JP2009099241A - Perpendicular magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a perpendicular magnetic recording medium reducing noise by further reducing the size of magnetic particles and isolating each of the particles in a magnetic recording layer, and improving SNR to increase a recording density. <P>SOLUTION: The perpendicular magnetic recording medium 100 is provided with a magnetic recording layer 22 having a granular structure 22 in which a nonmagnetic particle boundary portion is formed between magnetic particles continuously grown into a columnar shape. The particle boundary portion contains a plurality of types of oxides. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a perpendicular magnetic recording medium mounted on a perpendicular magnetic recording type HDD (hard disk drive) or the like.

  Various information recording techniques have been developed with the recent increase in information processing capacity. In particular, the surface recording density of HDDs using magnetic recording technology continues to increase at an annual rate of about 100%. Recently, an information recording capacity exceeding 160 GB has been required for a 2.5-inch diameter perpendicular magnetic recording medium used for HDDs and the like. In order to meet such a demand, one square is required. It is required to realize an information recording density exceeding 250 Gbits per inch.

  In order to achieve a high recording density in a magnetic recording medium used for an HDD or the like, a perpendicular magnetic recording medium of a perpendicular magnetic recording system has recently been proposed. The perpendicular magnetic recording system is adjusted so that the easy axis of magnetization of the magnetic recording layer is oriented in a direction perpendicular to the substrate surface. The perpendicular magnetic recording method can suppress the thermal fluctuation phenomenon as compared with the conventional in-plane recording method, and is suitable for increasing the recording density.

As a magnetic recording medium used in the perpendicular magnetic recording system, a CoCrPt—SiO ₂ perpendicular magnetic recording medium (see Non-Patent Document 1) has been proposed because it exhibits high thermal stability and good recording characteristics. This constitutes a granular structure in which nonmagnetic grain boundary portions are formed between magnetic grains continuously grown in a columnar shape in the magnetic recording layer, and it is intended to combine the refinement of the magnetic grains and the improvement of the coercive force Hc. is there. It is known that an oxide is used for a nonmagnetic grain boundary (a nonmagnetic portion between magnetic grains). For example, any one of SiO ₂ , Cr ₂ O ₃ , TiO, TiO ₂ and Ta ₂ O ₅ is used. Has been proposed (Patent Document 1).
T. Oikawa et.al., IEEE Trans. Magn, vol.38, 1976-1978 (2002) JP 2006-024346 A

  Although the magnetic recording medium has a higher recording density as described above, further improvement in the recording density is required in the future. As important factors for increasing the recording density, there are various factors such as improvement in coercive force Hc and overwrite characteristics, improvement in SNR (Signal-Noise Ratio) and reduction in track width. Among them, an important improvement in SNR is performed mainly by reducing magnetization transition region noise of the magnetic recording layer. In order to reduce noise, it is necessary to improve the crystal orientation of the magnetic recording layer, reduce the particle size of the magnetic particles, and isolate the magnetic particles. In other words, in order to increase the recording density of the medium, it is desirable to make the particle diameter of the magnetic particles uniform and fine, and to make a bent state in which the individual magnetic particles are magnetically separated.

  By the way, the Co-based perpendicular magnetic recording layer, particularly the CoPt-based perpendicular magnetic recording layer, has a high coercive force (Hc) and can have a reverse magnetic domain nucleation magnetic field (Hn) as small as less than zero, so it is resistant to thermal fluctuations. Is preferable, and a high SNR can be obtained. By including an element such as Cr in the perpendicular magnetic recording layer, it is possible to segregate Cr in the grain boundary portion of the magnetic particles, so that the magnetic particles are isolated and the exchange interaction is cut off, and the high recording density Can contribute.

Further, in the above-described CoCrPt—SiO ₂ type perpendicular magnetic recording medium, by adding an oxide such as SiO ₂ , the oxide can be segregated at the grain boundary without hindering the epitaxial growth of CoPt. Thereby, the SNR (Signal-Noise Ratio) can be improved by miniaturizing the magnetic particles and promoting isolation between the magnetic particles.

  The refinement and isolation of magnetic particles are affected by the thickness in the horizontal direction (in-plane direction) of the oxide segregated at the grain boundaries. Increasing the amount of oxide improves the SNR at high recording density. On the other hand, when the amount of oxide is excessively increased, the perpendicular magnetic anisotropy is deteriorated, and deterioration of thermal stability and increase of noise become problems. That is, it is effective to contain an oxide at the grain boundary, but the amount of the oxide to be contained naturally has an upper limit, and a limit is beginning to appear in refinement and improvement of isolation.

  The present invention provides a perpendicular magnetic recording medium capable of reducing noise by further miniaturizing and isolating magnetic particles of a magnetic recording layer and improving the SNR to increase the recording density. It is aimed.

