JP3136133B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium having a magnetic film suitable for high-density magnetic recording.

[0002]

2. Description of the Related Art Magnetic disk drives currently in practical use employ an in-plane magnetic recording system. In the in-plane magnetic recording system, it is a technical problem to form in-plane magnetic domains parallel to the substrate at high density on an in-plane magnetic recording medium which is easily magnetized in a direction parallel to the disk substrate surface. In order to increase the recording density of this longitudinal magnetic recording medium, the coercive force must be improved and the magnetic film thickness must be reduced. However, if the magnetic film thickness is too small, a problem is encountered that the recording magnetization decreases or disappears under the influence of heat. The magnetic film thickness at which the influence of the thermal fluctuation of magnetization becomes remarkable is set to 20 nm or less in a Co alloy system.

On the other hand, the perpendicular magnetic recording method has attracted attention as a method that is strong against thermal fluctuation and suitable for high-density magnetic recording because the magnetic film thickness can be made larger than that of an in-plane medium.
A medium structure suitable for perpendicular magnetic recording has been proposed. According to the perpendicular magnetization film made of a Co alloy material, 300
It has been reported that a high linear recording density higher than KFCI can be realized.

[0004]

In a longitudinal magnetic recording medium, if the density of a recording medium using a Co alloy-based magnetic film is increased, the trend up to now can be extended to 10 Gb.
It is expected that the thickness of the magnetic film must be set to 20 nm or less in order to realize a recording density of / in ² or more.
In order to improve the recording density by preventing the effects of thermal fluctuation,
It is conceivable to use an ordered alloy such as Sm-Co or Pt-Co as a substitute material in which the magnetic anisotropy energy of the magnetic film is higher than that of the Co alloy-based material. However, a magnetic recording medium needs to satisfy other conditions such as recording resolution, medium noise, and corrosion resistance in addition to heat fluctuation resistance. For example, ordered alloys such as Sm-Co and Pt-Co are not necessarily used. These conditions have not reached the stage where they can be put to practical use.

In a perpendicular magnetic recording medium, 10 Gb /
To achieve the recording density of in ² is adapted to require that a reduction in media noise. Thus, 10G
As a recording medium capable of high-density magnetic recording of b / in ² or more, it is necessary to improve the thermal fluctuation characteristics in a longitudinal magnetic recording medium and to reduce medium noise in a perpendicular magnetic recording medium. The present invention provides an in-plane magnetic recording medium excellent in heat fluctuation resistance and a perpendicular magnetic recording medium with low noise, thereby facilitating the realization of a high-density magnetic recording / reproducing apparatus of 10 Gb / in ² or more. The purpose is to:

[0006]

As a result of a detailed examination of the thermal fluctuation characteristics of the longitudinal magnetic recording medium, a region having a low magnetic anisotropy energy is formed in a part of the magnetic film, and the recording magnetization is deteriorated from this region. Was found to progress. Therefore, in order to improve the thermal fluctuation characteristics, it is effective to suppress the formation of this region.

[0007] As a result of examining the recording magnetization state of the perpendicular magnetic recording medium by a magnetic force microscope or a scanning type spin electron detection microscope, most of the noise is caused by reverse domains existing on the medium surface and micro fluctuations of magnetization. It turned out to be the cause. In order to reduce medium noise, it is necessary to reduce the number of reverse magnetic domains and the fluctuation of microscopic magnetization existing on the surface or the back surface of the medium.

As a result of experiments, it has become clear that the following method can be used to achieve the above object. Most commonly used in longitudinal magnetic recording and perpendicular magnetic recording,
The magnetic film material of the medium under study is hexagonal dense (hc
p) It is a Co alloy material having a structure. In a Co alloy-based in-plane magnetic recording medium, a region having low magnetic anisotropy energy exists near the interface between the lower and upper layers of the film. In other words, there is a region with inferior crystallinity in the lower layer corresponding to the initial layer of the magnetic film, and the upper layer has undulations or a magnetic anisotropy caused by a decrease in segregation of elements constituting the magnetic film. It was found that there was a region with low sexual energy. It was confirmed that the magnetic anisotropy energy of the region having poor crystallinity in the lower layer portion was also reduced.

In order to provide an improved medium structure, the present invention solves the above problem by employing a magnetic film having at least three layers.
Here layer (substrate side) and the upper magnetic film anisotropy energy of the (surface side) (the substrate side: Ku _b, the surface side: Ku _s) the intermediate magnetic layer anisotropy energy (Ku _m) It is to make it larger than.

