JP2006127736A - Vertical magnetic recording medium and vertical magnetic recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a vertical magnetic recording medium at high productivity by forming a soft magnetic layer to be provided between a substrate and vertical magnetic recording layer of the recording medium in such a manner that rapid formation of thick films is possible and spike noise and soft magnetic layer noise are reduced. <P>SOLUTION: The vertical magnetic recording medium is obtained by successively forming a crystalline Ni-P alloy plating layer 2, a soft magnetic backing layer 3 composed of a plating layer of an Ni-Fe-B alloy, a soft magnetic buffer layer 4 composed of two layers of an Ni-Fe alloy and Co-Fe, an antiferromagnetic layer 5, a base layer 6, and a vertical magnetic recording layer 7, from the lower side, on a substrate 1 provided with an amorphous Ni-P alloy plating layer 1b on an aluminum sheet or aluminum alloy sheet. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  Conventionally, as a magnetic recording medium mounted on a magnetic recording device such as a hard disk drive (HDD), data is recorded with a magnetization direction fixed in a direction parallel to the surface of the recording medium, that is, in an in-plane direction of the magnetic recording layer. The in-plane recording method is used. In this in-plane recording method, it is required to further increase the recording density per unit area, and it has been dealt with by increasing the coercive force. However, if the coercive force becomes too high, there are problems such as data writing using a ring head becoming impossible.

  On the other hand, in the perpendicular magnetic recording method in which data is recorded in a direction perpendicular to the surface of the recording medium using a single magnetic pole head, it is possible to record even a recording medium having a high coercive force. A recording density higher than that of the method can be obtained. For this reason, research and development of recording media using the perpendicular magnetic recording method has been conventionally performed. As the perpendicular magnetic recording medium, a perpendicular magnetic recording medium having a structure in which a soft magnetic layer and a perpendicular magnetic recording layer are provided on a recording medium substrate is used. In this perpendicular magnetic recording medium having a two-layer structure, a soft magnetic layer made of an amorphous material such as a permalloy-based crystalline material or CoZrNb having a thickness 10 times or more that of the perpendicular magnetic recording layer is provided by a sputtering method. However, there is a drawback that spike noise frequently occurs due to leakage of magnetic flux from the domain wall formed in the soft magnetic layer.

  In order to suppress the occurrence of spike noise, the following techniques have been proposed. For example, 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 the soft magnetic layer is made of exchange coupling. A method of suppressing the occurrence of spike noise by fixing the magnetization to prevent the domain wall formation in the soft magnetic layer is disclosed (for example, see Patent Document 1). In this method, an antiferromagnetic thin film 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 may be an antiferromagnetic thin film layer or a magnetic recording layer. For example, it is necessary to form a thick film up to nearly 10 times the thickness of the film, which necessitates a long-time sputtering process, resulting in poor productivity.

Further, 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 layer is disposed between the perpendicular magnetization film and the antiferromagnetic layer, Disclosed is a method for reducing spike noise generated from a backing soft magnetic layer by providing a layer composed of a nonmagnetic intermediate layer and a ferromagnetic layer (soft magnetic film) between a perpendicular magnetization film and an antiferromagnetic layer. (For example, refer to Patent Document 2). Even in this method, each of these layers is formed by 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. Forced and poor productivity.
Japanese Patent Laid-Open No. 2001-291224 Japanese Patent Laid-Open No. 2002-298326

  In the present invention, the soft magnetic layer provided between the substrate of the recording medium and the perpendicular magnetic recording layer can be formed thick in a short time, and spike noise and soft magnetic layer noise are reduced, resulting in high productivity. An object of the present invention is to provide a perpendicular magnetic recording medium that can be used, and a perpendicular magnetic recording apparatus using the same.

