JP4408210B2 - Method for manufacturing perpendicular magnetic recording medium - Google Patents

Description

  The present invention relates to a perpendicular magnetic recording medium, a method of manufacturing the same, and a perpendicular magnetic storage device, and more particularly to a perpendicular magnetic recording medium having a recording layer with a magnetization film having an easy axis oriented perpendicular to a substrate.

  The magnetic recording system in practical use is a longitudinal recording system using a magnetic film having an easy magnetization axis in a direction parallel to the substrate surface. However, in this method, the magnetization directions of adjacent magnetic domains serving as signal sources are opposite to each other, and repel each other and weaken each other.

  Furthermore, in order to enable high density, it is indispensable to make the magnetic particles that make up the magnetic domain fine. However, the reduction due to the thermal disturbance that occurs due to the volume reduction of the magnetic particles accompanying the miniaturization. The magnetic effect cannot be ignored, and the thermal stability deteriorates.

  As an example of a method for avoiding the adverse effects of high-density recording, as an example, perpendicular magnetic recording using a magnetic film having a magnetic material with a large magnetic anisotropy energy Ku and an axis of easy magnetization in the direction perpendicular to the substrate surface is used. The method is being tried. In this method, the magnetizations that are adjacent to each other in the opposite direction are advantageous in terms of magnetostatic energy, so the characteristics become more stable as the density becomes higher. Also, adjacent magnetic domains magnetized in opposite directions are advantageously stabilized with respect to magnetostatic energy.

  In general, in order to write a signal to the magnetic recording layer, the magnetic particles in the magnetic domain of the magnetic recording layer must be saturated and magnetized by the magnetic field leaking from the magnetic head. It is known that it is better to make the magnetic recording layer as thin as possible.

  On the other hand, in the perpendicular magnetic recording system, if a superposition type medium in which a soft magnetic film having a high saturation magnetic flux density is provided below the perpendicular magnetic recording layer and a single pole head are used, the soft magnetic film serving as the base film is the magnetic head. The magnetic field leaked from the magnetic field is strongly drawn back and returned to the magnetic head, and saturation recording of the magnetic recording layer is facilitated without reducing the thickness of the magnetic recording layer.

  The above-mentioned soft magnetic film preferably has a high magnetic permeability and a high saturation magnetic flux density. However, since a domain wall is generally generated in the soft magnetic film itself, spike noise is generated due to domain wall movement and domain wall fluctuation. And the recording magnetization such as demagnetization and demagnetization of recording due to the domain wall movement caused by the external stray magnetic field becomes unstable (for example, Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4). Non-patent document 1 and Non-patent document 2).

Further, Patent Document 5 describes a stripe magnetic domain by a plating method and a method for producing a perpendicular magnetization film. However, in a thin film produced by an electroless plating method, it is perpendicular to the substrate. There is no report on the production of a thin film having an easy magnetization axis, and in general, an easy magnetization axis is easily formed in a direction parallel to the substrate.
The under film referred to in the present invention does not refer to a generally described under film of a magnetic film, but generally refers to what is called a backing layer (film).

JP-A-6-187628 JP-A-5-81662 JP-A-7-105501 Japanese Patent Laid-Open No. 7-220921 Patent No. 2911050 The Journal of Electroanalytical Chemistry, 2000, No. 491, p. 197-202 25th Annual Meeting of the Japan Society of Applied Magnetics, 2001, 26aA-2

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a perpendicular magnetic recording medium which has no domain wall and has a low noise underlayer.

