JP2005190506A - Perpendicular magnetic recording medium and manufacturing method thereof - Google Patents

Abstract

A perpendicular magnetic recording medium having high perpendicular magnetic anisotropy and perpendicular coercive force and large saturation magnetization is provided.
SOLUTION: A nonmagnetic substrate, a soft magnetic layer, a nonmagnetic crystal orientation control layer made of a metal or alloy having a hexagonal close packed structure or a face-centered cubic structure, Cu, Ir, Rh, Pd, Pt, C, Os. , Re, Ru, Tc and Zn, any alloy of Cu, Ir, Rh, Pd, Pt, C, Os, Re, Ru, Tc and Zn, non-magnetic Ni alloy And a nonmagnetic template layer made of a metal or alloy having a hexagonal close packed structure or a face-centered cubic structure selected from the group consisting of nonmagnetic Co alloys, ferromagnetic crystal grains containing Co and Pt, and nonmagnetic crystal grains A perpendicular magnetic recording medium comprising a perpendicular magnetic layer in which a void corresponding to a boundary or a crystal grain boundary is formed, and a protective layer.
[Selection] Figure 1

Description

  The present invention relates to a perpendicular magnetic recording medium used in a high-density magnetic recording apparatus and a manufacturing method thereof.

  Conventionally, in a perpendicular magnetic recording medium, by adding Cr to a Co-based alloy as a magnetic layer, a granular structure in which a Cr-rich nonmagnetic layer is phase-separated around a ferromagnetic Co-rich crystal particle, The magnetic interaction between magnetic particles has been reduced to increase the perpendicular coercive force and lower the medium S / N.

However, in such a Co—Cr alloy, a large signal output cannot be obtained due to a decrease in saturation magnetization due to the addition of Cr. Further, the perpendicular magnetic anisotropy energy of the Co—Cr alloy is as small as about 2 × 10 ⁶ / cm ³ and the perpendicular coercive force is at most about ³ kOc, so that sufficient thermal stability capable of holding recorded information can be secured. There wasn't. Furthermore, in order to realize the phase separation structure, it is necessary to heat the substrate to a high temperature when depositing the Co—Cr-based alloy, and a heat-resistant substrate such as a glass substrate or an aluminum alloy substrate must be used. In other words, it could not be produced on a non-heat resistant substrate such as plastic.

Recently, a material in which an oxide such as SiO ₂ or oxygen is added to Co—Cr—Pt has been proposed (see, for example, Patent Document 1), and has a larger perpendicular magnetic anisotropy than a conventional Co—Cr (—Pt) alloy medium. And perpendicular coercive force is obtained. In the medium to which SiO ₂ is added, since the magnetic interaction between the magnetic particles can be reduced, a surface recording density of 169 Gbit / in ² is achieved as a low noise medium. However, in order to exhibit sufficient magnetic properties in such a medium, a metal or alloy such as Ru having a thickness of 20 nm or more is required as the underlayer of the (Co—Cr—Pt) —SiO ₂ ferromagnetic phase, and more optimal. The composition of Co—Cr—Pt and the addition amount of SiO ₂ for obtaining excellent magnetic characteristics must be controlled very accurately, and there is difficulty in actual mass productivity.

  Further, the Co—Pt alloy conventionally used as a magneto-optical recording material has a large perpendicular magnetic anisotropy but a small perpendicular coercive force, and cannot be used as a magnetic recording material.

On the other hand, a perpendicular magnetic recording medium using a so-called artificial lattice film in which Co and a very thin layer such as Pd or Pt are laminated has a very large perpendicular magnetic anisotropy and perpendicular coercive force, and perpendicular magnetic recording. Although it is promising as a medium (see, for example, Non-Patent Document 1), there is a drawback that the interaction between magnetic particles is usually very large and medium noise is large. In order to eliminate this drawback, if an attempt is made to reduce the magnetic interaction by adjusting the underlayer and adjusting the deposition conditions (sputtering gas pressure, etc.) or by adding an additive to Co, Pd or Pt, The thermal stability is deteriorated and the appropriate conditions for a high-density magnetic recording medium are not satisfied. Further, the artificial lattice film has a drawback that the saturation magnetization is essentially small.
JP 2003-77122 A IEEE Trans. Magn., 30, 4014 (1994)

  An object of the present invention is to provide a perpendicular magnetic recording medium having high perpendicular magnetic anisotropy and perpendicular coercive force, and large saturation magnetization.

