JP2008059749A - Manufacturing method of perpendicular magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a perpendicular magnetic recording medium having a high S/N ratio and high thermal agitation resistance and to provide a manufacturing method thereof. <P>SOLUTION: A perpendicular magnetic recording layer as a magnetic layer is provided with magnetic crystal grains and a crystal grain boundary interposed between the magnetic crystal grains and composed of a non-magnetic layer. In the manufacturing method of the perpendicular magnetic recording medium for forming at least the magnetic layer on a substrate, a correlation between the thickness of the grain boundary and a magnetization inversion nucleation field Hn is previously calculated, the thickness of the grain boundary for a prescribed magnetization inversion nucleation field Hn is determined based on the correlation and the medium is manufactured with the determined thickness of the grain boundary. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium for a magnetic disk mounted in a hard disk drive (magnetic disk device) or the like, and more particularly to a perpendicular magnetic recording medium for a magnetic disk.

  Various information recording techniques have been developed with the recent increase in information processing capacity. In particular, the surface recording density of a hard disk drive using magnetic recording technology has been increasing at a rate of ˜100% / year in recent years. In order to achieve a high surface recording density, it is naturally essential to improve the performance of both a medium for recording information signals, a so-called magnetic recording medium, and a magnetic head for recording and reproducing information signals. is there. In particular, in order to improve the performance of a magnetic recording medium, that is, to secure a sufficient S / N ratio at a high surface recording density, the magnetic layer of the ferromagnetic layer responsible for recording information signals is made finer and the layer It is necessary to reduce the thickness.

Conventionally, an in-plane recording system (also called a horizontal recording system or a longitudinal recording system) has been adopted as a recording system for magnetic recording media. However, in the in-plane recording method, as a result of progress in the miniaturization of magnetic crystal grains and the reduction in the thickness of the magnetic layer in response to the increase in recording density, the resistance to thermal disturbance due to the superparamagnetic phenomenon has come to occur. As a result, there has been a problem that the recorded information signal disappears with the passage of time.
Several methods have been proposed to overcome this, and one of them is a perpendicular magnetic recording method. This perpendicular magnetic recording system is attracting attention as a method that can achieve a sufficient S / N ratio while maintaining good thermal disturbance resistance in a high surface recording density region.

  A recording medium used in a conventional perpendicular magnetic recording system will be described with reference to FIGS. 2 and 3 are schematic sectional views of a conventional perpendicular magnetic recording medium. FIG. 2 is a so-called single-layer perpendicular magnetic recording medium, and FIG. 3 is a so-called two-layer perpendicular magnetic recording medium. In the figure, 21 and 31 are substrates made of glass or Al alloy, 22 is a crystal axis control layer (nonmagnetic underlayer) made of Ti or Ti alloy film, 23 and 34 are perpendicular magnetic recording made of CoCrPt alloy film, etc. Layers, 24 and 35 are protective layers made of a C film, 32 is a base soft magnetic layer made of a CoNbZr amorphous alloy film, etc., 33 is a magnetic exchange coupling between the base soft magnetic layer 32 and the perpendicular magnetic recording layer 34. The intermediate layers 25 and 36 for blocking are lubricating layers.

  The perpendicular magnetic recording layer as shown in these figures is a polycrystalline body that is an aggregate of fine crystal grains, as in the case of the longitudinal recording medium. However, the average easy axis of magnetization of the crystal grains is substantially parallel to the normal direction of the substrate surface. The information signal is recorded as a change in position in the magnetization direction of the perpendicular magnetic recording layer.

  In the case of a perpendicular magnetic recording medium, the average magnetization direction in the recording bit is the vertical direction perpendicular to the substrate surface, whereas in the case of a longitudinal recording medium, the average magnetization direction is in the substrate surface and circular. It is parallel to the circumferential direction and is the running direction of the recording head or the opposite direction. This difference in the magnetization direction in the recording state is the reason why a sufficient S / N ratio can be achieved while maintaining the characteristics of the perpendicular magnetic recording method described above and good thermal disturbance resistance. (Reference: H.N. Bertram and M. Williams, “SNR and Density Limit Estimations: A Comparison of Longitudinal and Perpendicular Recording”, IEEE Trans. Magn., Vol.36, pp4-9 (2000))

However, in the conventional perpendicular magnetic recording medium, the potential of the perpendicular magnetic recording method described above could not be sufficiently extracted due to problems with the magnetic characteristics. Hereinafter, problems to be solved by the present invention, that is, problems of the conventional perpendicular magnetic recording medium will be described with reference to FIGS.
FIG. 4 is a schematic diagram showing a microscopic structure in a recording state of the perpendicular magnetic recording layer. In the figure, 41 is a perpendicular magnetic recording layer, 42 is a crystal grain forming the perpendicular magnetic recording layer, 43 is a magnetization transition line, 44 and 45 are arrows indicating the average magnetization direction in each recording bit, 46 is each recording In the bit, the reverse magnetic domain is oriented in a direction different from the average magnetization direction.