The inventors have examined oxides that form grain boundaries for the purpose of miniaturization and isolation of magnetic particles. The effect of oxides is not only on the amount but also on the type of oxide. Pay attention. As a result of intensive studies on the influence depending on the type of oxide, it was found that SiO ₂ tends to promote miniaturization of magnetic particles, and TiO ₂ tends to improve electromagnetic conversion characteristics (especially SNR). .

  Thus, the oxide has characteristics depending on the type and can be selected according to the desired performance. However, this characteristic has advantages and disadvantages, and any oxide does not always meet future high recording density.

  Therefore, the inventors examined whether it is possible to have the characteristics of a plurality of oxides together, and found that the characteristics can be obtained without offsetting the characteristics by appropriately using a plurality of oxides, thereby completing the present invention. I arrived.

  That is, a typical configuration of the perpendicular magnetic recording medium according to the present invention is a perpendicular magnetic recording medium having a magnetic recording layer having a granular structure in which nonmagnetic grain boundary portions are formed between magnetic grains continuously grown in a columnar shape. And the grain boundary part is characterized by containing a plurality of types of oxides.

  According to the above configuration, characteristics of a plurality of oxides can be obtained, noise is reduced by further miniaturization and isolation of the magnetic particles of the magnetic recording layer, and SNR is improved to increase the recording density. Thus, a perpendicular magnetic recording medium capable of achieving the above can be obtained.

The plurality of types of oxides may contain both SiO ₂ and TiO ₂ . SiO ₂ promotes miniaturization and isolation of magnetic particles, and TiO ₂ has a characteristic of improving electromagnetic conversion characteristics (especially SNR). By combining these oxides and segregating at the grain boundaries of the magnetic recording layer, both benefits can be obtained.

  It is preferable that content of several types of oxides is 6 mol%-12 mol% as the whole oxide. When it is in the above range, the action of a single oxide contained can be exceeded, and a high coercive force and SNR can be obtained.

  When a plurality of magnetic recording layers having a granular structure are provided, at least one magnetic recording layer may contain a plurality of types of oxides at the grain boundary portion. Furthermore, two or more or all of the plurality of magnetic recording layers may contain a plurality of types of oxides.

  According to the perpendicular magnetic recording medium of the present invention, it is possible to reduce the noise by further miniaturizing and isolating the magnetic particles in the magnetic recording layer, and to improve the SNR and increase the recording density.

[First Embodiment]
A first embodiment of a method for manufacturing a perpendicular magnetic recording medium according to the present invention will be described. FIG. 1 is a diagram for explaining the configuration of a perpendicular magnetic recording medium according to this embodiment. Note that dimensions, materials, and other specific numerical values shown in the following embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified.

  FIG. 1 is a diagram for explaining the configuration of a perpendicular magnetic recording medium 100 according to the present embodiment. The perpendicular magnetic recording medium 100 shown in FIG. 1 includes a disk substrate 10, an adhesion layer 12, a first soft magnetic layer 14a, a spacer layer 14b, a second soft magnetic layer 14c, an orientation control layer 16, a first underlayer 18a, and a second layer. The underlayer 18b, the miniaturization promoting layer 20, the first magnetic recording layer 22a, the second magnetic recording layer 22b, the auxiliary recording layer 24, the medium protective layer 26, and the lubricating layer 28 are formed. The first soft magnetic layer 14a, the spacer layer 14b, and the second soft magnetic layer 14c together constitute the soft magnetic layer 14. The first base layer 18a and the second base layer 18b together constitute the base layer 18. The first magnetic recording layer 22a and the second magnetic recording layer 22b together constitute the magnetic recording layer 22.

  As will be described below, the perpendicular magnetic recording medium 100 shown in the present embodiment includes a plurality of types of oxides (hereinafter referred to as “composite oxides”) in the second magnetic recording layer 22b of the magnetic recording layer 22. As a result, the composite oxide is segregated at the nonmagnetic grain boundaries.

  First, an amorphous aluminosilicate glass was formed into a disk shape by direct pressing to produce a glass disk. The glass disk was subjected to grinding, polishing, and chemical strengthening in order to obtain a smooth non-magnetic disk base 10 made of a chemically strengthened glass disk.

  On the disk base 10 obtained, a film forming apparatus that has been evacuated is used to sequentially form a film from the adhesion layer 12 to the auxiliary recording layer 24 in an Ar atmosphere by a DC magnetron sputtering method, thereby protecting the medium protective layer. No. 26 was formed by CVD. Thereafter, the lubricating layer 28 was formed by dip coating. Note that it is also preferable to use an in-line film forming method in terms of high productivity. Hereinafter, the configuration and manufacturing method of each layer will be described.

  The adhesion layer 12 was formed using a Ti alloy target so as to be a 10 nm Ti alloy layer. By forming the adhesion layer 12, the adhesion between the disk base 10 and the soft magnetic layer 14 can be improved, so that the soft magnetic layer 14 can be prevented from peeling off. As a material of the adhesion layer 12, for example, a CrTi alloy can be used.