As a result of intensive studies to achieve the above object, the present inventor has formed a metal nucleus or a seed layer on a non-magnetic substrate and formed thereon by an electroless plating method, such as phosphorus (P) or It is a soft magnetic film containing boron (B), and the magnetic properties of this soft magnetic film are magnetically isotropic especially in the in-plane direction of the substrate, or magnetized in the direction perpendicular to the substrate. If it has an easy axis | shaft, it discovered that the said subject relevant to a domain wall was solved, and came to make this invention. That is, the present invention relates to the following.
(1) On a nonmagnetic substrate, at least a soft magnetic underlayer made of a soft magnetic material, an orientation control film for controlling the orientation of the film immediately above, and a perpendicular whose easy axis is oriented perpendicularly to the substrate A method of manufacturing a perpendicular magnetic recording medium provided with a magnetic film and a protective layer ,
When a metal core or seed layer is formed on a nonmagnetic substrate and a soft magnetic underlayer is formed thereon by electroless plating, a parallel magnetic field is applied to the nonmagnetic substrate in the radial direction from the outside. The soft magnetic underlayer is formed while rotating in parallel and rotating, and the ratio of Hs of the soft magnetic underlayer in the circumferential direction of the substrate (minimum strength of the applied magnetic field obtained when measuring the saturation magnetic flux density) to Hs in the radial direction isotropic A method of manufacturing a perpendicular magnetic recording medium, wherein the property is within 1.0 ± 0.2 .
(2) The perpendicular magnetic anisotropy magnetic field (Hk ) of the soft magnetic underlayer is in the range of 395 A / m to 3950 A / m (5 Oe to 50 Oe). A method of manufacturing a perpendicular magnetic recording medium .
(3) The method for producing a perpendicular magnetic recording medium according to (1) or (2), wherein the crystal grain size of the soft magnetic underlayer is a microcrystalline or amorphous structure of 5 nm or less .
(4) The method of manufacturing a perpendicular magnetic recording medium according to any one of claims 1 to 3, wherein the thickness of the soft magnetic underlayer is in the range of 50 nm to 5000 nm .
(5) The perpendicular magnetic field according to any one of claims 1 to 4, wherein the average surface roughness Ra of the soft magnetic underlayer on the side where the perpendicular magnetic recording layer is laminated is 0.8 nm or less. A method for manufacturing a recording medium .
(6) The method for producing a perpendicular magnetic recording medium according to any one of (1) to (5 ), wherein the soft magnetic underlayer includes phosphorus .
(7) The method of manufacturing a perpendicular magnetic recording medium according to any one of (1) to (6 ), wherein the soft magnetic underlayer includes boron .
(8) The method for manufacturing a perpendicular magnetic recording medium according to any one of (1) to (7 ), wherein the nonmagnetic substrate is a silicon substrate.

  According to the present invention, it is possible to obtain a base film in which no domain wall is observed, and by using this, a perpendicular magnetic recording medium and a perpendicular magnetic recording / reproducing apparatus having high thermal stability, excellent noise characteristics, and capable of high density recording Can be provided.

  Hereinafter, the present invention will be described in more detail. 1A and 1B are cross-sectional views showing a magnetic recording medium according to an embodiment of the present invention. The magnetic recording medium shown in FIG. 1A includes a soft magnetic underlayer 2, an orientation control film 3, an intermediate film 4, a perpendicular magnetic recording film 5, and a protective film 6 on a nonmagnetic substrate 1. The lubricating film 7 is sequentially laminated. Hereinafter, the configuration will be described sequentially from the nonmagnetic substrate 1 side.

As shown in FIG. 1B, the soft magnetic underlayer of the present invention is formed from, for example, a soft magnetic film in which a metal nucleus or a seed layer 8 is formed on a nonmagnetic substrate and formed thereon by an electroless plating method. And the underlying film is magnetically isotropic.
In the perpendicular magnetic recording medium of the present invention, it is preferable that the soft magnetic underlayer is magnetically isotropic in the in-plane direction of the substrate.
More specifically, when the base film is formed on the disk-shaped substrate, the ratio (isotropicity) of Hs in the circumferential direction and Hs in the radial direction is within 1.0 ± 0.2. Is preferred.

  FIG. 2 is a conceptual diagram showing the magnetic characteristics of the soft magnetic underlayer according to the present invention. The magnetic properties of the base film are measured with a VSM (Vibrating Sample Magnetometer), such a hysteresis loop is obtained, and Hs is obtained from the saturation magnetic flux density (Bs).

  Usually, when a soft magnetic film is formed in electroless plating, an orientation, for example, an anisotropic crystal orientation occurs, which appears as a domain wall. Therefore, spike noise has not been used so far for a base film for perpendicular magnetic recording. Etc. were not enough.

