JP2006277950A - Vertical magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vertical magnetic recording medium superior in electromagnetic conversion characteristics, durability and productivity, without the elution of Co from a granular magnetic layer. <P>SOLUTION: The magnetic layer of the vertical magnetic recording medium is constituted of a first magnetic layer 14 of a CoCr-based alloy, in a granular structure for which a nonmagnetic grain boundary is composed of a metal oxide or nitride, and a second magnetic layer 15 of the CoCr-based alloy in a non-granular structure for which the nonmagnetic grain boundary does not contain the metal oxide or nitride. Thus, while the first magnetic layer 14 secures superior electromagnetic conversion characteristics due to the granular structure, the second magnetic layer 15 blocks Co atoms eluted from the nonmagnetic grain boundary of the first magnetic layer and enables securing of high durability for the medium. Furthermore, by imparting a multilayered base layer 22 and a magnetic domain control layer 23 between a nonmagnetic base body 21 and a soft magnetic backing layer 24, spike noise generated due to the soft magnetic backing layer 24 is substantially suppressed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a perpendicular magnetic recording medium, and more particularly to a perpendicular magnetic recording medium having excellent electromagnetic conversion characteristics and good durability and excellent productivity.

  As a technique for realizing a high density magnetic recording, a perpendicular magnetic recording system is drawing attention in place of the conventional longitudinal magnetic recording system.

  As a material for a magnetic recording layer for a perpendicular magnetic recording medium, a CoCr-based alloy crystalline film is currently being studied. A CoCr-based material having a hexagonal close-packed (hcp) structure is used for perpendicular magnetic recording. The crystal orientation is controlled so that the c-axis of the alloy is perpendicular to the film surface (c-plane is parallel to the film surface). In order to further increase the density of CoCr-based alloys in the future, attempts have been made to refine the CoCr-based crystal grains, reduce the grain size distribution, reduce the magnetic interaction between grains, and the like.

  On the other hand, as one method of controlling the magnetic layer structure for increasing the density of the longitudinal recording medium, for example, in JP-A-8-255342 and US Pat. No. 5,679,473, the periphery of magnetic crystal grains generally called a granular magnetic layer is disclosed. A magnetic layer having a structure in which is surrounded by a non-magnetic non-metallic material such as oxide or nitride has been proposed. In such a granular magnetic film, since the nonmagnetic nonmetallic grain boundary phase physically separates the magnetic particles, the magnetic interaction between the magnetic particles is reduced, and the zigzag domain wall generated in the transition region of the recording bit is reduced. Since formation is suppressed, it is considered that low noise characteristics can be obtained, and it has been proposed to use a granular magnetic layer as a recording layer of a perpendicular magnetic recording medium. For example, IEEE Trans., Mag., Vol. 36, 2393 (2000) describes a perpendicular recording medium in which Ru is a base layer and a CoPtCrO alloy having a granular structure is a magnetic layer. As the film thickness of the Ru layer as the underlayer is increased, the c-axis orientation is improved, and accordingly, excellent magnetic characteristics and electromagnetic conversion characteristics are obtained.

  On the other hand, in a magnetic recording apparatus using a floating type magnetic head, since the distance between the magnetic head and the magnetic recording medium is as small as several tens of nanometers, the friction wear characteristics between the head and the medium contribute to the durability of the apparatus. It has a strong influence. Therefore, it is a common practice to improve the frictional wear characteristics with the head by applying a liquid lubricant having a molecular weight of several thousand to the surface of the medium. Here, when Co atoms contained in the magnetic layer of the medium are deposited on the surface of the medium, the Co atoms accelerate the decomposition of the liquid lubricant on the surface of the medium, which may significantly deteriorate the durability of the medium. Are known. Therefore, in order to prevent such precipitation of Co atoms, management of the thickness and quality of the medium protective film and control of the surface roughness of the medium are indispensable for producing the medium.

  However, according to the study by the present inventors, it has been found that when a granular magnetic layer is used as the magnetic layer, Co atoms contained in the magnetic layer easily precipitate on the medium surface. In particular, when the Ar gas pressure during sputtering film formation is increased in order to obtain excellent magnetic characteristics and electromagnetic conversion characteristics, the Co elution amount becomes more prominent. When Co atoms are deposited on the medium surface, the Co atoms decompose the liquid lubricant molecules on the medium surface, thereby causing a problem that the friction wear durability of the medium is significantly deteriorated.

