JP2009245480A - Vertical magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vertical magnetic recording medium which attains higher recording density by raising electromagnetic conversion characteristics (especially OW characteristics and SNR) while rasing magnetostatic characteristics (especially holding force Hc). <P>SOLUTION: Typical configuration of the vertical magnetic recording medium is characterized in that, in a magnetic recording medium 100 of a vertical magnetic recording system having at least a first magnetic recording layer 122a, and a second magnetic recording layer 122b formed in this order on a substrate, the first magnetic recording layer and the second magnetic recording layer are ferro-magnetic layers of granular structure in which non-magnetic grain boundary parts are formed between magnetic particles which continue and grow in the shape of a pillar, each of the grain boundary parts of the first magnetic recording layer and the second magnetic recording layer contains a plurality of kinds of oxides, and when film thickness of the first magnetic recording layer is denoted as Anm, and film thickness of the second magnetic recording layer is denoted as Bnm, A/(A+B) is within a range of 0.12<A/(A+B)<0.64. <P>COPYRIGHT: (C)2010,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. Compared to the conventional in-plane recording method, the perpendicular magnetic recording method can suppress the so-called thermal fluctuation phenomenon in which the thermal stability of the recording signal is lost due to the superparamagnetic phenomenon, and the recording signal disappears. Suitable for higher 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 increasing the recording density include improvements in magnetostatic characteristics such as coercivity Hc and reverse domain nucleation magnetic field Hn, and electromagnetic characteristics such as overwrite characteristics (OW characteristics) and SNR (Signal-Noise Ratio). There are various things such as improvement of conversion characteristics and narrowing of the track width. Among them, the improvement in SNR is important in order to read and write accurately and at high speed even in a recording bit having a small area. Such an improvement in SNR is performed mainly by reducing the 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, to reduce the particle size of the magnetic particles, and to isolate the magnetic particles. It is necessary to improve Hc.

  The coercive force Hc is improved by optimizing materials such as a magnetic layer and an underlayer, crystal orientation, and film configuration. Therefore, in order to improve the above 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 state in which the individual magnetic particles are magnetically separated.

  By the way, the Co-based perpendicular magnetic recording layer, especially the CoPt-based perpendicular magnetic recording layer has a high coercive force Hc, and the reverse magnetic domain nucleation magnetic field (Hn) can be set to a small value less than zero, thereby improving the resistance to thermal fluctuation. And 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 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.

  Further, as an important factor for increasing the recording density, the ease of writing on the magnetic recording medium by the magnetic head, that is, the improvement of the OW characteristics can be mentioned. The OW characteristic decreases in inverse proportion to the improvement of the coercive force Hc. That is, when the coercive force Hc is improved, a high recording density can be achieved, but writing with a magnetic head tends to be difficult. This is because as the coercive force Hc of the magnetic recording layer improves, the magnetization of the magnetic recording layer becomes difficult to reverse, and a strong magnetic field needs to be applied when writing by the magnetic head.

  As described above, in order to achieve higher recording density, it is necessary to improve the coercive force Hc. In order to improve the coercive force Hc, a method of increasing the film thickness of the magnetic recording layer is conceivable. However, when the film thickness is increased, the OW characteristics and the SNR are deteriorated.

  Therefore, the inventors of the present application have found that the OW characteristics and the SNR are improved while the coercive force Hc is improved by making the magnetic recording layer have a two-layer structure. However, as a result of examining the magnetic recording layer having a two-layer structure in more detail, the inventors of the present application have found that the SNR is not improved in all perpendicular magnetic recording media.

  The present invention has been made in view of the above problems of the magnetic recording layer, and the object of the present invention is to improve the magnetostatic characteristics (particularly, the coercive force Hc) in the magnetic recording layer having a two-layer structure, while performing electromagnetic conversion. An object of the present invention is to provide a perpendicular magnetic recording medium capable of further increasing the recording density by improving the characteristics (particularly the OW characteristics and SNR).