  A perpendicular magnetic recording medium according to the present invention includes a nonmagnetic substrate; a soft magnetic layer formed on the nonmagnetic substrate; a metal having a hexagonal close packed structure or a face-centered cubic structure formed on the soft magnetic layer. Or a nonmagnetic crystal orientation control layer made of an alloy; any one of Cu, Ir, Rh, Pd, Pt, C, Os, Re, Ru, Tc, and Zn formed on the nonmagnetic crystal orientation control layer Selected from the group consisting of metals, Cu, Ir, Rh, Pd, Pt, C, Os, Re, Ru, Tc and Zn, nonmagnetic Ni alloys, and nonmagnetic Co alloys. A nonmagnetic template layer made of a metal or alloy having a hexagonal close-packed structure or a face-centered cubic structure; a ferromagnetic crystal grain containing Co and Pt and a nonmagnetic grain boundary formed on the nonmagnetic template layer Also And having a protective layer formed on the perpendicular magnetization layer; grain perpendicular magnetization layer void and are formed corresponding to circles and.

  In the method for manufacturing a perpendicular magnetic recording medium according to the present invention, when the above-described perpendicular magnetic recording medium is manufactured, the non-magnetic template layer and the perpendicular magnetic layer are made of (sputter gas pressure) × (target-substrate distance) of 15 Pa. It is characterized by being deposited by sputtering under conditions of not less than cm and not more than 200 Pa · cm.

  In the manufacturing method of the present invention, the nonmagnetic substrate is held in an unheated state when all the layers constituting the perpendicular magnetic recording medium are deposited.

  The present invention can be applied to a perpendicular magnetic recording medium having high perpendicular magnetic anisotropy energy, perpendicular coercive force, and large saturation magnetization, and capable of high density.

  FIG. 1 is a schematic configuration diagram showing an example of a perpendicular magnetic recording medium according to the present invention. The perpendicular magnetic recording medium 100 of FIG. 1 has a structure in which a soft magnetic layer 20, a nonmagnetic crystal orientation control layer 30, a nonmagnetic template layer 40, a perpendicular magnetization layer 50, and a protective layer 60 are sequentially formed on a nonmagnetic substrate 10. Have

  As the nonmagnetic substrate 10, for example, a glass substrate, an aluminum alloy substrate, a plastic substrate, or the like can be used.

  In the perpendicular magnetic recording medium according to the present invention, a perpendicular magnetic layer 50 (hereinafter referred to as Co-Pt) in which ferromagnetic crystal grains containing Co and Pt and nonmagnetic crystal grain boundaries or voids corresponding to crystal grain boundaries are formed. A perpendicular magnetic layer). The Co—Pt perpendicular magnetization layer has a hexagonal close packed structure (hcp) crystal structure.

  The soft magnetic layer 20 has a function of strengthening magnetic interaction with the magnetic head during recording on the perpendicular magnetic recording medium.

  The nonmagnetic crystal orientation control layer 30 is made of a single film or a laminated film of a metal or alloy having a hexagonal close packed structure (hcp) or a face centered cubic structure (fcc). The nonmagnetic crystal orientation control layer 30 has a function of controlling the crystal orientation of the Co—Pt perpendicular magnetization layer having the hcp structure. As a typical nonmagnetic crystal orientation control layer, for example, nonmagnetic Co—Cr having a hexagonal close-packed structure (Cr composition is 30 at% or more) can be given. The thickness of the nonmagnetic crystal orientation control layer 30 is preferably 0.1 nm or more and 10 nm or less.

  The nonmagnetic template layer 40 is made of any one of Cu, Ir, Rh, Pd, Pt, C, Os, Re, Ru, Tc, and Zn, Cu, Ir, Rh, Pd, Pt, C, Os, Re. , Ru, Tc, and Zn, a hexagonal close packed structure or a face-centered cubic structure metal or alloy selected from the group consisting of an alloy containing at least one of Ru, Tc, and Zn, a nonmagnetic Ni alloy, and a nonmagnetic Co alloy. The nonmagnetic template layer 40 includes fine crystal grains and has a function of becoming a template (template) of ferromagnetic crystal grains of the Co—Pt perpendicular magnetization layer. In addition, since the hcp structure Co—Pt perpendicular magnetization layer is epitaxially grown on the nonmagnetic template layer 40, the hcp structure or fcc structure is used. The thickness of the nonmagnetic template layer 40 is preferably 0.1 nm or more and 10 nm or less.