  The soft magnetic layer 14 includes AFC (Antiferro-magnetic exchange coupling) by interposing a nonmagnetic spacer layer 14b between the first soft magnetic layer 14a and the second soft magnetic layer 14c. It was configured as follows. As a result, the magnetization direction of the soft magnetic layer 14 can be aligned along the magnetic path (magnetic circuit) with high accuracy, and the perpendicular component of the magnetization direction is extremely reduced, so that noise generated from the soft magnetic layer 14 is reduced. Can do. Specifically, the composition of the first soft magnetic layer 14a and the second soft magnetic layer 14c was CoFeTaZr, and the composition of the spacer layer 14b was Ru (ruthenium).

  The orientation control layer 16 has an action of protecting the soft magnetic layer 14 and an action of promoting alignment of crystal grains of the underlayer 18. The material of the orientation control layer can be selected from Ni, Cu, Pt, Pd, Zr, Hf, and Nb. Furthermore, it is good also as an alloy which contains these metals as a main component and contains any one or more additional elements of Ti, V, Ta, Cr, Mo, and W. For example, NiW, CuW, or CuCr can be suitably selected.

  The underlayer 18 has an hcp structure, and the crystal of the hcp structure of the magnetic recording layer 22 can be grown as a granular structure. Therefore, the higher the crystal orientation of the underlayer 18 is, the more the orientation of the magnetic recording layer 22 can be improved. The material of the underlayer can be selected from RuCr and RuCo in addition to Ru. Ru has an hcp structure and can satisfactorily orient a magnetic recording layer containing Co as a main component.

  In the present embodiment, the underlayer 18 has a two-layer structure made of Ru. When forming the second base layer 18b on the upper layer side, the Ar gas pressure is set higher than when forming the first base layer 18a on the lower layer side. When the gas pressure is increased, the free movement distance of the plasma ions to be sputtered is shortened, so that the film formation rate is reduced and the crystal orientation can be improved. Further, by increasing the pressure, the size of the crystal lattice is reduced. Since the size of the Ru crystal lattice is larger than that of the Co crystal lattice, if the Ru crystal lattice is made smaller, it approaches that of Co, and the crystal orientation of the Co granular layer can be further improved.

The miniaturization promoting layer 20 is a nonmagnetic granular layer. A nonmagnetic granular layer is formed on the hcp crystal structure of the underlayer 18, and the granular layer of the first magnetic recording layer 22 a is grown thereon, so that the magnetic granular layer can be grown from the initial growth stage (rise). Has the effect of separating. The composition of the miniaturization promoting layer 20 was nonmagnetic CoCr—SiO ₂ .

  The magnetic recording layer 22 is composed of a thin first magnetic recording layer 22a and a thick second magnetic recording layer 22b.

The first magnetic recording layer 22a uses a hard magnetic target made of CoCrPt containing chromium oxide (Cr ₂ O ₃ ) as an example of a nonmagnetic material, and has an hcp crystal structure of ₂ nm CoCrPt—Cr ₂ O _3. Formed. Nonmagnetic substances segregated around the magnetic substance to form grain boundaries, and the magnetic grains (magnetic grains) formed a columnar granular structure. The magnetic grains were epitaxially grown continuously from the granular structure of the miniaturization promoting layer 20.

The second magnetic recording layer 22b contains SiO ₂ and TiO ₂ as an example of a composite oxide (a plurality of types of oxides), and forms a hcp crystal structure of CoCrPt—SiO ₂ —TiO ₂ . In this embodiment, it adopted as those containing SiO ₂ and TiO ₂ by 3 mol% respectively, those containing SiO ₂ and TiO ₂ by 5 mol%, respectively. Also in the second magnetic recording layer 22b, the magnetic grains formed a granular structure.

  The auxiliary recording layer 24 is a thin film (auxiliary recording layer) showing high perpendicular magnetic anisotropy and high saturation magnetization MS on the granular magnetic layer. The auxiliary recording layer 24 is intended to improve the reverse domain nucleation magnetic field Hn, the heat-resistant fluctuation characteristics, and the overwrite characteristics. The composition of the auxiliary recording layer 24 was CoCrPtB.

  The medium protective layer 26 was formed by depositing carbon by a CVD method while maintaining a vacuum. The medium protective layer 26 is a protective layer for protecting the perpendicular magnetic recording layer from the impact of the magnetic head. In general, carbon deposited by the CVD method has improved film hardness compared to that deposited by the sputtering method, so that the perpendicular magnetic recording layer can be protected more effectively against the impact from the magnetic head.

  The lubricating layer 28 was formed by dip coating using PFPE (perfluoropolyether). The film thickness of the lubricating layer 28 is about 1 nm.

