JP2005092924A - Perpendicular magnetic recording medium and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a perpendicular magnetic recording medium with high productivity, wherein spike noise and soft magnetic layer noise are reduced by forming a soft magnetic layer provided between a substrate and a perpendicular magnetic recording layer of the recording medium by using an alloy plating method by which a thick film can be formed in a short period of time. <P>SOLUTION: A soft magnetic backing layer 2 consisting of an alloy plating layer is formed on the substrate 1 formed by providing a Ni-P alloy plating layer 1b on an aluminum plate or an aluminum alloy plate, a soft magnetic buffer layer 3 is formed on the soft magnetic backing layer, an anti-ferromagnetic layer 4 is formed on the soft magnetic buffer layer, a base layer 5 is formed on the anti-ferromagnetic layer and the perpendicular magnetic recording layer 6 is formed on the base layer to form the perpendicular magnetic recording medium. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a perpendicular magnetic recording medium that can suppress noise caused by a soft magnetic underlayer, particularly spike noise, and can be suitably applied as a recording medium such as a hard disk or a magnetic tape, and a perpendicular magnetic recording apparatus using the perpendicular magnetic recording medium.

  In a magnetic recording medium mounted on a conventional magnetic recording device such as a hard disk drive (HDD), longitudinal recording is performed in which data is recorded by fixing the magnetization direction in the in-plane direction of the magnetic recording layer and inverting this magnetization. The system (longitudinal recording) is used. In this method, in order to increase the recording density per unit area, development of a magnetic recording medium capable of mainly reducing the length in the magnetization reversal direction, that is, increasing the so-called linear recording density has been advanced.

  By the way, in this longitudinal recording type magnetic recording medium, it is known that shortening of the magnetization reversal length is effective in increasing the linear recording density, and this corresponds to the increase in the linear recording density. In addition, it is required to increase the coercive force of the ferromagnetic layer, which is a magnetic recording layer, and to reduce the residual magnetic flux density and film thickness of the ferromagnetic layer.

  However, if the film thickness of the ferromagnetic layer is reduced in order to increase the linear recording density, the magnetic crystal grains constituting the ferromagnetic layer are reduced in size, so that the volume (V) tends to decrease. When Ku · V, which is the product of the anisotropy constant (Ku) of the magnetic crystal grains and the volume (V) of the magnetic crystal grains, is below a certain value, the magnetization direction of the magnetic crystal grains is unstable due to the influence of heat. There is a risk that a thermal magnetic relaxation phenomenon, so-called thermal disturbance, will occur. This thermal magnetic relaxation phenomenon becomes more apparent as the volume (V) of the magnetic crystal grains becomes smaller. Therefore, a magnetic material having a large anisotropy constant (Ku) is required to maintain the thermal stability of magnetic recording. Become.

  This longitudinal recording type magnetic recording medium has been dealt with by increasing the coercive force of the ferromagnetic layer in order to increase the surface recording density. However, since the coercive force is too high, data can be written depending on the ring head. Evil due to the improvement of the coercive force, such as the possibility of disappearing, has been seen. On the other hand, in a perpendicular recording system (perpendicular recording) in which data is recorded by reversing the magnetization in a direction perpendicular to the surface of the medium using a bar magnet-shaped recording head called a single magnetic pole head, the coercive force is Since recording can be performed on a high medium, a surface recording density equal to or higher than that of the longitudinal recording method can be obtained, and various developments and researches have been conducted.

  In this perpendicular recording method, even if the crystal grains of the ferromagnetic layer are reduced, the volume (V) of the crystal grains can be maintained in the thickness direction by maintaining an appropriate thickness. Since the magnetization direction has a feature that it is easy to maintain thermal stability, it has been attracting attention as a technique that can avoid the problem of thermal disturbance, which is a concern in the conventional longitudinal recording method.

  As a perpendicular magnetic recording medium applied to such a perpendicular recording system, a two-layer film medium is proposed in which a soft magnetic film that is easily magnetized in the in-plane direction is provided between a substrate and a perpendicular recording layer. (For example, refer nonpatent literature 1). For this soft magnetic film, a crystalline material such as a permalloy type represented by a Ni-Fe alloy or a sendust type material such as a FeSiAl alloy or an amorphous material such as CoZrNb is preferably used, and a ferromagnetic material which is a perpendicular recording layer It has a film thickness 10 times or more that of the layer.