In general, it is known that noise sources in a perpendicular magnetic recording medium are (1) irregular magnetization transition line shape and (2) occurrence of reverse magnetic domain. In other words, when developing a high S / N medium, it is important to minimize the magnetization transition lines with good linearity and the frequency of occurrence of reverse magnetic domains. In particular, in order to ensure the linearity of the magnetization transition line, it is indispensable to cut off the magnetic exchange interaction acting between crystal grains.
As described above, the main points of the perpendicular magnetic recording layer for extracting the excellent potential of the perpendicular magnetic recording system are suppression of reverse magnetic domain generation and interruption of intergranular exchange interaction.

The occurrence tendency of the reverse magnetic domain and the magnitude of the intergranular exchange interaction can be evaluated by the shape of the MH curve. FIG. 5 shows an MH curve relating to a conventional perpendicular magnetic recording medium.
In FIG. 5, Hc is a coercive force, Ms is a saturation magnetization, Mr is a residual magnetization, and Hn is a magnetization reversal nucleation magnetic field.
Hn is obtained as the value of the magnetic field when the magnetization amount becomes the saturation magnetization Ms at the tangent line of the MH curve at the coercive force Hc (the magnetization amount is expressed as a linear function of the magnetic field).
The tendency to generate reverse magnetic domains can be evaluated by the Mr / Ms ratio (hereinafter referred to as squareness ratio). The smaller the squareness ratio, the higher the frequency of occurrence of reverse magnetic domains. From the viewpoint of preventing reverse magnetic domains, the squareness ratio is preferably close to 1.

The magnitude of the grain boundary exchange interaction can be evaluated by the slope of the MH curve at the coercive force Hc. The larger the slope of the MH curve in the coercive force Hc, the greater the intergranular exchange interaction. In order to suppress the grain boundary exchange interaction, the closer to 1 / (4π) (π is the circularity, CGS unit system), which is the theoretical lower limit of the slope of the MH curve in the coercive force Hc, is preferable.
Further, it is known that the thermal disturbance resistance and the Hn have a certain relationship, and the smaller the Hn is, the higher the thermal disturbance resistance tends to be. Therefore, in order to improve thermal disturbance tolerance, it is preferable that the value be as small as possible.
However, in the conventional perpendicular magnetic recording medium, the above-mentioned preferable characteristics required for each of (1) reverse magnetic domain, (2) grain boundary exchange interaction, and (3) resistance to thermal disturbance cannot be simultaneously achieved. .

  An object of the present invention is to achieve a high S / N ratio in a perpendicular magnetic recording medium by simultaneously satisfying desirable characteristics required for (1) reverse magnetic domain, (2) grain boundary exchange interaction, and (3) resistance to thermal disturbance. The present invention provides a perpendicular magnetic recording medium for a magnetic disk and a method for manufacturing the same, which is excellent in thermal disturbance resistance.

In order to solve the above problems and achieve a desired object, the present invention is configured as follows.
(1) In a perpendicular magnetic recording medium having at least a magnetic layer on a substrate,
The magnetic crystal grains constituting the magnetic layer have a particle size of 5 nm to 20 nm,
A perpendicular magnetic recording medium having a grain boundary thickness of 0.5 nm or more made of a non-magnetic material interposed between the magnetic crystal grains was used.
(2) In a perpendicular magnetic recording medium having at least a magnetic layer on a substrate,
A perpendicular magnetic recording medium having a magnetization reversal nucleation magnetic field of Hn <0, a squareness ratio of 0.75 or more, and a slope of the MH curve with a coercive force Hc of approximately 1 / (4π) was used.

(3) In the perpendicular magnetic recording medium of (1),
A perpendicular magnetic recording medium having a magnetization reversal nucleation magnetic field of Hn <0, a squareness ratio of 0.75 or more, and a slope of the MH curve with a coercive force Hc of approximately 1 / (4π) was used.

(4) A method of manufacturing a perpendicular magnetic recording medium in which at least a magnetic layer is formed on a substrate,
The magnetic layer includes magnetic crystal grains and a crystal grain boundary made of a nonmagnetic material interposed between the magnetic crystal grains,
In advance, a correlation between the grain boundary thickness and the magnetization reversal nucleation magnetic field Hn is obtained,
Based on the correlation, a crystal grain boundary thickness at which a predetermined magnetization reversal nucleation magnetic field Hn is obtained is selected, and the perpendicular magnetic recording medium manufacturing method is manufactured to achieve the selected crystal grain boundary thickness.

  These perpendicular magnetic recording media according to the present invention are configured so that the magnetic exchange interaction between the magnetic crystal grains is blocked by the non-magnetic material, and the material of the magnetic layer is Co and It may be configured to contain Cr and Pt.

  According to the present invention, it is possible to provide a perpendicular magnetic recording medium for a magnetic disk having a high S / N ratio and good thermal disturbance resistance.

