JP5115853B2 - Magnetic recording medium and method for manufacturing the same - Google Patents

Description

  The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium used for an external storage device of a computer. Furthermore, the present invention relates to a method for manufacturing the magnetic recording medium.

  As the recording density of the magnetic disk device increases, the flying height of the head slider becomes less than 10 nm, and intermittent contact between the head slider and the magnetic recording medium is inevitable. In order to prevent solid contact between the head slider and the magnetic recording medium, a protective layer made of carbon is formed on the magnetic layer on the surface of the magnetic recording medium, and a fluorine-based lubrication called PFPE (perfluoropolyether) is formed thereon. The agent layer is applied with a film thickness of about 1.0 to 2.0 nm. However, when the film thickness is 1.0 to 2.0 nm, it is impossible to completely cover the carbon layer, and solid contact that occurs during intermittent contact between the head slider and the magnetic recording medium cannot be avoided. Sometimes a high frictional force is generated, which causes wear on the head slider or magnetic recording medium.

  On the other hand, in order to completely cover the carbon layer with the lubricant layer, it is necessary to increase the film thickness of the lubricant layer more than the current level. However, when the film thickness is 2.0 nm or more, the interaction between the lubricant molecules is given priority over the interaction between the lubricant molecules and the carbon protective layer surface. Cause it to happen. Such aggregation of lubricant molecules hinders stable flying of the head slider.

  As a means for avoiding the solid contact without increasing the film thickness of the lubricant layer, for example, Patent Document 1 discloses a technique using a lubricant having a low number molecular weight with a number average molecular weight of a certain value or more and a specific molecular weight or less. Has been disclosed and tested under high temperature and high humidity conditions.

JP 2000-235709 A

  However, with the improvement of only the lubricant, there is a limit in avoiding contact between the head slider and the magnetic recording medium.

  Accordingly, the problem to be solved by the present invention is that magnetic recording that can avoid the occurrence of wear of the slider or the magnetic recording medium without generating a large frictional force even if contact occurs between the magnetic head slider and the magnetic recording medium. To provide a medium.

The present invention is a method for manufacturing a magnetic recording medium. (1) preparing a non-magnetic substrate, forming at least a magnetic layer, a protective layer and a lubricant layer on the non-magnetic substrate to produce a magnetic recording substrate; (2) the magnetic recording a step of heating the substrate, (3) the by leaving the magnetic recording substrate in a high-temperature high-humidity environment, a step of forming a moisture adsorption layer with a film thickness of not less than 0.3nm on the lubricant layer in this order Including. In the present invention, the high-temperature and high-humidity environment is an environment having a humidity of 70 to 90% and a temperature of 65 to 90 ° C., and the leaving time of the magnetic recording substrate in this environment is 40 to 60 hours. . Preferably, the high-temperature and high-humidity environment is an environment having a humidity of 80% and a temperature of 70 ° C., and the magnetic recording substrate is left in this environment for 50 hours.

  According to the present invention, a magnetic recording substrate coated with a lubricant (PFPE) is left in a high-temperature and high-humidity environment, and then left in a normal-temperature and normal-humidity environment to form a moisture adsorption layer on the surface of the magnetic recording substrate. By forming 0.3 nm or more, the frictional force when the head slider slides can be reduced as compared with the conventional magnetic recording medium.

  The first of the present invention relates to a magnetic recording medium. The magnetic recording medium of the present invention comprises at least a magnetic layer, a protective layer, and a lubricant layer provided on a nonmagnetic substrate, and a moisture adsorption layer is further provided on the lubricant layer with a predetermined thickness. .

  Next, the magnetic recording medium of the present invention will be described in detail. The magnetic recording medium of the present invention includes at least a magnetic layer, a protective layer, a lubricant layer, and a moisture adsorption layer on a nonmagnetic substrate. As an example, it has a structure as shown in FIG. That is, the magnetic layer 102, the protective layer 104, the lubricant layer 106, and the moisture adsorption layer 108 are provided on the nonmagnetic substrate 100.

  The nonmagnetic substrate is not particularly limited as long as it is conventionally used for a magnetic recording medium. For example, a non-magnetic metal layer (plating layer) 120 such as Ni-P is formed by electroless plating on a substrate 110 made of aluminum alloy or the like that has been conventionally used as shown in FIG. Alternatively, it may be made of a material such as glass, ceramic, or plastic.

  In the magnetic recording medium of the present invention, if necessary, a nonmagnetic underlayer, a soft magnetic layer, a seed layer, an intermediate layer, and the like may be provided between the nonmagnetic substrate and the magnetic layer.

  The optional nonmagnetic underlayer can be formed using a nonmagnetic material containing Cr, such as Ta, Ti, or a CrTi alloy.