  The perpendicular magnetic recording medium of the present invention that achieves the object of the present invention is a perpendicular magnetic recording medium having a perpendicular magnetic recording layer via a soft magnetic underlayer, and is formed by forming a Ni-- film formed by electroless plating with a substrate. The soft magnetic underlayer made of Fe-B alloy plating, an antiferromagnetic layer formed on the soft magnetic underlayer, and a lower layer formed on the antiferromagnetic layer by sputtering. It is characterized by comprising a base layer and a perpendicular magnetic recording layer formed on the base layer by sputtering. With the above configuration, the soft magnetic backing layer can be formed into a thick film in a short time using the electroless plating method. Therefore, the productivity is higher than when a thick soft magnetic backing layer is provided only by the conventional sputtering method. Thus, a perpendicular magnetic recording medium can be manufactured, and the occurrence of spike noise can be suppressed by providing antiferromagnetism thereon. In the perpendicular magnetic recording medium having the above structure, the underlayer formed between the antiferromagnetic layer and the perpendicular magnetic recording layer may be either a single layer or a multilayer structure. The underlayer promotes the formation of a perpendicular magnetic film on the perpendicular recording layer formed thereon, and is desirably formed with an accurate layer thickness using a sputtering method.

  In the perpendicular magnetic recording medium having the above configuration, the saturation magnetic flux density is maintained at 1.2 T or more by setting the Fe content in the soft magnetic underlayer made of Ni—Fe—B alloy plating in the range of 30 to 50% by weight. The force can be 5 Oe or less, and the crystal structure can be made crystalline. If the Fe content is less than 30% by weight, the saturation magnetic flux density is less than 1.2T, and if it exceeds 50% by weight, there is no problem with the saturation magnetic flux density. A range of% by weight is preferred. The soft magnetic backing layer preferably has a thickness after polishing of 100 to 1000 nm and a surface roughness Ra (JIS B 0601) of 0.5 nm or less. If it is less than 100 nm, it will be difficult to ensure sufficient polishing accuracy, and if it exceeds 1000 nm, the advantage of improving the recording density will not be improved and it will not be economically advantageous.

  Furthermore, in the perpendicular magnetic recording medium having the above configuration, a substrate in which an amorphous Ni—P alloy plating layer is formed on an aluminum substrate can be adopted as the substrate. As long as the substrate is a non-magnetic material, the material such as metal, resin, glass, ceramics is not limited, but by adopting a substrate in which an amorphous Ni-P alloy plating layer is formed on an aluminum substrate, electroless plating is possible. There is an advantage that a plating apparatus and plating waste liquid treatment equipment having a common structure with the soft magnetic backing layer formed by the method can be used.

  Furthermore, in the perpendicular magnetic recording medium having the above configuration, it is desirable to provide a crystalline Ni—P alloy plating layer between the substrate and the soft magnetic underlayer. In that case, the content of P in the crystalline Ni—P alloy plating layer is desirably 5% or less. By providing a crystalline Ni—P alloy plating layer between the substrate and the soft magnetic buffer layer, the deposition rate of the soft magnetic backing layer can be improved and the productivity can be increased. If the content of P in the crystalline Ni—P alloy plating layer exceeds 5%, the Ni—P alloy becomes amorphous and the precipitation rate of the Ni—Fe—B alloy decreases.

Furthermore, in the perpendicular magnetic recording medium having the above configuration, a soft magnetic buffer layer can be provided between the soft magnetic underlayer and the antiferromagnetic layer. By providing a soft magnetic buffer layer, crystal growth and crystal orientation control of the antiferromagnetic layer can be performed, which can contribute to inducing unidirectional magnetic anisotropy. The soft magnetic buffer layer is not particularly limited, but a single layer of a soft magnetic material capable of exhibiting the above performance or a laminated structure can be adopted. The laminated structure includes a lower Ni—Fe alloy layer and an upper layer. A two-layer structure with a Co—Fe alloy layer can be suitably employed.
Using the perpendicular magnetic recording medium configured as described above, a perpendicular magnetic recording apparatus with excellent productivity and reduced spike noise and soft magnetic layer noise can be configured.

