WO2015001768A1

WO2015001768A1 - Method for producing magnetic recording medium

Info

Publication number: WO2015001768A1
Application number: PCT/JP2014/003400
Authority: WO
Inventors: 由沢　剛; 島津　武仁
Original assignee: 富士電機株式会社
Priority date: 2013-07-03
Filing date: 2014-06-25
Publication date: 2015-01-08
Also published as: JP2015015062A

Abstract

Provided is a method for producing a magnetic recording medium which comprises a magnetic recording layer having excellent thermal stability and good writability. The present invention relates to a method for producing a magnetic recording medium which comprises a non-magnetic base and a magnetic recording layer that is composed of a first magnetic recording layer containing a binary ordered alloy which is composed of a first element and a second element and a second magnetic recording layer containing a ternary or higher-order ordered alloy which is composed of a first element, a second element and one or more additional elements. This method for producing a magnetic recording medium comprises (A) a step for forming the first magnetic recording layer by depositing the binary ordered alloy, while monotonically changing the temperature of the non-magnetic base, and (B) a step for forming the second magnetic recording layer by depositing the ternary or higher-order ordered alloy, while monotonically changing the deposition rate of the additional element(s).

Description

Method for manufacturing magnetic recording medium

The present invention relates to a method for manufacturing a magnetic recording medium. More specifically, the present invention relates to a method of manufacturing a magnetic recording medium that can achieve both excellent thermal stability and good writeability.

垂直 Perpendicular magnetic recording is used as a technology for realizing high density magnetic recording. The perpendicular magnetic recording medium includes at least a nonmagnetic substrate and a magnetic recording layer formed of a hard magnetic material. The perpendicular magnetic recording medium optionally includes a soft magnetic backing layer that plays a role of concentrating the magnetic flux generated by the magnetic head on the magnetic recording layer, and an underlayer for orienting the hard magnetic material of the magnetic recording layer in a desired direction Further, it may further include a protective film for protecting the surface of the magnetic recording layer.

Conventionally, CoCr-based disordered alloy magnetic layers such as CoCrPt have been mainly studied as metal magnetic materials for perpendicular magnetic recording media. In recent years, there has been an urgent need to reduce the grain size of magnetic crystal grains in a magnetic layer for the purpose of further improving the recording density of a perpendicular magnetic recording medium. On the other hand, the reduction in the grain size of the magnetic crystal grains reduces the thermal stability of the recorded magnetization (also referred to as a recording signal). Therefore, in order to compensate for the decrease in thermal stability due to the reduction in the grain size of the magnetic crystal grains, it is required to form the magnetic crystal grains in the magnetic layer using a material having higher magnetocrystalline anisotropy. ing.

As a material having a high crystal magnetic anisotropy required, L1 ₀ type ordered alloys have been proposed. Japanese Patent No. 3318204, Japanese Patent No. 3010156, Japanese Patent Application Laid-Open No. 2001-101645, Japanese Patent Application Laid-Open No. 2004-178653, and Japanese Translation of PCT International Publication No. 2010-503139 are selected from the group consisting of Fe, Co, and Ni. proposes at least one element, Pt, Pd, an L1 ₀ type ordered alloy containing at least one element selected from the group consisting of Au and Ir (see Patent documents 1-5). These L1 ₀ type ordered alloy include FePt, CoPt, FePd, CoPd the like. Furthermore, these documents propose various manufacturing methods L1 ₀ type ordered alloy thin film.

On the other hand, since the thickness of the magnetic recording layer is basically uniform in the in-plane direction of the medium, reducing the magnetic crystal grain reduces the cross-sectional area of the magnetic crystal grain having a certain height. Means. As a result, the demagnetizing field acting on the magnetic crystal grains themselves is reduced, and the magnetic field (reversal magnetic field) necessary for reversing the magnetization of the magnetic crystal grains is increased. Thus, when considered in terms of the shape of magnetic crystal grains, the improvement in recording density means that a larger magnetic field is required when writing magnetization (or recording signals). In other words, as the recording density increases, the problem that the writeability of the magnetic recording medium decreases becomes obvious.

In an attempt to improve the writeability of magnetic recording media while maintaining the thermal stability of the recording signal, Chen et al. Describe a bottom layer having a high magnetic anisotropy constant (Ku), a middle layer having a moderate Ku, and a low Ku. A magnetic recording medium having a graded magnetic recording layer that is stacked in the order of the top layer having a magnetic layer has been proposed (see Non-Patent Document 1). Here, the bottom layer, middle layer and top layer has a granular structure consisting of L1 ₀ type FePt ordered alloy and C grain boundaries. Then, the bottom layer, by changing the formation temperature of the middle layer and top layer was adjusted rules of the L1 ₀ type FePt ordered alloy, and controls the respective layers of Ku. Chen et al. Reported that the high Ku layer alone had a coercivity of 11.4 kOe (about 907 A / mm), but the three-layer configuration described above reduced the coercivity to 5.9 kOe (about 470 A / mm). is doing.