  The optional soft magnetic layer includes a crystalline material such as FeTaC, Sendust (FeSiAl) alloy; a microcrystalline material such as FeTaC, CoFeNi, CoNiP; or a Co alloy such as CoZrNd, CoZrNb, CoTaZr. It can be formed using an amorphous material. The thickness of the soft magnetic layer is a layer for concentrating the magnetic field in the perpendicular direction on the magnetic layer, and the optimum value varies depending on the structure and characteristics of the magnetic head used for recording, but it is generally about 10 nm to 500 nm. This is desirable from the viewpoint of productivity.

  The seed layer which may be optionally provided can be formed using a metal or alloy having a face-centered cubic lattice structure, Ta or Ta alloy. As a metal or alloy having a face-centered cubic lattice structure, Cu, Pd, Pt, Ni or an alloy containing one or more of these; a permalloy-based material such as NiFe, NiFeSi, NiFeNb, NiFeB, NiFeCr, etc .; CoNiFe, A material obtained by further adding Co to a permalloy-based material such as CoNiFeSi, CoNiFeB, CoNiFeNb, or CoNiFeCr; Co; or a Co-based alloy such as CoB, CoSi, CoNi, or CoFe can be used. The seed layer desirably has a film thickness sufficient to control the crystal structure of the magnetic layer. In general, the seed layer desirably has a film thickness of 3 nm to 50 nm.

  The intermediate layer which may be optionally provided can be formed using Ru or an alloy containing Ru as a main component, or Co or an alloy containing Co as a main component. Further, these metals or alloys can be used by being laminated. The intermediate layer usually has a thickness of 0.1 nm to 30 nm. By setting the film thickness within such a range, it is possible to impart characteristics necessary for high-density recording to the magnetic layer without deteriorating the magnetic characteristics and electromagnetic conversion characteristics of the magnetic layer.

  The magnetic layer can be preferably formed using a ferromagnetic material of an alloy containing at least Co and Pt. In order to perform perpendicular magnetic recording, the easy axis of magnetization (c-axis of hexagonal close-packed (hcp) structure) of the material of the magnetic layer is perpendicular to the surface of the recording medium (that is, the main surface of the magnetic recording medium substrate). It must be oriented. The magnetic layer can be formed using an alloy material such as CoPt, CoCrPt, CoCrPtB, and CoCrPtTa. The film thickness of the magnetic layer is not particularly limited. However, from the viewpoint of improving productivity and recording density, the magnetic layer preferably has a thickness of 30 nm or less, more preferably 15 nm or less.

Alternatively, the magnetic layer may be formed using a material having a granular structure in which magnetic crystal grains are dispersed in a matrix of nonmagnetic oxide or nonmagnetic nitride. Materials having a granular structure that can be used include CoPt—SiO ₂ , CoCrPtO, CoCrPt—TiO ₂ , CoCrPt—SiO ₂ , CoCrPt—Al ₂ O ₃ , CoPt—AlN, CoCrPt—Si ₃ N _4, etc. It is not limited to these. When a material having a granular structure is used, it is possible to promote magnetic separation between adjacent magnetic crystal grains in the magnetic layer and improve magnetic recording characteristics such as noise reduction, SNR improvement and recording resolution improvement. it can.

  The protective layer can be formed using various thin layer materials known as carbon (diamond-like carbon, amorphous carbon, etc.) or a material for a protective layer of a magnetic recording medium. The protective layer is a layer for protecting each constituent layer below the magnetic layer underneath. In the magnetic recording medium of the present invention, the protective layer is preferably diamond-like carbon.

  As the material for the lubricant layer, those usually used for magnetic recording media can be used. For example, a perfluoropolyether lubricant can be used. As the film thickness of the lubricant layer, the film thickness used in a normal perpendicular magnetic recording medium can be applied.

  The moisture adsorption layer is obtained by leaving a magnetic recording substrate coated with a lubricant in a high temperature and high humidity environment, adsorbing moisture on the substrate surface, and forming a moisture film. The moisture adsorption layer needs to be formed with a film thickness of 0.3 nm or more, preferably 0.3 to 0.5 nm. In the present invention, the friction between the head slider and the surface of the magnetic recording medium can be remarkably reduced by providing the moisture adsorption layer with a predetermined thickness or more.

  Next, a method for manufacturing the magnetic recording medium of the present invention will be described. The method for manufacturing a magnetic recording medium of the present invention includes the following steps.

(1) preparing a non-magnetic substrate, forming at least a magnetic layer, a protective layer and a lubricant layer on the non-magnetic substrate to produce a magnetic recording substrate;
(2) A step of forming a moisture adsorption layer with a film thickness of 0.3 nm or more on the lubricant layer by leaving the magnetic recording substrate in a high temperature and high humidity environment and then in a normal temperature and normal humidity environment.