Further, it has been found that the main noise factor of the perpendicular magnetic recording medium is a reverse magnetic domain formed in the magnetic film. The cause is that when the perpendicular magnetization film is perpendicularly magnetized in one direction, a strong demagnetizing field acts on the medium surface. By the action of this demagnetizing field, a so-called reverse magnetic domain having a direction opposite to the direction of perpendicular magnetization is formed. Things. The formation of the reverse magnetic domains occurs not only from the front side but also from the back side of the magnetic film. In order to prevent the formation of the reverse magnetic domain, it is necessary to employ a perpendicular magnetization film having high magnetic anisotropy energy. It is desirable that the magnetic anisotropy energy be 3 × 10 ⁶ erg / cc or more. However, if the entire magnetic film is made of a material having high magnetic anisotropy energy, there arises a problem that the medium noise increases or the medium coercive force becomes too large to make recording with a recording head difficult.

Therefore, in the present invention, as in the case of the in-plane medium, the above problem is solved by employing a magnetic film having at least three magnetic films. Wherein the magnetic film of the magnetic anisotropy energy of the lower layer (substrate side) and the upper layer (surface side) (the substrate side: Ku _b, the surface side: Ku _s) compared to the magnetic anisotropic energy Ku _m of the intermediate magnetic layer To make it bigger. The desirable range of Ku _b and Ku _s is 3 × 1
_{^{0 6 erg / cc ≦ Ku b}} ≦ 5 × 10 7 erg / cc, 3
^{× 10 6 erg / cc ≦ Ku} s ≦ 5 × 10 7 erg / cc
It is. Below 3 × 10 ⁶ erg / cc, it is difficult to prevent the formation of reverse magnetic domains, and 5 × 10 ⁷ erg / cc
If it exceeds / cc, undesirable effects such as difficulty in recording by the recording head and an increase in medium noise occur.

The magnetic anisotropy energy Ku of the intermediate magnetic layer
The value of ^{_{m, 1 × 10 6 erg /}} cc <Ku m <3 ×
A range of 10 ⁶ erg / cc is appropriate. This is a typical value of a Co alloy-based magnetic film having low noise characteristics, and is in a practically usable range. Since the value of the magnetic anisotropy energy depends on the composition of the magnetic film, it can be determined by forming a single-layer magnetic film and measuring the magnetic torque characteristics. In order to obtain an accurate value, it is appropriate to adopt a method of forming a single crystal film of a magnetic film having each composition and obtaining a value of magnetic anisotropic energy from a magnetic torque curve.

It has been confirmed that the intended effect can be obtained also in the longitudinal magnetic recording medium if the magnetic anisotropy energy range of each magnetic film is set in the same manner as in the perpendicular magnetic recording medium. Here, it is desirable that the magnetic film layer having a high magnetic anisotropy energy provided on the lower layer side has an hcp structure which is the same crystal structure as the Co alloy magnetic film used for the intermediate layer. This is because the magnetic film that forms the medium is a polycrystalline film, but the individual magnetic crystal grains that make up the polycrystalline film grow by epitaxial growth with the underlying film. This is because it is desirable to have the same crystal structure in order to grow. On the other hand, a film having a high magnetic anisotropy energy provided in the upper layer is not necessarily hc
There is no need to use a p-structure. Pt / C other than Co alloy
A perpendicular magnetic film composed of a multilayer film of o, Pd / Co or the like or a perpendicular magnetic film having an amorphous structure containing a rare earth element such as TbFeCo has a magnetic anisotropy energy of 3
It is × 10 ⁶ erg / cc or more, but such a film can also be used.

