JP6607291B2 - Magnetic recording medium - Google Patents

Description

  The invention described in this specification relates to a magnetic recording medium. Specifically, the invention described in the present specification relates to a magnetic recording medium used in an energy assisted magnetic recording system. More specifically, the invention described in this specification relates to a magnetic recording medium used in a heat-assisted magnetic recording system.

  As a technique for realizing high density magnetic recording, a perpendicular magnetic recording system is adopted. 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 is optionally formed of a soft magnetic material, and 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 a hard magnetic material of the magnetic recording layer. It may further include a seed layer for orientation in the direction, a protective film for protecting the surface of the magnetic recording layer, and the like.

  In recent years, there has been an urgent need to reduce the grain size of magnetic crystal grains in a magnetic recording 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 (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 using a material having higher magnetocrystalline anisotropy.

As a material having a high crystal magnetic anisotropy required, L1 ₀ type ordered alloys have been proposed. International Publication No. 2013/140469 (Patent Document 1) discloses at least one element selected from the group consisting of Fe, Co and Ni and at least one selected from the group consisting of Pt, Pd, Au and Ir. It describes an L1 ₀ type ordered alloy containing seeds elements. Typical L1 ₀ type ordered alloys include FePt, CoPt, FePd, CoPd, and the like.

  However, a magnetic recording medium having a magnetic recording layer formed of a material having high magnetic anisotropy has a large coercive force, and recording of magnetization (signal) is difficult. In order to overcome this recording difficulty, energy assisted magnetic recording methods such as a heat assisted recording method and a microwave assisted recording method have been proposed. The heat-assisted recording method utilizes the temperature dependence of the magnetic anisotropy constant (Ku) in the magnetic material, that is, the characteristic that Ku becomes smaller as the temperature increases. In this method, a head having a function of heating the magnetic recording layer is used. That is, by increasing the temperature of the magnetic recording layer and temporarily lowering Ku, the reversal magnetic field is reduced, and writing is performed during that time. Since Ku returns to the original high value after the temperature is lowered, the recording signal (magnetization) can be held stably. International Publication No. 2013/140469 (Patent Document 1) proposes a method for facilitating heat-assisted magnetic recording by increasing the temperature gradient in the in-plane direction of the magnetic recording layer during recording.

  When the heat-assisted recording method is used, it is necessary to provide means for heating the magnetic recording layer in the magnetic head used for recording. However, there are limitations on the heating means that can be employed due to various requirements for the magnetic head. Considering this point, it is desirable to lower the heating temperature of the magnetic recording layer during recording as much as possible. One index of the heating temperature is the Curie temperature Tc. The Curie temperature Tc of the magnetic material means a temperature at which the magnetism of the material is lost. By reducing the Curie temperature Tc of the material of the magnetic recording layer, the magnetic anisotropy constant Ku at a given temperature is lowered, and recording at a lower heating temperature is possible.

However, there is a strong correlation between the Curie temperature Tc of the magnetic material and the magnetic anisotropy constant Ku. In general, a material having a large magnetic anisotropy constant Ku has a high Curie temperature Tc. For this reason, conventionally, the reduction of the heating temperature is prioritized, and the magnetic anisotropy constant Ku is reduced to lower the Curie temperature Tc. Regarding this problem, Japanese Patent Application Laid-Open No. 2009-059461 (Patent Document 2) relaxes the correlation between Ku and Tc by providing a plurality of magnetic layers and setting different Ku and Tc in each magnetic layer. Proposals have been made. Specifically, this document proposes a magnetic recording layer that includes a first layer having a _first Curie temperature Tc ₁ and a second layer having a second Curie temperature Tc ₂ , where Tc ₁ is higher than Tc _2. doing. In this magnetic recording layer, by heating to a temperature equal to or higher than Tc ₂ , exchange coupling between the first layer and the second layer disappears, and magnetization can be recorded in the first layer.