  Step (1) is a step of manufacturing a magnetic recording substrate, and a conventional method of manufacturing a magnetic recording medium can be applied. For example, the above-mentioned optional nonmagnetic underlayer, soft magnetic layer, seed layer, and intermediate layer are formed in the related art such as sputtering (including DC magnetron sputtering, RF magnetron sputtering), vacuum deposition, etc. It can be carried out using any known method. The formation of the magnetic layer can be carried out using any method known in the art such as sputtering (including DC magnetron sputtering, RF magnetron sputtering, etc.), vacuum deposition, and the like. The protective layer can be generally formed using a sputtering method (including a DC magnetron sputtering method, an RF magnetron sputtering method, etc.), a vacuum deposition method, a CVD method, or the like. The lubricant layer can be formed using any coating method known in the art such as a dip coating method and a spin coating method. The conditions for forming these layers differ depending on the materials used, but the conditions disclosed for the conventional method of manufacturing a magnetic recording medium may be applied.

Step (2) is a step of forming a moisture adsorption layer. In the present invention, the moisture adsorption layer is formed by surface treatment according to the following procedure.
(I) The magnetic recording substrate coated with the lubricant is left in a high-temperature and high-humidity environment to form a moisture adsorption layer of 0.3 nm or more on the surface of the magnetic recording substrate.
(Ii) After the moisture adsorption layer is formed, the environment of the magnetic recording substrate is shifted from a high temperature and high humidity environment to a normal temperature and normal humidity environment.

  In the present invention, the high temperature and high humidity environment is, for example, an environment having a humidity of 70 to 90% and a temperature of 65 to 90 ° C. The normal temperature and normal humidity environment is, for example, an environment having a humidity of 30 to 50% and a temperature of 15 to 25 ° C. The magnetic recording substrate is preferably left in the high temperature and high humidity environment for 40 to 60 hours, and preferably in a normal temperature and normal humidity environment for 1 to 240 hours. A particularly preferable high-temperature and high-humidity environment is an environment with a humidity of 80% and a temperature of 70 ° C., and the time for which the magnetic recording substrate is left in this environment is 50 hours. A particularly preferred ambient temperature and humidity environment is an environment with a humidity of 40% and a temperature of 25 ° C., and the magnetic recording substrate is left in this environment for 24 hours.

  In the present invention, the surface treatment of the magnetic recording medium is performed by the following procedure to form a moisture adsorption layer of 0.3 nm or more on the surface of the magnetic recording substrate. In the present invention, the moisture adsorption layer is particularly preferably in the range of 0.3 nm to 0.5 nm.

  It is preferable that the moisture adsorption layer is formed in a predetermined chamber (for example, a VC-10 chamber manufactured by VENA) so that impurities other than moisture are not mixed.

  In the magnetic recording medium of the present invention, if moisture in the moisture adsorption layer existing on the surface penetrates to the magnetic layer inside the magnetic recording medium, it may cause corrosion. Therefore, it is necessary for the magnetic recording medium of the present invention to enhance the coverage of the lubricant layer with respect to the protective layer as much as possible and suppress the penetration of moisture into the lower layer.

  Therefore, it is preferable to heat-treat the magnetic recording medium of the present invention at a temperature of 100 ° C. or higher, preferably 100 ° C. to 150 ° C. after applying the lubricant. By performing the heat treatment, the viscosity of the lubricant can be temporarily reduced, and re-diffusion of the lubricant on the surface of the magnetic recording medium can be promoted. As a result, the lubricant is diffused and adsorbed on the portion of the magnetic recording medium that is not coated with the lubricant, and as a result, the coverage of the lubricant is improved.

  Examples of the present invention will be described below, but the following examples are merely representative examples for explaining the present invention and do not limit the present invention in any way.

(1) Production of magnetic recording substrate A magnetic recording substrate was produced by the following procedure.
A chemically tempered glass substrate (N-5 glass substrate, manufactured by HOYA) having a smooth surface is used as a nonmagnetic substrate, and this is introduced into a sputtering apparatus after cleaning, and CoZrNb amorphous by a DC magnetron sputtering method using a Co85Zr10Nb5 target. A soft soft magnetic underlayer was deposited to 110 nm, and a Ru nonmagnetic metal layer was subsequently deposited at 0.8 nm under an Ar gas pressure of 4.0 Pa by a DC magnetron sputtering method using a Ru target.
Next, the surface of the Ru nonmagnetic metal layer was exposed to nitrogen for 3 seconds under an atmosphere of 10 mTorr using Ar gas (Ar-10% N 2 gas) containing 10 at% nitrogen gas. Again, a CoZrNb amorphous soft magnetic backing upper layer was deposited to 90 nm under Ar gas pressure of 1.2 Pa by DC magnetron sputtering using a Co85Zr10Nb5 target.