Through the above manufacturing process, the perpendicular magnetic recording medium 100 was obtained. The effectiveness of the present invention will be described below using examples and comparative examples.
[Evaluation]

[Examples and evaluation]
FIG. 2 is a graph showing the relationship between the SNR and the mixing ratio of oxides or composite oxides in Examples and Comparative Examples. In Example 1, as described in the above embodiment, the first magnetic recording layer 22a contains Cr ₂ O ₃ as an oxide, and the second magnetic recording layer 22b contains SiO ₂ and TiO ₂ as complex oxides, respectively. Each of them is contained at 3 mol% or 5 mol%. In Comparative Example 1, the second magnetic recording layer 22b contains SiO ₂ as an oxide, and in Comparative Example 2, the second magnetic recording layer 22b contains TiO ₂ as an oxide. In addition, since the data of Example 1 have few plots, it is extrapolated based on the inclination of these diagrams as showing the same tendency as Comparative Example 1 and Comparative Example 2 (each shown by a broken line in the figure). .

As can be seen from FIG. 2, the SNR is better in Comparative Example 2 (TiO ₂ ) than in Comparative Example 1 (SiO ₂ ). As a difference between SiO ₂ and TiO ₂ , it is known that TiO ₂ has larger magnetic grains. In general, when the magnetic grains are large, the SNR deteriorates. However, in the case of TiO ₂ , the magnetic grains tend to be uniform above that, so it is considered that the SNR shows a better value than that of SiO ₂ .

In Example 1 using the composite oxide, the SNR was better than that of Comparative Example 1 and Comparative Example 2. This is considered to have contributed to the improvement of SNR because isolation was obtained as a function of SiO ₂ and magnetic particles became large as a result of TiO ₂ .

  If FIG. 2 is referred here, when content of complex oxide is 6 mol%-12 mol% as the whole oxide, the electromagnetic conversion characteristic which exceeds the comparative example 2 is shown. That is, when it exists in said range, it turns out that it can exceed the characteristic of one oxide which comprises composite oxide, and is preferable as content of composite oxide.

FIG. 3 is a diagram showing the SNR and coercive force Hc when the content of the complex oxide is changed as a whole oxide. The content of SiO2 and TiO2 that time is assumed to be the same (for example, when the total amount is 10 mol%, SiO ₂ and TiO ₂ are each 5 mol%, respectively). Here, the content of the composite oxide in each Example and Comparative Example is 3 mol% in Comparative Example 10, 6 mol% to 12 mol% in Examples 10 to 14, and 13 mol% to 15 mol in Comparative Examples 11 to 13 %.

  As can be seen from FIG. 3, the SNR is improved by increasing the total content of the composite oxide, and has a maximum value at 10 mol%. Furthermore, the SNR gradually decreases as the total content of the composite oxide increases. The holding force Hc also has the same tendency, is improved by increasing the total content of the composite oxide, has a maximum value at 10 mol%, and gradually decreases as the total content increases.

  On the other hand, as a required amount of each parameter, the coercive force Hc is required to be 4000 [Oe] or more from the viewpoint of high recording density (narrow track width) and resistance to thermal fluctuation. Therefore, it can be seen that Comparative Examples 10 to 13 do not satisfy the required amount, and the content is required to be 6 mol% (Example 10) or more and 12 mol% or less (Example 14). When the SNR is higher within the coercive force Hc and OW characteristics limit ranges, an HDD with a higher recording density can be produced. Therefore, it can be seen that the total content of oxides that can satisfy these conditions is 6 mol% to 12 mol%.

[Second Embodiment]
A second embodiment of the method for manufacturing a perpendicular magnetic recording medium according to the present invention will be described. Note that dimensions, materials, and other specific numerical values shown in the following embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. The same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted.

  FIG. 4 is a diagram illustrating the configuration of the perpendicular magnetic recording medium 102 according to the second embodiment. The perpendicular magnetic recording medium 102 shown in FIG. 4 includes a disk substrate 110, an adhesion layer 112, a first soft magnetic layer 114a, a spacer layer 114b, a second soft magnetic layer 114c, an orientation control layer 116, a first underlayer 118a, and a second layer. The underlayer 118b, the miniaturization promoting layer 120, the first magnetic recording layer 122a, the second magnetic recording layer 122b, the auxiliary recording layer 124, the medium protective layer 126, and the lubricating layer 128 are included. The first soft magnetic layer 114a, the spacer layer 114b, and the second soft magnetic layer 114c together constitute the soft magnetic layer 114. The first base layer 118a and the second base layer 118b together constitute the base layer 118. The first magnetic recording layer 122a and the second magnetic recording layer 122b together constitute the magnetic recording layer 122.

  As will be described below, the perpendicular magnetic recording medium 102 shown in the present embodiment has a plurality of types of oxides (one or both of the first magnetic recording layer 122a and the second magnetic recording layer 122b of the magnetic recording layer 122). Hereinafter, the composite oxide is segregated at the nonmagnetic grain boundaries by containing “composite oxide”.

