JP2009099242A - Perpendicular magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a perpendicular magnetic recording medium increasing recording density by improving electromagnetic conversion characteristics (especially SNR) while improving magnetostatic characteristics (especially coercive force Hc). <P>SOLUTION: The perpendicular magnetic recording medium of a perpendicular magnetic recording system includes at least a first magnetic recording layer 22a and a second magnetic recording layer 22b successively on a substrate. Each of the first and second magnetic recording layers 22a and 22b is a ferromagnetic layer of a granular structure in which a nonmagnetic boundary portion is formed between magnetic particles continuously grown into a columnar shape. The boundary portion of each of the first and second magnetic layers contains a plurality of types of oxides. <P>COPYRIGHT: (C)2009,JPO&amp;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. Important factors for achieving high recording density include improved magnetostatic characteristics such as coercivity Hc and reverse domain nucleation magnetic field Hn, and improved electromagnetic conversion characteristics such as overwrite characteristics and SNR (Signal-Noise Ratio). There are various things. In particular, in order to increase the recording density, it is necessary to isolate and refine the magnetic particles, but it is also necessary to improve the coercive force Hc of the magnetic particles that are minimized. Further, in order to read and write accurately and at high speed even in a recording bit having a small area, improvement of SNR is extremely important.

  Further, the coercive force Hc is improved by optimizing materials such as a magnetic layer and an underlayer, crystal orientation, and film configuration. The SNR is improved mainly by reducing the magnetization transition region noise of the magnetic recording layer. In order to improve the coercive force Hc and SNR, it is desirable to make the particle size of the magnetic particles uniform and fine, and to have a bent-down 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 coercive force Hc and the perpendicular magnetic anisotropy deteriorate, 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.

  Accordingly, an object of the present invention is to provide a perpendicular magnetic recording medium capable of further increasing the recording density by enhancing the electromagnetic conversion characteristics (especially SNR) while enhancing the magnetostatic characteristics (particularly the coercive force Hc). It is said.

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 type magnetic recording medium having at least a first magnetic recording layer and a second magnetic recording layer in this order on a substrate. And the second magnetic recording layer is a ferromagnetic layer having a granular structure in which nonmagnetic grain boundary portions are formed between magnetic grains continuously grown in a columnar shape, and each of the first magnetic recording layer and the second magnetic recording layer Each grain boundary part contains a plurality of types of oxides.

  According to the above configuration, characteristics of a plurality of oxides can be obtained, and electromagnetic conversion can be performed while enhancing the magnetostatic characteristics (particularly the coercive force Hc) by further miniaturizing and isolating the magnetic particles of the magnetic recording layer. By increasing the characteristics (particularly SNR), a perpendicular magnetic recording medium capable of further increasing the recording density can be obtained.

  Assuming that the total content of the plurality of types of oxides included in the first magnetic recording layer is Amol% and the total content of the plurality of types of oxides included in the second magnetic recording layer is Bmol%, A < B is preferred. This is because the OW characteristics can be improved while maintaining the coercive force Hc and the high SNR.

  The total content of the plurality of types of oxides contained in the first magnetic recording layer or the second magnetic recording layer is preferably 6 mol% to 12 mol%. This is because when it is within the above range, the action of a single oxide contained can be exceeded.

The plurality of types of oxides can be selected from SiO ₂ , TiO ₂ , CrO ₂ , Cr ₂ O ₃ , ZrO ₂ , and Ta ₂ O ₅ . The oxide may be any substance that can form a grain boundary around the magnetic grains so that the exchange interaction between the magnetic grains (magnetic grains) is suppressed or blocked. In particular, it is preferable that both SiO ₂ and TiO ₂ are included. In particular, the first magnetic recording layer is preferably a combination of any one of Cr ₂ O ₃ + SiO ₂ , Cr ₂ O ₃ + TiO ₂ , and SiO ₂ + 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.

  The total content of the plurality of types of oxides included in the first magnetic recording layer is 5 to 8 mol%, and the total content of the plurality of types of oxides included in the first magnetic recording layer is Amol. %, It is preferable that A <B, where Bmol% is the total content of the plurality of types of oxides included in the second magnetic recording layer.