Zha et al. Also proposed a gradient magnetic film having a magnetic recording layer made of an (FePt) _100-x Cu _x alloy and monotonically decreasing the Cu content x from 30 at the bottom to 0 at the top. (See Non-Patent Document 2). Zha et al. Reported that (Fe ₅₃ Pt ₄₇ ) _100- was compared with a magnetic film of uniform composition made of (Fe ₅₃ Pt ₄₇ ) ₈₅ Cu ₁₅ alloy having a coercive force of 7.21 kOe (about 574 A / mm). It is reported that the gradient magnetic film made of _x Cu _x alloy (x monotonously decreases from 30 to 0) has a coercive force of 5.67 kOe (about 451 A / mm).

Further, International Publication No. 2012/105908 pamphlet performs ion implantation into a magnetic recording medium, and the peak of the ion implantation amount is used as the top surface of the magnetic recording layer, so that the ion implantation amount is gradually decreased in the depth direction. The formation of a magnetic recording layer is disclosed (see Patent Document 6). Here, the ions to be implanted are selected from the group consisting of He ⁺ , C ⁺ , N ²⁺ , Ar ⁺ , Co ⁺ and Sb ⁺ .

Japanese Patent No. 3318204 Japanese Patent No. 3010156 JP 2001-101645 A Japanese Patent Application Laid-Open No. 2004-178753 Special table 2010-503139 International Publication No. 2012/105908 Pamphlet

It includes an L1 ₀ type ordered alloys, demand for a method of manufacturing a magnetic recording medium comprising a magnetic recording layer having excellent thermal stability and good writer capability exists.

A method of manufacturing a magnetic recording medium according to the present invention includes a nonmagnetic substrate, a first magnetic recording layer containing a binary ordered alloy composed of a first element and a second element, a first element, a second element, and one kind. Or a method for producing a magnetic recording medium comprising a magnetic recording layer comprising a second magnetic recording layer comprising a ternary or higher order ordered alloy comprising a plurality of additional elements,
(A) depositing a binary ordered alloy while monotonically changing the temperature of the nonmagnetic substrate to form a first magnetic recording layer;
(B) forming a second magnetic recording layer by depositing a ternary or higher order ordered alloy while monotonically changing the deposition rate of the additional element. Here, it is preferable that the step (A) is performed before the step (B) to form the second magnetic recording layer on the first magnetic recording layer.

Further, when the step (A) is performed before the step (B), it is desirable that the temperature of the non-magnetic substrate is monotonously lowered in the step (A). The temperature of the nonmagnetic substrate at the end of the step (A) is a temperature not less than the maximum value of the temperature range in which the binary ordered alloy transitions from the disordered phase to the ordered phase, more preferably from the disordered phase to the ordered phase. It can be set to a temperature that is 20 ° C. or more higher than the maximum value of the above-mentioned temperature range where the transition occurs.

Furthermore, when the step (A) is performed before the step (B), it is desirable to monotonically increase the deposition rate of the additional element in the step (B). Specifically, the deposition rate of the additional element can be monotonously increased by performing the step (B) by a sputtering method and increasing the sputtering power. Preferably, the sputtering power of the additional element is 0 at the start of step (B), and the temperature of the nonmagnetic substrate can be made equal to the temperature of the nonmagnetic substrate at the end of step (A).

In the first magnetic recording layer and the second magnetic recording layer, the first element is at least one element selected from the group consisting of Fe, Co, and Ni, and the second element is Pt, Pd, Au And at least one element selected from the group consisting of Ir and Ir. In addition, each of the first magnetic recording layer and the second magnetic recording layer may further include a nonmagnetic grain boundary material. The nonmagnetic grain boundary material that can be used is at least one selected from the group consisting of C, B, Ag, Ge, W, SiO ₂ , Al ₂ O ₃ , TiO ₂ , GeO _2, and B ₂ O ₃ . Material can be included.

By adopting the above configuration, a magnetic recording layer having excellent thermal stability and good writeability and a magnetic recording medium including the magnetic recording layer can be manufactured by a simple method.

It is sectional drawing which shows the structural example of the magnetic recording medium obtained by the method of this invention. 3 is a graph showing a substrate temperature profile when forming a first magnetic recording layer in Example 1. FIG. 3 is a graph showing a sputtering power profile of a Cu target when forming a second magnetic recording layer in Example 1. FIG. 6 is a graph showing a substrate temperature profile when forming a first magnetic recording layer in Comparative Example 1; 10 is a graph showing a sputtering power profile of a Cu target when forming a second magnetic recording layer in Comparative Example 2.