In order to realize a recording density of 10 Gb / in ² or more in a longitudinal magnetic recording medium, the total thickness of the magnetic layer is appropriately in the range of 5 to 25 nm. The thickness of each of the upper layer and the lower layer is at least 1 nm.
Is necessary, and the total of the upper layer and the lower layer is preferably smaller than the thickness of the intermediate layer. In a perpendicular magnetic recording medium, 10
In order to realize a recording density of Gb / in ² or more, the total thickness of the magnetic film is suitably in the range of 10 to 50 nm. Also in this case, the thickness of each of the upper layer and the lower layer needs to be at least 1 nm, and the total of the upper layer and the lower layer is preferably smaller than the thickness of the intermediate layer.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view showing the configuration of a magnetic recording medium according to the present invention. A base film 12 for controlling the crystal orientation of the magnetic film and the magnetic crystal grain size is formed on the nonmagnetic substrate 11. The base film 12 may be formed as a multilayer film of two or more layers. In a perpendicular magnetic recording medium, a soft magnetic film may be provided on the entire or a part of the underlayer. The magnetic film is composed of at least three layers of a lower magnetic film 13, an intermediate magnetic film 14, and an upper magnetic film 15, and the relationship between the magnetic anisotropy energies is 3 ×.
_{^{10 6 erg / cc <Ku b}} , Ku s <5 × 10 7 erg /
^{cc, 1 × 10 6 erg /} cc <Ku m <3 × 10 6 er
g / cc. Here, the magnetic anisotropy energy values are as follows: substrate side: Ku _b , surface side: Ku _s , intermediate layer: Ku _m
It is. A protective film 16 and a lubricating film 17 are formed on the upper magnetic film 15.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. [Example 1] Using a glass substrate having a diameter of 2.5 inches,
An in-plane magnetic recording medium having a cross-sectional structure shown in FIG. 1 was manufactured by a DC magnetron sputtering method. An underlayer 12, a lower magnetic film 13, an intermediate magnetic film 14, an upper magnetic film 15, and a protective film 16 were formed on a substrate 11 in this order.
A Cr-10 at% Ti target for the underlayer, a Co-5 at% Cr-8 at% Pt target for the lower magnetic film,
Co-17at% Cr-5at% Pt- for intermediate magnetic film
3 at% Ta target, Co-5 at for upper magnetic film
% Cr-8 at% Pt target, and a carbon target for the protective film. Ar gas pressure for sputtering is 3mT
orr, sputter power 10 W / cm ² , substrate temperature 2
Under conditions of 50C, the CrTi film was 30 nm, and the lower magnetic film was 2 nm.
The thickness of the intermediate magnetic film was 16 nm, the thickness of the upper magnetic film was 2 nm, and the thickness of the carbon film was 10 nm. A perfluoropolyether-based film was applied as a lubricating film. The magnetic anisotropy energy value of each magnetic film is Cr-10 at% Ti
It was calculated from the magnetic torque curve of a sample in which each magnetic film was formed to a thickness of 20 nm on the lower ground.

As a comparative sample, an in-plane magnetic recording medium made of a magnetic film having a thickness of 20 nm, which is a lower layer and an intermediate layer, was prepared. The evaluation of the coercive force Hc and the recording / reproducing characteristics of these magnetic recording media was performed using a vibrating magnetometer (VSM), a magnetic torque meter, and a recording / reproducing separated magnetic head, respectively. The gap length of the recording head was 0.2 μm, the shield interval of the spin valve head for reproduction was 0.2 μm, and the spacing at the time of measurement was 0.04 μm. Recording density measures the output half recording density D ₅₀ which is half of the reproduction output of the low frequency, the ratio S / N of the signal and noise in the case of performing the magnetic recording of 20kFCI a relative value with respect to S / N of the comparative sample Indicated by Stability of the magnetic recording signals 300kFCI was evaluated as reproduced output S _{t = 100} ratio after regeneration output S _{t = 0} and 100 hours after recording _{(S t = 100 / S t} = 0).
Table 1 shows the results.

[0018]

[Table 1]

The magnetic recording medium of the present embodiment is more balanced than the comparative example in terms of D ₅₀ , S / N, and stability of a recording signal, and is thus found to be desirable as a high-density magnetic recording medium. Using the magnetic recording medium manufactured in this example,
A 2.5-inch magnetic recording / reproducing apparatus using a spin valve head as a reproducing element was manufactured. Surface recording density 12Gb
It was confirmed that an error rate of 10 ^-9 could be secured under the condition of / in ^{2 and that} the device operated as an ultra-high density recording / reproducing apparatus.