  This is because if the total content of the first magnetic recording layer is too much or too little, the coercive force Hc tends to decrease, and a high coercive force Hc can be obtained when it is in the above range. In the above range, when the total content of the second magnetic recording layer is 10 mol%, the coercive force Hc has a maximum value.

  According to the perpendicular magnetic recording medium of the present invention, the recording density can be further increased by increasing the electromagnetic conversion characteristics (especially SNR) while enhancing the magnetostatic characteristics (particularly the coercive force Hc).

[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 first 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 this embodiment includes a plurality of types of oxides (hereinafter referred to as “composite oxidation”) on the first magnetic recording layer 22a and the second magnetic recording layer 22b of the magnetic recording layer 22. The compound 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 contained 3 mol% each of SiO ₂ and TiO ₂ as examples of complex oxides (plural types of oxides), and formed an hcp crystal structure of CoCrPt-3SiO ₂ -3TiO ₂ . The thickness of the first magnetic recording layer 22a was 5 nm. The nonmagnetic substance Cr and the composite oxide segregated around the magnetic substance Co 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.

The second magnetic recording layer 22b contained 5 mol% each of SiO ₂ and TiO ₂ as examples of complex oxides (plural types of oxides), and formed an hcp crystal structure of CoCrPt-5SiO ₂ -5TiO ₂ . The film thickness of the second magnetic recording layer 22b was 10 nm. Also in the second magnetic recording layer 22b, the magnetic grains formed a granular structure.

  That is, the grain boundary portions of the first magnetic recording layer and the second magnetic recording layer each contain a plurality of types of oxides. When the total content of the plurality of types of oxides included in the first magnetic recording layer is Amol% and the total content of the plurality of types of oxides included in the second magnetic recording layer is Bmol%, A <B.

  Accordingly, a granular columnar structure can be formed even if the film thickness is small. That is, when the Co crystal is epitaxially grown continuously from the granular structure of the miniaturization promoting layer 20, the columnar structure can be easily formed because the crystal grains are large in the first magnetic recording layer 22a with a small amount of oxide. The second magnetic recording layer 22b as the main recording layer can be miniaturized by growing small crystal grains in the second magnetic recording layer 22b continuously from the crystal grains in the first magnetic recording layer 22a. Accordingly, high crystal orientation and refinement can be improved from the stage where the film thickness is small, and SNR can be improved.

  In addition, by increasing the total amount of oxide in the second magnetic recording layer 22b as compared with the first magnetic recording layer 22a, the second magnetic recording layer 22b has smaller hcp crystal structure crystal grains containing Co. . Therefore, the second magnetic recording layer 22b has a high overwrite characteristic, and the first magnetic recording layer 22a has a high coercive force. Therefore, even if the coercive force is increased to such an extent that writing by the magnetic head is difficult in the first magnetic recording layer 22a, first, the magnetization transition is started by the writing magnetic field of the magnetic head in the second magnetic recording layer 22b on the surface layer side. The first magnetic recording layer 22a also undergoes magnetization transition, and writing becomes possible. When a magnetic field is not applied from the magnetic head, a large coercive force is exhibited by the large magnetic grains of the first magnetic recording layer 22a, so that the first magnetic recording layer 22a can be thinned. In combination with these, the coercive force (Hc) can be improved so that the overwriting characteristic (overwrite characteristic: O / W) can be improved while maintaining the coercive force (Hc) high enough not to affect the thermal fluctuation resistance. The thickness of the magnetic recording layer 22 can be reduced.

  The auxiliary recording layer 24 is a thin film (continuous layer) that exhibits 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]
FIG. 2 is a diagram illustrating the relationship between the coercive force Hc and the SNR in Examples and Comparative Examples. In Example 1, as described in the first embodiment, 3 mol% each of SiO ₂ and TiO ₂ are mixed in the first magnetic recording layer 22 as a complex oxide, and as a complex oxide in the second magnetic recording layer 22 b. Each of them contains 5 mol% of SiO ₂ and TiO ₂ . In Comparative Example 1, the recording layer is a single layer and contains 9 mol% of TiO ₂ as an oxide. In Comparative Example 2, the recording layer is a single layer and contains 10 mol% of TiO ₂ as an oxide. Comparative Example 3 is a two-layer similarly to the magnetic layer in Example 1, 9 mol% of TiO ₂ in the first magnetic recording layer 22, as in the second magnetic recording layer 22b having a TiO ₂ is contained 10 mol% It is.