  In the perpendicular magnetic recording medium of the present invention, a soft magnetic backing layer provided between the substrate of the recording medium and the perpendicular magnetic recording layer is formed by forming a thick film in a short time using an electroless plating method. A perpendicular magnetic recording medium can be obtained with high productivity as compared with the case where a thick soft magnetic backing layer is provided only by the method. In particular, when using a substrate on which an Ni-P alloy plating layer for ensuring surface hardness is formed by electroless alloy plating, 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 backing layer by electroless alloy plating, which is a wet film forming method, it is possible to form a film with extremely high efficiency and high productivity. In addition, by providing a soft magnetic buffer layer using a sputtering method on a soft magnetic backing layer formed using an electroless plating method, and further providing an antiferromagnetic layer thereon, the occurrence of spike noise is suppressed. be able to.

  Hereinafter, an embodiment of a perpendicular magnetic recording medium of the present invention and a magnetic recording apparatus including the perpendicular magnetic recording medium 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 crystalline Ni—P alloy plating layer 2, a soft magnetic backing layer 3, a Ni—Fe alloy layer 4 c, and a Co—Fe alloy that are selectively provided on the substrate 1 in order from the bottom on the drawing. A soft magnetic buffer layer 4, an antiferromagnetic layer 5, an underlayer 6, a perpendicular magnetic recording layer 7, a protective film 8, and a lubricating film 9 are formed. FIG. 2 is a schematic cross-sectional view showing another example of the embodiment of the perpendicular magnetic recording medium of the present invention, in which a substrate 1a made of an aluminum substrate and an amorphous Ni—P alloy plating layer 1b formed thereon is used. FIG.

  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 a 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. Can be used. 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 amorphous Ni—P alloy plating layer 1b formed on the substrate 1a is also a nonmagnetic film.

  The present invention is characterized in that the soft magnetic backing layer 3 is formed by an electroless plating method which is a wet film forming method. Therefore, an amorphous Ni-P alloy is similarly formed on an aluminum substrate 1a (including an aluminum alloy plate, hereinafter the same) as shown in FIG. 2, which is also widely manufactured as a magnetic disk substrate using the wet film formation method. Use of the substrate 1 on which the plating layer 1b is formed is preferable from the viewpoint of productivity because a plating apparatus or plating waste liquid treatment equipment having a common structure can be used.

  When an aluminum plate or an aluminum alloy plate 1a on which an amorphous Ni—P alloy plating layer 1b is formed as the substrate 1, an electroless plating method is used to thin the amorphous Ni—P alloy plating layer 1b. It is preferable to provide a crystalline Ni—P alloy plating layer 2. When the crystalline Ni—P alloy plating layer 2 is not provided, when the soft magnetic backing layer 3 made of Ni—Fe—B alloy plating is formed thereon using an electroless plating method, the soft magnetic backing layer 3 is formed. The deposition rate is extremely lowered, which is not preferable from the viewpoint of productivity. In addition, when this crystalline Ni—P alloy plating is applied, the P content in the plating film is preferably set to 5% or less, and when the P content exceeds 5%, the Ni—P alloy becomes amorphous. The precipitation rate of the Ni—Fe—B alloy is extremely reduced. In order to make the content of P in the plating film 5% or less, the temperature of the plating bath is changed in Ni-P alloy plating, and the precipitation rate of the alloy is adjusted or the pH of the plating bath is changed appropriately. Can be adjusted. The thickness of the crystalline Ni—P alloy plating layer 2 is preferably 100 nm or less. If it exceeds 100 nm, the adhesion of the Ni—Fe—B alloy plating film formed on the Ni film decreases and it becomes easy to peel off. The amorphous Ni—P alloy plating layer referred to here refers to a layer in which a halo pattern is observed in an electron diffraction image by a transmission electron microscope, and the other is referred to as a crystalline Ni—P alloy plating layer.

  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 in order for the magnetic head to 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. Accordingly, the substrate for the perpendicular magnetic recording medium is preferably one having excellent surface smoothness, and further, one in which the parallelism of the front and back surfaces of the substrate and the circumferential waviness of the substrate are appropriately controlled. preferable.