  The inventors of the present invention can eliminate the orientation of the soft magnetic film and make it isotropic by forming the soft magnetic film by an electroless plating method in a parallel magnetic field applied from the outside. It came. First, in VSM measurement, the strength of the measurement applied magnetic field when Bs is obtained is defined as Hs (see FIG. 2). This Hs serves as an index for determining the easy magnetization direction. The smaller the Hs, the easier the magnetization axis is in that direction, and the ratio (isotropy) in directions different by 90 ° indicates the magnetic orientation (isotropy) of the entire film. The closer the value is to 1.0, the more magnetically isotropic. Since the soft magnetic film formed by the conventional electroless plating method has an orientation, the same Bs value can be obtained in the radial direction and the circumferential direction when measured by the VSM, but the measurement can obtain this Bs value. There is a difference in the applied magnetic field. Therefore, the base film formed on the disk-shaped nonmagnetic substrate is cut out together with the substrate as shown in FIG. 3, and Hs is obtained in the circumferential direction and the radial direction, respectively, and the degree of isotropicity is determined according to the following equation. .

Isotropic degree = Hs (circumferential direction) / Hs (radial direction)

In general, even if the applied magnetic field changes in the vicinity of Bs, the change in B is small. Therefore, for convenience, Hs calculated from the value B of a certain coefficient value, such as 95% of the Bs value, may be used. .

  When a soft magnetic film is formed by ordinary electroless plating, the films are oriented, so that the Hs values when the respective Bs values are obtained are different. For example, if it is oriented in the circumferential direction, Hs (radial direction)> Hs (circumferential direction) because the easy axis of magnetization is oriented in the circumferential direction.

  In the present invention, the substrate that can be used may be non-magnetic, and the crystal structure may be single crystal, polycrystalline, or amorphous. For example, a glass wafer, a silicon wafer, an aluminum disk, etc. are mentioned. In particular, a silicon wafer and a glass wafer are preferable. In addition, even if a non-magnetic material such as Ni-P is previously formed on these substrates, there is no problem in the present invention.

  In the present invention, the soft magnetic material containing P, for example, of the base film is formed by an electroless plating method. The important thing is that a magnetic field parallel to the in-plane direction of the substrate is applied in advance from the outside in parallel during the electroless plating. Applying and rotating the substrate further in its parallel plane. That is, by creating a situation in which a magnetic field is always exerted from the outside in the radial direction of the substrate in advance, plating can be performed magnetically isotropically under such conditions. The degree of parallelism is preferably within ± 20 ° with respect to the substrate. FIG. 4 shows a conceptual diagram of the plating method.

  The strength of the external magnetic field for plating that can be used in the present invention is preferably about 10 G to 500 G (10000 G = 1T), more preferably 25 G to 150 G, near the center of the substrate. The magnet that can be used to obtain the magnetic field strength can be a permanent magnet such as ferrite, neodymium-iron-boron, or samarium-cobalt, or an electromagnet, and is not particularly limited. . Further, in the present invention, the magnet is fixed and the substrate is rotated. However, even if the substrate is fixed and the magnet is rotated, the same effect as in the present invention can be obtained. Alternatively, as shown in FIG. 4, there is no problem even if the substrate swings up and down in a parallel magnetic field.

  As the soft magnetic material containing, for example, P used in the present invention, Co—Ni—P, Co—Fe—P, Co—Ni—Fe—P, etc. are preferably used. Further preferred is a composition having Alternatively, B-based Co—Ni—Fe—B is also preferable.

  Further, before forming the soft magnetic film on the substrate, it is necessary to form a surface having catalytic activity for electroless plating in order to promote film formation. Examples of the method for forming a surface having catalytic activity include a conventional catalytic treatment and a method of forming a metal nucleus or a seed layer on a substrate. The method for forming such a surface differs depending on the substrate and needs to be selected as appropriate. However, there is no particular limitation as long as the electroless reaction of the soft magnetic film of the base film can be started uniformly.

  Examples of the catalyzing treatment include a conventional one-component Pd catalyzing method, a two-component Pd catalyzing method, and a Pd catalyzing method by substitution. Further, prior to the activation treatment, a known pretreatment such as phosphoric acid treatment or acid treatment, or an ashing treatment using oxygen plasma or the like may be performed. Examples of the metal nuclei include metal nuclei such as Ni nuclei and Cu nuclei on the surface. As a method for imparting Ni nuclei or Cu nuclei, Ni or Cu is directly deposited on a Si wafer. It is possible to form. The metal nucleus is preferably nonmagnetic.