  In the comparative example, the thickness of the magnetic recording layer was changed from 8 nm to 11 nm in units of 1 nm, and Hc and SN were measured. As described in the first embodiment, the film thickness of Example 1 is 5 nm for the first magnetic recording layer 22a and 10 nm for the second magnetic recording layer 22b.

  As can be seen from FIG. 2, in all of Comparative Examples 1 to 3, the coercive force Hc tends to increase as the film thickness increases. This is considered to be because when the thickness of the magnetic recording layer is increased, the magnetic particles grown in a columnar shape become longer, the demagnetizing field is reduced, and as a result, the coercive force Hc is improved. Further, referring to Comparative Examples 1 and 2, in the case of a single recording layer, the SN increases as the film thickness increases, and decreases after the peak. According to the improvement of the coercive force Hc, the SNR is improved because writing blur due to the leakage magnetic field is initially reduced. However, the coercive force Hc is excessively increased and the overwrite characteristic is deteriorated, so that the SNR is decreased. Conceivable.

  Compared to Comparative Example 1, Comparative Example 2 has a lower coercive force Hc but an improved SNR. This is considered to be due to the increase in the amount of oxides, the magnetic particles become smaller, the coercive force Hc decreases, the isolation progresses, and the SNR improves.

  In Comparative Example 3, the coercive force Hc is slightly improved as compared with Comparative Example 2, but it can be seen that the SNR is significantly improved. Considering that, in Comparative Example 3, the first magnetic recording layer has a high crystal orientation because it has few oxides, and the second magnetic recording layer has a large amount of oxide, so that the magnetic particles become small and fine isolation is achieved. It is done. From these things, it is thought that SNR improved.

In Example 1 using the composite oxide, the coercive force Hc is comparable to that in Comparative Example 3, but the SNR is further improved significantly. 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 .

  That is, the characteristics of a plurality of oxides can be obtained by including a plurality of types of oxides in the grain boundary portions of the first magnetic recording layer and the second magnetic recording layer, respectively. Accordingly, it is possible to obtain a perpendicular magnetic recording medium that can improve the electromagnetic conversion characteristics (especially SNR) while improving the magnetostatic characteristics (particularly the coercive force Hc) and can further increase the recording density.

FIG. 3 is a diagram showing the coercive force Hc and SNR when the total contents of the oxides contained in the first and second magnetic recording layers are different. 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). The total content of the plurality of types of oxides included in the first magnetic recording layer 122a is Amol%, and the total content of the plurality of types of oxides included in the second magnetic recording layer 122b is Bmol%. In the case of A <B, Examples 10 to 12 are used, and in the case of A> B, Comparative Examples 10 to 15 are used.

  As can be seen from FIG. 3, when Example 10 (6:10) and Comparative Example 11 (10: 6), Example 11 (6:12) and Comparative Example 13 (12: 6) in which the composition ratio is reversed are compared. It can be seen that the holding force Hc and SNR are higher when A <B.

  However, when Example 12 (10:12) and Comparative Example 14 (12:10) are compared, the Example is rather low. That is, there is a region where the above relationship does not hold.

  FIG. 4 is a diagram showing the coercive force Hc when the total content of oxides contained in the first magnetic recording layer is different when the content of oxide in the second magnetic recording layer is fixed at 10 mol%. Referring to FIG. 4, it can be seen that there is an optimum value for the amount of oxide in the first magnetic recording layer, the value is 6 mol%, and a preferable range is 5 to 8 mol% when Hc ≧ 4000. That is, in any case, if A <B, good results are not obtained. When A is in the range of 5 to 8 mol% and A <B, good SNR and holding force Hc are obtained. Can be obtained.

[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. 5 is a diagram for explaining the configuration of the perpendicular magnetic recording medium 102 according to the second embodiment. The perpendicular magnetic recording medium 102 shown in FIG. 5 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.