  Table 1 summarizes the crystal system, lattice constants, nearest atom spacing, and inconsistency (mismatch) with Co lattice constants for Co and other metals. The data in Table 1 are extracted from the “X-ray diffraction handbook” of Rigaku Corporation and calculated.

As shown in Table 1, the lattice constant of a metal element (indicated by a circle in the suitability column) that is preferably used as the nonmagnetic template layer in the present invention is approximately 10% of mismatch (mismatch) with the lattice constant of Co. Is within. Thus, since the mismatch of lattice constant is small, it is considered that the Co—Pt perpendicular magnetization layer deposited on the nonmagnetic template layer maintains the original magnetic characteristics.

  An example of the protective layer 60 is a carbon film. Usually, a fluorocarbon-based lubricant is applied on the protective layer 60.

  The reason why the thicknesses of the nonmagnetic crystal orientation control layer 30 and the nonmagnetic template layer 40 are defined to be 0.1 nm or more and 10 nm or less is as follows. That is, in order to increase the magnetic interaction between the magnetic head and the soft magnetic layer 20 during recording on the perpendicular magnetic recording medium, the thickness of each of the nonmagnetic crystal orientation control layer 30 and the nonmagnetic template layer 40 is made as thin as possible. It is preferable. For this reason, the thickness of each layer is defined as 10 nm or less. In addition, in order for the nonmagnetic crystal compounding control layer and the nonmagnetic template layer to exhibit their respective functions, it is necessary to deposit one or more atoms, so the thickness of each layer is defined to be 0.1 nm or more. Yes.

  Each layer forming the perpendicular magnetic recording medium 100 is formed by sputtering, and each layer is deposited by holding a nonmagnetic substrate in a non-heated state.

  When forming the nonmagnetic crystal orientation control layer 30, it is preferable to deposit under the condition that (sputtering gas pressure) × (target-substrate distance) is about 15 Pa · cm or less. Under such conditions, the nonmagnetic crystal orientation control layer 30 that is close to a continuous film and excellent in crystal orientation can be formed.

  On the other hand, when the nonmagnetic template layer 40 and the perpendicular magnetization layer 50 are formed, they are deposited under the condition that (sputtering gas pressure) × (target-substrate distance) is 15 Pa · cm or more and 200 Pa · cm or less. preferable. When the nonmagnetic template layer 40 is deposited under the above conditions, it is possible to inherit the good crystal orientation of the nonmagnetic crystal orientation control layer and make the crystal grains fine. When the perpendicular magnetic layer 50 is deposited under the above conditions, the crystal grains can be made fine while maintaining good crystal orientation.

(Example)
EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, these are for describing this invention suitably, and are not intending to limit to these.

  In all of the following examples, a 2.5-inch magnetic disk glass substrate was used as the nonmagnetic substrate 10 and all layers were deposited by magnetron sputtering without heating the glass substrate. A practical perpendicular magnetic recording medium has a soft magnetic layer 20 on a nonmagnetic substrate 10 as shown in FIG. However, since the soft magnetic layer 20 can be crystalline or amorphous, when the nonmagnetic crystal orientation control layer 30, the nonmagnetic template layer 40, and the perpendicular magnetization layer 50 are formed on the soft magnetic layer 20, the soft magnetic layer 20 It becomes difficult to purely examine the influence of the nonmagnetic crystal orientation control layer 30 and the nonmagnetic template layer 40 on the perpendicular magnetic layer 50 by eliminating the influence of the magnetic field 20. Therefore, in the following embodiments, the nonmagnetic crystal orientation control layer 30, the nonmagnetic template layer 40, and the perpendicular magnetization layer 50 are formed on the nonmagnetic substrate 10 without providing the soft magnetic layer 20, The influence of the magnetic crystal orientation control layer 30 and the nonmagnetic template layer 40 on the perpendicular magnetic layer 50 is examined.

  After producing the perpendicular magnetic recording medium, the magnetic properties were measured with a vibrating sample magnetometer (VSM) and a Kerr effect magnetometer. The crystallinity was evaluated using an X-ray diffractometer.

Example 1
The following perpendicular magnetic recording media were produced, and the relationship between the crystal orientation (Δθ ₅₀ ) of the underlayer and the perpendicular coercive force (Hc) was examined. The result is shown in FIG.