Further, in order to improve other various performances, attempts to introduce various additional element L1 ₀ type ordered alloy have been made. For example, JP 2003-313659 (Patent Document 3), and elements constituting the L1 ₀ type ordered alloy, and a added element, the oxygen content is proposed sputtering sintered target is 1000ppm or less Yes. Thin film formed by using this target is described as rules of L1 ₀ type ordered alloy at lower annealing temperatures can be achieved. In particular, Cu, when added Au or the like is to be further promoted ordering of the L1 ₀ type ordered alloy. Further, JP 2003-313659 discloses that be separated by non-magnetic material between the magnetic crystal grains of L1 ₀ type structure contributes to the improvement of magnetic recording density. Nonmagnetic elements and nonmagnetic compounds arranged around the magnetic crystal grains to magnetically separate the magnetic crystal grains are listed. As examples of such materials, various materials including Ru, Rh and the like are described.

On the other hand, U.S. Patent Application Publication No. 2003/0162055 Pat (Patent Document 4), (CoX) ₃ Pt or (CoX) ₃ having a composition of PtY, polycrystalline rules having different ordered structure is an L1 ₀ type A magnetic recording layer made of an alloy has been proposed. Here, the additive element X has the effect of moving to the crystal grain boundary and promoting magnetic separation between the magnetic crystal grains, and the additive material Y includes the magnetic properties of the obtained polycrystalline ordered alloy, the magnetic crystal grains It has the effect of facilitating the control of distribution and magnetic separation. US 2003/0162055 describes various materials including Ru, Rh, etc. as examples of the additive element X.

  However, at present, research on Ru as a material added to ordered alloys has hardly progressed. Little research has been done on the magnetic properties of ordered alloys with the addition of Ru, in particular the gradient of the anisotropic magnetic field with temperature in such ordered alloys.

International Publication No. 2013/140469 JP 2009-059461 A JP 2003-313659 A US Patent Application Publication No. 2003/0162055

H. J. Richter et al., "Direct Measurement of the Thermal Gradient in Heat Assisted Magnetic Recording" IEEE Transactions on Magnetics, Vol. 49, No. 10, pp. 5378-5381 (2013) Igarashi Manaka, et al., “Examination of heat-assisted recording by simulation: Examination of recording method”, IEICE Technical Report, vol. 104, pp. 1-6 (2004)

  The problem to be solved by the present invention is to provide a magnetic recording medium capable of realizing a high recording density by reducing the bit transition width in the heat recording process of the heat-assisted magnetic recording medium. More specifically, the problem to be solved by the present invention is to provide a magnetic recording medium having a magnetic recording layer having a large gradient of an anisotropic magnetic field with respect to a temperature change.

One configuration example of the magnetic recording medium according to the first embodiment of the present invention includes a nonmagnetic substrate and a magnetic recording layer, and the magnetic recording layer includes an ordered alloy containing Fe, Pt, and Ru, and the ordered alloy. Includes, based on the total number of atoms of Fe, Pt and Ru, x atomic% Fe, y atomic% Pt and z atomic% Ru, and the x, y and z are represented by the following formula ( i) to (v):
(I) 0.85 ≦ x / y ≦ 1.3;
(Ii) x ≦ 53;
(Iii) y ≦ 51;
(Iv) 0.6 ≦ z ≦ 20; and (v) x + y + z = 100
It is characterized by satisfying. Here, the ordered alloy may be a L1 ₀ type ordered alloy. The magnetic recording layer may have a granular structure including magnetic crystal grains including the ordered alloy and nonmagnetic crystal grain boundaries. The nonmagnetic grain boundary may include at least one material selected from the group consisting of carbon, boron, carbide, oxide, and nitride.

One configuration example of the magnetic recording medium of the second embodiment of the present invention is the same as the configuration example of the first embodiment described above, wherein the magnetic recording layer includes a plurality of magnetic layers, At least one is a magnetic layer containing the ordered alloy. Here, the ordered alloy may be a L1 ₀ type ordered alloy. The magnetic layer containing the ordered alloy may have a granular structure including magnetic crystal grains containing the ordered alloy and nonmagnetic crystal grain boundaries. The nonmagnetic grain boundary may include at least one material selected from the group consisting of carbon, boron, carbide, oxide, and nitride.

  By adopting the above configuration, it is possible to provide a magnetic recording medium having a magnetic recording layer having a large gradient of an anisotropic magnetic field with respect to a temperature change. The obtained magnetic recording medium has a reduced bit transition width in the heating recording process and can cope with high-density magnetic recording.