  The inventors of the present application have made extensive studies on the above problems, and as a result, the magnetostatic characteristics (particularly the coercive force Hc) and the electromagnetic conversion characteristics (particularly the OW characteristics and SNR) depend on the thickness of the magnetic recording layer in the vertical direction. Focused on that. Regarding the influence of the film thickness of the magnetic recording layer on the above characteristics, the magnetostatic characteristics (particularly, by controlling the film thickness ratio between the film thickness of the first magnetic recording layer and the film thickness of the second magnetic recording layer). It was found that both the coercive force Hc) and the electromagnetic conversion characteristics (particularly the OW characteristics and SNR) are improved.

Moreover, when the oxide which forms a grain boundary was also examined, it was noted that the influence of the oxide is not only the amount but also the influence depending on the kind of the oxide. As for 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). The above oxides have characteristics depending on the type, and can be selected according to the desired performance. However, the characteristics have advantages and disadvantages, and any oxide does not necessarily meet future high recording density. Absent.

  As a result of the examination of the above items by the inventors, the film thickness ratio of the first magnetic recording layer to the second magnetic recording layer is controlled, and a plurality of oxides are appropriately used for each magnetic recording layer. Thus, it was found that the magnetostatic characteristics and the electromagnetic conversion characteristics can be obtained without canceling out, and the present invention has been completed.

  That is, in order to solve the above-described problems, a typical configuration of the perpendicular magnetic recording medium according to the present invention is a perpendicular magnetic recording system in which at least a first magnetic recording layer and a second magnetic recording layer are provided in this order on a substrate. In the recording medium, the first magnetic recording layer and the second magnetic recording layer are ferromagnetic layers having a granular structure in which nonmagnetic grain boundary portions are formed between magnetic grains continuously grown in a columnar shape, and the first magnetic recording layer is a first magnetic recording layer. The grain boundary portions of the recording layer and the second magnetic recording layer each contain a plurality of types of oxides, and when the film thickness of the first magnetic recording layer is Anm and the film thickness of the second magnetic recording layer is Bnm, A / (A + B) is in the range of 0.12 <A / (A + B) <0.64.

  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. It is possible to improve characteristics (particularly OW characteristics and SNR). Further, when the film thickness ratio between the first magnetic recording layer and the second magnetic recording layer is within the above range, the OW characteristics required for the perpendicular magnetic recording medium are -30 dB or more and the coercive force Hc is 4000 Oe or more. Can be achieved. Thereby, a perpendicular magnetic recording medium capable of further increasing the recording density can be obtained. Here, the reference value that the OW characteristic is −30 dB or more is a value based on the fact that writing to the magnetic recording medium cannot be performed when the OW characteristic is less than −30 dB. In addition, the reference value of coercive force Hc of 4000 Oe or more enables data retention even in a track width that becomes narrower as the recording density becomes higher, in order to obtain thermal fluctuation resistance necessary for preventing data loss. Is necessary for.

  When the film thickness of the first magnetic recording layer is Anm and the film thickness of the second magnetic recording layer is Bnm, A + B is preferably in the range of 11 <A + B <27.

  As the total thickness A + B of the magnetic layer increases, the coercive force Hc tends to improve. However, in inverse proportion to this, the OW characteristics and the SNR are reduced. Accordingly, in order to improve both characteristics without canceling out the magnetostatic characteristics (particularly the coercive force Hc) and the electromagnetic conversion characteristics (particularly the OW characteristic and SNR), A + B is preferably within the above range.

  When the total content of the plurality of types of oxides included in the first magnetic recording layer is α mol% and the total content of the plurality of types of oxides included in the second magnetic recording layer is β mol%, The content relationship is preferably α ≦ β. This is because OW characteristics can be improved while maintaining high coercive force Hc and SNR.

The plurality of types of oxides may 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. 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.

