ₂ is 0 to 10 mol%. The glass for magnetic recording media substrates of any one of Claims 1-5. The total content of SiO ₂ , ZrO ₂ , TiO ₂ , Y ₂ O ₃ , La ₂ O ₃ , Gd ₂ O ₃ , Yb ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ and HfO ₂ is 66 mol% or more. The glass for a magnetic recording medium substrate according to claim 5 or 6. The magnetic recording medium glass substrate according to any one of claims 1 to 7 ZrO ₂ content of 0-6 mol%. The glass for a magnetic recording medium substrate according to claim 1, wherein the total content of SiO ₂ and ZrO ₂ is 66 mol% or more. The average linear expansion coefficient at 100 to 300 ° C. is 50 × 10 ⁻⁷ / ° C. or more,
Young's modulus is 75 GPa or more and specific modulus is 25 MNm / kg or more,
The glass for a magnetic recording medium substrate according to any one of claims 1 to 9. The glass substrate for magnetic recording media which consists of chemically strengthened glass obtained by chemically strengthening the glass for magnetic recording medium substrates of any one of Claims 1-10. The chemically tempered glass has a convex tensile stress distribution in a stress profile in a virtual cross section perpendicular to two main surfaces obtained by the Babinet method, but the convex shape does not include a dent that is recessed toward the compressive stress side. The glass substrate for a magnetic recording medium according to claim 11, which is a tempered glass. In the chemically strengthened glass, the average value Tav of tensile stress and the maximum value Tmax of tensile stress obtained by the Babinet method are expressed by the following formula (1):
Tav / Tmax ≧ 0.5
The glass substrate for magnetic recording media according to claim 11, wherein the glass substrate is a chemically strengthened glass. The glass substrate for a magnetic recording medium according to any one of claims 11 to 13 , wherein the chemically strengthened glass is glass that has been chemically strengthened by immersion in a molten salt containing a sodium salt and a potassium salt. The glass substrate for a magnetic recording medium according to claim 14 , wherein the glass substrate is a glass that is chemically strengthened by immersing glass containing 0.1 mol% or more of Li ₂ O in the molten salt. The glass substrate for a magnetic recording medium according to any one of claims 11 to 15 , wherein the fracture toughness value _K1c is 0.8 MPa · m1 / ² or more. The magnetism according to any one of claims 11 to 16 , wherein an arithmetic mean roughness (Ra) of the main surface is 0.15 nm or less as measured with an atomic force microscope at a resolution of 512 x 256 pixels at 1 µm square. Glass substrate for recording media. The glass substrate for a magnetic recording medium according to any one of claims 11 to 17 , wherein a plate thickness is 0.5 mm or more. The glass substrate for a magnetic recording medium according to any one of claims 11 to 18 , which is a glass substrate for a magnetic recording medium used in a magnetic recording apparatus having a rotational speed of 5000 rpm or more. The glass substrate for a magnetic recording medium according to any one of claims 11 to 19 , which is a glass substrate for a magnetic recording medium used in a magnetic recording apparatus equipped with a DFH (Dynamic Flying Height) head. 21. The glass substrate for a magnetic recording medium according to any one of claims 11 to 20 , which is used for a magnetic recording medium for energy-assisted magnetic recording. In mol%
The SiO ₂ 55~78%,
Li ₂ O exceeds 0% and 5% or less,
The Na ₂ O 3~15%,
10 to 25% in total of MgO, CaO, SrO and BaO,
Including
The molar ratio of the content of CaO to the total content of MgO, CaO, SrO and BaO (CaO / (MgO + CaO + SrO + BaO)) is 0.20 or less,
Glass transition temperature of 650 ° C. or higher,
A glass substrate blank for a magnetic recording medium. The glass substrate blank for a magnetic recording medium according to claim 22 , which has a disk shape. In mol%
The SiO ₂ 55~78%,
Li ₂ O exceeds 0% and 5% or less,
The Na ₂ O 3~15%,
10 to 25% in total of MgO, CaO, SrO and BaO,
Including
The molar ratio of the content of CaO to the total content of MgO, CaO, SrO and BaO (CaO / (MgO + CaO + SrO + BaO)) is 0.20 or less,
Glass transition temperature of 650 ° C. or higher,
Formulating the glass raw material so that a glass is obtained,
Melting the prepared glass raw material to obtain a molten glass; and
Producing a substrate blank made of glass by press-molding the obtained molten glass;
The manufacturing method of the glass substrate blank for magnetic recording media containing this. The method for producing a glass substrate blank for a magnetic recording medium according to claim 24 , wherein the molten glass is press-molded into a disk shape. The method for producing a glass substrate blank for a magnetic recording medium according to claim 24 or 25 , wherein molten glass in the air is press-molded. The manufacturing method of the glass substrate for magnetic recording media including processing the glass substrate blank for magnetic recording media of Claim 22 or 23 . To produce a glass substrate blank for a magnetic recording medium by the method according to any one of claims 24-26, and,
Processing the substrate blank;
The manufacturing method of the glass substrate for magnetic recording media containing this. The method for producing a glass substrate for a magnetic recording medium according to claim 27 or 28 , comprising immersing the glass in a molten salt containing a sodium salt and a potassium salt to chemically strengthen the glass. Method of manufacturing a glass substrate for a magnetic recording medium of claim 29, chemical strengthening glass that contains a li 2 _O 0.1 mol% or more immersed in the molten salt. The average value Tav of the tensile stress obtained by the Babinet method and the maximum value Tmax of the tensile stress are expressed by the following formula (1):
Tav / Tmax ≧ 0.5
The method for producing a glass substrate for a magnetic recording medium according to claim 29 or 30 , wherein the chemical strengthening is performed so as to be a chemically strengthened glass satisfying the above. In the stress profile in the virtual cross section perpendicular to the two main surfaces obtained by the Babinet method, the tensile stress distribution has a convex shape, provided that the convex shape is a chemically strengthened glass that does not include a concave portion recessed to the compressive stress side. The method for producing a glass substrate for a magnetic recording medium according to claim 29 or 30 , wherein the chemical strengthening is performed. The magnetic recording medium having a magnetic recording layer on the magnetic recording medium glass substrate according to any one of claims 11 to 19. The magnetic recording layer and the Fe and / or Co, a magnetic recording layer containing magnetic material mainly composed of an alloy of Pt, to claim 33 wherein the magnetic recording medium is an energy-assisted magnetic recording for a magnetic recording medium The magnetic recording medium described. An annealing treatment after forming a magnetic material mainly composed of an alloy of Fe and / or Co and Pt on the main surface of the glass substrate for a magnetic recording medium according to any one of claims 11 to 21. A method of manufacturing a magnetic recording medium including forming a magnetic recording layer by performing 35. A heat-assisted magnetic recording head having at least a heat source for heating the main surface of the magnetic recording medium, a recording element portion, and a reproducing element portion, and energy-assisted magnetism having the magnetic recording medium according to claim 33 or 34 Recording type magnetic recording device. The magnetic recording apparatus according to claim 36 , wherein the rotational speed is 5000 rpm or more. 38. The magnetic recording apparatus according to claim 36 or 37 , wherein a DFH (Dynamic Flying Height) head is mounted.