The inventors of the present invention have made extensive studies in view of the above-mentioned object. As a result, in the perpendicular magnetic recording medium, each of the magnetization reversal nucleation magnetic field Hn, the squareness ratio Mr / Ms, and the slope of the MH curve at the coercive force Hc. It has been found that the above characteristics are closely related to the thickness of the nonmagnetic material formed at the grain boundary of the magnetic crystal grains in the magnetic layer (perpendicular magnetic recording layer), that is, the grain boundary thickness. As a result of research based on this knowledge, when the grain size of the magnetic crystal grains is 5 nm to 20 nm and the grain boundary thickness is 0.5 nm or more, the magnetization reversal nucleation magnetic field Hn, the squareness ratio Mr / Ms It was discovered that each of the slopes of the MH curve at the coercive force Hc can be simultaneously set to the above-described preferred value.
According to the present invention, Hn <0, Mr / Ms can be 0.75 or more, and the slope of the MH curve at the coercive force Hc is approximately 1 / (4π) (CGS unit system). This is preferable.
Based on experiments by the present researchers, the perpendicular magnetic recording medium according to the present invention can obtain a high S / N ratio and excellent thermal disturbance resistance, so that the perpendicular magnetic recording medium suitable for high recording density can be obtained. Is preferable.
According to the study by the present inventors, the effects obtained by the present invention are considered as follows.

Hereinafter, the solution according to the present invention will be described with reference to FIG. FIG. 6 is a schematic sectional side view showing the film structure of the perpendicular magnetic recording medium. In the figure, 61 is a substrate, 62 is a nonmagnetic underlayer, 63 is a perpendicular magnetic recording layer made of a Co-based polycrystalline alloy film, 64 is a magnetic crystal particle constituting the perpendicular magnetic recording layer 63, and 65 is between the crystal grains. It is a nonmagnetic grain boundary. The nonmagnetic underlayer 62 has functions such as controlling the preferential orientation of the crystal axes of the perpendicular magnetic recording layer 63 or the size of the crystal grains 63, and is not necessarily a single nonmagnetic layer. There is no need, and a so-called multilayer structure in which a plurality of thin films are laminated may be employed.
At this time, the nonmagnetic crystal grain boundaries 65 to be arranged have a nonmagnetic average arrangement interval as an average value of the intervals (shortest distances) between the nonmagnetic crystal grain boundaries 65 separating the magnetic crystal grains 64. This may be called “the thickness of the crystal grain boundary 65”.

Based on the results of research conducted by the inventors regarding the configuration of the present invention, the inventors conducted numerical analysis by simulation. The results are listed in FIG. The horizontal axis in FIG. 7 is the grain boundary thickness made of a non-magnetic material, and the vertical axis is the magnetization reversal nucleation magnetic field (Hn) and the coercive force (Hc). A curve 71 in FIG. 7 shows the analysis result for Hn, and a curve 72 shows the analysis result for Hc. Here, exchange interaction between magnetic crystal grains does not work, Ms: 300 emu / cc, magnetocrystalline anisotropy energy: 1 × 10 ⁻⁶ erg / cc, magnetic crystal grain size: 10 nm, Numerical simulation was performed assuming that the vertical height of magnetic crystal grains was 30 nm.
From the analysis results of the present inventors, as shown in the same figure, the magnetization reversal nucleation magnetic field Hn becomes a small value less than zero along with the average thickness of the crystal grain boundary made of a non-magnetic material. The increasing correlation of the coercive force Hc was calculated.

The simulation results can be understood qualitatively as follows. That is, as described above, only the magnetic crystal grains 64 have magnetization, and the nonmagnetic crystal grain boundary 65 has no magnetization. Therefore, when the grain boundary thickness made of a non-magnetic material is zero, the saturation magnetization value viewed as the perpendicular magnetic recording layer 63 matches the saturation magnetization value Ms of the magnetic crystal grain 64, but the non-magnetic crystal grain It decreases with increasing field thickness. As a result, the magnetization reversal nucleation magnetic field Hn increases from the relationship shown in Expression (1) to the negative side.
The result shown in FIG. 7 is merely an example, and the dependence of the magnetization reversal nucleation magnetic field Hn and the coercive force Hc on the grain boundary thickness is essential, and the size and saturation of a specific crystal grain 64 It is not a unique phenomenon that appears only in magnetization Ms and magnetocrystalline anisotropy energy.

In the configuration of the present invention, by setting the grain boundary thickness made of a non-magnetic material within a predetermined range, the exchange interaction between the magnetic crystal grains is almost suppressed or completely blocked. It is considered that the slope of the curve can be suppressed to approximately 1 / (4π).
Conventionally, in the perpendicular magnetic recording medium, the correlation between the grain boundary thickness, which is a non-magnetic material, and the magnetization reversal nucleation magnetic field, which the present inventors have found, has not been clarified.
Therefore, no means for simultaneously realizing the condition that Hn <0, the squareness ratio is 0.75 or more, and the slope of the MH curve at the coercive force Hc is approximately 1 / (4π) has not been provided.

  The reason will be described in detail. When the slope of the MH curve is kept small, it is important to suppress the exchange interaction between the magnetic particles 64 as described above. However, the perpendicular magnetic recording medium does not have the exchange interaction. Assuming that, the magnetization reversal nucleation magnetic field Hn is approximately given by (1) when expressed in the cgs unit system.

式(1)において、πは円周率である。

In equation (1), π is the circumference ratio.