  On the other hand, when forming the seed layer, it is preferable to form the seed layer with a metal having activity against the reducing agent in the electroless plating bath (plating solution) of the underlayer described later, for example, Ni, Cu or alloys thereof. Preferably, a seed layer having a thickness of 5 to 100 nm, particularly preferably 10 to 50 nm is formed. When forming the seed layer, it is preferable to add Zn to the seed layer in order to improve the adhesion between the substrate and the seed layer.

  Examples of the method for forming the seed layer include dry methods such as sputtering and vapor deposition, and wet methods such as displacement plating and electroless plating. In addition, when forming a seed layer by electroless plating, it is necessary to form a metal nucleus before forming a seed layer. In this case, it is desirable to form by conventional Pd activation treatment. Also in this case, a known pretreatment such as phosphoric acid treatment or acid treatment, or ashing treatment using oxygen plasma or the like may be performed before forming the metal nucleus.

  When forming the seed layer, an adhesion layer such as Ti or Cr may be formed between the substrate and the seed layer by a known method such as sputtering in order to improve the adhesion between the substrate and the seed layer. preferable. In this case, the thickness of the adhesion layer is preferably 5 to 50 nm, particularly 10 to 30 nm.

  In the present invention, as the electroless plating bath for forming the base film, for example, metal ions such as cobalt ions, nickel ions and iron ions, hypophosphorous acid, or phosphorus-based reducing agents such as sodium hypophosphite Alternatively, a material containing a boron-based reducing material such as dimethylamine borane and a complexing agent of the above metal ions is used.

Examples of the metal ion supply source include water-soluble cobalt salts such as cobalt sulfate, nickel sulfate, and iron sulfate, nickel salts, and iron salts. The composition ratio (composition ratio of cobalt, nickel, and iron) is desired. And the concentration of the metal salt in the plating bath is appropriately selected. The total metal salt concentration is 0.01 to 3.0 mol / dm ³ , particularly 0.05. It is preferable to set it to -0.3 mol / dm < ³ >.

Moreover, although the density | concentration of a reducing agent is also selected suitably, it is preferable to set it as 0.01-0.5 mol / dm < ³ > in a plating bath, especially 0.01-0.2 mol / dm < ³ >.

On the other hand, as the complexing agent, a known complexing agent of the above metal ions such as a carboxylate such as sodium citrate and sodium tartrate, and an ammonium salt such as ammonium sulfate is used, and its concentration is 0.05 mol in the plating bath. / Dm ³ or more is preferable, and 0.1 to 1.0 mol / dm ³ is more preferable. In addition, it is preferable to use a crystal modifier such as phosphorous acid in the plating bath, and it is particularly preferable to use it at a concentration of 0.01 mol / dm ³ or more.

  A pH buffer such as boric acid may be used in the plating bath. Further, a surfactant may be used to improve the uniformity of the electroless plating film, and as the surfactant, sodium dodecyl sulfate or polyethylene glycol is preferable. Further, a conventional additive (such as sulfur) may be used to improve the smoothness of the film. In order to improve the smoothness of the film, a conventional first-type brightener such as saccharin or a conventional second-type brightener such as thiourea may be used alone or in combination. In particular, a sulfur brightener is preferably used.

  The temperature and pH of the plating bath are appropriately determined depending on the bath composition. The bath temperature is preferably 50 ° C. or higher, and the pH is preferably 8 or higher. Particularly preferred are 70 to 95 ° C. and a pH of around 9. Furthermore, the base film formed by the electroless plating bath may be heat-treated in order to improve soft magnetic properties. In this case, the heat treatment temperature is preferably 150 to 300 ° C.

  The base film of the present invention preferably has an isotropic degree of 1.0 ± 0.2 or less, and more preferably 1.0 ± 0.15 or less. Further, the saturation magnetic flux density Bs is preferably 0.2 T or more and 1.7 T or less, and more preferably 0.8 T or more and 1.5 T or less. Further, the thickness (t) is preferably 50 nm or more and 5000 nm or less, and more preferably 200 nm or more and 3000 nm or less. Further, the crystal grain size of the soft magnetic underlayer is preferably 5 nm or less, more preferably 3 nm or less, and a fine crystal or amorphous structure.