  FIG. 6 is a diagram showing SNR, coercive force Hc, and overwrite characteristics when the composition of the nonmagnetic substance is changed. Here, the total amount of the nonmagnetic substance content is equally 10 mol%. In FIG. 6, only the oxide is shown for easy understanding.

In Comparative 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 20, 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 , and second magnetic recording. The layer 122b contained SiO ₂ and TiO ₂ as examples of the composite oxide. In Example 21, 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 22, 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.

Comparative Example 21 and Comparative Example 22 are examples in which the magnetic recording layer is a single layer. FIG. 7 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. 7, 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 Comparative Example 21, the oxide of the magnetic recording layer 123 is a composite oxide of SiO ₂ and TiO ₂ . In Comparative Example 22, 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. 6, 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 , SNR, coercive force Hc, OW The characteristics meet the requirements. On the other hand, in Comparative Example 22, 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.

Also, the SNR and coercive force Hc are improved in Examples 20 to 22 in which a plurality of magnetic recording layers are provided in a multilayer structure compared to Comparative Example 21 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. For these reasons, the recording density can be further increased. The reason why both SiO ₂ and TiO ₂ are improved is not clear, but it is considered that the refinement by SiO ₂ and the uniformization of magnetic grains by TiO ₂ cooperated well.

  Further, it can be seen that, among the configurations provided with a plurality of magnetic recording layers, the first magnetic recording layer 122a is more preferable when the non-magnetic substance contains a complex oxide because the SNR is improved. The reason for this is not clear, but it is thought that the growth of magnetic grains was suppressed by using a composite oxide.

  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.

  The present invention can be used as 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 coercive force Hc and SNR in an Example and a comparative example. It is a figure which shows coercive force Hc and SNR about the case where the whole content of the oxide contained in each of the 1st and 2nd magnetic recording layers differs. It is a figure which shows the coercive force Hc in the case where the whole content of the oxide contained in a 1st magnetic recording layer when the content oxide content of a 2nd magnetic recording layer is fixed to 10 mol%. It is a figure explaining the structure of the perpendicular magnetic recording medium concerning 2nd Embodiment. It is a figure which shows SNR, coercive force Hc, and an overwrite characteristic when changing a composition of a nonmagnetic substance. 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 ... 1st underlayer 18b ... 2nd Underlayer 20 ... miniaturization promoting layer 22 ... magnetic recording layer 22a ... first magnetic recording layer 22b ... second magnetic recording layer 24 ... auxiliary recording layer 26 ... medium protective layer 28 ... lubricating layer 100 ... perpendicular magnetic recording medium 102 ... perpendicular Magnetic recording medium 110 ... disk substrate 112 ... adhesion layer 114 ... soft magnetic layer 114a ... first soft 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 122b ... second magnetic recording layer 124 ... auxiliary recording layer 126 ... media protection 128 ... lubricating layer

Claims (4)

In a perpendicular magnetic recording type magnetic recording medium comprising at least a first magnetic recording layer and a second magnetic recording layer in this order on a substrate,
The first magnetic recording layer and the second magnetic recording layer are a ferromagnetic layer having a granular structure in which nonmagnetic grain boundary portions are formed between magnetic grains continuously grown in a columnar shape,
The perpendicular magnetic recording medium, wherein the grain boundary portions of the first magnetic recording layer and the second magnetic recording layer each contain a plurality of types of oxides. The total content of the plurality of types of oxides contained in the first magnetic recording layer is Amol%,
When the total content of the plurality of types of oxides contained in the second magnetic recording layer is Bmol%,
The perpendicular magnetic recording medium according to claim 1, wherein A <B. _2. The perpendicular magnetic recording medium according to claim 1, wherein the plurality of types of oxides are selected from SiO ₂ , TiO ₂ , CrO ₂ , Cr ₂ O ₃ , ZrO ₂ , and Ta ₂ O ₅ . The total content of the plurality of types of oxides contained in the first magnetic recording layer is 5 to 8 mol%, and
The total content of the plurality of types of oxides contained in the first magnetic recording layer is Amol%,
When the total content of the plurality of types of oxides contained in the second magnetic recording layer is Bmol%,
The perpendicular magnetic recording medium according to claim 1, wherein A <B.

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