It is sectional drawing which shows one structural example of the magnetic recording medium of 1st Embodiment. It is sectional drawing which shows one structural example of the magnetic recording medium of 2nd Embodiment. It is a graph which shows the relationship between the composition of a magnetic-recording layer, and Curie temperature Tc. It is a graph which shows the relationship between the composition of a magnetic-recording layer, and the gradient dHk / dT of an anisotropic magnetic field with respect to a temperature change in the temperature lower than Curie temperature Tc by 60 degreeC. It is a graph which shows the relationship between the composition of a magnetic-recording layer, and the gradient dHk / dT of the anisotropy magnetic field with respect to a temperature change in the temperature 40 degreeC lower than Curie temperature Tc. 6 is a graph showing the relationship between the composition of a magnetic recording layer and the gradient dHk / dT of an anisotropic magnetic field with respect to temperature change at a temperature 20 ° C. lower than the Curie temperature Tc. It is a graph which shows the relationship between the composition of a magnetic-recording layer, and the anisotropic magnetic field Hk in room temperature.

One configuration example of the magnetic recording medium of the first embodiment includes a nonmagnetic substrate and a magnetic recording layer, the magnetic recording layer includes an ordered alloy containing Fe, Pt, and Ru, and the ordered alloy includes Fe , Pt and Ru based on the total number of atoms, including x atom% Fe, y atom% Pt, and z atom% Ru, wherein x, y and z are represented by the following formulas (i) to (V):
(I) 0.85 ≦ x / y ≦ 1.3;
(Ii) x ≦ 53;
(Iii) y ≦ 51;
(Iv) 0.6 ≦ z ≦ 20; and (v) x + y + z = 100
Meet. For example, in the configuration example shown in FIG. 1, the magnetic recording medium includes a nonmagnetic substrate 10, a magnetic recording layer 30, and an optionally provided seed layer 20.

  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 magnetic recording media (Al alloy plated with NiP, tempered glass, crystallized glass, etc.), MgO, or the like.

The magnetic recording layer 30 may be a single layer. The magnetic recording layer 30 composed of a single layer includes an ordered alloy containing Fe, Pt, and Ru. It ordered alloy can be a L1 ₀ type ordered alloy. The contents x, y, and z of Fe, Pt, and Ru expressed in atomic% satisfy the above-described formulas (i) to (v).

  In the heating recording process in the heat-assisted recording system, the magnetic recording layer 30 is heated to near the Curie temperature Tc, and then recorded in the process of being cooled. Hereinafter, the temperature at which magnetization is actually recorded is referred to as “substantially recording temperature”. The Curie temperature Tc of the magnetic material means a temperature at which the ferromagnetism of the magnetic material is lost. As the magnetic crystal grains become finer, the Curie temperature Tc of the magnetic crystal grains is lower than the Curie temperature Tc of the bulk material. In addition, since the recording magnetic field is applied, the heat-assisted recording method can write and fix the magnetization at a temperature lower than the Curie temperature Tc.

  In the heat-assisted recording method, the center of the heating spot by the heating means mounted on the head and the center of the write magnetic pole exist at different positions. Generally, the heating means includes a laser. The distance between the center of the heating spot and the center of the write pole is preferably set to about the bit length. For this reason, the temperature at the center of the write pole at which writing is actually performed (that is, the actual recording temperature) is lower than the maximum heating temperature at the center of the heating spot. The actual recording temperature is estimated to be about the product of the temperature gradient in the heating spot and the bit length. Table 1 shows the relationship between a temperature gradient (° C./nm) and a bit length (nm) at a typical areal recording density (terabit US square inch, Tbpsi) used in a heat-assisted recording type magnetic recording medium.