A magnetic recording medium produced by the method according to the present invention includes a nonmagnetic substrate and a magnetic recording layer, and the magnetic recording layer includes a first ordered magnetic recording including a binary ordered alloy composed of a first element and a second element. And a second magnetic recording layer including a ternary or higher order ordered alloy composed of a first element, a second element, and one or more additional elements. A configuration example of a magnetic recording medium is shown in FIG. In the configuration example of FIG. 1, the magnetic recording medium includes a nonmagnetic substrate 10, a soft magnetic backing layer 20, a seed layer 30, a magnetic recording layer 40, a protective layer 50, and a liquid lubricant layer 60. The first magnetic recording layer 41 and the second magnetic recording layer 42 are included. Here, the soft magnetic backing layer 20, the seed layer 30, the protective layer 50, and the liquid lubricant layer 60 are optional constituent layers that can be provided as necessary. The magnetic recording medium manufactured by the method according to the present invention may further include an adhesion layer, an intermediate layer, and the like between the nonmagnetic substrate 10 and the magnetic recording layer 40.

The nonmagnetic substrate 10 may be various substrates having a smooth surface. For example, the nonmagnetic substrate 10 can be formed using a material generally used for a magnetic recording medium (Al alloy plated with NiP, tempered glass, crystallized glass, etc.).

The soft magnetic backing layer 20 which may be optionally provided controls the magnetic flux from the magnetic head and improves the recording / reproducing characteristics of the magnetic recording medium. Materials for forming the soft magnetic backing layer 20 include NiFe alloy, Sendust (FeSiAl) alloy, crystalline material such as CoFe alloy, microcrystalline material such as FeTaC, CoFeNi, CoNiP, and Co alloy such as CoZrNb and CoTaZr. Including amorphous material. The optimum value of the thickness of the soft magnetic underlayer 20 depends on the structure and characteristics of the magnetic head used for magnetic recording. When the soft magnetic backing layer 20 is formed by continuous film formation with other layers, the soft magnetic backing layer 20 preferably has a thickness in the range of 10 nm to 500 nm (including both ends) in consideration of productivity. .

An adhesion layer (not shown) that may be optionally provided is used to improve adhesion between a layer formed thereon and a layer (including the nonmagnetic substrate 10) formed thereunder. When the adhesion layer is provided on the upper surface of the nonmagnetic substrate 10, the adhesion layer can be formed using a material having good adhesion to the material of the nonmagnetic substrate 10 described above. Such materials include CrTi alloys and the like. Alternatively, when the adhesion layer 20 is formed between two constituent layers other than the non-magnetic substrate 10, the material for forming the adhesion layer is a metal such as Ni, W, Ta, Cr, Ru, or the aforementioned metal. Including alloys. The adhesion layer may be a single layer or may have a laminated structure of a plurality of layers.

The function of the seed layer 30 is to control the grain size and crystal orientation of the magnetic crystal grains in the upper magnetic recording layer 40. The seed layer 30 may have a function of ensuring adhesion between the layer under the seed layer 30 and the magnetic recording layer 40. Further, another layer such as an intermediate layer may be disposed between the seed layer 30 and the magnetic recording layer 40. When an intermediate layer or the like is disposed, the seed layer 30 has a function of controlling the grain size and crystal orientation of the magnetic crystal grains of the magnetic recording layer 40 by controlling the grain size and crystal orientation of the crystal grains of the intermediate layer and the like. Will bear. The seed layer 30 is preferably nonmagnetic. The material of the seed layer 30 is appropriately selected according to the material of the magnetic recording layer 40. More specifically, the material of the seed layer 30 is selected according to the material of the magnetic crystal grains of the magnetic recording layer. For example, if the magnetic crystal grains in the magnetic recording layer 40 is formed by L1 ₀ type ordered alloy, it is preferable to form the seed layer 30 by using a NaCl-type compounds. Particularly preferably, the seed layer 30 is formed using an oxide such as MgO or SrTiO ₃ or a nitride such as TiN. The seed layer 30 can also be formed by stacking a plurality of layers made of the above materials. From the viewpoint of improving the crystallinity of the magnetic crystal grains of the magnetic recording layer 40 and improving the productivity, the seed layer 30 preferably has a thickness of 1 nm to 60 nm, preferably 1 nm to 20 nm. The seed layer 30 can be formed using any method known in the art, such as sputtering (including RF magnetron sputtering, DC magnetron sputtering, etc.), vacuum deposition, and the like.