  According to the perpendicular magnetic recording medium of the present invention, it is possible to further increase the recording density by enhancing the electromagnetic conversion characteristics (particularly the OW characteristics and SNR) while enhancing the magnetostatic characteristics (particularly the coercive force Hc). it can.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

  FIG. 1 is a diagram illustrating the configuration of a perpendicular magnetic recording medium 100 according to the present embodiment. A perpendicular magnetic recording medium 100 shown in FIG. 1 includes a disk substrate 110 as a substrate, an adhesion layer 112, a first soft magnetic layer 114a, a spacer layer 114b, a second soft magnetic layer 114c, a pre-underlayer 116, and a first underlayer 118a. , A second underlayer 118b, a nonmagnetic granular layer 120, a first magnetic recording layer 122a, a second magnetic recording layer 122b, a continuous layer 124, a medium protective layer 126, and a lubricating layer 128. 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 100 shown in the present embodiment includes 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 substrate 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 disk are not particularly limited. Examples of the material of the glass disk include aluminosilicate glass, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, or glass ceramic such as crystallized glass. It is done. The glass disk is subjected to grinding, polishing, and chemical strengthening sequentially to obtain a smooth non-magnetic disk base 110 made of a chemically strengthened glass disk.

  On the disk substrate 110, a film is sequentially formed from the adhesion layer 112 to the continuous layer 124 by a DC magnetron sputtering method, and the medium protective layer 126 can be formed by a CVD method. 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 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, and the crystal grains of each layer formed thereon are finely divided. It has a function to make it uniform and uniform. When the disk substrate 110 is made of amorphous glass, the adhesion layer 112 is preferably an amorphous (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 pre-underlayer 116 is a non-magnetic 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. A function for aligning in the vertical direction is provided. The pre-underlayer 116 preferably has a (111) plane having a face-centered cubic structure (fcc structure) or a (110) plane having a body-centered cubic structure (bcc structure) parallel to the main surface of the disk substrate 110. Further, the pre-underlayer 116 may have a configuration in which these crystal structures and amorphous are mixed. The material of the front ground 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 122 as a granular structure. Therefore, the higher the crystal orientation of the underlayer 118, 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 nonmagnetic granular 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 nonmagnetic granular layer 120 can be a granular structure by forming a grain boundary by segregating a nonmagnetic substance between nonmagnetic crystal grains made of a Co-based alloy. 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 nonmagnetic granular layer 120, the magnetic grains can be continuously epitaxially grown from the granular structure. Although the magnetic recording layer 122 may be a single layer, in this embodiment, the magnetic recording layer 122 includes 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 both _SiO 2 _is also a non-magnetic _{material, CrO 2, Cr 2 O 3} , TiO 2, ZrO 2, B 2 O 3, Fe 2 O 3, Ta An oxide such as ₂ O ₅ , a nitride such as BN, or a carbide 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 122a contains Cr ₂ O ₃ and SiO ₂ as an example of a composite oxide (a plurality of types of oxides) at the grain boundary, and an hcp crystal of CoCrPt—Cr ₂ O ₃ —SiO ₂ . A structure can be formed. 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 nonmagnetic granular layer.

Further, for example, the second magnetic recording layer 122b can contain 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 . Also in the second magnetic recording layer 122b, the magnetic grains formed a granular structure.

  When the film thickness of the first magnetic recording layer 122a is Anm and the film thickness of the second magnetic recording layer 122b is Bnm, A / (A + B) is in the range of 0.12 <A / (A + B) <0.64. It is preferable that As a result, it is possible to obtain a perpendicular magnetic recording medium that achieves the standards required for the perpendicular magnetic recording medium, such as OW characteristics of −30 dB or more and a coercive force Hc of 4000 Oe or more, and further increasing the recording density. The reference value that the OW characteristic is −30 dB or more is a value that is based on the fact that writing to the magnetic recording medium is impossible when the OW characteristic is less than −30 dB. In addition, the reference value of coercive force Hc of 4000 Oe or more enables data retention even in a track width that becomes narrower as the recording density becomes higher, in order to obtain thermal fluctuation resistance necessary for preventing data loss. Is necessary for.