  Normally, the coercive force Hc is 1/4 to 1/3 of the anisotropy magnetic field Hk, so Hc = (1/3) × Hk, and here, the condition that Hn <0 is substituted into the equation (1). Then, (2) is obtained.

  For the perpendicular magnetic recording layer, a Co-based alloy having a hexagonal close-packed structure (for example, a CoCr-based alloy or a CoPt-based alloy) is used. In the case of these Co-based alloys, if Ms is reduced, In conjunction with this, Hk also decreases. For this reason, it was considered that the condition of the formula (2) could not be satisfied practically.

  In the present invention, the characteristics of Hn have been researched and developed from the viewpoint of the average thickness (grain boundary thickness) of the non-magnetic material based on the above-described numerical analysis results, and the invention based on this knowledge has been completed. It is.

  In the present invention, one of the reasons why a suitable characteristic is obtained is that, as can be seen from the result of the numerical analysis, Hc improves (numerical value decreases) and Hc increases (numerical value increases). It can also be mentioned that it acts in the direction of further improving Hn.

  In the present invention, the average thickness of the crystal grain boundary, which is a nonmagnetic material, is more preferably 0.5 nm to 10 nm, and more preferably 1.5 nm to 5 nm. If it is less than 0.5 nm, the effect of improving (decreasing) Hn is insufficient, and the effect of blocking the exchange interaction between magnetic crystal grains is not sufficient, and it is preferable because it enters the region where the slope of the MH curve increases. Absent. On the other hand, if it exceeds 10 nm, the saturation magnetization is remarkably reduced, and the reproduction output of the recording signal tends to be lowered. In this case, it may be difficult to obtain a sufficient S / N.

The particle diameter of the magnetic crystal grains of the perpendicular magnetic recording medium according to the present invention is particularly preferably 5 to 20 nm. If it is less than 5 nm, the thermal disturbance resistance deteriorates, which is not preferable. If it exceeds 20 nm, medium noise increases and S / N tends to deteriorate. From the viewpoint of S / N, it is particularly preferable that the thickness is 15 nm or less.
The thickness of the perpendicular magnetic recording layer (magnetic layer) of the perpendicular magnetic recording medium is preferably 10 to 50 nm, more preferably 10 to 30 nm, and more preferably 20 to 30 nm. If it is less than 10 nm, the resistance to thermal disturbance deteriorates, and if it exceeds 50 nm, the S / N ratio tends to deteriorate.

The magnetization reversal nucleation magnetic field Hn obtained by the configuration of the present invention is desirably a negative value less than 0 for the reasons described above. In particular, in a high recording density medium of 60 Gbit / inch ² or more, it is desirable that it is −0.5 kOe or less from the relationship between thermal fluctuation and medium noise. In the present invention, the squareness ratio (Mr / Ms ratio) is preferably 0.75 or more, and more preferably 0.90 or more. In this case, the occurrence of reverse magnetic domains is substantially suppressed, which is preferable.

In the present invention, the slope of the MH curve at the coercive force Hc is preferably approximately 1 / (4π). In the configuration of the present invention, the material of the perpendicular magnetic recording layer is preferably a Co-based alloy, particularly a CoCr-based alloy, a CoPt-based alloy, or a CoCrPt-based alloy in that a high recording density can be achieved. Inclusion of Cr in Co promotes the formation of non-magnetic material between magnetic crystal grains, and inclusion of Pt facilitates high coercivity, thus reducing media noise and resistance to thermal fluctuations. It is also advantageous for improvement. From this point of view, the CoCrPt system including both of them is particularly useful for the perpendicular magnetic recording medium capable of 60 Gbit / inch ² or more provided in the present invention.

  As an alloy material of this system, a CoCrPtB alloy is preferable because the S / N ratio is particularly high. Nonmagnetic materials that form grain boundaries and are arranged between magnetic crystal grains include materials containing Cr, Si, Cu, Ag, Au, B, C, etc., or oxides thereof. Nitride is preferred. This is because when these substances and the substance that is the material of the magnetic layer are formed at the same time, a vertical boundary in which a crystal grain boundary made of the non-magnetic material is formed around the magnetic particles made of the material of the magnetic layer. This is because a magnetic recording layer is formed.

  In the configuration of the present invention, in order to further promote the effect of increasing the recording density, a crystal axis control layer (nonmagnetic underlayer) that increases the perpendicular orientation of the perpendicular magnetic recording layer between the substrate and the perpendicular magnetic recording layer. In this case, an intermediate layer that enhances the lattice coupling between the crystal axis control layer and the perpendicular magnetic recording layer is also preferably provided between the crystal axis control layer and the perpendicular magnetic recording layer. . As a material for the crystal axis control layer, Ti or a Ti-based alloy having an hcp structure, which has a large effect of improving the perpendicular orientation of the perpendicular magnetic recording layer, is preferable. Examples of Ti-based alloys include TiCr-based alloys. The material for the intermediate layer is preferably a CoCrTa alloy. The film thickness of the crystal axis control layer is not particularly limited, but is preferably 5 nm to 20 nm from the viewpoint of vertical alignment.