  The base film formed according to the present invention may have an easy magnetization axis in a direction perpendicular to the substrate. The easy axis of magnetization in the vertical direction is very effective for making it difficult to form a domain wall. At this time, the axis of easy magnetization in the vertical direction, that is, the anisotropic magnetic field (Hk) of perpendicular magnetic anisotropy is preferably 5 to 50 Oe, and more preferably 10 to 30 Oe. 1 Oe is about 79 A / m.

  When perpendicular magnetic anisotropy is recognized, this anisotropic magnetic field (Hk) is a magnetic field obtained by obtaining Bs from the hysteresis loop of the VSM as described above (see FIG. 9).

  Thus, by making the magnetic properties of the underlayer isotropic, a domain wall is not generated and a high-performance perpendicular magnetic recording medium with low noise can be obtained, and the S / N ratio and the overwrite property can be improved. . The coercive force Hc of the soft magnetic film as the undercoat film is not particularly limited, but is preferably 40 Oe (1 Oe = about 79 A / m) or less, and more preferably 10 Oe or less.

  A high-performance perpendicular magnetic recording medium can be obtained by smoothing the surface and forming a perpendicular magnetic recording layer by a conventional method using the substrate having the base film of the present invention. An example is shown below.

  The substrate surface is smoothed after the soft magnetic underlayer is formed, the seed layer is smoothed before the soft magnetic underlayer is formed, and then the soft magnetic underlayer is formed. There are a method of smoothing, a method of smoothing only the seed layer, a method of using them together, and any method can be suitably used in the present invention. In particular, it is preferable to use these methods in combination to smooth the substrate surface to a higher degree.

In addition, it is also preferable to perform an operation of removing the distortion of the substrate and the film by performing heat treatment on the entire substrate immediately before the smoothing step. The heat treatment temperature is preferably in the range of 100 ° C to 350 ° C, and the treatment time is preferably about 10 minutes to 60 minutes.
A specific example of the smoothing step is preferably performed by a chemical mechanical polishing method using a polishing liquid containing an abrasive mainly composed of alumina or silica (colloidal silica). In that case, as surface smoothness, it is preferable that the average height (Ra) is 2 nm-0.05 nm, and it is more preferable that it is 0.8 nm-0.05 nm.

The perpendicular magnetic film only needs to be a magnetic film whose easy axis of magnetization is mainly perpendicular to the substrate, and the composition is not particularly limited. In general, a Co-based alloy (for example, CoCrPt, CoCrPtB, CoCrPt—SiO ₂ , Co / Pd multilayer, CoB / PdB multilayer, CoSiO ₂ / PdSiO ₂ multilayer, etc.) is preferably used.

  The perpendicular magnetic film may have a single-layer structure made of the Co-based material, or a structure of two or more layers including a layer made of a Co-based alloy material and a layer made of a material different from the Co-based alloy material. You can also

  Further, a structure in which a Co-based alloy layer and a Pd-based alloy layer are stacked, or a multilayer structure including an amorphous material layer such as TbFeCo and a CoCrPt-based alloy material layer is also preferable.

  The thickness of the perpendicular magnetic film is preferably 3 to 60 nm (more preferably 5 to 40 nm). If the thickness of the perpendicular magnetic film is less than the above range, sufficient magnetic flux cannot be obtained, and the reproduction output is lowered. On the other hand, if the thickness of the perpendicular magnetic film exceeds the above range, the magnetic particles in the perpendicular magnetic film are coarsened and the recording / reproducing characteristics are deteriorated.

  The coercive force Hc of the perpendicular magnetic film is preferably 3000 Oe or more. A magnetic recording medium having a coercive force of less than 3000 Oe is not preferable because it is unsuitable for increasing the recording density and inferior in thermal fluctuation resistance.

  The ratio Mr / Ms between the residual magnetization (Mr) and the saturation magnetization (Ms) of the perpendicular magnetic film is preferably 0.9 or more. A magnetic recording medium having an Mr / Ms of less than 0.9 is not preferable because it is inferior in thermal fluctuation resistance.