  The present invention has been made in view of such problems, and the object of the present invention is to achieve both excellent electromagnetic conversion characteristics and good durability by suppressing elution of Co from the granular magnetic layer. And providing a perpendicular magnetic recording medium having excellent productivity.

  In order to achieve the above object, the present invention provides a soft magnetic backing layer, an intermediate layer, a magnetic layer of a CoCr-based alloy layer, and a protective layer on a nonmagnetic substrate. And a liquid lubricant layer are sequentially stacked, and the magnetic layer is provided on the intermediate layer side with a first magnetic layer having a granular structure and on the protective layer side. And a second magnetic layer having a non-granular structure.

  The invention according to claim 2 is the perpendicular magnetic recording medium according to claim 1, wherein the intermediate layer is any one of Ti, Re, Ru, and Os having a hexagonal close-packed (hcp) crystal structure. Or an alloy containing at least one of Ti, Re, Ru, and Os.

  Further, the invention according to claim 3 is the perpendicular magnetic recording medium according to claim 1 or 2, wherein the underlayer on the nonmagnetic substrate side and the underlayer on the nonmagnetic substrate side are disposed between the nonmagnetic substrate and the soft magnetic backing layer. The magnetic domain control layer on the soft magnetic backing layer side is sequentially laminated.

  In the perpendicular magnetic recording medium of the present invention, the magnetic layer for performing magnetic recording is composed of two layers, and the first magnetic layer on the nonmagnetic substrate side is made of an oxide or nitride whose nonmagnetic grain boundary is a metal. And a second magnetic layer provided thereon is made of a non-granular CoCr alloy that does not contain metal oxides or nitrides in the nonmagnetic grain boundaries. . Of these magnetic layers, the first magnetic layer ensures good electromagnetic conversion characteristics due to its granular structure, while the second magnetic layer elutes from the nonmagnetic grain boundaries of the first magnetic layer. Since it is configured to block the incoming Co atoms to ensure high durability of the medium, it has excellent magnetic characteristics and electromagnetic conversion characteristics, and it is 96 in a high temperature and high humidity environment of 80% RH at 85 ° C. Even if it is left for more than an hour, the amount of Co extracted by shaking for 3 minutes in 50 ml of pure water is measured by ICP emission spectroscopic analysis, and the value is suppressed to 10 μg or less per 1 m 2 of disk area. A medium having the characteristics can be realized.

  Furthermore, by providing an underlayer consisting of one or more layers and a magnetic domain control layer between the nonmagnetic substrate and the soft magnetic backing layer, spike noise generated due to the soft magnetic backing layer is greatly suppressed. It becomes possible.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram for explaining a configuration example of a perpendicular magnetic recording medium according to the present invention. The perpendicular magnetic recording medium includes a soft magnetic backing layer 12, an intermediate layer 13, and a first magnetic layer on a nonmagnetic substrate 11. 14, a second magnetic layer 15, and a protective layer 16 are sequentially laminated, and a liquid lubricant layer 17 is formed on the protective layer 16.

  FIG. 2 is a diagram for explaining another configuration example of the perpendicular magnetic recording medium of the present invention. The perpendicular magnetic recording medium has a multilayer underlayer 22 composed of a plurality of layers on a nonmagnetic substrate 21. A magnetic domain control layer 23, a soft magnetic backing layer 24, an intermediate layer 25, a first magnetic layer 26, a second magnetic layer 27, and a protective layer 28 are sequentially laminated. An agent layer 29 is formed.

  In the perpendicular magnetic recording medium of the present invention, the nonmagnetic substrates 11 and 21 can be made of an Al alloy plated with NiP, tempered glass, crystallized glass, or the like used for ordinary magnetic recording media. As the control layer 23, an antiferromagnetic film such as PtMn or IrMn made of an alloy containing Mn, or a hard magnetic film such as a CoCrTa, CoCrPt, or CoCrPtB film whose magnetization is oriented in the radial direction of the nonmagnetic substrate 21 is used. be able to. The magnetic domain control layer 23 preferably has a thickness of about 5 to 300 nm.