  This two-layer film medium is characterized in that writing can be performed on a perpendicular recording layer having a larger coercive force and the reproduction voltage can be increased as compared with a single-layer medium comprising only a perpendicular recording layer. Further, the soft magnetic film has a feature that the magnetic flux generated from the main pole of the magnetic head can be converged with high density in the space of the tip of the main pole, and the magnetic field near the main pole can be increased ( For example, refer nonpatent literature 2).

  However, in this two-layer film medium, for example, an amorphous material such as a permalloy-based crystalline material or CoZrNb, the structure factor (S) that is an index of local magnetization dispersion (skew) is remarkably small. Since a large number of 180-degree domain wall structures are formed in the soft magnetic film, there is a problem in that spike noise frequently occurs due to leakage magnetic flux from the domain walls.

  Permalloy-based crystalline materials are usually deposited using a sputtering system, but in this manufacturing process, irregularities are formed on the thin film surface due to the island-like initial growth mode of crystal grains. Therefore, there has been a disadvantage that periodic noise is generated due to the leakage magnetic flux from the magnetic pole caused by the uneven portion. That is, when a columnar grown crystalline material produced by sputtering is used as the backing layer, there is a problem that noise increases in a low frequency region of 80 MHz or less in the noise power spectrum. The presence of irregularities on the surface of the backing layer causes an irregular structure on the outermost layer of the medium, which is also a problem from the viewpoint of stable running of the flying head.

  As described above, in the above-described two-layer film medium, noise caused by the soft magnetic film having a film thickness 10 times or more that of the ferromagnetic layer as the perpendicular recording layer has been a serious problem.

  In order to suppress the occurrence of spike noise, the following techniques have been proposed. In Patent Document 1, an antiferromagnetic thin film made of a Mn alloy containing Co or a Mn alloy containing Ir is formed between a base and a soft magnetic layer made of an amorphous Co alloy, and soft coupling is performed using exchange coupling. A method is disclosed in which the generation of spike noise is suppressed by fixing the magnetization of the magnetic layer to prevent the domain wall formation in the soft magnetic layer. In this publication, an antiferromagnetic layer, a soft magnetic layer, a magnetic recording layer, and the like are formed on a substrate using a sputtering method. The thickness of the soft magnetic layer is the thickness of the antiferromagnetic layer, the magnetic recording layer, or the like. There is a problem that it is necessary to form the film to a thickness approximately 10 times the thickness of the film, and a long-time sputtering process is required, resulting in poor productivity.

  In Patent Document 2, an antiferromagnetic layer is provided between the perpendicular magnetization film and the backing soft magnetic layer at a distance of 100 nm or less from the perpendicular magnetization film, and a nonmagnetic intermediate is provided between the perpendicular magnetization film and the antiferromagnetic layer. Spike-like noise generated from the backing soft magnetic layer is reduced by disposing a layer and providing a layer composed of a nonmagnetic intermediate layer and a ferromagnetic layer (soft magnetic film) between the perpendicular magnetization film and the antiferromagnetic layer. A method is disclosed. Also in this publication, each of these layers is formed using a sputtering method. However, the thickness of the soft magnetic layer must be 10 times or more the thickness of each layer, and a long-time sputtering process is required. There was a problem that it was forced and poor productivity.

  Furthermore, the soft magnetic backing layer formed using the above sputtering method has a high noise power in a frequency region of 80 MHz or less compared to the soft magnetic backing layer formed using the electroless plating method in addition to spike noise. have.

  Prior art information relating to the present application includes the following.

S. Iwasaki, Y. Nakamura and K. Ouchi: IEEE Trans. Magn. MAG-15 (1979) 1456 Shunichi Iwasaki, Shinji Tanabe: IEICE Transactions J66-C 740 (1983) JP 2001-291224 A JP 2002-298326 A

  The present invention has been made to solve the above problems, and is an electroless plating capable of forming a thick film in a short time on a soft magnetic layer provided between a substrate of a recording medium and a perpendicular magnetic recording layer. Another object of the present invention is to provide a perpendicular magnetic recording medium that suppresses the occurrence of spike noise by forming it with high productivity using a method and exchange coupling with an antiferromagnetic layer stacked on a soft magnetic layer.