  (1) A perpendicular magnetic recording medium according to this example was manufactured as follows. On a glass substrate, a nonmagnetic Co—Cr (Cr: about 35 atm) having a thickness of about 2 nm as a nonmagnetic crystal orientation control layer on the condition that (sputtering gas pressure) × (target-substrate distance) is less than 15 Pa · cm. %) Was deposited. Next, Pt having a thickness of 5 to 10 nm is deposited as a nonmagnetic template layer under the condition that (sputtering gas pressure) × (target-substrate distance) is 15 Pa · cm or more and 200 Pa · cm or less, and further perpendicular magnetization is performed. Co—Pt was deposited as a layer (indicated as Pt / CoCr in FIG. 2).

  (2) For the purpose of investigating the influence of the crystal orientation of the underlayer, a perpendicular magnetic recording medium of a reference example was produced as follows. On the glass substrate, Co—Pt (Pt: about 20 at%) having a thickness of about 2 nm and Pt having a thickness of about 5 nm were deposited. Co-Pt has an hcp structure and functions as a crystal orientation control layer, but is not nonmagnetic. Next, Ru having a thickness of 5 to 10 nm was deposited as a nonmagnetic template layer, and Co—Pt was further deposited as a perpendicular magnetization layer (indicated as Ru / Pt / CoPt in FIG. 2).

  (3) A perpendicular magnetic recording medium of a comparative example was produced as follows. On the glass substrate, Ti, Pt or Au was deposited as an underlayer corresponding to the nonmagnetic template layer without depositing a crystal orientation control layer, and Co—Pt was deposited thereon as a perpendicular magnetization layer (FIG. 2). And Ti, Pt, and Au).

In the perpendicular magnetic recording medium (3), the Δθ _{50 of} the underlayer is a large value of about 10 degrees or more, and the crystal orientation is deteriorated. Correspondingly, the perpendicular magnetic recording medium (3) has a small value of perpendicular coercive force Hc of 3000 Oe or less, and is not suitable as a perpendicular magnetic recording medium.

In the perpendicular magnetic recording media (1) and (2) provided with the crystal orientation control layer and the nonmagnetic template layer, the Δθ ₅₀ of the underlayer is a small value of about 7 degrees or less, and exhibits excellent crystal orientation. Yes. Correspondingly, the perpendicular magnetic recording media of (1) and (2) have a large value of the perpendicular coercive force Hc of 3000 Oe or more. Thus, it has been found that by forming the crystal orientation control layer and the nonmagnetic template layer as the underlayer, the crystal orientation of the underlayer is improved and the magnetic properties of the perpendicular magnetic layer deposited thereon are improved. However, the crystal orientation control layer exhibiting magnetism in the perpendicular magnetic recording medium (2) cannot be employed because of problems such as magnetic coupling with the perpendicular magnetization layer.

Example 2
On the glass substrate, nonmagnetic Co—Cr (Cr: about 35 at%) having a thickness of about 2 nm and Pt having a thickness of about 5 nm were deposited as a nonmagnetic crystal orientation control layer. Next, the value of (sputter gas pressure P) × (target-substrate distance D) (hereinafter referred to as “P * D product”) is changed from 5 Pa · cm to 250 Pa · cm to obtain a thickness of about non-magnetic template layer. 5 nm of Pt was deposited, and 15 nm thick Co—Pt was further deposited as a perpendicular magnetization layer.

  FIG. 3 shows the results of examining the relationship between the P * D product and the magnetic characteristics (the perpendicular coercive force Hc and the squareness ratio SQ).

  As shown in FIG. 3, when the P * D product is approximately 15 to 200 Pa · cm, and optimally in the range of 20 to 150 Pa · cm, the perpendicular coercive force Hc increases, and the squareness ratio is close to 1. ing. Accordingly, it is considered that excellent crystal orientation of the nonmagnetic crystal orientation control layer was maintained up to the perpendicular magnetization layer through the nonmagnetic template layer, and excellent magnetic properties were obtained.

  FIG. 4 shows the results of examining the relationship between the P * D product, the saturation magnetization Ms, and the perpendicular anisotropy energy Ku.

As shown in FIG. 4, when the P * D product is 15 to 200 Pa · cm, optimally in the range of 20 to 150 Pa · cm, Ms is a large value of 700 cmu / cm ³ or more, and Ku is also 6 to 10 × 10 6. It is a large value of ⁶ erg / cm ³ .