  In the case of using a Mn alloy-based antiferromagnetic film as the magnetic domain control layer 23 as the multilayer underlayer 22, a nonmagnetic single metal such as Cu or Ir having a face-centered cubic (fcc) structure, or a nonmagnetic single metal such as NiFeCr is used. It is desirable to use a magnetic alloy or the like. In this case, in order to control the fine structure of these nonmagnetic single metal film or nonmagnetic alloy film, a layer of Ta, Zr, Nb or the like having a thickness of 3 to 30 nm may be provided in the lower layer. . When a hard magnetic film is used as the magnetic domain control layer 23, a Cr alloy such as CrMo or CrW can be used as the multilayer base layer 22. Also in this case, an underlayer may be provided in the lower layer in order to control the microstructure of these Cr alloy films. The multilayer base layer 22 is not necessarily a multilayer base layer composed of a plurality of layers, and may be a single layer base layer as desired.

  As the soft magnetic underlayers 12 and 24, NiFe alloy, Sendust (FeSiAl) alloy, or the like can be used. By using an amorphous Co alloy such as CoNbZr or CoTaZr, good electromagnetic characteristics can be obtained. Can do. The optimum value of the film thickness of the soft magnetic underlayers 12 and 24 varies depending on the structure and characteristics of the magnetic head used for magnetic recording, but is preferably 10 nm or more and 300 nm or less in view of productivity.

  As the intermediate layers 13 and 25, materials for suitably controlling the crystal orientation, crystal grain size, and grain boundary segregation of the first magnetic layers 14 and 26 can be used as appropriate. From the viewpoint of controlling the crystal orientation of the layers 14 and 26, at least one of Ti, Re, Ru, and Os having a hexagonal close-packed (hcp) crystal structure, or at least one of Ti, Re, Ru, and Os An alloy containing a kind of metal is desirable. The film thickness is not particularly limited, but from the viewpoint of improvement in recording / reproducing resolution and productivity, it is the minimum required for controlling the crystal structure of the first magnetic layers 14 and 26. It is desirable to use a film thickness.

  The first magnetic layers 14 and 26 are so-called granular materials comprising CoCr-based alloy crystal grains having ferromagnetism and nonmagnetic grain boundaries surrounding the crystal grains, and the nonmagnetic grain boundaries comprising a metal oxide or nitride. It is a magnetic layer. This granular structure is produced by, for example, sputtering using a ferromagnetic metal containing an oxide that constitutes a nonmagnetic grain boundary, or reactive sputtering using a ferromagnetic metal as a target in an Ar gas atmosphere containing oxygen. can do. In order to obtain good characteristics as a granular magnetic layer, the gas pressure during film formation needs to be 10 mTorr or more.

  Here, a CoCr-based alloy is preferably used as a material for forming a ferromagnetic crystal, and in particular, from the viewpoint of obtaining excellent magnetic characteristics and recording / reproducing characteristics, the CoCr alloy is made of Pt, Ni, Ta. It is desirable to add at least one of these elements. On the other hand, as the material constituting the nonmagnetic grain boundary, an oxide of at least one element of Cr, Co, Si, Al, Ti, Ta, Hf, and Zr is used from the viewpoint of forming a stable granular structure. The film thickness is desirably 30 nm or less in order to increase the recording / reproducing resolution.

  The second magnetic layers 15 and 27 are made of a non-granular CoCr-based alloy crystalline film containing no metal oxide or nitride at the nonmagnetic grain boundaries. Examples of materials that can be used for forming the CoCr-based alloy crystalline film include alloy-based materials such as CoCr, CoCrTa, CoCrPt, CoCrPtTa, and CoCrPtB. In order to manufacture a perpendicular magnetic recording medium with excellent durability, the gas pressure when forming the second magnetic layers 14 and 27 must be 15 mTorr or less, and the film thickness is 20 nm or less. It is desirable to be.

  That is, in the perpendicular magnetic recording medium of the present invention, the magnetic layer for performing magnetic recording is composed of two layers, and the first magnetic layer on the nonmagnetic substrate side is made of an oxide or nitride of which the nonmagnetic grain boundary is a metal. It is composed of a granular CoCr alloy composed of a material, and the second magnetic layer provided thereon is composed of a non-granular CoCr alloy that does not contain metal oxide or nitride at the nonmagnetic grain boundary. ing. Of these magnetic layers, the first magnetic layer ensures good electromagnetic conversion characteristics due to its granular structure, while the second magnetic layer elutes from the nonmagnetic grain boundaries of the first magnetic layer. It is configured to block the Co atoms coming and ensure the high durability of the medium.