  As the disk base 110, a glass disk obtained by forming amorphous aluminosilicate glass into a disk shape by direct pressing can be used. The type, size, thickness, etc. of the glass substrate are not particularly limited. Examples of the glass substrate material include glass ceramics such as aluminosilicate glass, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, or crystallized glass. It is done. The glass disk is subjected to grinding, polishing, and chemical strengthening sequentially to obtain a smooth nonmagnetic disk base 10 made of a chemically strengthened glass disk.

  On the disk substrate 110, the adhesion layer 112 to the auxiliary recording layer 124 are sequentially formed by DC magnetron sputtering, and the medium protective layer 126 can be formed by CVD. Thereafter, the lubricating layer 128 can be formed by dip coating. Note that it is also preferable to use an in-line film forming method in terms of high productivity. Hereinafter, the configuration and manufacturing method of each layer will be described.

  The adhesion layer 112 is an amorphous underlayer, which is formed in contact with the disk substrate 110 and has a function of increasing the peel strength between the soft magnetic layer 114 formed on the disk substrate 110 and the disk substrate 110. It has a function of miniaturizing and homogenizing the crystal grain of each layer to be formed. When the disk substrate 110 is made of amorphous glass, the adhesion layer 112 is preferably an amorphous alloy film so as to correspond to the amorphous glass surface.

  The adhesion layer 112 can be selected from, for example, a CrTi amorphous layer, a CoW amorphous layer, a CrW amorphous layer, a CrTa amorphous layer, and a CrNb amorphous layer. Among these, a CoW alloy film is particularly preferable because it forms an amorphous metal film containing microcrystals. The adhesion layer 112 may be a single layer made of a single material, or may be formed by laminating a plurality of layers. For example, a CoW layer or a CrW layer may be formed on the CrTi layer. These adhesion layers 112 are preferably formed by sputtering with a material containing carbon dioxide, carbon monoxide, nitrogen, or oxygen, or the surface layer is exposed with these gases.

  The soft magnetic layer 114 is a layer that temporarily forms a magnetic path during recording in order to pass magnetic flux in a direction perpendicular to the recording layer in the perpendicular magnetic recording method. The soft magnetic layer 114 is provided with AFC (Antiferro-magnetic exchange coupling) by interposing a nonmagnetic spacer layer 114b between the first soft magnetic layer 114a and the second soft magnetic layer 114c. Can be configured. As a result, the magnetization direction of the soft magnetic layer 114 can be aligned along the magnetic path (magnetic circuit) with high accuracy, and the vertical component of the magnetization direction is extremely reduced, so that noise generated from the soft magnetic layer 114 is reduced. Can do. The compositions of the first soft magnetic layer 114a and the second soft magnetic layer 114c include a Co-based alloy such as CoTaZr, a Co-Fe based alloy such as CoCrFeB, and a Ni-Fe such as a [Ni-Fe / Sn] n multilayer structure. A system alloy or the like can be used.

  The orientation control layer 116 is a nonmagnetic alloy layer, and acts to protect the soft magnetic layer 114 and the easy magnetization axis of the hexagonal close-packed structure (hcp structure) included in the underlayer 118 formed thereon is a disk. It has the function of aligning vertically. In the orientation control layer 116, the (111) plane of the face-centered cubic structure (fcc structure) or the (110) plane of the body-centered cubic structure (bcc structure) is preferably parallel to the main surface of the disk substrate 110. Further, the orientation control layer 116 may have a configuration in which these crystal structures and amorphous are mixed. The material of the orientation control layer can be selected from Ni, Cu, Pt, Pd, Zr, Hf, Nb, and Ta. Furthermore, it is good also as an alloy which contains these metals as a main component and contains any one or more additional elements of Ti, V, Ta, Cr, Mo, and W. For example, NiW, CuW, CuCr as the fcc structure, and Ta as the bcc structure can be suitably selected.

  The underlayer 118 has an hcp structure, and has a function of growing a Co hcp crystal of the magnetic recording layer 22 as a granular structure. Therefore, the higher the crystal orientation of the underlayer 18, that is, the more the (0001) plane of the crystal of the underlayer 118 is parallel to the main surface of the disk substrate 110, the more the orientation of the magnetic recording layer 22 is improved. Can do. Ru is a typical material for the underlayer, but in addition, it can be selected from RuCr and RuCo. Since Ru has an hcp structure and the lattice spacing of crystals is close to Co, a magnetic recording layer containing Co as a main component can be well oriented.