  In the present invention, a soft magnetic layer may be provided on the substrate side separately from the perpendicular magnetic recording layer. This soft magnetic layer appropriately controls a magnetic circuit during recording in a perpendicular magnetic recording medium. Examples of the material of the soft magnetic layer include amorphous materials such as CoNbZr, and materials such as FeMn, InMn, NiMi, and NiFe. When the soft magnetic layer is provided, an intermediate layer for blocking the magnetic exchange interaction between the soft magnetic layer and the perpendicular magnetic recording layer may be provided. As can be seen from the above description, the present invention can be applied without being limited to a single layer type perpendicular magnetic recording medium or a double type perpendicular magnetic recording medium.

In the present invention, the substrate is not particularly limited. A glass substrate, an Al alloy substrate, a carbon substrate, a ceramic substrate, a silicon substrate, or the like can be used. Examples of the glass substrate include a chemically strengthened glass substrate and a crystallized glass substrate. Since the glass substrate is excellent in flatness, smoothness, and rigidity, it is particularly preferable in a high recording density region such as 60 Gbit / inch ² or more provided by the present invention. Furthermore, since the glass substrate has high heat resistance, the glass substrate is formed and manufactured at a high temperature, and is highly useful for increasing the recording density. Examples of the glass type of the glass substrate include aluminosilicate glass, soda lime glass, aluminoporosilicate glass, polosilicate glass, crystallized glass, and quartz glass.

  In the present invention, the film forming method is not particularly limited, but a sputtering method that can easily increase the recording density is preferable. The sputtering method may be either a DC sputtering method or an RF sputtering method. Moreover, any manufacturing method such as an inline type or a single wafer type may be used. The average thickness (crystal grain boundary thickness) of the nonmagnetic material can be controlled by the blending ratio of the material for the perpendicular magnetic recording layer and the material for the nonmagnetic material, which is contained in the sputtering target for forming the magnetic layer. For the inclusion method, the sputtering target may be included directly, or a non-magnetic material pelletized may be placed on the sputtering target. Further, the average thickness of the non-magnetic material can be appropriately controlled by a film forming method such as a film forming speed, a film forming temperature, a degree of vacuum during film forming, and bias application.

  When the non-magnetic material is an oxide or nitride, it is included in the sputtering target, or an oxygen-containing gas (oxygen gas, ozone gas, water, carbon dioxide gas, nitrogen monoxide gas, nitrogen dioxide) during film formation. Gas, etc.), nitrogen-containing gas (nitrogen gas, nitrogen monoxide gas, nitrogen dioxide gas, cyanide gas, ammonia gas, etc.) and sputtering gas (argon gas etc.) are mixed and controlled by controlling the mixing amount. When the nonmagnetic material is an oxide or a nitride, grain boundaries are well formed, which is highly useful.

  In the present invention, if necessary, a protective layer and a lubricating layer can be formed on the magnetic layer. The protective layer is formed for the purpose of protecting the magnetic layer from contact with the magnetic head and improving reliability. The lubrication layer is provided to reduce the sliding resistance between the magnetic head and the medium, and examples thereof include a PFPE (perfluoropolyether) lubricant. As a coating method, a known method such as a dip method, a spin coating method, or a spray method can be used.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the following is merely an example of the present invention and does not limit the technical scope of the present invention.
<Example 1>
A first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic sectional view showing the structure of a perpendicular magnetic recording medium according to the present invention. In the figure, 11 is a disk-shaped glass substrate made of chemically strengthened aluminosilicate glass, 12 is a nonmagnetic underlayer (crystal axis control layer) made of Ti, 13 is Cr: 32 at%, Ta: 3 at%, Co: CoCrTa alloy intermediate layer consisting of bal., 14 is Cr: 17 at%, Pt: 15 at%, B: 8 at%, CoCrPtB alloy perpendicular magnetic recording layer (magnetic layer) consisting of Co: bal., 15 is a protection consisting of C Is a layer. The Ti layer 12 is a crystal control layer provided for the purpose of promoting the C-axis preferential orientation of the CoCrTa alloy layer 13 and the CoCrPtB alloy perpendicular magnetic recording layer 14, and the layer thickness is 10 nm. The CoCrTa alloy layer 13 is a non-magnetic material, and is an intermediate layer provided to match the lattice constant with the CoCrPtB alloy recording layer 14 and suppress the generation of an initial growth layer (not shown) having poor magnetic properties. is there. The layer thickness is 10 nm. The CoCrPtB alloy perpendicular magnetic recording layer 14 has a thickness of 30 nm, and the C (carbon) protective layer has a thickness of 5 nm. Reference numeral 16 denotes a lubricating layer (layer thickness: 0.9 nm) made of PFPE. Hereinafter, a method for manufacturing the perpendicular magnetic recording medium will be described.

First, the Ti layer 12 was formed on the substrate 11 in a pure Ar atmosphere by RF sputtering. Thereafter, similarly, a CoCrTa alloy layer 13 and a CoCrPtB alloy perpendicular magnetic recording layer 14 (magnetic layer) were sequentially formed in a pure Ar atmosphere by RF sputtering. Finally, the C protective layer 15 was formed in a mixed atmosphere of (Ar + H ₂ ). Here, although the RF sputtering method is used as the film forming method, for example, a CVD method, a DC sputtering method, or the like may be used as another method. Thereafter, a lubricating layer 16 made of PFPE is formed by 0.9 nm by dipping.