The intermediate layer (not shown) is a layer disposed to increase the crystal orientation of the magnetic recording layer 40 and to control the size of the magnetic crystal grains in the magnetic recording layer 40. The intermediate layer may have a function of inheriting the crystal structure of the layer formed under the intermediate layer and inheriting it to the magnetic recording layer 40. Further, when the soft magnetic backing layer 20 is provided, the intermediate layer may have a function of suppressing the magnetic influence of the soft magnetic backing layer 20 on the magnetic recording layer 40. The intermediate layer is preferably nonmagnetic. Materials for forming the intermediate layer include metals such as Cr and Ta, NiW alloys, and alloys based on Cr such as CrTi, CrZr, CrTa, and CrW. The intermediate layer can be formed using any method known in the art, such as sputtering.

The protective layer 50 can be formed using a material conventionally used in the field of magnetic recording media. Specifically, the protective layer 50 can be formed using a carbon-based material such as diamond-like carbon or a silicon-based material such as silicon nitride. The protective layer 50 may be a single layer or may have a laminated structure. The laminated protective layer 50 may be, for example, a laminated structure of two types of carbon materials having different characteristics, a laminated structure of a metal and a carbon material, or a laminated structure of a metal oxide film and a carbon material. Good. The protective layer 50 can be formed using any method known in the art, such as CVD, sputtering (including DC magnetron sputtering), and vacuum deposition.

Also, optionally, the magnetic recording medium of the present invention may further include a liquid lubricant layer 60 provided on the protective layer 50. The liquid lubricant layer 60 can be formed using a material conventionally used in the field of magnetic recording media (for example, a perfluoropolyether lubricant). The liquid lubricant layer 60 can be formed using, for example, a coating method such as a dip coating method or a spin coating method.

The magnetic recording layer 40 includes a first magnetic recording layer 41 including a binary ordered alloy composed of a first element and a second element, a first element, a second element, and three or more kinds of additional elements. And a second magnetic recording layer 42 containing an ordered alloy of the original or higher system. The stacking order of the first magnetic recording layer 41 and the second magnetic recording layer 42 can be arbitrarily set. A configuration in which the first magnetic recording layer 41 is a layer close to the nonmagnetic substrate 10 and the second magnetic recording layer 42 is formed on the first magnetic recording layer 41 is preferable. FIG. 1 shows a preferred configuration in which a first magnetic recording layer 41 and a second magnetic recording layer 42 are laminated in order from the nonmagnetic substrate 10 side.

The first magnetic recording layer 41 may be composed of only a binary ordered alloy or has a granular structure composed of magnetic crystal grains composed of a binary ordered alloy and nonmagnetic grain boundaries. May be. Similarly, the second magnetic recording layer 42 may be composed of only a ternary or higher order ordered alloy, or a magnetic crystal grain made of a ternary or higher order ordered alloy and a nonmagnetic grain boundary. You may have the granular structure comprised.

The binary ordered alloy in the first magnetic recording layer 41 is composed of a first element and a second element. Preferably, binary ordered alloy is L1 ₀ type ordered alloy. The first element includes at least one element selected from the group consisting of Fe, Co, and Ni. The second element includes at least one element selected from the group consisting of Pt, Pd, Au, and Ir. Preferred binary ordered alloys include FePt, CoPt, FePd, CoPd, and the like. The ordered alloy of the ternary or higher system in the second magnetic recording layer 42 is composed of a first element, a second element, and one or more additional elements. Preferably, it ordered alloy ternary or more systems are L1 ₀ type ordered alloy. The first element and the second element are equivalent to the binary ordered alloy in the first magnetic recording layer 41. The additional elements include nonmagnetic elements such as Cu, Mn, Ni, Ag, and Ti. Preferred ternary or higher order ordered alloys include FePtCu, FePtMn, CoPtNi, and the like.

When the first magnetic recording layer 41 and / or the second magnetic recording layer 42 has a granular structure, the material of the nonmagnetic grain boundary is at least one selected from the group consisting of C, B, Ag, Ge, and W Or an oxide selected from the group consisting of SiO ₂ , Al ₂ O ₃ , TiO ₂ , GeO ₂ and B ₂ O ₃ .

The first magnetic recording layer 41 and the second magnetic recording layer 42 can be formed by a sputtering method. When forming the first magnetic recording layer 41, it is preferable to use a target containing the first element and the second element in a predetermined ratio. For the formation of the first magnetic recording layer 41 having a granular structure, a target including a first element, a second element, and a nonmagnetic grain boundary material in a predetermined ratio can be used.

In forming the second magnetic recording layer 42, it is preferable to use a target containing the first element and the second element at a predetermined ratio and a target containing an additional element. In forming the second magnetic recording layer 42, it is necessary to independently control the sputtering power for the target containing the first element and the second element and the sputtering power for the target containing the additional element. . In forming the second magnetic recording layer 42 having a granular structure, a nonmagnetic grain boundary material in a predetermined ratio is added to a target including the first element and the second element.