  When the underlayer 118 is made of Ru, a two-layer structure made of Ru can be obtained by changing the gas pressure during sputtering. Specifically, when forming the second base layer 118b on the upper layer side, the Ar gas pressure is set higher than when forming the first base layer 118a on the lower layer side. When the gas pressure is increased, the free movement distance of the plasma ions to be sputtered is shortened, so that the film formation rate is reduced and the crystal orientation can be improved. Further, by increasing the pressure, the size of the crystal lattice is reduced. Since the size of the Ru crystal lattice is larger than that of the Co crystal lattice, if the Ru crystal lattice is made smaller, it approaches that of Co, and the crystal orientation of the Co granular layer can be further improved.

The miniaturization promoting layer 120 is a nonmagnetic granular layer. A nonmagnetic granular layer is formed on the hcp crystal structure of the underlayer 118, and the granular layer of the first magnetic recording layer 122a is grown thereon, so that the magnetic granular layer can be grown from the initial growth stage (rise). Has the effect of separating. The composition of the miniaturization promoting layer 120 can have a granular structure by segregating a nonmagnetic substance between nonmagnetic crystal grains made of a Co-based alloy to form a grain boundary. In particular, CoCr—SiO ₂ and CoCrRu—SiO ₂ can be preferably used, and Rh (rhodium), Pd (palladium), Ag (silver), Os (osmium), Ir (iridium), Au (in addition to Ru) Gold) can also be used. A nonmagnetic substance is a substance that can form a grain boundary around magnetic grains so that exchange interaction between magnetic grains (magnetic grains) is suppressed or blocked, and is cobalt (Co). Any non-magnetic substance that does not dissolve in solution can be used. Examples thereof include silicon oxide (SiOx), chromium (Cr), chromium oxide (CrO ₂ ), titanium oxide (TiO ₂ ), zircon oxide (ZrO ₂ ), and tantalum oxide (Ta ₂ O ₅ ).

The magnetic recording layer 122 has a columnar granular structure in which a nonmagnetic substance is segregated around a magnetic particle of a hard magnetic material selected from a Co-based alloy, an Fe-based alloy, and a Ni-based alloy to form a grain boundary. Yes. By providing the miniaturization promoting layer 20, the magnetic grains can be continuously epitaxially grown from the granular structure. The magnetic recording layer may be a single layer, but in this embodiment, the magnetic recording layer is composed of a first magnetic recording layer 122a and a second magnetic recording layer 122b having different compositions and film thicknesses. The first magnetic recording layer 122a and the second magnetic recording layer 122b are all non-magnetic materials such as oxides such as SiO ₂ , Cr ₂ O ₃ , TiO ₂ , B ₂ O ₃ , Fe ₂ O ₃ , BN, etc. Nitride and carbides such as B ₄ C ₃ can be preferably used.

Furthermore, in this embodiment, two or more nonmagnetic substances are used in combination in either or both of the first magnetic recording layer 122a and the second magnetic recording layer 122b. Although there is no limitation on the kind of nonmagnetic substance contained at this time, it is particularly preferable to include SiO ₂ and TiO ₂ , and Cr ₂ O ₃ can be suitably used instead of / in addition to either of them. For example, the first magnetic recording layer 22a contains Cr ₂ O ₃ and SiO ₂ as an example of a complex oxide (a plurality of types of oxides) at the grain boundary portion, and an hcp crystal of CoCrPt—Cr ₂ O ₃ —SiO ₂ . A structure can be formed. Further, for example, the second magnetic recording layer 22b contains SiO ₂ and TiO ₂ as an example of a composite oxide at the grain boundary part, and can form an hcp crystal structure of CoCrPt—SiO ₂ —TiO ₂ .

  The auxiliary recording layer 124 is a layer (also called a continuous layer) that is magnetically continuous in the in-plane direction on the magnetic recording layer 122 having a granular structure. Although the auxiliary recording layer 124 is not necessarily required, by providing the auxiliary recording layer 124, in addition to the high density recording property and low noise property of the magnetic recording layer 122, the reverse domain nucleation magnetic field Hn is improved, the heat-resistant fluctuation characteristic is improved, and the overwrite is performed. The characteristics can be improved.

  The auxiliary recording layer 124 may be a CGC structure (Coupled Granular Continuous) that forms a thin film (continuous layer) exhibiting high perpendicular magnetic anisotropy and high saturation magnetization MS instead of a single layer. The CGC structure is an exchange energy control layer comprising a magnetic recording layer having a granular structure, a thin film coupling control layer made of a nonmagnetic material such as Pd or Pt, and an alternating laminated film in which thin films of CoB and Pd are laminated. It can consist of.

  The medium protective layer 126 can be formed by forming a carbon film by a CVD method while maintaining a vacuum. The medium protective layer 126 is a protective layer for protecting the perpendicular magnetic recording layer from the impact of the magnetic head. In general, carbon deposited by the CVD method has improved film hardness compared to that deposited by the sputtering method, so that the perpendicular magnetic recording layer can be protected more effectively against the impact from the magnetic head.