  From the relationship shown above, the actual recording temperature is approximately 140 ° C. lower than the maximum heating temperature. In order to perform heat-assisted magnetic recording, it is necessary to make the actual recording temperature sufficiently close to the Curie temperature Tc. Therefore, it is necessary to set the maximum heating temperature to a temperature sufficiently higher than the Curie temperature Tc. On the other hand, it is desirable to make the maximum heating temperature as low as possible in order not to apply an excessive load to the heating means. For example, as disclosed in HJ Richter et al., IEEE Transactions on Magnetics, Vol. 49, No. 10, pp. 5378-5381 (2013) (Non-Patent Document 1), the maximum heating temperature is usually the Curie temperature Tc. The temperature is set to about 100 ° C. higher than that. As a result, the actual recording temperature is set to a temperature approximately 40 ° C. lower than the Curie temperature Tc.

  The actual actual recording temperature varies depending on the design concept of the magnetic recording apparatus. Preferably, the substantial recording temperature is assumed to be in a range from a temperature 60 ° C. lower than the Curie temperature Tc to a temperature 20 ° C. lower than the Curie temperature Tc, centering on a temperature 40 ° C. lower than the Curie temperature Tc.

  In order to improve the recording density, it is necessary to increase the gradient (dHk / dT) of the anisotropic magnetic field (Hk) with respect to the temperature change at the actual recording temperature. This is because the bit transition width between recording bits can be reduced by increasing dHk / dT. “Bit transition between recording bits” in a magnetic recording medium means, for example, a region between a region where the magnetization is vertically upward and a region where the magnetization is vertically downward. Igarashi Manaka, et al., “Examination of heat-assisted recording by simulation: Examination of recording method”, IEICE Technical Report, vol. 104, pp. According to 1-6 (2004) (Non-Patent Document 2), the bit transition width is defined by a length that does not invert the magnetization of adjacent bits during recording, and more specifically is 0.5 × bit length. Assuming that the recording magnetic field is Hsw and the recording magnetic field gradient variance is σHsw, the bit transition width is given by 5 × (2 × σHsw) / (dHsw / dT) when the bit transition width is estimated with an accuracy of 5σ. Here, the recording magnetic field gradient dHsw / dx = (dHsw / dT) × (dT / dx), and approximately dHsw / dT = 0.5 × (dHk / dT). Temperature gradient dT / dx = 5 ° C./nm, recording magnetic field Hsw = 2.5 kOe (about 199 A / mm), standardized recording magnetic field dispersion σHsw / Hsw = 7%, which is assumed in current heat-assisted magnetic recording Under the conditions, dHk / dT is preferably larger than 170 Oe / ° C. (13.5 A / mm · ° C.) in order to satisfy a bit length of 8.0 nm with an areal recording density of 4.0 Tbpsi. Therefore, it is required to satisfy the condition of dHk / dT> 170 Oe / ° C. (13.5 A / mm · ° C.) over the entire range of the assumed actual recording temperature. In heat-assisted magnetic recording, magnetic recording becomes more difficult as the actual recording temperature decreases. Therefore, dHk / dT should be greater than 170 Oe / ° C. (13.5 A / mm · ° C.) at a temperature 60 ° C. lower than the Curie temperature Tc. Can satisfy the above requirements. The present inventors have found that the above requirement can be satisfied by using an FePtRu ordered alloy that satisfies the above formulas (i) to (v).

  Further, by forming the ordered alloy of the magnetic recording layer 30 with Ru used as the third element, a low Tc can be obtained while maintaining a high Ku. The reason for this is not yet fully understood and is not bound by theory, but can be considered as follows.

  It is well known that adjacent ferromagnetic layers are antiferromagnetically exchange coupled by sandwiching a thin coupling layer made of a nonmagnetic transition metal such as Ru, Cu, or Cr between the ferromagnetic layers. The antiferromagnetic coupling energy varies depending on the type of element, the structure of the sandwiched layers, and the like. Comparing the maximum value of antiferromagnetic exchange coupling energy in each element, it becomes larger when Ru is used as the coupling layer. The antiferromagnetic exchange coupling energy when Ru is used is particularly large, and takes a value that is 10 times or more that when other elements such as Cu are used. In addition, it is known that Ru can exhibit the above-described effects even with a small film thickness. According to the experiments by the present inventors, when Ru is added to an ordered alloy such as FePt, the saturation magnetization Ms is reduced at the same Ku as compared with the case where other elements such as Cu are added. There was found. Considering these points collectively, it is presumed that a phenomenon similar to antiferromagnetic coupling in which a couple having opposite spin directions is generated through the added Ru. In this way, antiferromagnetic coupling via Ru used as the third element occurs in a part of the inside of the ordered alloy, so that it becomes easy to cause the entire spin disorder at a relatively low temperature. It is considered that the