The first magnetic recording layer 41 and the second magnetic recording layer 42 each have uniaxial magnetic anisotropy in a direction perpendicular to the surface of the layer (that is, the film formation surface of the nonmagnetic substrate 10). The magnetic recording layer 40 has a distribution of a magnetic anisotropy constant Ku that monotonously changes from the outer surface of the first magnetic recording layer 41 toward the outer surface of the second magnetic recording layer 42. In this specification, the “outer surface” of the first magnetic recording layer 41 and the second magnetic recording layer 42 is opposite to the interface between the first magnetic recording layer 41 and the second magnetic recording layer 42 in each layer. Means the side face. Preferably, the magnetic recording layer 40 has a distribution of a magnetic anisotropy constant Ku that continuously changes from the outer surface of the first magnetic recording layer 41 toward the outer surface of the second magnetic recording layer 42. The “monotonic change” in this specification means that a certain characteristic value always increases or decreases along the film thickness direction. Monotonic changes allow the presence of discontinuities in characteristic values. The “continuous change” in this specification means a monotonous change in which there is no discontinuous point of the characteristic value.

The distribution of the magnetic anisotropy constant Ku in the first magnetic recording layer 41 is such that the temperature of the nonmagnetic substrate at the time of formation (hereinafter simply referred to as “substrate temperature”) is monotonously changed, and the degree of order of the binary ordered alloy is changed. Can be obtained by changing monotonously. Ku may be increased from the lower surface to the upper surface of the first magnetic recording layer 41 by monotonically increasing the substrate temperature at the time of formation and monotonically increasing the degree of order of the binary ordered alloy. Alternatively, Ku may be decreased from the lower surface to the upper surface of the first magnetic recording layer 41 by monotonically lowering the substrate temperature during formation and monotonously lowering the degree of order of the binary ordered alloy. . The change in the substrate temperature during formation is preferably continuous. It is desirable that the minimum temperature at the time of forming the first magnetic recording layer 41 be equal to or higher than the maximum value in the temperature region where the transition between the disordered phase and the ordered phase of the binary ordered alloy occurs. More preferably, the minimum temperature at the time of forming the first magnetic recording layer 41 is set to a temperature that is 20 ° C. or more higher than the maximum value in the temperature range where the transition between the disordered phase and the ordered phase of the binary ordered alloy occurs. be able to. The lowest temperature when forming the first magnetic recording layer 41 is the substrate temperature at the end of the formation of the first magnetic recording layer 41 when the substrate temperature is monotonously lowered, and when the substrate temperature is monotonically raised, the first magnetic recording layer is formed. This is the substrate temperature at the start of layer 41 formation.

The distribution of the magnetic anisotropy constant Ku in the second magnetic recording layer 42 can be obtained by monotonically changing the sputtering power of the additional element and monotonically changing the deposition rate of the additional element at the time of formation. Ku may be decreased from the lower surface to the upper surface of the second magnetic recording layer 42 by monotonically increasing the sputtering power of the additional element during the formation and monotonically increasing the deposition rate of the additional element. Alternatively, Ku may be increased from the lower surface to the upper surface of the second magnetic recording layer 42 by monotonically decreasing the sputtering power of the additional element and monotonically decreasing the deposition rate of the additional element during formation. The change in sputtering power of the additional element during formation is preferably continuous.

In order to make the distribution of the magnetic anisotropy constant Ku of the magnetic recording layer 40 continuous, it is preferable to match the sputtering conditions of both layers at the interface between the first magnetic recording layer 41 and the second magnetic recording layer 42. The sputtering conditions to be matched include the types and ratios of the first element and the second element, the ratio of the additional element, and the substrate temperature. It is desirable that the first element and the second element used in the first magnetic recording layer 41 and the second magnetic recording layer 42 are the same and the ratios thereof are also the same. In the case of forming the first magnetic recording layer 41 and the second magnetic recording layer 42 in this order from the nonmagnetic substrate 10 side, the substrate temperature at the time of forming the first magnetic recording layer 41 is monotonously lowered, and the second magnetic recording layer 42 is formed. The substrate temperature during the formation of the first magnetic recording layer 41 is set as the temperature at the end of the formation of the first magnetic recording layer 41, and the sputtering power of the additional element during the formation of the second magnetic recording layer 42 is monotonously increased from 0, thereby increasing the magnetic anisotropy. A continuous distribution of the constant Ku can be achieved. On the other hand, when the second magnetic recording layer 42 and the first magnetic recording layer 41 are formed in this order from the non-magnetic substrate 10 side, the sputtering power of the additional element at the time of forming the second magnetic recording layer 42 is monotonously decreased to be the final. The substrate temperature at the time of forming the first magnetic recording layer 41 is monotonically increased from the temperature at the end of the formation of the second magnetic recording layer 42, thereby achieving a continuous distribution of the magnetic anisotropy constant Ku. can do.