  As the protective layers 16 and 28, a conventionally used protective film can be used. For example, a protective film mainly composed of carbon can be used. The liquid lubricant layers 17 and 29 can also be made of a conventionally used material, for example, a perfluoropolyether lubricant. The conditions such as the film thickness of the protective layers 16 and 28 and the conditions such as the film thickness of the liquid lubricant layers 17 and 29 can be the same as those used in ordinary magnetic recording media.

  Examples of the method for manufacturing a perpendicular magnetic recording medium according to the present invention will be described below. These examples are merely representative examples for suitably explaining the method of manufacturing the perpendicular magnetic recording medium of the present invention, and the present invention is not limited to these examples.

Example 1
As the nonmagnetic substrate, a chemically strengthened glass substrate (for example, N-5 glass substrate manufactured by HOYA) having a smooth surface was used, and this was introduced into the sputtering apparatus after cleaning, and a CoZrNb amorphous soft magnetic backing layer was formed to 200 nm, After the intermediate layer was deposited to 30 nm, the first magnetic layer was formed to 20 nm by RF sputtering using a CoCrPt—SiO 2 target, and the second magnetic layer was further formed to 10 nm using the CoCrPtB target. Here, the first magnetic layer and the second magnetic layer are formed under conditions in which the gas pressure is variously changed. Finally, after forming a protective layer 5 nm made of carbon, it was taken out from the vacuum apparatus, and then a liquid lubricant layer 2 nm made of perfluoropolyether was formed by a dip method to obtain a perpendicular magnetic recording medium. In addition, the substrate heating prior to the film formation and the heating / quenching process after the magnetic layer formation are not performed.

  The perpendicular magnetic recording medium thus prepared was left in a high-temperature and high-humidity environment of 80% RH at 85 ° C. for 96 hours, and then the eluted Co was extracted by shaking in 50 ml of pure water for 3 minutes. The concentration was measured by ICP emission spectroscopy. The magnetic properties of the medium on which the first and second magnetic layers were formed were measured with a vibrating sample magnetometer, and the magnetic characteristics were evaluated. Evaluation was performed by a spin stand tester provided.

  Table 1 summarizes the Co elution amounts of perpendicular magnetic recording media manufactured by variously changing the gas pressure when forming the first and second magnetic layers.

  As is apparent from this table, the amount of Co elution can be suppressed by reducing the gas pressure during film formation for both the first magnetic layer and the second magnetic layer. In particular, when the gas pressure of the second magnetic layer is set to 15 mTorr or less, the elution amount of Co can be suppressed to 10 μg / m 2 or less regardless of the gas pressure of the first magnetic layer.

  Table 2 summarizes the SNR (ratio of electromagnetic conversion characteristic signal to noise) at 350 kFCl of a perpendicular magnetic recording medium manufactured by variously changing the gas pressure during the formation of the first and second magnetic layers. is there.

  As can be seen from this table, when the gas pressure during film formation of the first magnetic layer is set to 15 mTorr or more, good electromagnetic conversion of 15 dB or more regardless of the gas pressure during film formation of the second magnetic layer. Characteristics are obtained. Further, in the region where the gas pressure during film formation of the second magnetic layer is 15 mTorr or less, a value of 15 dB or more is obtained even in a medium where the gas pressure during film formation of the first magnetic layer is 10 mTorr or more.

  Thus, in order to suppress the Co elution amount to 10 μg / m 2 or less and increase the SNR value at a recording density of 350 kFCl to 15 dB or more, the gas pressure at the time of forming the first magnetic layer is set to 10 mTorr or more. And it turns out that the gas pressure at the time of film-forming of a 2nd magnetic layer needs to be 15 mTorr or less.

(Example 2)
Example 1 described above except that substrate heating (preheating) prior to film formation, heating after film formation of the second magnetic layer (post heating), and rapid cooling treatment were performed in the same apparatus. A magnetic recording medium was produced in the same manner. However, the gas pressure at the time of forming the first magnetic layer was fixed at 50 mTorr, and the gas pressure at the time of forming the second magnetic layer was fixed at 5 mTorr.