  The present invention also provides a perpendicular magnetic recording medium in which the noise power found in the noise power spectrum is reduced by improving the surface flatness of the soft magnetic layer formed using the electroless plating method by polishing. This is another purpose.

  The perpendicular magnetic recording medium of the present invention comprises a soft magnetic backing layer made of an alloy plating layer formed by an electroless plating method, a soft magnetic buffer layer formed on the soft magnetic backing layer, and the soft magnetic backing layer. An antiferromagnetic layer formed on the magnetic buffer layer, an underlayer formed on the antiferromagnetic layer using a sputtering method, and formed on the underlayer using a sputtering method A perpendicular magnetic recording medium comprising: a perpendicular magnetic recording layer comprising:

  A soft magnetic backing layer comprising an alloy plating layer formed by electroless plating in order from the substrate side on a substrate on which an Ni-P alloy plating layer is formed on an aluminum plate or an aluminum alloy plate, on the soft magnetic backing layer A soft magnetic buffer layer formed, an antiferromagnetic layer formed on the soft magnetic buffer layer, an underlayer formed by sputtering on the antiferromagnetic layer, and the underlayer A perpendicular magnetic recording medium formed by sequentially forming a perpendicular magnetic recording layer formed thereon using a sputtering method;

  In the perpendicular magnetic recording medium of the above (Claim 1 or 2), the soft magnetic backing layer is unidirectional with respect to the easy magnetization axis by an exchange coupling action with the antiferromagnetic layer deposited on the soft magnetic backing layer. It is characterized by imparting magnetic anisotropy (Claim 3), and

  In the perpendicular magnetic recording medium of the above (claims 1 to 3), the soft magnetic underlayer is a layer made of a crystalline alloy (claim 4),

  In the perpendicular magnetic recording medium of the above (Claim 1 to 4), the soft magnetic underlayer is a layer made of Ni—Fe—P alloy plating (Claim 5).

  In the perpendicular magnetic recording medium of the above (Claim 1 to 5), the soft magnetic backing layer has a surface roughness Ra (JIS B 0601) of 0.5 nm or less (Claim 6).

  In the perpendicular magnetic recording medium of the above (claims 1 to 6), the soft magnetic backing layer has a saturation magnetic flux density of 0.8 T or more and a coercive force of 5 Oe or less (claim 7).

  The perpendicular magnetic recording apparatus of the present invention is a perpendicular magnetic recording apparatus (invention 8) using any of the perpendicular magnetic recording media described above (inventions 1 to 7).

  In the perpendicular magnetic recording medium of the present invention, the soft magnetic backing layer provided between the recording medium substrate and the perpendicular magnetic recording layer is formed using an electroless plating method capable of forming a thick film in a short time. A perpendicular magnetic recording medium can be obtained with high productivity. In particular, when using a substrate on which an Ni-P alloy plating layer for ensuring surface hardness is formed by an electroless alloy plating method, which is a wet film formation method, on an aluminum plate or an aluminum alloy plate, the film formation method is subsequently changed. Without forming, the soft magnetic layer is formed by the electroless alloy plating method which is a wet film forming method, so that the film can be formed with extremely high efficiency and high productivity. In addition, since the soft magnetic underlayer formed by electroless plating can improve surface flatness by polishing, it has low noise power especially in the low frequency region, and furthermore, the sputtering method is applied to the soft magnetic underlayer by electroless plating. It is possible to suppress the occurrence of spike noise by laminating an antiferromagnetic layer formed with a film.

  Hereinafter, an embodiment of a perpendicular magnetic recording medium of the present invention and a magnetic recording apparatus including the same will be described with reference to the drawings. These embodiments are specifically described for better understanding of the gist of the invention, and do not limit the present invention unless otherwise specified.

  FIG. 1 is a schematic sectional view showing an example of an embodiment of the perpendicular magnetic recording medium of the present invention. The perpendicular recording medium 10 includes a soft magnetic backing layer 2, a soft magnetic buffer layer 3, an antiferromagnetic layer 4, an underlayer 5, a perpendicular magnetic recording layer 6, a protective film 7, and a lubricant on a substrate 1 in order from the bottom in the drawing. The film 8 is formed. FIG. 2 is a schematic sectional view showing another example of the embodiment of the perpendicular magnetic recording medium of the present invention, and shows an example of a substrate used for the perpendicular magnetic recording medium of the present invention. In FIG. 2, a substrate in which a Ni—P alloy plating layer 1b is formed on a substrate 1a made of an aluminum substrate is used.