The reverse magnetic domain nucleation magnetic field (-Hn) of the perpendicular magnetic film is preferably 0 Oe or more and 2500 Oe or less. A magnetic recording medium having a reverse domain nucleation magnetic field (-Hn) of less than 0 Oe is not preferable because it is inferior in thermal fluctuation resistance.
Hereinafter, the reverse magnetic domain nucleation magnetic field (-Hn) will be described.

  As shown in FIG. 6, in the MH curve, a point where the external magnetic field becomes 0 in the process of decreasing the external magnetic field from a state where the magnetization is saturated is a, a point where the magnetization becomes 0 is b, and a point b If the intersection of the tangent line of the MH curve and the straight line indicating the saturation magnetization is c, the reverse domain nucleation magnetic field (-Hn) can be expressed by the distance (Oe) between the point a and the point c.

  The reverse domain nucleation magnetic field (-Hn) takes a positive value when the point c is in a region where the external magnetic field is negative (see FIG. 6), and conversely, in the region where the external magnetic field is positive. It takes a negative value when there is a point c (see FIG. 7).

  In this magnetic recording medium, the orientation control film is made of a nonmagnetic material containing 33 to 80 at% Ni and containing one or more of Sc, Y, Ti, Zr, Hf, Nb, and Ta. Excellent error rate and heat fluctuation resistance can be obtained.

  Further, a magnetic storage device can be configured by combining a magnetic recording medium using the base film of the present invention with a known composite head. In this case, it is preferable that the composite recording head can generate a writing magnetic field of 3.0 kOe or more. FIG. 8 is a conceptual diagram of a perpendicular magnetic recording / reproducing apparatus using the perpendicular magnetic recording medium of the present invention.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated concretely, this invention is not limited to the following Example.

  After chemically cleaning a glass substrate having an average roughness Ra of 0.5 nm or less, an adhesion layer made of a Ti film with a thickness of 10 nm and a seed layer made of a Ni film with a thickness of 20 nm are successively formed by DC magnetron sputtering. did. Next, after performing a conventional pretreatment, a CoNiFeP soft magnetic film having a film thickness of 3000 nm was formed as a base film using an electroless plating bath shown in Table 1 below. At this time, ferrite magnets were set on both sides of the plating tank so that an external magnetic field was applied in the radial direction of the glass substrate (see FIG. 5). FIG. 5 is an explanatory view showing an example of a plating apparatus used in the present invention. The plating tank 21 is an example of the plating apparatus 21 on which the soft magnetic film is formed. A plating tank 28 filled with a plating solution is installed in a water tank 22, and a rotating mechanism (not shown) is provided in the plating tank 28. A glass substrate 30 on which the seed layer formed on the substrate holding jig 29 provided is formed is immersed. The substrate holding jig 29 is supported by the substrate holding jig 27 so as to be swingable up and down. Further, in order to apply an external magnetic field in the radial direction of the glass substrate on which the seed layer is formed, an N-pole magnet 25 and an S-pole magnet 26 are provided with a plating tank 28 interposed therebetween. Further, in order to make the water temperature in the water tank 22 constant, a stirring rod 24 having a stirring blade 23 at the lower end is provided in the water tank 22. Using the above plating apparatus, a magnetic flux of 35 G is applied to the center of the glass substrate, and the rotation speed of the glass substrate is 6.5 r. p. As m, a soft magnetic film was formed on a glass substrate.

  Next, chemical mechanical polishing was performed on the obtained base film using a polishing liquid mainly composed of alumina and silica. Thus, the average roughness Ra of the base film was set to 0.6 to 0.8 nm (measured with TMS2000 (Texture Measurement System) manufactured by Veeco). From TEM observation, the particle size in the underlayer was 2 to 5 nm, and X-ray diffraction revealed that the particles were amorphous. The ground film thickness after polishing was 300 nm and the saturation magnetic flux density Bs was 1.3T. Further, the isotropic degree was determined to be 1.11 by measuring Hs in the circumferential direction and the radial direction by VSM measurement. As described above, the easy axis of magnetization was recognized in the vertical direction, and the perpendicular magnetic anisotropy obtained from the hysteresis loop was 10 Oe. Furthermore, when the presence or absence of a domain wall was observed with OSA (Optical Surface Analyzer), it was found that no domain wall was generated.