  The lubricating layer 128 can be formed of PFPE (perfluoropolyether) by dip coating. PFPE has a long chain molecular structure and binds with high affinity to N atoms on the surface of the medium protective layer 126. Due to the action of the lubricating layer 128, even if the magnetic head comes into contact with the surface of the perpendicular magnetic recording medium 102, damage or loss of the medium protective layer 126 can be prevented.

  Through the above manufacturing process, the perpendicular magnetic recording medium 102 can be obtained. The effectiveness of the present invention will be described below using examples and comparative examples.

[Examples and evaluation]
On the disk substrate 110, a film was formed in order from the adhesion layer 112 to the auxiliary recording layer 124 in an Ar atmosphere by a DC magnetron sputtering method using a vacuum deposition apparatus. The adhesion layer 112 was made of CrTi. In the soft magnetic layer 114, the composition of the first soft magnetic layer 114a and the second soft magnetic layer 114c was CoCrFeB, and the composition of the spacer layer 114b was Ru. The composition of the orientation control layer 116 is a NiW alloy having an fcc structure. For the underlayer 118, the first underlayer 118a was formed with Ru under high pressure Ar, and the second underlayer 118b was formed with Ru under low pressure Ar. The composition of the miniaturization promoting layer 120 was nonmagnetic CoCr—SiO ₂ . The magnetic recording layer 122 was formed with the configurations of the following examples and comparative examples. The composition of the auxiliary recording layer 124 was CoCrPtB. The medium protective layer 126 was formed using C ₂ H ₄ and CN by the CVD method, and the lubricating layer 128 was formed using PFPE by the dip coating method.

  5A and 5B are diagrams for explaining the case where the composition of the nonmagnetic substance is changed. FIG. 5A is a diagram showing the SNR and the coercive force Hc, and FIG. 5B is a diagram explaining the thermal fluctuation characteristics. is there. Here, the total amount of the nonmagnetic substance content is equally 10 mol%. In FIG. 5A, only the oxide is shown for easy understanding.

In Example 20, the first magnetic recording layer 122a contains Cr ₂ O ₃ as an oxide, and the second magnetic recording layer 122b contains SiO ₂ and TiO ₂ as examples of complex oxides (plural types of oxides). An hcp crystal structure of CoCrPt—SiO ₂ —TiO ₂ was formed. In Example 21, the first magnetic recording layer 122a contains Cr ₂ O ₃ and SiO ₂ as an example of a composite oxide to form an hcp crystal structure of CoCrPt—Cr ₂ O ₃ —SiO _2. The layer 122b contained SiO ₂ and TiO ₂ as examples of the composite oxide. In Example 22, the first magnetic recording layer 122a contained SiO ₂ and TiO ₂ as an example of a complex oxide, and the second magnetic recording layer 122b contained SiO ₂ and TiO ₂ as an example of a complex oxide. In Example 23, the first magnetic recording layer 122a contains Cr ₂ O ₃ and TiO ₂ as an example of a complex oxide, and the second magnetic recording layer 122b contains SiO ₂ and TiO ₂ as an example of a complex oxide. It was.

Example 24 and Comparative Example 20 are examples in which the magnetic recording layer is a single layer. FIG. 6 is a diagram showing a configuration in which the magnetic recording layer is a single layer. In the perpendicular magnetic recording medium 104 shown in FIG. 6, a single magnetic recording layer 123 is provided on the miniaturization promoting layer 120. In the magnetic recording layer 123, similarly to the above-described second magnetic recording layer 122b, the nonmagnetic substance segregates around the magnetic substance to form a grain boundary, and the magnetic grains (magnetic grains) form a columnar granular structure. ing. In Example 24, the oxide of the magnetic recording layer 123 is a composite oxide of SiO ₂ and TiO ₂ . In Comparative Example 20, the oxide of the magnetic recording layer 123 is a composite oxide of YiO ₃ (yttrium oxide) and TiO ₂ .

As can be seen from FIG. 5A, the second magnetic recording layer 122b, which is the main recording layer, or the magnetic recording layer 123, which is a single layer, is a composite oxide of SiO ₂ and TiO ₂ with a high SNR. The magnetic force Hc is shown. On the other hand, in Comparative Example 20, Hc does not satisfy the required amount. From this, it is understood that it is not necessary to simply combine a plurality of oxides, and a composite oxide of SiO ₂ and TiO ₂ is suitable as a nonmagnetic substance for the magnetic recording layer.

In addition, the SNR and the coercive force Hc are improved in Examples 20 to 23 in which a plurality of magnetic recording layers are provided in a multilayer structure compared to Example 24 in which a single magnetic recording layer 23 is provided. By improving the coercive force Hc, the track width can be reduced. Further, the recording bit length can be shortened by improving the SNR. From these facts, it can be seen that the recording density can be further increased if the magnetic recording layer has a multilayer structure. The reason why both the holding power Hc and the SNR are improved when SiO ₂ and TiO ₂ are mixed is not clear, but it is considered that the refinement by SiO ₂ and the homogenization of magnetic grains by TiO ₂ cooperated well. .