  These values of Hc, Ms, and Ku satisfy the conditions required for the next generation perpendicular magnetic recording media.

Example 3
Various materials were used as the nonmagnetic template layer, and the relationship between the film thickness of the nonmagnetic template layer and the perpendicular coercive force Hc was examined. FIG. 5 shows the result.

  When the nonmagnetic template layer was not used, the value of the perpendicular coercive force Hc was only about 3000 Oe. In contrast, when Pt, Pd, or Ru is used as the nonmagnetic template layer, it can be seen that the perpendicular coercive force Hc is a large value of 3000 Oc or more. These metals have a face-centered cubic structure (fcc) or a hexagonal close packed structure (hcp), have a heteroepitaxial relationship with the Co—Pt layer (hcp), which is a perpendicular magnetization layer, and exhibit excellent magnetic properties. It is thought that

  On the other hand, with a metal having a body-centered cubic lattice structure (bcc) such as Cr or Ta, Hc is generally a small value of 2000 Oe or less regardless of the thickness of the template layer, and is not suitable as a high-density magnetic recording medium. I understand that.

  Although the perpendicular magnetic recording medium described in the above embodiments does not have a soft magnetic film, the perpendicular magnetic recording medium in which a soft magnetic film is formed between the substrate and the nonmagnetic crystal orientation control layer may also be used. Similar to the above example, the effect of the nonmagnetic crystal orientation control layer and the nonmagnetic template film is recognized.

1 is a cross-sectional view showing an example of a perpendicular magnetic recording medium according to the present invention. FIG. 3 is a diagram showing the relationship between the crystal orientation of the underlayer and the perpendicular coercive force with respect to the perpendicular magnetic recording medium of Example 1. The figure which shows the relationship between P * D product [(sputtering gas pressure) x (target-substrate distance)], perpendicular coercive force Hc, and squareness ratio SQ about the perpendicular magnetic recording medium of Example 2. The figure which shows the relationship between P * D product [(sputtering gas pressure) x (target-substrate distance)], saturation magnetization Ms, and perpendicular anisotropy energy Ku about the perpendicular magnetic recording medium of Example 2. FIG. 10 is a graph showing the relationship between the thickness of the nonmagnetic template layer and the perpendicular coercive force Hc for the perpendicular magnetic recording medium of Example 3.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Nonmagnetic board | substrate, 20 ... Soft magnetic layer, 30 ... Nonmagnetic crystal orientation control layer, 40 ... Nonmagnetic template layer, 50 ... Perpendicular magnetization layer, 60 ... Protective layer, 100 ... Perpendicular magnetic recording medium.

Claims (3)

A non-magnetic substrate;
A soft magnetic layer formed on the non-magnetic substrate;
A nonmagnetic crystal orientation control layer made of a metal or alloy having a hexagonal close-packed structure or a face-centered cubic structure formed on the soft magnetic layer;
Any one of Cu, Ir, Rh, Pd, Pt, C, Os, Re, Ru, Tc and Zn, Cu, Ir, Rh, Pd, Pt formed on the nonmagnetic crystal orientation control layer. , C, Os, Re, Ru, Tc and Zn, a hexagonal close-packed structure or a face-centered cubic structure selected from the group consisting of an alloy containing at least one of Zn, a nonmagnetic Ni alloy, and a nonmagnetic Co alloy A nonmagnetic template layer made of metal or alloy;
A perpendicular magnetization layer formed on the nonmagnetic template layer and formed with ferromagnetic crystal grains containing Co and Pt and nonmagnetic crystal grain boundaries or voids corresponding to crystal grain boundaries;
A perpendicular magnetic recording medium comprising: a protective layer formed on the perpendicular magnetic layer.   In manufacturing the perpendicular magnetic recording medium according to claim 1, the nonmagnetic template layer and the perpendicular magnetization layer have a (sputter gas pressure) × (target-substrate distance) of 15 Pa · cm or more and 200 Pa · cm or less. A method of manufacturing a perpendicular magnetic recording medium, characterized by depositing by sputtering under certain conditions.   3. The method of manufacturing a perpendicular magnetic recording medium according to claim 2, wherein the nonmagnetic substrate is held in an unheated state when all the layers constituting the perpendicular magnetic recording medium are deposited.

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