  Next, an Si layer having a film thickness of 5 nm and a Pd film having a film thickness of 5 nm were formed at room temperature on the base film dried in a clean environment by a DC magnetron sputtering method to form an intermediate layer. The laminated film of the Si film and the Pd film has a structure in which Si and Pd are partially diffused.

  Next, after forming an intermediate layer, 10 layers of Co layers having a thickness of 0.2 nm and Pd layers having a thickness of 0.8 nm were alternately stacked to form a perpendicular magnetic recording layer having a total thickness of 10 nm.

  Further, after forming a perpendicular magnetic recording layer, a C film having a thickness of 5 nm was formed as a protective layer to obtain a magnetic recording medium. The obtained magnetic recording medium was evaluated for MF-S / N ratio by measuring electromagnetic conversion characteristics using a composite type head in which the writing part was composed of a single magnetic pole type head and the reading part was a shield type magnetoresistive head. The results are shown in Table 4 together with the domain wall results.

  Example 1 was the same as Example 1 except that the strength of the magnetic field applied from the outside during plating was changed from 35 G to 100 G (neodymium-iron-boron magnet). Table 4 shows Bs, isotropic degree, perpendicular magnetic anisotropy, MF-S / N ratio, and presence / absence of a domain wall.

  Example 1 was the same as Example 1 except that the composition of the plating bath was changed as shown in Table 2. Table 4 shows Bs, isotropic degree, perpendicular magnetic anisotropy, MF-S / N ratio, and presence / absence of a domain wall.

In Example 1, except for using the plating bath without the addition of FeSO _4, and in the same manner as in Example 1. Table 4 shows Bs, isotropic degree, perpendicular magnetic anisotropy, MF-S / N ratio, and presence / absence of a domain wall.

  The same procedure as in Example 1 was performed except that a 1-inch silicon wafer having an average roughness Ra of 0.3 nm or less was used as the substrate instead of the glass substrate in Example 1. Table 4 shows Bs, isotropic degree, perpendicular magnetic anisotropy, MF-S / N ratio, and presence / absence of a domain wall.

  Example 1 was the same as Example 1 except that the composition of the plating bath was changed as shown in Table 3 for the B system. Table 4 shows Bs, isotropic degree, perpendicular magnetic anisotropy, MF-S / N ratio, and presence / absence of a domain wall.

  In Example 1, a 2.5-inch Al substrate was used instead of the glass substrate. Both surfaces were polished and activated by a conventional method, and NiP plating with a film thickness of 12 μm was applied as a seed layer. Next, a heat treatment was performed at 250 ° C. for 30 minutes to remove the distortion of the plating film, and then the surface was polished by about 2 μm using a polishing liquid mainly composed of an alumina-based abrasive to obtain an average roughness Ra of 2 nm. Subsequently, a CoNiFeP soft magnetic film having a thickness of 600 nm was formed as a base film by an electroless plating bath under the same conditions as in Example 1. Further, after heat treatment at 150 ° C. for 15 minutes, the substrate was polished by about 300 nm using a polishing liquid containing silica as a main component so that the average roughness Ra of the base film was 0.1 to 0.3 nm. Thereafter, the same operation as in Example 1 was performed. Table 4 shows Bs, isotropic degree, perpendicular magnetic anisotropy, MF-S / N ratio, and presence / absence of a domain wall.

(Comparative Example 1)
In Example 1, the same operation as in Example 1 was performed except that the ferrite magnet was not set at the time of plating, and the base film was formed by electroless plating in the absence of an external parallel magnetic field. A medium was obtained. Although Bs was 1.3T and the film thickness was 300 nm, the domain wall was recognized by OSA.

(Comparative Example 2)
A magnetic recording medium was obtained in the same manner as in Example 1 except that a NiFe soft magnetic film having a film thickness of 100 nm and a saturation magnetic flux density Bs of 1.0 T was formed as a base film by sputtering and used without being flattened. It was. With respect to the obtained magnetic recording medium, the electromagnetic conversion characteristics were measured in the same manner as in Example 1 to evaluate the S / N ratio. Further, the presence or absence of a domain wall was observed by OSA measurement.