  Table 3 shows that the pre-heating temperature is 200 ° C., the post-heating temperature is 200 ° C., and the cooling process step performed continuously after the post-heating treatment is adjusted so that the substrate temperature after 10 seconds becomes 100 ° C. It is the result of summarizing the coercive force (Hc) depending on the presence or absence and the SNR value.

  As can be seen from this table, the magnetic properties and the SNR are drastically decreased by performing the preheating treatment. When the granular magnetic layer as the first magnetic layer is formed, it is not heated in advance. It is necessary to perform a membrane process. In addition, when the post-heating treatment is performed, the magnetic characteristics and SNR values are greatly increased. This is because the characteristics of the CoCr-based alloy crystalline film which is the second magnetic layer are improved by the post-heating treatment. Furthermore, it turns out that the characteristic is further improved by performing the rapid cooling process continuously after a post-heating process.

(Example 3)
Table 4 shows the X-ray diffraction method of the hcp (002) diffraction line of the magnetic layer of the magnetic recording medium produced in the same manner as in Example 1 except that various materials were used as the intermediate layer and the film thickness was 30 nm. This is a result of summarizing the half-value width Δθ50 value of the rocking curve obtained by the above. For comparison, the case where Ta and Cr having a body-centered cubic (bcc) structure are used as the intermediate layer is also shown.

  From this table, compared to the case of using Ta or Cr having a bcc structure as the nonmagnetic underlayer, Δθ50 is improved when various materials having an hcp structure are used, and the crystal orientation control of the magnetic layer is effectively performed. I understand that.

Example 4
In the manufacturing method described in Example 1, between the nonmagnetic substrate and the soft magnetic underlayer, a Ta target is used to form a first Ta underlayer 5 nm, a NiFeCr target is used to form a NiFeCr second underlayer 5 nm, and A magnetic recording medium was prepared in the same procedure as in Example 1 except that a magnetic domain control layer of IrMn was formed to 10 nm.

  There was no particular difference in magnetic properties and SNR between the perpendicular magnetic recording medium produced by this method and the perpendicular magnetic recording medium produced by the method of Example 1.

  FIG. 3 shows a comparison of output waveforms for one round by a spin stand tester of a perpendicular magnetic recording medium produced by each of these methods. In the perpendicular magnetic recording medium manufactured by the method shown in Example 1 having a structure not including the underlayer and the magnetic domain control layer, spike noise is generated nonuniformly over the entire circumference, whereas the underlayer and the magnetic domain control are performed. It can be seen that spike noise is remarkably reduced by employing a configuration including layers. This is because by providing the base layer and the magnetic domain control layer on the nonmagnetic substrate, the domain wall is not formed on the soft magnetic backing layer that is subsequently laminated.

It is a figure for demonstrating the structural example of the perpendicular magnetic recording medium of this invention. It is a figure for demonstrating the other structural example of the perpendicular magnetic recording medium of this invention. It is a figure for demonstrating the output waveform for one round by the spin stand tester of the perpendicular magnetic recording medium of this invention.

Explanation of symbols

11, 21 Nonmagnetic substrate 12, 24 Soft magnetic backing layer 13, 25 Intermediate layer 14, 26 First magnetic layer 15, 27 Second magnetic layer 16, 28 Protective layer 17, 29 Liquid lubricant layer 22 Multilayer underlayer 23 Magnetic domain control layer

Claims (3)

A perpendicular magnetic recording medium in which a soft magnetic backing layer, an intermediate layer, a magnetic layer of a CoCr-based alloy layer, a protective layer, and a liquid lubricant layer are sequentially laminated on a nonmagnetic substrate,
The magnetic layer is composed of a granular first magnetic layer provided on the intermediate layer side and a non-granular second magnetic layer provided on the protective layer side. Perpendicular magnetic recording medium.   The intermediate layer is made of any one of Ti, Re, Ru, and Os having a hexagonal close-packed (hcp) crystal structure, or an alloy containing at least one of Ti, Re, Ru, and Os. The perpendicular magnetic recording medium according to claim 1, wherein the perpendicular magnetic recording medium is configured.   3. The underlayer on the nonmagnetic substrate side and the magnetic domain control layer on the soft magnetic backing layer side are sequentially laminated between the nonmagnetic substrate and the soft magnetic backing layer. The perpendicular magnetic recording medium described.

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