  Examples of the substrate 1 include a disk made of a nonmagnetic metal or resin for a magnetic disk or another nonmagnetic film formed thereon. As a disk made of nonmagnetic metal or resin, a disk made of aluminum, titanium, an alloy mainly containing them, glass, silicon, carbon, ceramics, resin, or a composite made of two or more of these is used. be able to. Films formed on these disks do not become magnetized even when heated to high temperatures, have electrical conductivity, have excellent thermal conductivity, can be easily machined such as polishing, and must be handled easily. A non-magnetic film having an appropriate hardness that is difficult to stick to is used, and there is a film made of an alloy such as Ni-P, Ni-Ta, Ni-Ti, Ni-Al, a sputtering method, a vapor deposition method, and a plating method. The film can be formed using, for example.

  The present invention is characterized in that the soft magnetic backing layer 2 is formed by an electroless plating method which is a wet film forming method. Therefore, similarly, a Ni-P alloy plating layer is formed on an aluminum substrate 1a (including an aluminum alloy plate, the same shall apply hereinafter) as shown in FIG. 2, which is widely manufactured as a magnetic disk substrate using a wet film formation method. Use of the substrate 1 on which 1b is formed is preferable from the viewpoint of productivity because a plating apparatus having a common structure, a plating waste liquid treatment facility, and the like can be used.

  In general, in the case of a perpendicular magnetic recording medium, it is preferable that the gap between the magnetic head and the perpendicular magnetic recording medium is small so that the magnetic head can satisfactorily read a signal written on the perpendicular magnetic recording medium. In particular, when the magnetic head performs recording / reproduction while flying above the perpendicular magnetic recording medium, the flying height is preferably as small as possible. Further, it is more preferable that recording / reproduction can be performed by bringing the magnetic head into contact with the surface of the perpendicular magnetic recording medium without flying. Therefore, it is desirable that the substrate (including the substrate) for the perpendicular magnetic recording medium has an excellent surface smoothness. Furthermore, the parallelism of both the front and back surfaces of the substrate and the circumferential waviness of the substrate are appropriate. A controlled one is preferred.

  Since the soft magnetic backing layer 2 provided on the substrate 1 functions as a part of the head system magnetic circuit, it is used by being deposited as thick as 50 to 500 nm. Therefore, from the viewpoint of productivity, it is more advantageous to use a wet film forming method such as electroless plating than to use a film forming method such as sputtering or vapor deposition. In particular, when an aluminum plate on which a Ni-P alloy plating layer is formed is used as the substrate 1, it is more advantageous because a plating apparatus having a common structure, a common plating waste liquid treatment facility, and the like can be used as described above.

  As the soft magnetic backing layer 2, Ni—Fe, Ni—Fe—Co, Co—Zr—Nb, Fe—Al—Si, Co—Ta—Zr, Fe—Ta—C, Fe— Although an alloy such as N can be used, in the present invention, since a film is formed using an electroless plating method which is a wet film forming method, Ni-Fe-P plating using a P compound or a B compound as a reducing agent is used. A Ni—Fe—B plating layer, a Ni—Fe alloy plating layer such as Co—Fe—B, and a Co—Fe alloy plating layer are applied as the soft magnetic backing layer 2. When using the aluminum plate which formed the Ni-P alloy plating layer in the board | substrate 1, it is more preferable from a viewpoint of productivity to form the Ni-Fe-P plating layer which uses a common reducing agent as electroless plating.

  When the Ni—Fe based alloy plating layer is applied as the soft magnetic backing layer 2, the saturation magnetic flux density is 0.8 T or more by setting the Fe content in the Ni—Fe based alloy plating layer to 14 to 20 wt%. The coercive force can be 5 Oe or less, and the crystal structure becomes crystalline. In the Ni—Fe-based alloy plating, in order to make the Fe content in the above range, the bath temperature is changed in the alloy plating to adjust the deposition rate of the plating layer or the pH of the plating is appropriately adjusted. If the Fe content is less than the above range, the P content increases, so that the crystal structure of the plating layer becomes amorphous and the saturation magnetic flux density cannot be obtained. Further, even if the Fe content exceeds the above range, the saturation magnetic flux density does not increase.