  Since the soft magnetic backing layer 3 provided on the substrate 1 functions as a part of the head magnetic circuit, the soft magnetic backing layer 3 is deposited as thick as 100 to 1000 nm, and then the surface is polished for use. 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 3, Ni—Fe, Ni—Fe—Co, Co—Zr—Nb, Fe—Al—Si, Co—Ta—Zr, Fe—Ta—C, Fe— An alloy such as N can be used, but in the present invention, a Ni—Fe—B alloy plating layer using B as a reducing agent by an electroless plating method which is a wet film forming method is used as the soft magnetic backing layer 3. Apply. When an aluminum plate having an amorphous Ni-P alloy plating layer formed on the substrate 1 is used, a thin crystalline Ni-P alloy plating layer 2 is formed on the amorphous Ni-P alloy plating layer by using an electroless plating method. And a Ni—Fe—B alloy plating layer is formed thereon using an electroless plating method.

  When the Ni—Fe—B alloy plating layer is applied as the soft magnetic backing layer 3, the saturation magnetic flux density is set to 1.2 T by setting the Fe content in the Ni—Fe—B alloy plating layer to 30 to 50% by weight. As described above, the coercive force can be 5 Oe or less, and the crystal structure becomes crystalline. In Ni-Fe-B alloy plating, in order to keep the Fe content within the above range, the plating bath temperature is changed by changing the plating bath temperature in the alloy plating, or the plating pH is changed. Adjust as appropriate. On the other hand, in the soft magnetic backing layer made of the Ni—Fe—B alloy plating layer, when the Ni content is 68% or less, the saturation magnetic flux density is 1.2 T or more, which is favorable. Therefore, the amount of B in the Ni—Fe—B alloy plating layer is not particularly limited as long as both the amount of Ni and the amount of Fe satisfy the above conditions, but the amount of B is preferably much smaller than the amounts of Ni and Fe. For example, it may be 2% by weight or less.

FIG. 5 is a graph showing the results of an experiment conducted to examine the relationship between the amount of Ni and the saturation magnetic flux density in the soft magnetic backing layer composed of the Ni—Fe—B alloy plating layer, and the vertical axis represents the saturation magnetic flux density (T). The amount of Ni (weight percent) is shown on the horizontal axis. The experiment was conducted on the 10 samples having the blending components shown in Table 1 in the soft magnetic underlayer in ascending order of Ni content. As is apparent from the graph, the saturation magnetic flux density (T) decreases as the Ni content increases, and when the Ni content is 68% or less, the saturation magnetic flux density is 1.2 T or more.

Each sample used in the above experiment is formed by forming a crystalline Ni-alloy plating layer on a substrate having an amorphous Ni-P alloy plating layer on an aluminum substrate, and forming a Ni-Fe-B alloy plating layer thereon. A soft magnetic backing layer is formed, and the conditions of each layer are as follows.
(1) Substrate thickness:
Aluminum substrate 1.27mm
Amorphous Ni-P alloy plating layer (P content 12% by weight) 11 μm
(2) Crystalline Ni-P plating layer:
P content 3% by weight, thickness 0.05μm
(3) Thickness of soft magnetic backing layer: 0.5 μm
The measurement conditions for the saturation magnetic flux density are as follows.
Sample size: 10 mm square Maximum applied magnetic field: 5 KOe
Sweep speed: 20 minutes / loop

  The thickness of the soft magnetic backing layer 3 is preferably 100 to 1000 nm, more preferably 300 to 500 nm, as a thickness after polishing. If it is less than 100 nm, it will be difficult to ensure sufficient polishing accuracy during polishing, and if it exceeds 1000 nm, the advantage of improving the recording density will not be improved and it will not be economically advantageous.