  Subsequently, a carbon protective layer was formed with a film thickness of 3.0 nm by the CVD method, and then taken out from the vacuum apparatus. Thereafter, a perfluoropolyether (PFPE) lubricant (product name: Z-tetraol) generally used for a magnetic recording medium is applied onto the obtained substrate on a carbon protective layer formed by a CVD film forming method. Was applied to 1.2 nm. A magnetic recording substrate was prepared from the above procedure.

Next, the surface treatment of the obtained magnetic recording substrate was performed according to the following procedure.
The magnetic recording substrate produced by the above process was left for a long time in a high temperature and high humidity (70 ° C., 80%) environment in a VC-10 chamber manufactured by VENA (see FIG. 2 for the leaving time).

  FIG. 2 shows the relationship between the film thickness of the moisture adsorption layer formed on the surface of the magnetic recording substrate and the standing time. The film thickness of the moisture adsorption layer tended to increase as the time of leaving in the high temperature and high humidity environment became longer. In the magnetic recording substrate used in this example, the film thickness reached 0.3 nm after standing for 50 hours. The film thickness of the moisture adsorption layer was measured using a scanning ellipsometer (OSA5100).

  Further, FIG. 3 shows the film thickness of the moisture adsorbing layer immediately after being taken out from the chamber and the change over time in the film thickness of the moisture adsorbing layer when left in a room temperature and normal humidity (25 ° C., 40%) environment after taking out from the chamber. Shown in It was shown that the film thickness of the moisture adsorbing layer hardly changed even after 1 week immediately after standing.

A sliding test (Drag test) was performed on the surface of the magnetic recording medium sample produced by the above process using a 30% size (1.2 mm × 1.0 mm) head slider. The conditions of the sliding test are shown below.
Measured magnetic recording medium:
-Size 95mm in diameter (3.5 inch size)
-Protective layer Carbon protective layer (thickness 3.0 nm)
-Lubricant layer Z-tetraol (thickness 1.2 nm)
-Magnetic recording media left for the following time in a high temperature and high humidity environment (70 ° C, 80%) Standing time: 0, 2, 10, 30, 50, 63 hours (6 conditions)

Number of rotations of magnetic recording medium: 7200 rpm → 700 rpm (decrease in 10 seconds) → 7200 rpm (increase in 10 seconds)
Test radius position: 25 mm
Slider load: 2.5 gf
Measurement item: Friction force (measured by strain sensor)

  As a result of the sliding test, almost no frictional force was measured between the head slider and the magnetic recording medium surface in the magnetic recording medium having a moisture adsorption layer thickness of 0.3 nm (standing time 50 hours) or more. On the other hand, in the magnetic recording medium having a moisture adsorption layer thickness of less than 0.3 nm (less than 50 hours), it can be seen that a maximum frictional force of about 5 gf is generated by the sliding operation.

  FIG. 4 shows the results showing the frictional force during the sliding test (when the rotation speed of the magnetic recording medium is 700 rpm) when the film thickness of the moisture adsorption layer is used as a parameter. It can be seen that when the film thickness of the moisture adsorption layer is less than 0.3 nm, a high frictional force is detected. That is, the effect of reducing the frictional force between the head slider and the magnetic recording medium surface is that the film thickness of the moisture adsorption layer is 0.3 nm or more.

It is the schematic which shows the structure of the magnetic recording medium of this invention. It is a graph which shows the relationship between the film thickness of the water | moisture-content adsorption layer formed in the magnetic recording substrate surface based on this invention, and standing time. It is a graph which shows the time-dependent change of the film thickness of a water | moisture-content adsorption | suction layer measured with the scanning ellipsometer when the magnetic recording substrate of this invention was left to stand in normal temperature normal humidity environment. It is a graph which shows the relationship between the film thickness of a water | moisture-content adsorption layer at the time of sliding operation | movement, and frictional force (at the time of the rotation speed of a magnetic recording medium 700 rpm).

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Nonmagnetic substrate 102 Magnetic layer 104 Protective layer 106 Lubricant layer 108 Moisture adsorption layer 110 Substrate 120 Nonmagnetic metal layer (plating layer)

Claims (2)

(1) preparing a non-magnetic substrate, forming at least a magnetic layer, a protective layer and a lubricant layer on the non-magnetic substrate to produce a magnetic recording substrate;
(2) heat-treating the magnetic recording substrate;
( 3 ) forming the moisture adsorption layer with a film thickness of 0.3 nm or more on the lubricant layer by leaving the magnetic recording substrate in a high temperature and high humidity environment ;
In this order, a method for manufacturing a magnetic recording medium. The high-temperature and high-humidity environment, moisture 70% to 90%, the temperature 65 to 90 ° C. environment claim 1, wherein the standing time of the magnetic recording substrate to the environment is 40 to 60 hours A method for producing the magnetic recording medium according to 1.

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