  The thickness of these soft magnetic backing layers 2 is preferably 100 to 1000 nm after polishing. If the thickness is less than 100 nm, it is difficult to ensure sufficient polishing accuracy at the time of polishing.

  Further, the surface roughness Ra (JIS B 0601) of these soft magnetic backing layers 2 needs to be 0.5 nm or less. When the surface roughness Ra (JIS B 0601) exceeds 0.5 nm, not only the noise power observed in the noise power spectrum increases, but also head crashes easily occur. For that purpose, when using an aluminum plate on which a Ni—P alloy plating layer is formed as the substrate 1, the surface is polished so that the surface roughness Ra (JIS B 0601) is 0.2 nm or less after the Ni—P alloy plating. The surface roughness Ra (JIS B 0601) can be reduced to 0.5 nm or less by forming a crystalline alloy plating layer on the Ni-P alloy plating layer and repolishing the surface.

  The soft magnetic backing layer formed and flattened by using the electroless plating method obtained in this manner is effective in suppressing SUL noise as the background of the recording signal of the perpendicular magnetization recording layer. Table 2 shows a Ni—Fe—P layer (Sample No. 2) formed using an electroless plating method and a Ni—Fe—Mo layer (Sample Nos. 1, 3, 4, 5) formed using a sputtering method. ) Shows an example of the result of measuring the noise power (dBm / Hz) of the SUL noise in the frequency range of 0 to 100 MHz. In the soft magnetic underlayer by sputtering, the noise power is as high as −83 to −107 dBm / Hz in the low frequency range of 0 to 80 MHz, and noise cannot be stably suppressed from the low frequency range to the high frequency range. . On the other hand, in the flattened soft magnetic backing layer produced by the electroless plating method, the noise power is as low as −100 dBm / Hz even in a low frequency region slightly exceeding 0 MHz, and stably −110 dBm / in the frequency region above 10 MHz. It shows a low value of Hz. Thus, when the soft magnetic backing layer is formed using an alloy plating method, the noise power can be stably suppressed regardless of the frequency. However, this noise power can be suppressed only when the surface roughness Ra (JIS B 0601) is 0.5 nm (sample numbers 1, 3, 4). Noise power in the low frequency region is increased.

  As described above, the antiferromagnetic layer 4 laminated after the soft magnetic backing layer 2 is provided on the substrate 1 has spike noise without forming a Bloch domain wall in the soft magnetic backing layer 2 due to the exchange coupling action of both. It is a layer provided to suppress In particular, fixing the magnetization of the soft magnetic backing layer 2 in the radial direction of the substrate (disk) 1 and making it a single magnetic domain in the residual magnetization state can completely eliminate the leakage magnetic flux from the Bloch domain wall, resulting in spike noise. Since generation | occurrence | production can be suppressed, it is preferable. In order to induce a large unidirectional magnetic anisotropy by exchange coupling with the soft magnetic layer, for the purpose of controlling crystal growth and crystal orientation of the antiferromagnetic layer, it is interposed between the soft magnetic underlayer 2 and the antiferromagnetic layer 4. A soft magnetic buffer layer 3 may be provided. The soft magnetic buffer layer 3 is not particularly limited, but a soft magnetic material that can control the structure of the antiferromagnetic layer without depending on the structure of the plated soft magnetic layer, A soft magnetic material that can induce a large unidirectional anisotropy by a combination of these, or a laminated structure thereof may be used. Specifically, a single layer made of Co—Fe, or a laminate made of Ni—Fe / Co—Fe, Co—Zr—Nb / Ni—Fe / Co—Fe, or Co—Ta—Zr / N— from the substrate side. It is preferable to use a laminate made of iFe / Co—Fe. The thickness of the soft magnetic buffer layer 3 is preferably 1 to 20 nm from the viewpoint of productivity. Either the wet film formation method or the dry film formation method can be applied to the formation of the soft magnetic buffer layer 3, but dry film formation such as sputtering is preferable from the viewpoint of strict control of the film thickness.

  The antiferromagnetic layer 4 includes alloys such as Mn—Ir, Co—Mn, Ni—Mn, and Pt—Mn, and other metals as long as they do not adversely affect the properties of the antiferromagnetic layer. What added the above can be used. Since the thickness is a spacing loss from the viewpoint of the head system magnetic circuit, the thickness is preferably thin enough not to impair the function of inducing unidirectional magnetic anisotropy. Specifically, it is preferable to provide a layer having a thickness of 1 to 10 nm. Both the wet film formation method and the dry film formation method can be applied to the formation of the antiferromagnetic layer 4, but a dry film formation method such as a sputtering method is more preferable from the viewpoint of strict control of the film thickness.