(Comparative Example 3)
In Comparative Example 2, the same procedure was performed except that a CoNiFe soft magnetic film was formed instead of NiFe. The results are shown in Table 4.

  According to Table 4, it can be seen that the MF-S / N ratio of the example is higher than that of the comparative example, and no domain wall is generated. In particular, Example 1 showed a higher S / N ratio because the use of a soft magnetic film having a high Bs value for the base film achieved high focusing of the leakage magnetic field of the recording head. This is presumed to be due to an increase in the reproduction signal.

(A) (b) is sectional drawing which shows the magnetic-recording medium based on one Example of this invention. It is a conceptual diagram of the magnetic characteristic of a soft-magnetic underlayer. It is a figure which shows the VSM measurement procedure of the base film of this invention. It is a conceptual diagram which shows the application | coating degree of an external magnetic field at the time of plating of this invention, and a motion of a board | substrate. It is explanatory drawing which shows an example of the plating apparatus used for this invention. It is a graph which shows an example of MH curve. It is a graph which shows the other example of MH curve. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows an example of the perpendicular magnetic recording / reproducing apparatus of this invention, (a) shows the whole structure, (b) shows a magnetic head. It is a measurement example of perpendicular magnetic anisotropy (Hk) of the present invention. The symbol after Hk in the center of the right side of the figure indicates vertical.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nonmagnetic substrate 2 Soft magnetic base film 3 Orientation control film 4 Intermediate film 5 Vertical magnetic film 6 Protective film 7 Lubricating film 8 Metal nucleus or seed layer 10 Magnetic recording medium 11 Medium drive unit 12 Magnetic head 12a Main magnetic pole 12b Auxiliary magnetic pole 12c Connecting part 12d Coil 13 Head drive part 14 Recording / reproducing signal processing system 21 Plating apparatus 22 Water tank 23 Stirring blade 24 Stirring rod 25 N pole magnet 26 S pole magnet 27 Substrate holding jig 28 Plating tank 29 Substrate holding jig 30 Glass substrate

Claims (8)

On a nonmagnetic substrate, at least a soft magnetic underlayer made of a soft magnetic material, an orientation control film for controlling the orientation of the film immediately above, and a perpendicular magnetic film having an easy axis of magnetization oriented perpendicularly to the substrate A method for producing a perpendicular magnetic recording medium provided with a protective layer ,
When a metal core or seed layer is formed on a nonmagnetic substrate and a soft magnetic underlayer is formed thereon by electroless plating, a parallel magnetic field is applied to the nonmagnetic substrate in the radial direction from the outside. The soft magnetic underlayer is formed while rotating in parallel and rotating, and the ratio of Hs of the soft magnetic underlayer in the circumferential direction of the substrate (minimum strength of the applied magnetic field obtained when measuring the saturation magnetic flux density) to Hs in the radial direction isotropic A method of manufacturing a perpendicular magnetic recording medium, wherein the property is within 1.0 ± 0.2. 2. The perpendicular magnetic recording according to claim 1, wherein an anisotropic magnetic field (Hk) of perpendicular magnetic anisotropy of the soft magnetic underlayer is in a range of 395 A / m to 3950 A / m (5 Oe to 50 Oe). A method for manufacturing a medium . 3. The method of manufacturing a perpendicular magnetic recording medium according to claim 1, wherein the crystal grain size of the soft magnetic underlayer is a microcrystalline or amorphous structure of 5 nm or less. The method for manufacturing a perpendicular magnetic recording medium according to any one of claims 1 to 3, wherein the thickness of the soft magnetic underlayer is in the range of 50 nm to 5000 nm. 5. The perpendicular magnetic recording medium according to claim 1, wherein an average surface roughness Ra of the soft magnetic underlayer on the side where the perpendicular magnetic recording layer is laminated is 0.8 nm or less. Manufacturing method . The method of manufacturing a perpendicular magnetic recording medium according to claim 1, wherein the soft magnetic underlayer includes phosphorus . The method for manufacturing a perpendicular magnetic recording medium according to claim 1, wherein the soft magnetic underlayer includes boron . The method of manufacturing a perpendicular magnetic recording medium according to claim 1, wherein the nonmagnetic substrate is a silicon substrate .

Images