[Embodiment 2] Using a silicon substrate having a diameter of 2.5 inches, a DC magnetron sputtering method was used.
A perpendicular magnetic recording medium having the cross-sectional structure shown in FIG. 2 was manufactured. On a substrate 21, a first underlayer 22, a second underlayer 23,
A lower perpendicular magnetic film 24, an intermediate perpendicular magnetic film 25, an upper perpendicular magnetic film 26, and a protective film 27 were formed in this order. A Ti-10 at% Cr target for the first underlayer, a Co-35 at% Cr target for the second underlayer, a Co-5 at% Cr-8 at% Pt target for the lower perpendicular magnetization film, and a Co for the middle perpendicular magnetization film. -16at% Cr-8at% Pt-
3 at% Ta target, Co and P for upper perpendicular magnetization film
A carbon target was used for the target of t and the protective film. Ar gas pressure for sputtering is 3 mTorr, sputtering power is 10 W / cm ² , and substrate temperature is 280C.
An iCr film was formed to a thickness of 15 nm, a CoCr film was formed to a thickness of 10 nm, a lower perpendicular magnetic film was formed to a thickness of 2 nm, an intermediate perpendicular magnetic film was formed to a thickness of 24 nm, an upper perpendicular magnetic film was formed to a Co / Pt multilayer film of a thickness of 4 nm, and a carbon film was formed to a thickness of 7 nm. Here, the upper perpendicular magnetization film C
The o / Pt multilayer film is formed by alternately using Co and Pt targets for 2 cycles each having a thickness of 1 nm, for a total of 4
A perpendicular magnetic film having a thickness of nm was formed, and a perpendicular magnetic recording medium whose sectional structure was shown in FIG. 2 was formed.

As a comparative sample, a magnetic recording medium having the same structure as that of the first embodiment except that the lower perpendicular magnetic film, the intermediate perpendicular magnetic film, and the upper perpendicular magnetic film were each provided with a thickness of 30 nm on the underlayer. The coercive force Hc of these perpendicular magnetic recording media
And the evaluation of the recording / reproducing characteristics were performed using a vibrating magnetometer (VS
M), using a magnetic torque meter and a recording / reproducing separation type magnetic head. The gap length of the recording head is 0.2 μm,
The giant magnetoresistive (GMR) head for reproduction has a shield interval of 0.15 μm and a measuring spacing of 0.0.
4 μm. The recording density was determined by measuring the output half-density recording density (D ₅₀ ), which is half of the low-frequency reproduction output, and the signal-to-noise ratio S / S when magnetic recording of 20 kFCI was performed.
N is shown as a relative value to S / N of the sample of the present invention.
Stability of the magnetic recording signals 300kFCI was evaluated as reproduced output S _{t = 100} ratio after regeneration output S _{t = 0} and 100 hours after recording _{(S t = 100 / S t} = 0). Table 2 shows the results.

[0022]

[Table 2]

The magnetic recording medium of this embodiment is more desirable as a high-density magnetic recording medium in all of the characteristics of D ₅₀ , S / N, and signal stability than the comparative example. S / N is improved. Using the magnetic recording medium manufactured in this example, a 2.5-inch magnetic recording and reproducing apparatus using a GMR head as a reproducing element was manufactured. It was confirmed that an error rate of 10 ^-9 could be secured under the condition of a surface recording density of 20 Gb / in ² , and that the device operated as an ultra-high density recording / reproducing apparatus.

Further, instead of the Co / Pt multilayer film as the upper magnetic film, a Co / Pd multilayer film (Ku
= 1.2 × 10 ⁷ erg / cc) or CoCr ₅ Pt
_{8 It} was also confirmed that even when a (4 nm) magnetic film was used, the noise was significantly reduced and the characteristics desired as a high-density magnetic recording medium were exhibited.

Example 3 In the perpendicular magnetic recording medium experimentally manufactured in Example 2, the lower and upper perpendicular magnetic films were CoCr ₅ Pt ₈ (2 nm), and the intermediate perpendicular magnetic film was C.
oCr _x Ta ₄ (26 nm) with a Cr composition of 5 to 20 a
A medium sample was prepared in the range of t%. As a comparative sample, a perpendicular magnetic recording medium in which a recording magnetic film having a thickness of 30 nm was produced using only the intermediate perpendicular magnetic film was produced. CoCr _x Ta
₄ Dependence of the saturation magnetization and magnetic anisotropy energy of the (26 nm) film on the Cr composition and the coercive force (H
c) and the measurement results of the medium S / N are shown in FIGS. 3, 4, and 5, respectively.

The region exhibiting high desirable as a high-density magnetic recording medium coercivity and high media S / N, the value of magnetic anisotropy energy Ku _m intermediate perpendicular magnetization film is 1 × 10 ⁶ erg /
It has become clear that the range of _{cc <Ku m <3 × 10} 6 erg / cc. ^{_{Ku m <1 × 10 6 erg}} / cc 2kOe more coercive force required for high-density magnetic recording in becomes difficult to obtain, also ^{3 × 10 6 erg / cc <} Ku _m In the noise is increased 10Gb / in ² or more The required medium noise could not be obtained at the recording density. Further, when Ku _m is too large, it was found that also reduces the effect of providing a lower layer and the upper layer of higher magnetic film having magnetic anisotropy energy.