  Next, the underlayer 5 may be provided on the antiferromagnetic layer 4 by sputtering. The underlayer 5 may be any material as long as it is a material for crystal growth of the perpendicular recording layer 6 formed thereon. In addition to the single layer structure, the base layer may have a multilayer structure of two or more layers.

  The perpendicular magnetic recording layer 6 is not particularly limited as long as it is a ferromagnetic material in which the easy axis of magnetization is oriented with magnetic anisotropy in one direction substantially perpendicular to the film surface. Co-Cr system having a hexagonal closest packed structure (hcp) in which Co and Cr are the main components and the easy axis of magnetization is oriented with magnetic anisotropy in one direction substantially perpendicular to the film surface Ferromagnetic materials are preferably used. This Co—Cr based ferromagnetic material may be added with other elements as required.

  Specific examples of the Co—Cr based ferromagnetic material include Co—Cr (Cr <25 at%), Co—Cr—Ni, Co—Cr—Ta, Co—Cr—Pt, Co—Cr—Pt—Ta, and Co. Examples include Co—Cr alloys such as —Cr—Pt—B. Further, the grain size control and grain segregation control of the perpendicular magnetic recording layer 6, the crystal magnetic anisotropy constant (Ku) of the crystal grain, the control of the crystal grain size, the corrosion resistance control, and the low temperature process are supported. For these purposes, O, SiOx, Fe, Mo, V, Si, B, Ir, W, Hf, Nb, Ru, rare earth elements, and the like may be appropriately added to these alloys.

  In addition, ferromagnetic materials other than the above Co-Cr alloys, for example, materials excellent in thermal disturbance resistance such as Co-Pt, Co-Pd, and Fe-Pt, and B, N, A material to which O, SiOx, Zr or the like is added may be used. Furthermore, a perpendicular recording layer having a multilayer structure in which a large number of Co layers and Pt layers are laminated is also applicable. As such a perpendicular recording layer having a multilayer structure, a perpendicular recording layer having a multilayer structure in which a Co layer and a Pd layer, an Fe layer and a Pd layer, or the like are combined, or B, N, O, Zr, SiOx, etc. Those added with can also be applied. Regardless of which recording layer material is selected, the thickness of the perpendicular magnetic recording layer 6 is preferably 5 to 100 nm.

  In this way, the perpendicular magnetic recording medium of the present invention can be obtained. However, when actually used in a drive, it is necessary to provide the protective film 7 on the perpendicular magnetic recording layer 6 and the lubricating film 8 on the protective film 7. There is. The protective layer 7 is for protecting the surface of the perpendicular magnetic recording layer 6 and may have any mechanical strength, heat resistance, oxidation resistance, corrosion resistance, etc. required as a protective film, Although the material composition is not limited, for example, carbon is preferably used. The lubricating film 8 is for stably flying the magnetic head when the substrate is rotating. For example, perfluoropolyether is preferably used.

  It is preferable to introduce a process in which the antiferromagnetic layer strongly develops unidirectional anisotropy in any step after the formation of the antiferromagnetic layer. Although this process is not particularly limited, a step of cooling a substrate heated to a temperature equal to or higher than the blocking temperature of the antiferromagnetic layer in a magnetic field atmosphere in a desired direction is preferably used. Next, the underlayer 5 and the perpendicular magnetic recording layer 6 made of a Co—Cr alloy are formed on the antiferromagnetic layer 4 by sputtering. As the Co—Cr alloy, Co—Cr, Co—Cr—Ni, Co—Cr—Ta, Co—Cr—Pt, Co—Cr—Pt—Ta, and Co—Cr—Pt—B can be used. . The thickness of the perpendicular magnetic recording layer 6 is preferably 5 to 100 nm. In this way, the perpendicular magnetic recording medium of the present invention can be obtained. However, when actually used in a drive, the protective film 7 made of carbon on the perpendicular magnetic recording layer 6 and the perfluorocarbon on the carbon protective film 7 are obtained. It is necessary to provide the lubricating film 8 made of polyether.