In the preferred magnetic recording medium obtained by the method of the present invention, when forming the first magnetic recording layer 41 containing a binary ordered alloy having a relatively high Ku, the distribution of Ku is controlled by the substrate temperature at the time of formation. There is a problem that Ku cannot be appropriately controlled when Ku is to be changed greatly depending on the substrate temperature. For example, if the binary ordered alloy consisting of FePt, transition between the L1 ₀ ordered phase and A1 disordered phase in the temperature range of 300 ° C. ~ 350 ° C. is rapidly generated. Therefore, it is difficult to appropriately control Ku in a region where Ku is relatively low. In the method of the present invention, by combining with the second magnetic recording layer 42, the substrate temperature at the time of forming the first magnetic recording layer 41 is changed to a temperature at which a transition between an irregular phase and an ordered phase occurs (for example, FePt Therefore, the distribution of Ku in the first magnetic recording layer 41 can be satisfactorily controlled.

On the other hand, in the preferred magnetic recording medium obtained by the method of the present invention, when the second magnetic recording layer 42 containing a ternary or higher order ordered alloy having a relatively low Ku is formed, the deposition rate of the additional element causes the Ku to increase. Control the distribution. In a region where the amount of additional element added to the ordered alloy is a certain amount or more, there is a problem that the decrease in saturation magnetization (Ms) becomes significant. For this reason, obtaining a wide distribution of Ku only with the deposition rate of the additional element may reduce the uniformity of Ms. In the present invention, by combining with the first magnetic recording layer 41, the deposition rate of the additional element in the second magnetic recording layer 42 can be limited to a narrow range of a certain amount or less, and the uniformity of Ms is ensured. It becomes possible.

As a result, it is possible to continuously change Ku in the film thickness direction over a wide range that is impossible with the first magnetic recording layer 41 or the second magnetic recording layer 42 alone, and at the same time, the first magnetic recording layer 41 and the second magnetic recording layer. Uniformity of Ms in 42 can be ensured. The obtained magnetic recording layer 40 exhibits excellent writeability by sufficiently reducing the coercive force, and at the same time exhibits excellent thermal stability of the recording signal even when the recording density is improved.

Example 1
A chemically strengthened glass substrate having a smooth surface (N-10 glass substrate manufactured by HOYA) was washed to prepare a nonmagnetic substrate 10. The nonmagnetic substrate 10 after cleaning was introduced into the sputtering apparatus.

Then, the soft magnetic backing layer 20 was formed by a DC magnetron sputtering method using a NiFe target in Ar gas at a pressure of 0.67 Pa.

Next, a seed layer 30 having a two-layer structure composed of a Ta layer and an MgO layer was formed. Specifically, a 10 nm-thick Ta layer was formed by DC magnetron sputtering using a Ta target in Ar gas at a pressure of 0.67 Pa. Next, the stacked body on which the Ta layer is formed is heated to 250 ° C., an MgO layer having a thickness of 5 nm is formed by RF sputtering using an MgO target in an Ar gas having a pressure of 0.06 Pa, and the seed layer 30 is formed. Got.

Next, the stacked body on which the seed layer 30 was formed was heated to 500 ° C. A first magnetic recording layer 41 made of Fe ₅₀ Pt ₅₀ —SiO ₂ having a thickness of 10 nm is formed using an Fe ₅₀ Pt ₅₀ —SiO ₂ target in which 80 volume% Fe ₅₀ Pt ₅₀ and 20 volume percent SiO ₂ are mixed. Formed. Here, the film thickness of the deposited layer was monitored using a film thickness measurement sensor disposed in the chamber of the sputtering apparatus. In addition, as shown in FIG. 2, the substrate temperature was continuously lowered with respect to the film thickness, and the final substrate temperature was set to 370.degree.

Next, the second magnetic recording layer 42 made of (Fe ₅₀ Pt ₅₀ ) _x Cu _(1-x) ₂ -SiO ₂ with a film thickness of 10 nm is formed using the aforementioned Fe ₅₀ Pt ₅₀ —SiO ₂ target and Cu target. Thus, the magnetic recording layer 40 was obtained. Here, the substrate temperature was fixed at 370 ° C., which is the final substrate temperature when the first magnetic recording layer 41 was formed. In addition, the sputtering power of the Cu target was continuously increased as shown in FIG. 3 with respect to the film thickness monitored using the film thickness measurement sensor. In this example, the sputtering power of the Cu target was changed from 0 W at the start of formation to 80 W at the end of formation.