Next, the crystal structure and preferential orientation of the perpendicular magnetic recording medium obtained as described above were evaluated by X-ray diffraction. As a result, it was confirmed that the CoCrPtB alloy perpendicular magnetic recording layer had a hexagonal close-packed structure, and the c-axis was generally oriented in the normal direction of the substrate surface. The dispersion of the degree of orientation (Δθ ₅₀ ) was about 6 °. Next, the CoCrPtB alloy perpendicular magnetic recording layer portion of the perpendicular magnetic recording medium obtained as described above was observed with a transmission electron microscope. As a result, the crystal grain size of the magnetic crystal grains was 10 nm, and the grain boundary thickness of the nonmagnetic material was 1.5 nm. nm.
Next, the macroscopic magnetic properties (MH curve) of the perpendicular magnetic recording medium obtained as described above were measured with a vibrating sample magnetometer (VSM). The Mr / Ms ratio obtained from the MH curve is 0.93, the slope of the MH curve with coercive force Hc is approximately 1 / (4π) (π: pi, CGS unit system), and the magnetization reversal nucleation magnetic field Hn is −1 kOe. there were.

<Comparative example>
Then, the recording / reproduction characteristics of the perpendicular magnetic recording medium according to Example 1 are as follows. The magnetization reversal nucleation magnetic field Hn is +2 kOe, the Mr / Ms ratio is 0.6, and the slope of the MH curve at the holding force Hc is approximately 1 / (4π. ) (Π: Circumference ratio, CGS unit system) and the recording / reproduction characteristics of the perpendicular magnetic recording medium of the comparative example. The recording head was a ring-type head (track width: 3 μm), and a GMR head (track width: 0.5 μm) was used for reproduction.
Further, the perpendicular magnetic recording medium of the comparative example referred to here is one in which only the composition of the CoCrPtB alloy layer 14 is different from Cr: 17 at%, Pt: 15 at%, B: 3 at%, and Co: bal. The other film configurations are the same as those shown in FIG. 1, and the manufacturing method is the same as that of the perpendicular magnetic recording medium according to the first embodiment of the present invention. Further, the crystal grain size of the magnetic crystal grains of the perpendicular magnetic recording medium of the comparative example was 11 nm, and the grain boundary thickness made of the nonmagnetic material was 0.3 nm.
When recording was performed at a linear velocity of 9.8 m / s and a linear recording density of 500 kFCI (recording frequency: 96.45 MHz), the S / N of the perpendicular magnetic recording medium of Example 1 according to the present invention was 14 dB. The S / N of the perpendicular magnetic recording medium was 12 dB, and 2 dB S / N improvement was observed. In this case, S is an output at 500 kFCI, and N is an integration noise (integration band: 1 to 120 MHz).

  Furthermore, as a result of measuring the time-dependent change in signal output at 75 ° C. and 50 kFCI in the range of 1 to 10,000 seconds after recording, the attenuation factor of the perpendicular magnetic recording medium of Example 1 according to the present invention was 0.5% / decade. In contrast, the perpendicular magnetic recording medium of the comparative example was 2.5% / decade. From this result, it was confirmed that the signal attenuation rate of the perpendicular magnetic recording medium of Example 1 according to the present invention was 1/5 that of the perpendicular magnetic recording medium of the comparative example, and the thermal disturbance resistance was improved.

<Example 2>
As Example 2 of the present invention, a perpendicular magnetic recording layer of CoCrPtBCu alloy composed of Cr: 17 at%, Pt: 15 at%, B: 4 at%, Cu: 4 at%, Co: bal. A medium of the same type as the magnetic recording medium was created. The medium creation conditions are also the same as those described in the first embodiment.
The crystal structure and preferred orientation characteristics of perpendicular magnetic recording media using this CoCrPtBCu alloy perpendicular magnetic recording layer were evaluated by X-ray diffraction. The crystal structure was a hexagonal close-packed structure, and it was confirmed that the c-axis was generally oriented in the normal direction of the substrate surface. The dispersion of the degree of orientation (Δθ ₅₀ ) was 6 °. Next, the CoCrPtBCu alloy film perpendicular magnetic recording layer portion of the perpendicular magnetic recording medium obtained as described above was examined with a transmission electron microscope. As a result, the average particle size was 10 nm, and the grain boundary thickness made of nonmagnetic material was 2 nm.

Next, the macroscopic magnetic properties (MH curve) of the perpendicular magnetic recording medium obtained as described above were measured with a vibrating sample magnetometer (VSM). The Mr / Ms ratio obtained from the MH curve is 0.95, the slope of the MH curve at coercive force Hc is approximately 1 / (4π) (π: pi, CGS unit system), and the magnetization reversal nucleation magnetic field Hn is −1.5 kOe. there were.
The recording / reproduction characteristics of the perpendicular magnetic recording medium of Example 2 were compared and evaluated with the perpendicular magnetic recording medium of the comparative example. The evaluation method is the same as the method described in Example 1. As a result, the S / N of the perpendicular magnetic recording medium according to Example 2 was 14.5 dB, and an improvement of 2.5 dB in the S / N ratio was recognized as compared with the perpendicular magnetic recording medium of the comparative example. The signal decay rate with respect to the standing time was 0.5% / decade, which was 1/5 of the perpendicular magnetic recording medium of the comparative example.