  The total film thickness A + B of the first magnetic recording layer and the second magnetic recording layer is preferably in the range of 11 <A + B <27. As the total film thickness A + B of the magnetic layer increases, the coercive force Hc increases, but the OW characteristics and SNR decrease in inverse proportion thereto. Therefore, if A + B is within the above range, the magnetostatic characteristics (particularly the coercive force Hc) and the electromagnetic conversion characteristics (particularly the OW characteristic and SNR) are not canceled out, and both characteristics are improved.

  As described above, 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 α mol% and the total content of the plurality of types of oxides included in the second magnetic recording layer is β mol%, The quantity relationship is α ≦ β.

  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 nonmagnetic granular layer 120, if the first magnetic recording layer 122a has less oxide than the second magnetic recording layer 122b, the first magnetic recording layer Since 122a has larger crystal grains, it is easier to form a columnar structure. The second magnetic recording layer 122b as the main recording layer can be miniaturized by growing small crystal grains in the second magnetic recording layer 122b continuously from the crystal grains in the first magnetic recording layer 122a. Accordingly, high crystal orientation and refinement can be improved from the stage where the film thickness is small, and SNR can be improved.

  The continuous layer 124 is a layer (also referred to as a continuous layer) that is magnetically continuous in the in-plane direction on the magnetic recording layer 122 having a granular structure. Although the continuous layer 124 is not always necessary, in addition to the high density recording property and low noise property of the magnetic recording layer 122, the continuous layer 124 improves the reverse domain nucleation magnetic field Hn, improves the heat-resistant fluctuation characteristics, and improves the OW characteristics. Improvements can be made.

  The continuous layer 124 may not be a single layer but 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. 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 100, damage or loss of the medium protective layer 126 can be prevented.

  Through the above manufacturing process, the perpendicular magnetic recording medium 100 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 continuous layer 124 in an Ar atmosphere by a DC magnetron sputtering method using a film forming apparatus that was evacuated. 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 pre-underlayer 116 was 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 nonmagnetic granular layer 120 was nonmagnetic CoCr—SiO ₂ . The first magnetic recording layer 122a contains Cr ₂ O ₃ and SiO ₂ as examples of complex oxides (plural types of oxides) at the grain boundary, and has an hcp crystal structure of CoCrPt—Cr ₂ O ₃ —SiO _2. Formed. The second magnetic recording layer 122b contains SiO ₂ and TiO ₂ as an example of a composite oxide at the grain boundary portion, and has a CoCrPt—SiO ₂ —TiO ₂ hcp crystal structure. The composition of the continuous 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.

  FIG. 2 is a diagram showing the values of the magnetic recording layer thickness and its thickness ratio A / (A + B), the total thickness A + B, the coercive force Hc, the OW characteristics, and the SNR in the examples and comparative examples. The film thickness A of the first magnetic recording layer and the film thickness B of the second magnetic recording layer, the total film thickness A + B of the magnetic recording layer, the ratio A / (A + B), and the numerical values of various parameters in each example and comparative example Is as shown in FIG. Here, the larger the absolute value of the OW characteristic, the better the performance.

  In FIG. 2, in series 1, the thickness of the first magnetic recording layer 122a is fixed at 2.9 nm, and the thickness of the second magnetic recording layer 122b is changed. In series 2, the film thickness of the second magnetic recording layer 122b is fixed to 9.7 nm when the OW characteristic is good in series 1, and the film thickness of the first magnetic recording layer 122a is changed. At this time, since the coercive force Hc showed the maximum value in the plot number 15 and the SNR showed the maximum value in the plot number 13, the plot number 14 was considered to have both the coercive force Hc and SNR characteristics in the most balanced manner. Therefore, in Series 3, the film thickness of the first magnetic recording layer 122a is fixed to 6.9 nm, which is the same as the plot number 14, and the film thickness of the second magnetic recording layer 122b is changed.