  Furthermore, among the configurations provided with a plurality of magnetic recording layers, Examples 21 to 23 in which the first magnetic recording layer 122a is also made of a non-magnetic substance containing a complex oxide are preferable because the SNR is improved. I understand that. The reason for this is not clear, but can be considered as follows.

FIG. 5B shows the evaluation results of the thermal fluctuation characteristics of CoCrPt—TiO ₂ (single oxide) and CoCrPt—SiO ₂ —TiO ₂ (composite oxide). Usually, the thermal fluctuation characteristic is an important factor for improving the SNR. The thermal fluctuation characteristic can be indicated by an index called KuV / KT. Here, Ku is the magnetic anisotropy energy specific to the material, V is the volume of the magnetic grains, K is the Boltzmann constant, and T is the temperature. In the experiment of FIG. 5B, the composition of CoCrPt—TiO ₂ and CoCrPt—SiO ₂ —TiO ₂ are almost the same, so the value of Ku of the magnetic grains is theoretically unchanged. Ku is a constant, and there is no difference between the two magnetic layers. Moreover, the temperature at the time of a measurement is room temperature, and T is also the same value. For this reason, the difference in KuV / KT can be considered to be a decrease in volume (decrease in V) of the magnetic grains due to magnetic isolation (miniaturization) of the magnetic grains. That is, it is considered that the first magnetic recording layer 122a also includes the composite oxide in the nonmagnetic material, thereby improving the thermal fluctuation characteristics of the first magnetic recording layer 122a and improving the SNR.

  Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  For example, in the above-described embodiments and examples, it has been described that the magnetic recording layer is composed of two layers of the first magnetic recording layer and the second magnetic recording layer, or one layer. However, even when the magnetic recording layer further comprises three or more layers, the benefits of the present invention can be obtained in the same manner as described above by incorporating a plurality of types of oxides into at least one magnetic recording layer. .

  The present invention can be used as a method of manufacturing a perpendicular magnetic recording medium mounted on a perpendicular magnetic recording type HDD or the like.

It is a figure explaining the structure of the perpendicular magnetic recording medium concerning 1st Embodiment. It is a figure which shows the relationship between the mixing ratio of the oxide or composite oxide and SNR in an Example and a comparative example. It is a figure which shows SNR and coercive force Hc when content of complex oxide is changed as the whole oxide. It is a figure explaining the structure of the perpendicular magnetic recording medium concerning 2nd Embodiment. It is a figure explaining the case where the composition of a nonmagnetic substance is changed. It is a figure which shows the structure which made the magnetic recording layer the single layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Disk base | substrate, 12 ... Adhesion layer, 14 ... Soft magnetic layer, 14a ... 1st soft magnetic layer, 14b ... Spacer layer, 14c ... 2nd soft magnetic layer, 16 ... Orientation control layer, 18 ... Underlayer, 18a ... First underlayer, 18b ... second underlayer, 20 ... miniaturization promoting layer, 22 ... magnetic recording layer, 22a ... first magnetic recording layer, 22b ... second magnetic recording layer, 23 ... magnetic recording layer (single layer) 24 ... auxiliary recording layer, 26 ... medium protective layer, 28 ... lubricating layer, 100, 102, 104 ... perpendicular magnetic recording medium, 110 ... disk substrate, 112 ... adhesion layer, 114 ... soft magnetic layer, 114a ... first soft layer Magnetic layer, 114b ... spacer layer, 114c ... second soft magnetic layer, 116 ... orientation control layer, 118 ... underlayer, 118a ... first underlayer, 118b ... second underlayer, 120 ... miniaturization promoting layer, 122 ... Magnetic recording layer, 122a... First magnetic recording layer, 1 2b ... second magnetic recording layer, 123 ... magnetic recording layer, 124 ... auxiliary recording layer, 126 ... medium protective layer, 128 ... lubricating layer

Claims (4)

A perpendicular magnetic recording medium comprising a magnetic recording layer having a granular structure in which a nonmagnetic grain boundary is formed between magnetic grains continuously grown in a columnar shape,
The perpendicular magnetic recording medium, wherein the grain boundary portion contains a plurality of types of oxides. The perpendicular magnetic recording medium according to claim 1, wherein the plurality of types of oxides include both SiO ₂ and TiO ₂ .   2. The perpendicular magnetic recording medium according to claim 1, wherein the content of the plurality of types of oxides is 6 mol% to 12 mol% as a whole of the oxides. A plurality of the magnetic recording layers having a granular structure;
2. The perpendicular magnetic recording medium according to claim 1, wherein at least one magnetic recording layer contains a plurality of types of oxides in the grain boundary portion.

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