  Further, the surface roughness Ra (JIS B 0601) of these soft magnetic backing layers 3 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 this purpose, when an aluminum plate having an amorphous Ni—P alloy plating layer is used as the substrate 1, the surface roughness Ra (JIS B 0601) is 0.2 nm or less after the amorphous Ni—P alloy plating. A crystalline Ni—P alloy plating layer having a thickness of 100 nm or less is formed on the amorphous Ni—P alloy plating layer whose surface is polished so that the Ni—Fe—B alloy plating layer is formed thereon. After forming with the thickness, the surface roughness Ra (JIS B 0601) can be reduced to 0.5 nm or less by repolishing the surface. Further, the surface polishing after the formation of the amorphous Ni-P alloy plating layer on the aluminum plate is omitted, and the crystalline Ni-P alloy plating layer and the Ni-Fe-B alloy plating layer are formed. The surface roughness Ra (JIS B 0601) may be 0.5 nm or less by polishing.

  In general, in a perpendicular magnetic recording medium, a soft magnetic layer is provided on a substrate and then an antiferromagnetic layer is provided thereon. The antiferromagnetic layer is a layer provided to suppress spike noise without forming a Bloch domain wall in the soft magnetic layer by an exchange coupling action with the soft magnetic layer. In particular, fixing the magnetization of the soft magnetic underlayer in the radial direction of the substrate (disk) and making it a single domain in the residual magnetization state can completely eliminate the leakage magnetic flux from the Bloch domain wall, thereby suppressing the occurrence of spike noise. Therefore, it is preferable. In order to induce large unidirectional magnetic anisotropy by exchange coupling with the soft magnetic layer, the soft magnetic buffer is interposed between the soft magnetic layer and the antiferromagnetic layer for the purpose of controlling crystal growth and crystal orientation of the antiferromagnetic layer. A layer may be provided. In the present invention, the Ni—Fe—B alloy plating layer is formed as the soft magnetic backing layer 3 on the crystalline Ni—P alloy plating layer 2 formed on the substrate 1 as described above, and the soft coating is formed thereon. The magnetic buffer layer 4 is formed. The soft magnetic buffer layer 4 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 capable of inducing a large unidirectional magnetic anisotropy by a combination with the antiferromagnetic layer 5 formed above, or a laminated structure thereof may be used. Specifically, it is preferable to use a single layer made of a Co—Fe alloy or two layers made of a Ni—Fe alloy 4c and a Co—Fe alloy 4b from the substrate side as shown in FIG. The thickness of the soft magnetic buffer layer 4 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 4, but dry film formation such as sputtering is preferred from the viewpoint of strict control of the film thickness.

  The antiferromagnetic layer 5 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 5, 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 6 may be provided on the antiferromagnetic layer 5 by sputtering. The underlayer 6 may be made of any material as long as it is a material for forming the perpendicular recording layer 7 formed thereon into a perpendicular magnetization film. For example, Ti, Ru, Hf, nonmagnetic CoCr, Pt, and Pd can be used. In addition to the single layer structure, the underlayer 6 may have a multilayer structure of two layers or more.

  The perpendicular magnetic recording layer 7 formed by sputtering may be a ferromagnetic material whose easy axis is oriented with magnetic anisotropy in one direction substantially perpendicular to the film surface, and its composition is particularly limited. However, for example, a hexagonal closest packed structure in which Co and Cr are main components and the easy magnetization axis is oriented with magnetic anisotropy in one direction substantially perpendicular to the film surface. Co-Cr-based ferromagnetic material having a) is preferably used. This Co—Cr based ferromagnetic material may be added with other elements as required.