<Example 3>
As Example 3 of the present invention, a perpendicular magnetic recording layer of CoCrPtBAg alloy composed of Cr: 17 at%, Pt: 15 at%, B: 4 at%, Ag: 4 at%, Co: bal. A medium of the same type as the magnetic recording medium was created. The medium creation conditions are also the same as those described in the first embodiment.
Regarding the perpendicular magnetic recording medium using this CoCrPtBAg alloy perpendicular magnetic recording layer, the crystal structure of the CoCrPtBAg alloy perpendicular magnetic recording layer, the c-axis preferred orientation, the magnetic properties, the crystal grain size, and the grain boundaries consisting of non-magnetic materials As a result of evaluating the thickness by the same method as described in Example 1 and Example 2, almost the same result as that obtained when the CoCrPtBCu alloy perpendicular magnetic recording layer described in Example 2 was used was obtained. Further, regarding the electromagnetic conversion characteristics, the same results as those obtained when the CoCrPtBCu alloy perpendicular magnetic recording layer described in Example 2 was used were obtained.

<Example 4>
As Example 4 of the present invention, a medium of the same type as the perpendicular magnetic recording medium described in Example 1 was prepared using a CoCrPt—SiO ₂ mixed perpendicular magnetic recording layer made of (CoCrPt) ₉₅ (SiO ₂ ) ₅ . The composition of the CoCrPt alloy is Cr: 15 at%, Pt: 13 at%, and Co: bal. Hereinafter, a method for manufacturing the magnetic recording medium will be described.
First, a nonmagnetic underlayer 12 made of Ti was formed on a chemically strengthened glass substrate 11 made of a disk-like aluminosilicate glass in the pure Ar atmosphere by RF sputtering in the same manner as in Example 1. Thereafter, an intermediate layer 13 made of a CoCrTa alloy was formed in the same manner as in Example 1 in a pure Ar atmosphere by RF sputtering. Next, the perpendicular magnetic recording layer 14 (magnetic layer) made of a CoCrPt—SiO ₂ mixed system was sequentially formed. The composition of the perpendicular magnetic recording layer was adjusted by the number of SiO ₂ pellets to be stuck on the CoCrPt alloy target.

The crystal orientation characteristics of a perpendicular magnetic recording medium using a perpendicular magnetic recording layer composed of a CoCrPt—SiO ₂ mixed system were evaluated by X-ray diffraction. As a result, it was confirmed that the crystal structure of the perpendicular magnetic recording layer was a hexagonal close-packed structure, and the c-axis was generally oriented in the normal direction of the substrate surface. The dispersion of the degree of orientation (Δθ ₅₀ ) was 8 °. Next, the perpendicular magnetic recording layer portion made of the CoCrPt—SiO ₂ mixed system of the perpendicular magnetic recording medium obtained as described above was observed with a transmission electron microscope. As a result, the average particle diameter was 12 nm, and the grain boundary thickness made of nonmagnetic material was 3.5 nm.

Next, the macroscopic magnetic properties (MH curve) of the perpendicular magnetic recording medium obtained as described above were measured with a vibrating sample magnetometer (VSM). The Mr / Ms ratio obtained from the MH curve is 0.98, the slope of the MH curve at coercive force Hc is approximately 1 / (4π) (π: pi, CGS unit system), and the magnetization reversal nucleation magnetic field Hn is about −2 kOe. there were.
The recording / reproduction characteristics of the perpendicular magnetic recording medium of Example 4 were compared and evaluated with the perpendicular magnetic recording medium described in the comparative example. As a result, the perpendicular magnetic recording medium according to Example 4 showed an improvement of 1.5 dB in S / N ratio as compared with the perpendicular magnetic recording medium of the comparative example at 13.5 dB. The signal attenuation was 0.6% / decade, which was 1/4 of the perpendicular magnetic recording medium of the comparative example.

<Example 5>
As Example 5 of the present invention, a medium of the same type as the perpendicular magnetic recording medium described in Example 1 was prepared using a CoCrPt-SiN mixed perpendicular magnetic recording layer made of (CoCrPt) ₉₅ (SiN) ₅ . The composition of the CoCrPt alloy is Cr: 15 at%, Pt: 13 at%, and Co: bal.
The medium preparation method is the same as in Example 4. In this example, the composition of the CoCrPt—SiN mixed system perpendicular magnetic recording layer was adjusted by adjusting the number of SiN pellets to be pasted on the CoCrPt alloy target. As a result of evaluating the crystal structure, preferential orientation and fine structure of the CoCrPt-SiN mixed perpendicular magnetic recording layer by the method described in Examples 1 to 4, the crystal structure is a hexagonal close-packed structure, and its c-axis It was confirmed that was generally oriented in the normal direction of the substrate surface. The dispersion of the degree of orientation (Δθ ₅₀ ) was 7 °. The crystal grain size was 12 nm, and the grain boundary thickness made of nonmagnetic material was 3.5 nm.