[0027]

According to the present invention, the stability of the heat resistance fluctuation of the magnetic recording medium can be ensured, the medium noise can be reduced, and the density of the magnetic disk drive can be increased, especially 10 Gb / in ^2. The above-described high-density magnetic recording becomes possible, and it is easy to reduce the size and capacity of the device.

[Brief description of the drawings]

FIG. 1 is a sectional view of a magnetic recording medium according to an embodiment of the present invention.

FIG. 2 is a sectional view of a magnetic recording medium according to an embodiment of the present invention.

FIG. 3 is a diagram showing the relationship between the Cr composition, saturation magnetization, and magnetic anisotropy energy of a Co alloy-based magnetic film of the present invention.

FIG. 4 is a diagram showing the relationship between the coercive force and the Cr composition of the perpendicular magnetic recording medium of the present invention.

FIG. 5 is a diagram showing the relationship between the S / N and the Cr composition of the perpendicular magnetic recording medium of the present invention.

[Explanation of symbols]

11 substrate, 12 base layer, 13 lower magnetic film, 14
Intermediate magnetic film, 15 ... Upper magnetic film, 16 ... Protective film, 17 ...
Lubricating film, 21: substrate, 22: first underlayer, 23: second underlayer, 24: lower perpendicular magnetization film, 25: intermediate perpendicular magnetization film, 2
6: Upper layer perpendicular magnetization film, 27: Protective film, 28: Lubricating film

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukio Honda 1-280 Higashi-Koigabo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. Central Research Laboratory (72) Inventor Teruaki Takeuchi 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Hitachi Central Research Laboratory (56) References JP-A 2000-76636 (JP, A) JP-A 11-102510 (JP) , A) JP-A-10-334440 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 5/66

Claims (5)

(57) [Claims] In the magnetic recording medium having a 1. A magnetic film and a protective film formed over the base film to a non-magnetic substrate and a non-magnetic substrate, said magnetic film is perforated at least three-layer structure
An in-plane magnetization film, a magnetic recording medium, wherein the magnetic anisotropic energy of the magnetic film substrate side of the layer and the surface side of the layer is larger than the magnetic anisotropy energy of the intermediate layer (the The magnetic anisotropy energy of each layer of the magnetic film is determined by forming each single-layer magnetic film and measuring its magnetic torque characteristics. 2. A non-magnetic substrate, and a base film on the non-magnetic substrate.
A magnetic film comprising a magnetic film formed through
In the recording medium, the magnetic film includes a lower layer on the substrate side, an intermediate layer, and a surface layer.
A perpendicular magnetization film having a three-layer structure of an upper layer on the surface side;
Layer and intermediate layer contain Co alloy material with hcp structure
And the magnetic anisotropy energy Ku _b ,
Ku _s is 3 × 10 ⁶ erg / cc ≦ K _b ≦ 5 × 10 ⁷ er
^{g / cc, 3 × 10 6} erg / cc ≦ Ku s ≦ 5 × 10 7
erg / cc, the magnetic anisotropy energy of the intermediate layer
Over Ku _m is ^{1 × 10 6 erg / cc <} Ku m <3 × 10 6 e
rg / cc.
The magnetic anisotropy energy of each layer of the magnetic film is
Forming a magnetic layer and measuring its magnetic torque characteristics.
And is determined by). 3. The magnetic recording medium according to claim 1 , wherein
The values of the magnetic anisotropy energy Ku _b of the layer on the substrate side, the magnetic anisotropy energy of the layer on the surface side, and the magnetic anisotropy energy Ku _m of the intermediate layer are 3 × 10 ⁶ erg /
_{cc ≦ Ku b ≦ 5 × 10} 7 erg / cc, 3 × 10 6 er
_{g / cc ≦ Ku s ≦ 5} × 10 7 erg / cc, 1 × 10 6
erg / cc <magnetic recording medium, characterized in that the range of ^{_{Ku m <3 × 10 6 erg}} / cc. 4. The magnetic recording medium according to claim 1 , wherein
A magnetic recording medium, wherein the magnetic film is made of a Co alloy material having a hexagonal close-packed structure. 5. The magnetic recording medium according to claim 1 , wherein
Co on the substrate side and the intermediate layer having a hexagonal close-packed structure
An alloy material, wherein the surface side layer is Co or Co
A magnetic recording medium comprising a laminated multilayer film made of an alloy and Pt, Pd or an alloy mainly containing these metals.