Next, a protective layer 50 made of carbon having a thickness of 2 nm was formed by a DC magnetron sputtering method using a carbon target in an Ar gas atmosphere. After the formation of the protective layer 50, the stacked body was taken out from the sputtering apparatus. Finally, perfluoropolyether was applied using a dip coating method to form a liquid lubricant layer 60 having a thickness of 2 nm to obtain the magnetic recording medium shown in FIG.

(Comparative Example 1)
The second magnetic recording layer 42 ((Fe ₅₀ Pt ₅₀ ) _x Cu _(1-x) ₂ —SiO ₂ layer) was not formed, and the film of the first magnetic recording layer 41 (Fe ₅₀ Pt ₅₀ —SiO ₂ layer) The procedure of Example 1 was repeated except that the thickness was 20 nm and the substrate temperature during the formation of the first magnetic recording layer 41 was continuously changed from 500 ° C. to 300 ° C. as shown in FIG. Thus, a magnetic recording medium having a single-layer magnetic recording layer was obtained.

(Comparative Example 2)
The first magnetic recording layer 41 (Fe ₅₀ Pt ₅₀ —SiO ₂ layer) was not formed, and the second magnetic recording layer 42 ((Fe ₅₀ Pt ₅₀ ) _x Cu _(1-x) —SiO ₂ layer) was formed. FIG. 5 shows the thickness of 20 nm, the substrate temperature at the time of forming the second magnetic recording layer 42 fixed at 370 ° C., and the sputtering power of the Cu target at the time of forming the second magnetic recording layer 42 with respect to the film thickness. Thus, the procedure of Example 1 was repeated except that the power was continuously increased from 0 W to 120 W to obtain a magnetic recording medium having a single-layered magnetic recording layer.

(Comparative Example 3)
The second magnetic recording layer 42 ((Fe ₅₀ Pt ₅₀ ) _x Cu _(1-x) ₂ —SiO ₂ layer) was not formed, and the film of the first magnetic recording layer 41 (Fe ₅₀ Pt ₅₀ —SiO ₂ layer) The procedure of Example 1 was repeated except that the thickness was 20 nm and the substrate temperature during the formation of the first magnetic recording layer 41 was fixed at 500 ° C. A medium was obtained.

(Comparative Example 4)
The procedure of Example 1 was performed except that the substrate temperature during the formation of the first magnetic recording layer 41 was fixed at 500 ° C. and the sputtering power of the Cu target during the formation of the second magnetic recording layer 42 was fixed at 120 W. Repeatedly, a magnetic recording medium having a two-layer magnetic recording layer was obtained.

(Evaluation)
For each of the magnetic recording media manufactured in Example 1 and Comparative Examples 1 to 4, the magnetization curve was measured with a vibrating sample magnetometer (VSM) to determine the coercive force Hc. Furthermore, the dynamic coercive force of each magnetic recording medium was measured at a plurality of kinds of time scales, by fitting the results to equations Sherlock, thermal stability index at an absolute temperature of 300K β (= ΔE / k b T, ΔE energy barrier, k _b is the Boltzmann constant, T is sought absolute temperature) it is. Table 1 shows the formation conditions, Hc and β of the magnetic recording layer of each magnetic recording medium.

As is apparent from Table 1, the magnetic recording medium of Example 1 according to the present invention has Hc of 7.5 kOe (about 597 A / mm), and has a magnetic recording layer composed only of the first magnetic recording layer 41. The magnetic recording medium of Comparative Example 3 had a Hc of 15.3 kOe (about 1220 A / mm). The magnetic recording medium of Example 1 has Hc reduced by about 50% compared to the magnetic recording medium of Comparative Example 3. On the other hand, compared with the magnetic recording medium of Comparative Example 3, the decrease in β of the magnetic recording medium of Example 1 was about 20%. From this, it can be seen that the magnetic recording medium of Example 1 according to the present invention achieves both excellent writeability and high thermal stability of the recording signal.

Further, in the magnetic recording medium including only the first magnetic recording layer 41 containing the binary system ordered alloy, the magnetic recording medium of Comparative Example 1 in which the substrate temperature change range is expanded to 500 ° C. to 300 ° C. is the same as that of Example 1. Although it showed the same β, it had a clearly higher Hc compared with Example 1. This is because the continuity of the change of Ku in the film thickness direction at 350 ° C. as a boundary is impaired by the abrupt transition from the L1 ₀ ordered phase to the A1 disordered phase in the temperature range of 300 ° C. to 350 ° C. This is thought to be due to this. On the other hand, in Example 1 of the present invention, the final substrate temperature during the first magnetic recording layer 41 formed is 370 ° C., transition from L1 ₀ ordered phase of FePt alloy with the A1 disordered phase is not generated, the ideal It is thought that a typical Ku distribution was obtained.