Next, the macroscopic magnetic properties (MH curve) of the perpendicular magnetic recording medium obtained as described above were measured with a vibrating sample magnetometer (VSM). The Mr / Ms ratio obtained from the MH curve is 0.98, the slope of the MH curve at coercive force Hc is approximately 1 / (4π) (π: pi, CGS unit system), and the magnetization reversal nucleation magnetic field Hn is −2 kOe. It was.
The recording / reproduction characteristics of the perpendicular magnetic recording medium of Example 5 were compared and evaluated with the perpendicular magnetic recording medium described in the comparative example. As a result, the perpendicular magnetic recording medium of Example 5 was 13 dB. Compared with the perpendicular magnetic recording medium of the comparative example, an improvement of 1 dB in S / N ratio was recognized. The signal decay rate with respect to the standing time was 0.5% / decade, which was 1/5 of the perpendicular magnetic recording medium of the comparative example.

It is a schematic sectional drawing which shows the structure of the perpendicular magnetic recording medium which consists of this invention. It is a schematic sectional drawing which shows the structure of the conventional single layer type perpendicular magnetic recording medium. It is a schematic sectional drawing which shows the structure of the conventional 2 layer type | mold perpendicular magnetic recording medium. It is the schematic which shows the microscopic structure in the recording state of a perpendicular magnetic perpendicular magnetic recording layer. It is MH curve of the conventional perpendicular magnetic recording layer. 1 is a schematic sectional side view showing a film structure of a perpendicular magnetic recording medium according to the present invention. It is the figure which showed the relationship between the grain boundary thickness which consists of a nonmagnetic material, a magnetization reversal nucleation magnetic field, and a coercive force by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Glass substrate 12 Ti layer 13 Nonmagnetic CoCrTa alloy layer 14 CoCrPtB alloy film perpendicular magnetic recording layer 15 C protective layer 16 Lubricating layer 21 Substrate 22 Crystal axis control layer 23 Perpendicular magnetic recording layer 24 Protective layer 25 Lubricating layer 31 Substrate 32 Underlayer soft Magnetic layer 33 Intermediate layer 34 Perpendicular magnetic recording layer 35 Protective layer 36 Lubricating layer 41 Perpendicular magnetic recording layer 42 Crystal grains forming perpendicular magnetic recording layer 43 Magnetization transition line 44 Arrow representing average magnetization direction in each recording bit 45 Each recording An arrow representing an average magnetization direction in the bit 46 In each recording bit, a reverse magnetic domain facing the direction different from the average magnetization direction 61 substrate 62 underlayer 63 perpendicular magnetic recording layer 64 magnetic crystal grain 65 nonmagnetic crystal grain boundary 71 magnetization reversal nucleus Dependence of generated magnetic field on grain boundary thickness 72 Dependence of coercive force on grain boundary thickness

Claims (8)

A method of manufacturing a perpendicular magnetic recording medium, wherein at least a magnetic layer is formed on a substrate,
The perpendicular magnetic recording layer, which is the magnetic layer, includes magnetic crystal grains and a crystal grain boundary composed of a nonmagnetic layer interposed between the magnetic crystal grains,
In advance, a correlation between the grain boundary thickness and the magnetization reversal nucleation magnetic field Hn is obtained,
A perpendicular magnetic recording medium is manufactured, wherein a grain boundary thickness at which a predetermined magnetization reversal nucleation magnetic field Hn is obtained is selected based on the correlation, and the selected grain boundary thickness is produced. Method.   2. The method of manufacturing a perpendicular magnetic recording medium according to claim 1, wherein a grain boundary thickness made of a non-magnetic material interposed between magnetic crystal grains of the perpendicular magnetic recording layer is 0.5 to 10 nm or more.   3. The method of manufacturing a perpendicular magnetic recording medium according to claim 1, wherein the magnetic crystal particles have a particle size of 5 to 20 nm.   The method for manufacturing a perpendicular magnetic recording medium according to claim 1, wherein the material of the magnetic layer contains CoCrPt.   The material of the nonmagnetic layer is a material containing any one or more of Cr, Si, Cu, Ag, Au, B, and C, or an oxide or nitride thereof. The method for manufacturing a perpendicular magnetic recording medium according to claim 1.   6. The method of manufacturing a perpendicular magnetic recording medium according to claim 1, wherein a nonmagnetic underlayer containing TiCr is formed between the substrate and the perpendicular magnetic recording layer. Forming a nonmagnetic underlayer between the substrate and the perpendicular magnetic recording layer;
7. The method for manufacturing a perpendicular magnetic recording medium according to claim 1, wherein an intermediate layer containing CoCrTa is formed between the nonmagnetic underlayer and the perpendicular magnetic recording layer.   The method for manufacturing a perpendicular magnetic recording medium according to claim 1, wherein the substrate is a glass substrate.

Images