  Specific examples of the CoCr-based ferromagnetic material include Co—Cr (Cr <25 at%), Co—Cr—Ni, Co—Cr—Ta, Co—Cr—Pt, Co—Cr—Pt—Ta, and Co—Cr. Co-Cr alloys such as -Pt-B can be mentioned. Also, the grain size control and grain segregation control of the perpendicular magnetic recording layer 7, crystal grain magnetic anisotropy constant (Ku), grain size control, corrosion resistance control, correspondence to low temperature process For these purposes, O, SiOx, MgOx, TaOx, ZrOx, 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, MgOx, TaOx, ZrOx, 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 7 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 8 on the perpendicular magnetic recording layer 7 and the lubricating film 9 on the protective film 8. There is. The protective layer 8 is for protecting the surface of the perpendicular magnetic recording layer 7 and may be any layer provided with mechanical strength, heat resistance, oxidation resistance, corrosion resistance, etc. necessary as a protective film. Although the material composition is not limited, for example, carbon is preferably used. The lubricating film is for stably floating the magnetic head when the substrate is rotating. For example, perfluoropolyether is preferably used.

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 pretreatment of this substrate, a Ni—P alloy plating bath having the following bath composition was used, and a crystalline Ni— with a thickness of 86 nm having a composition of Ni (97 wt%)-P (3 wt%) was used. A P alloy layer was formed.

[Ni-P alloy plating bath]
Nickel sulfate 14g / L
L (+)-tartaric acid 45g / L
Sodium hypophosphite 5.5g / L
pH (adjusted with ammonia water) 9.5
Bath temperature 80 ° C

  Next, Ni (62.3 wt%)-Fe (36.2) is formed on the crystalline Ni—P alloy layer formed as described above using a Ni—Fe—B alloy plating bath having the following bath composition. A Ni—Fe—B alloy layer having a composition of (wt%)-B (0.5 wt%) was formed. Next, the surface was polished with a colloidal silica polishing liquid to obtain a soft magnetic backing layer having a surface roughness of 0.29 nm Ra and a thickness of 300 nm, and a sample of sample number 1 was obtained. The soft magnetic properties of the soft magnetic underlayer of the sample No. 1 obtained as described above were measured using a vibrating sample magnetometer (VSM: BHV-35 manufactured by Riken Denshi Co., Ltd.). 5 Oe, saturation magnetic flux density: 1.3.

[Ni-Fe-B alloy plating bath]
Nickel sulfate 2.6g / L
Ferrous sulfate 5.7g / L
Sodium tartrate 45g / L
Trisodium citrate 10g / L
Ammonium sulfate 25g / L
Dimethylamine borane 1.5g / L
pH (adjusted with ammonia water) 9.5
Bath temperature 70 ° C

(Formation of soft magnetic buffer layer)
The sample of Sample No. 1 in which the Ni—Fe—B alloy plating layer was formed on the substrate as described above and the surface was polished was applied to the Ni (81 wt%)-Fe (19 Thickness: having a composition of 6 wt.%: A 6 nm Fe-Ni alloy layer and a thickness having a composition of Co (70 wt.%)-Fe (30 wt.%): 4 nm of a Co-Fe alloy layer. S: A 10 nm soft magnetic buffer layer was formed.

(Formation of antiferromagnetic layer)
On the soft magnetic buffer layer, a sputtering method is used to form an antiferromagnetic layer having a composition of Mn (75 wt%)-Ir (25 wt%): MnIr having a thickness of 6 nm in the radial direction. The easy axis of magnetization was induced. For comparison, a sample in which the antiferromagnetic layer was not provided on the sample of sample number 1 (hereinafter referred to as sample number 2) was also produced.

(Determination of spike noise)
By evaluating the magnetic domain structure of the disk-shaped soft magnetic layer using the optical surface analyzer for the sample No. 1 after forming the antiferromagnetic layer and the sample No. 2 without the antiferromagnetic layer, The presence or absence of spike noise was determined. The results are shown in FIG. 3 and FIG. FIG. 3 shows the magnetic domain structure of the disk-shaped soft magnetic layer 15 of Sample No. 2. A striped pattern 16 indicating the generation of a domain wall is recognized, and therefore spike noise is generated. On the other hand, FIG. 4 shows the magnetic domain structure of the disk-shaped soft magnetic layer 20 of Sample No. 1, no striped pattern indicating the generation of the domain wall is recognized, and no spike noise is generated.