Further, the magnetic recording medium of Comparative Example 2 in which the change range of the sputtering power of the Cu target is expanded from 0 W to 120 W in the magnetic recording medium consisting only of the second magnetic recording layer 42 made of the ternary ordered alloy is also an example. Although β of the same level as 1 was exhibited, it had a clearly higher Hc compared to Example 1. This is presumably because the Ms decrease with the increase of the Cu concentration becomes remarkable at the upper part of the second magnetic recording layer 42, and the uniformity of Ms in the film thickness direction is lowered. On the other hand, in Example 1 according to the present invention, the sputtering power of the Cu target at the time of forming the second magnetic recording layer 42 is 80 W at maximum, and it is considered that an excessive decrease in Ms was suppressed and an ideal Ku distribution was obtained. It is done.

In addition, the magnetic recording medium of Comparative Example 4 in which the substrate temperature at the time of forming the first magnetic recording layer 41 and the sputtering power of the Cu target at the time of forming the second magnetic recording layer 42 are fixed has a conventional hard / soft stack structure. It is a magnetic recording medium. In comparison with the magnetic recording medium of Comparative Example 4, the magnetic recording medium of Example 1 had a Hc decreased by about 34%, although a β reduction of about 6% was observed. From this, it can be seen that the magnetic recording medium of Example 1 according to the present invention has excellent writeability and high thermal stability of the recording signal as compared with the conventional magnetic recording medium.

DESCRIPTION OF SYMBOLS 10 Nonmagnetic base material 20 Soft magnetic backing layer 30 Seed layer 40 Magnetic recording layer 41 1st magnetic recording layer 42 2nd magnetic recording layer 50 Protective layer 60 Liquid lubricant layer

Claims

A nonmagnetic substrate, a first magnetic recording layer including a binary ordered alloy composed of a first element and a second element, and a ternary or more composed of a first element, a second element, and one or more additional elements. A magnetic recording medium comprising a magnetic recording layer comprising a second magnetic recording layer containing an ordered alloy of the following system:
(A) depositing a binary ordered alloy while monotonically changing the temperature of the nonmagnetic substrate to form a first magnetic recording layer;
And (B) depositing a ternary or higher system ordered alloy while monotonically changing the deposition rate of the additional element to form a second magnetic recording layer, and a method for manufacturing a magnetic recording medium .
2. The magnetic recording medium according to claim 1, wherein step (A) is performed before step (B) to form the second magnetic recording layer on the first magnetic recording layer. 3. Production method.
3. The method of manufacturing a magnetic recording medium according to claim 2, wherein in step (A), the temperature of the non-magnetic substrate is monotonously lowered.
The temperature of the nonmagnetic substrate at the end of the step (A) is equal to or higher than a maximum value in a temperature region in which a transition between the disordered phase and the ordered phase of the binary ordered alloy occurs. 4. A method for producing a magnetic recording medium according to item 3.
The temperature of the nonmagnetic substrate at the end of the step (A) is 20 ° C. or more higher than the maximum value in the temperature region where the transition between the disordered phase and the ordered phase of the binary ordered alloy occurs. The method for manufacturing a magnetic recording medium according to claim 4.
3. The method of manufacturing a magnetic recording medium according to claim 2, wherein in the step (B), the deposition rate of the additional element is monotonously increased.
7. The method of manufacturing a magnetic recording medium according to claim 6, wherein the step (B) is performed by a sputtering method, and the deposition rate of the additional element is monotonously increased by increasing the sputtering power.
The sputtering power of the additional element is 0 at the start of the step (B), and the temperature of the nonmagnetic substrate is equal to the temperature of the nonmagnetic substrate at the end of the step (A). Manufacturing method of magnetic recording medium.
The first element of the first magnetic recording layer and the second magnetic recording layer is at least one element selected from the group consisting of Fe, Co, and Ni, and the first magnetic recording layer and the second magnetic recording layer 2. The method of manufacturing a magnetic recording medium according to claim 1, wherein the second element of the recording layer is at least one element selected from the group consisting of Pt, Pd, Au, and Ir.
The method of manufacturing a magnetic recording medium according to claim 1, wherein each of the first magnetic recording layer and the second magnetic recording layer further includes a nonmagnetic grain boundary material.
The nonmagnetic grain boundary material includes at least one material selected from the group consisting of C, B, Ag, Ge, W, SiO 2 , Al 2 O 3 , TiO 2 , GeO 2, and B 2 O 3. The method of manufacturing a magnetic recording medium according to claim 10.