  Hereinafter, the present invention will be described in detail with reference to examples.

(Creation of substrate)
An amorphous Ni—P alloy plating is applied to a 2.5-inch diameter disc (diameter: 65 mm) made of an aluminum alloy for a magnetic disk and having a hole in the center, and then an alumina-based polishing liquid is used. After rough polishing using the resultant, final polishing was performed using a colloidal silica polishing liquid, and the surface roughness Ra (JIS B 0601) was polished to 0.3 nm to obtain a substrate.

(Formation of soft magnetic backing layer)
Without subjecting this substrate to pretreatment such as activation treatment, Ni—Fe—P alloy plating with the coating composition shown in Table 1 was applied using a Ni—Fe—P alloy plating bath having the following bath composition, and then The surface was polished using a colloidal silica polishing liquid to form a soft magnetic backing layer comprising a Ni—Fe—P alloy plating layer having the surface roughness and thickness shown in Table 1, and designated as sample No. 1. The soft magnetic properties of the soft magnetic backing layer of the sample No. 1 obtained in this way were measured using a vibrating sample magnetometer (VSM: BHV-35 manufactured by Riken Denshi Co.). The results are shown in Table 1. For comparison, a soft magnetic backing layer made of a Ni—Fe—Mo alloy layer was formed using a sputtering method, and a sample No. 2 was obtained. Further, samples with surface roughness changed with respect to sample number 1 were designated as sample numbers 3, 4, and 5. The noise power (dBm / Hz) of the soft magnetic underlayer by the plating method or sputtering method of the samples Nos. 1 to 5 thus obtained was measured under the following measurement conditions. The results are shown in Table 2.

[Ni-Fe-P alloy plating bath]
Nickel sulfate 0.05 mol / l
Ferrous sulfate 0.10 mol / l
L (+)-tartaric acid 0.30 mol / l
Sodium hypophosphite 0.08mol / l
pH (adjusted with aqueous ammonia) 8.5-9.5
Bath temperature 70-90 ° C

[Noise measurement conditions]
Head: MR head Track width: 250 nm
Head flying height: 14nm
Gap between shields: 80nm
Disk rotation speed: 4200 rpm
Measurement radius: 22.21 mm (peripheral speed: 9.77 m / s)
Measurement frequency: 1 to 100 MHz
RBW: 30 kHz
VBW: 100kHz

(Formation of soft magnetic buffer layer)
After the Ni—Fe—P alloy plating layer is formed on the substrate and the surface is polished as described above, the Co—Zr—Nb layer, Ni—Fe layer, Co ₇₀ Fe layer are sequentially formed on the surface from the substrate by sputtering. ₃₀ layers were provided, and a soft magnetic buffer layer having a thickness of 11 nm made of Co—Zr—Nb (2 nm) / Ni—Fe (5 nm) / Co ₇₀ Fe ₃₀ (4 nm) was formed.

(Formation of antiferromagnetic layer)
An antiferromagnetic layer made of MnIr with a thickness of 6 nm was formed on the soft magnetic buffer layer by sputtering, and a magnetic field application process was performed in the radial direction. For comparison, a sample without an antiferromagnetic layer was also produced. When the hysteresis loop in the radial direction on the disc was measured for the sample on which the antiferromagnetic layer was formed, as shown in FIG. A shift magnetic field of about 35 Oe is generated in the (hysteresis curve when a magnetic field is applied in the radial direction). It was confirmed that exchange bonds were expressed between them. Furthermore, when the magnetic domain structure of the entire backing layer was observed with a magnetic domain structure observation apparatus (Optoscope: BH-618, manufactured by Neoarc), it was confirmed that the magnetic domain structure was made into a single magnetic domain over the entire disk-shaped substrate. In FIG. 3, the vertical axis represents magnetization (unit: arbitrary scale), the horizontal axis represents holding force H, and Cir. Indicates a hysteresis curve when a magnetic field is applied in the circumferential direction.

(Measurement of spike noise)
The sample No. 1 after the formation of the antiferromagnetic layer and the sample No. 2 without the antiferromagnetic layer were examined for occurrence of spike noise using a spin stand tester. The results are shown in FIG. 4 (Sample No. 1) and FIG. 5 (Sample No. 2). 4 and 5 show the output (voltage, corresponding to the vertical axis) when the magnetic head is rotated around the disk (corresponding to the horizontal axis).