(Formation of underlayer and perpendicular magnetic recording layer)
Next, a Ti layer having a thickness of 25 nm was formed as an underlayer on the antiferromagnetic layer of the sample No. 1 sample, and then Co (65 wt%) was formed on the underlayer Ru layer. A perpendicular magnetic recording layer made of a Co—Cr—Pt alloy having a thickness of 22 nm and a composition of —Cr (20 wt%) — Pt (15 wt%) was formed.

(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. did. The perpendicular magnetic recording medium of the present invention was produced as described above. Thus, according to the present invention, since the Ni—Fe—B alloy layer is formed by the electroless plating method, a thick soft magnetic backing layer can be formed in a short time. As shown in FIG. 4, it was confirmed that a perpendicular magnetic recording medium having excellent performance and almost no spike noise was obtained.

  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. In addition, it is possible to obtain perpendicular magnetic recording media with high productivity and reduced spike noise compared to crystalline soft magnetic underlayers grown in a columnar shape by sputtering, and can be used as perpendicular magnetic recording media such as hard disks and magnetic tapes. High availability on.

It is a schematic sectional drawing which shows an example of the Example of the perpendicular magnetic recording medium of this invention. It is a schematic sectional drawing which shows an example of the board | substrate used for the perpendicular magnetic recording medium of this invention. It is a figure which shows the magnetic domain structure when not forming the antiferromagnetic layer for a comparison. It is a figure which shows the magnetic domain structure at the time of forming the antiferromagnetic layer of this invention. It is a figure which shows the relationship between Ni content rate and saturation magnetic flux density of the soft-magnetic underlayer of this invention.

Explanation of symbols

1 substrate 1a substrate (aluminum plate)
1b Amorphous Ni-P alloy plating layer 2 Crystalline Ni-P alloy plating layer 3 Soft magnetic backing layer 4 Soft magnetic buffer layer 4b Co-Fe alloy 4c Ni-Fe alloy 5 Antiferromagnetic layer 6 Underlayer 7 Perpendicular magnetism Recording layer 8 Protective film 9 Lubricating film 15 Disc-shaped soft magnetic layer 16 of sample 1 Striped pattern 20 Disc-shaped soft magnetic layer of sample 2

Claims (10)

  A perpendicular magnetic recording medium having a perpendicular magnetic recording layer through a soft magnetic backing layer, the substrate, the soft magnetic backing layer made of Ni-Fe-B alloy plating formed by an electroless plating method, and the soft magnetic backing layer An antiferromagnetic layer formed on the magnetic backing 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.   2. The perpendicular magnetic recording medium according to claim 1, wherein the content of Fe in the soft magnetic backing layer made of the Ni—Fe—B alloy plating is 30 to 50 wt%.   3. The perpendicular magnetic recording medium according to claim 1, wherein the soft magnetic underlayer has a polished thickness of 100 to 1000 nm and a surface roughness Ra (JIS B 0601) of 0.5 nm or less.   The perpendicular magnetic recording medium according to claim 1, wherein the soft magnetic underlayer has a saturation magnetic flux density of 1.2 T or more and a coercive force of 5 Oe or less.   The perpendicular magnetic recording medium according to claim 1, wherein the substrate is a substrate in which an amorphous Ni—P alloy plating layer is formed on an aluminum substrate.   The perpendicular magnetic recording medium according to claim 1, further comprising a crystalline Ni—P alloy plating layer between the substrate and the soft magnetic backing layer.   The perpendicular magnetic recording medium according to claim 6, wherein the content of P in the crystalline Ni—P alloy plating layer is 5% or less.   The perpendicular magnetic recording medium according to claim 1, wherein a soft magnetic buffer layer is provided between the soft magnetic underlayer and the antiferromagnetic layer.   9. The perpendicular magnetic recording medium according to claim 8, wherein the soft magnetic buffer layer comprises two layers, a lower Ni—Fe alloy layer and an upper Co—Fe alloy layer.   A perpendicular magnetic recording apparatus using the perpendicular magnetic recording medium according to claim 1.