  In FIG. 2, in both the example and the comparative example, the total content α of a plurality of types of oxides included in the first magnetic recording layer 122a is 5 mol% and included in the second magnetic recording layer 122b. The total content β of a plurality of types of oxides is 10 mol%. In addition, even when the experiment is performed by changing the composition of α and β in the range of α: β = 1: 2 to 1: 1, the numerical values of the various parameters show the same tendency as in FIG. In addition, this value is only an example and is not limited to this.

  Referring to FIG. 2, in all the series, as the total film thickness A + B increases, the absolute value of the OW characteristic decreases so as to be approximately inversely proportional thereto. From this, it can be seen that the smaller the total film thickness A + B, the more improved the OW characteristic, which is the ease of writing to the magnetic recording medium by the magnetic head.

  Further, it can be seen from FIG. 2 that there is a peak (maximum value) in the coercive force Hc in all series, and the coercive force Hc tends to decrease when the total film thickness A + B becomes too large. In series 2, since Comparative Examples 1 and 3 do not satisfy the required coercive force Hc, it can be seen that the total film thickness A + B is preferably in the range of 11 nm <A + B <27 nm.

  FIG. 3 is a diagram showing the relationship between the film thickness ratio A / (A + B), the coercive force Hc, and the OW characteristics of the magnetic recording layer in Examples and Comparative Examples.

  FIG. 3A is a diagram illustrating the relationship between the film thickness ratio A / (A + B) of the magnetic recording layer, the coercive force Hc, and the OW characteristics in series 1. FIG. As a result of keeping the film thickness A of the first magnetic recording layer 122a constant at 2.9 nm and increasing the film thickness B of the second magnetic recording layer 122b from 9.7 nm, both the first and comparative examples 1 and 2 maintained. The magnetic force Hc exceeds the required value of 4000 Oe. In the OW characteristics, when A / (A + B) in Example 1 is 0.23, the absolute value of the OW characteristics is -48.9 dB, which is the maximum value. However, in Comparative Example 1 in which A / (A + B) is 0.12 or less, the absolute value of the OW characteristic falls below the required value of −30 dB.

  Based on the above result, in series 2, the film thickness B of the second magnetic recording layer 122b is constant at a value of 9.7 nm when the absolute value of the OW characteristic is the maximum value in series 1. The film thickness A of the first magnetic recording layer 122a was changed, and the coercive force Hc and OW characteristics were measured. FIG. 3B is a graph showing the relationship between the film thickness ratio A / (A + B) of the magnetic recording layer, the coercive force Hc, and the OW characteristics in series 2. In FIG. 3B, the absolute value of the OW characteristic exceeds the required value of −30 dB in any of Example 2, Comparative Example 2, and Comparative Example 3.

  Further, from FIG. 3B, the coercive force Hc of the series 2 is less than 4000 Oe which is a value required in the comparative example 2. This shows that A / (A + B) needs to be larger than 0.12 even in the coercive force Hc. The coercive force Hc satisfies the standard of 4000 Oe, which is a value required in the range of Example 2, and has a peak when A / (A + B) is around 0.4 to 0.5. Thereafter, the value decreases as A / (A + B) increases, and in the range of Comparative Example 3, the coercive force Hc is less than 4000 Oe. From this, it can be seen that if the film thickness ratio A / (A + B) increases too much, not only the OW characteristics but also the coercive force Hc decreases, so A / (A + B) is preferably less than 0.64.

  Based on the above result, the film thickness A of the first magnetic recording layer 122a is constant at the value 6.9 nm of the film thickness A in the vicinity of the peak of the coercive force Hc in series 2, and the film thickness B of the second magnetic recording layer 122b. Was increased from 9.7 nm, and the coercive force Hc and OW characteristics were measured (series 3). FIG. 3C is a diagram showing the relationship between the film thickness ratio A / (A + B) of the magnetic recording layer, the coercive force Hc, and the OW characteristics in series 3. As shown in FIG. 3 (c), Example 3 satisfies the required standards for both the coercive force Hc and the OW characteristics.