  As shown in FIGS. 4 and 5, no spike noise was observed in the sample for the perpendicular magnetic recording medium of the present invention. On the other hand, two large spike noises 9 are observed in the sample for the comparative perpendicular magnetic recording medium.

(Formation of perpendicular magnetic recording layer)
Next, a perpendicular magnetic recording layer made of Co ₆₅ Cr ₂₀ Pt ₁₅ having a thickness of 22 nm was formed on the antiferromagnetic layer of the sample of sample number 1 using a sputtering method.

(Formation of protective film and lubricating film)
Next, a protective film made of carbon having a thickness of 7 nm is formed on the perpendicular magnetic recording layer by sputtering, and then a lubricating film made of perfluoropolyether having a thickness of 2 nm is formed by using an immersion method. Formed. The perpendicular magnetic recording medium of the present invention was produced as described above.

  The perpendicular magnetic recording medium of the present invention is configured as described above, and since the soft magnetic underlayer is formed by an electroless plating method that is a wet film forming method, it is simpler than a sputtering method that is a dry film forming method. A thick soft magnetic backing layer can be formed in a short time. Further, as compared with a crystalline soft magnetic underlayer grown in a columnar shape by sputtering, it can be flattened, resulting in a reduction in noise power, high productivity, and perpendicular magnetic recording in which both SUL noise and spike noise are reduced. A medium can be obtained.

Schematic sectional view showing an example of an embodiment of the perpendicular magnetic recording medium of the present invention Schematic sectional view showing an example of a substrate used in the perpendicular magnetic recording medium of the present invention Graph showing an example of noise power spectrum measurement results originating from a soft magnetic underlayer formed by plating and sputtering. Graph showing the occurrence of spike noise originating from the soft magnetic layer backing layer formed by plating and sputtering using exchange coupling with the antiferromagnetic layer of the present invention Graph showing the occurrence of spike noise originating from the soft magnetic underlayer formed using the comparative plating and sputtering methods

Explanation of symbols

1 substrate 1a substrate (aluminum plate)
1b Ni-P alloy plating layer 2 Soft magnetic backing layer 3 Soft magnetic buffer layer 4 Antiferromagnetic layer 5 Underlayer 6 Perpendicular magnetic recording layer 7 Protective film 8 Lubricating film 9 Spike noise 10 Perpendicular recording medium

Claims (8)

A soft magnetic backing layer made of an alloy plating layer formed by an electroless plating method, a soft magnetic buffer layer formed on the soft magnetic backing layer, and a film formed on the soft magnetic buffer layer An antiferromagnetic layer, an underlayer formed by sputtering on the antiferromagnetic layer, and a perpendicular magnetic recording layer formed by sputtering on the underlayer A perpendicular magnetic recording medium comprising: A soft magnetic backing layer comprising an alloy plating layer formed by electroless plating in order from the substrate side on a substrate on which an Ni-P alloy plating layer is formed on an aluminum plate or an aluminum alloy plate, on the soft magnetic backing layer A soft magnetic buffer layer formed, an antiferromagnetic layer formed on the soft magnetic buffer layer, an underlayer formed using a sputtering method on the antiferromagnetic layer, the underlayer A perpendicular magnetic recording medium comprising a perpendicular magnetic recording layer formed thereon by sputtering using a sputtering method. The unidirectional magnetic anisotropy is imparted to the easy axis of magnetization in the soft magnetic underlayer by an exchange coupling action with an antiferromagnetic layer deposited on the soft magnetic underlayer. Or the perpendicular magnetic recording medium of 2. 4. The perpendicular magnetic recording medium according to claim 1, wherein the soft magnetic underlayer is a layer made of a crystalline alloy. 5. The perpendicular magnetic recording medium according to claim 1, wherein the soft magnetic underlayer is a layer made of Ni—Fe—P alloy plating. 6. 6. The perpendicular magnetic recording medium according to claim 1, wherein the soft magnetic backing layer has a surface roughness Ra (JIS B 0601) of 0.5 nm or less. 7. The perpendicular magnetic recording medium according to claim 1, wherein the soft magnetic backing layer has a saturation magnetic flux density of 0.8 T or more and a coercive force of 5 Oe or less. A perpendicular magnetic recording apparatus using the perpendicular magnetic recording medium according to claim 1.