  FIG. 4 is a diagram showing the relationship between the film thickness ratio A / (A + B) of the magnetic recording layer and the SNR in the examples and comparative examples. As shown in FIG. 4, when the film thickness ratio A / (A + B) increases too much, the SNR decreases.

  From the above results, assuming that the film thickness of the first magnetic recording layer is Anm and the film thickness of the second magnetic recording layer is Bnm, the film thickness ratio A / (A + B) is 0.12 <A / (A + B) <0. By setting it within the range of .64, it is possible to avoid cancellation of the magnetostatic characteristics (particularly the coercive force Hc) and the electromagnetic conversion characteristics (particularly the OW characteristic and SNR). Accordingly, it is possible to obtain a perpendicular magnetic recording medium that can improve the electromagnetic conversion characteristics (particularly the OW characteristics and SNR) while improving the magnetostatic characteristics (particularly the coercive force Hc) and can further increase the recording density.

  Further, when the film thickness of the first magnetic recording layer is Anm and the film thickness of the second magnetic recording layer is Bnm, the total film thickness A + B is preferably in the range of 11 nm <A + B <27 nm. This is because if the total film thickness A + B is too thick, the OW characteristics deteriorate, and if it is too thin, a sufficient coercive force Hc cannot be obtained.

  As mentioned above, although the suitable Example of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this embodiment. 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 this embodiment. It is a figure which shows the numerical value of the film thickness of the magnetic recording layer and the total film thickness A + B, its film thickness ratio A / (A + B), coercive force Hc, OW characteristic, and SNR in an Example and a comparative example. It is a figure which shows the relationship of the film thickness ratio A / (A + B) of a magnetic recording layer, coercive force Hc, and OW characteristic in an Example and a comparative example. It is a figure which shows the film thickness ratio A / (A + B) of a magnetic recording layer, and the relationship of SNR in an Example and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Perpendicular magnetic recording medium, 110 ... Disk base | substrate, 112 ... Adhesion layer, 114 ... Soft magnetic layer, 114a ... 1st soft magnetic layer, 114b ... Spacer layer, 114c ... 2nd soft magnetic layer, 116 ... Pre-underlayer, 118 ... Underlayer, 118a ... First underlayer, 118b ... Second underlayer, 120 ... Non-magnetic granular layer, 122 ... Magnetic recording layer, 122a ... First magnetic recording layer, 122b ... Second magnetic recording layer, 124 ... Continuous layer, 126 ... medium protective layer, 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 grain boundary portions of the first magnetic recording layer and the second magnetic recording layer each contain a plurality of types of oxides,
The film thickness of the first magnetic recording layer is Anm,
When the film thickness of the second magnetic recording layer is Bnm,
A perpendicular magnetic recording medium, wherein A / (A + B) is within a range of 0.12 <A / (A + B) <0.64. The film thickness of the first magnetic recording layer is Anm,
When the film thickness of the second magnetic recording layer is Bnm,
2. The perpendicular magnetic recording medium according to claim 1, wherein A + B is within a range of 11 <A + B <27. The total content of a plurality of types of oxides contained in the first magnetic recording layer is α mol%,
When the total content of the plurality of types of oxides included in the second magnetic recording layer is β mol%,
The perpendicular magnetic recording medium according to claim 1, wherein the content relationship is α ≦ β. 4. The oxide according to claim 1, wherein the plurality of types of oxides are oxides selected from SiO ₂ , TiO ₂ , CrO ₂ , Cr ₂ O ₃ , ZrO ₂ , and Ta ₂ O _5. 2. The perpendicular magnetic recording medium according to claim 1.

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