In the present embodiment, in the ordered alloy, not all atoms need necessarily have an ordered structure. If the degree of order S representing the degree of the ordered structure is equal to or greater than a predetermined value, it can be used as the ordered alloy of this embodiment. The degree of order S is calculated by measuring the magnetic recording layer by X-ray diffraction (XRD) and calculating the ratio between the measured value and the theoretical value when it is completely ordered. For L1 ₀ type ordered alloy is calculated using from ordered alloy (001) and the integrated intensity of the (002) peak. The ratio of the (002) peak integrated intensity to the (001) peak integrated intensity calculated theoretically when the value of the ratio of the (002) peak integrated intensity to the measured (001) peak integrated intensity is perfectly ordered The regularity S can be obtained by dividing by. If the degree of order S obtained in this way is 0.5 or more, the magnetic recording medium has a practical magnetic anisotropy constant Ku.

Alternatively, the magnetic recording layer 30 composed of a single layer has a granular structure composed of magnetic crystal grains composed of the above-mentioned ordered alloy and nonmagnetic crystal grain boundaries surrounding the magnetic crystal grains. May be. The material constituting the nonmagnetic grain boundary includes carbon, boron, carbide, oxide, and nitride. Oxides that can be used for nonmagnetic grain boundaries include SiO ₂ , TiO ₂ , and ZnO. Nitrides that can be used for nonmagnetic grain boundaries include SiN and TiN. In the granular structure, each magnetic crystal grain is magnetically separated by a nonmagnetic grain boundary. This magnetic separation is effective for improving the SNR of the magnetic recording medium.

  One or more kinds of fourth elements may be further introduced into the ordered alloy used in the present embodiment. Various elements can be used as the fourth element as long as the effect of Ru is not impaired. For example, non-limiting examples of the fourth element include Ag, Cu, Co, Mn, Cr, Ti, Zr, Hf, Nb, Ts, Al, and Si.

The magnetic recording layer 30 is preferably formed by a sputtering method that involves heating the substrate. The substrate temperature when forming the magnetic recording layer 30 is preferably in the range of 300 to 800 ° C. Particularly preferably, the substrate temperature is in the range of 400-500 ° C. By employing a substrate temperature within this range, it is possible to improve the degree of order S of L1 ₀ type ordered alloy material in the magnetic recording layer 30. Or you may employ | adopt the sputtering method using two targets which are the target which consists of Fe and Pt, and the target which consists of Ru. Alternatively, a sputtering method using three targets that are a target made of Fe, a target made of Pt, and a target made of Ru may be adopted. In these cases, the ratio of Fe, Pt and Ru in the ordered alloy of the magnetic recording layer 30 can be controlled by supplying power to each target separately.

  When forming the magnetic recording layer 30 having a granular structure, a target in which a material for forming magnetic crystal grains and a material for forming nonmagnetic crystal grain boundaries are mixed at a predetermined ratio may be used. Alternatively, a target made of a material that forms magnetic crystal grains and a target made of a material that forms nonmagnetic crystal grain boundaries may be used. As described above, a plurality of targets may be used as targets for forming magnetic crystal grains. In this case, power can be separately supplied to each target to control the ratio of magnetic crystal grains and nonmagnetic crystal grain boundaries in the magnetic recording layer 30.

  One configuration example of the magnetic recording medium of the second embodiment is different from the magnetic recording medium of the first embodiment in that the magnetic recording layer includes a plurality of magnetic layers. In the present embodiment, at least one of the plurality of magnetic layers includes an FePtRu ordered alloy that satisfies the formulas (i) to (v) described in the first embodiment. In this specification, the magnetic layer containing the ordered alloy described in the first embodiment is referred to as “magnetic layer A”. The magnetic layer A may have a non-granular structure or a granular structure. When the magnetic recording layer includes a plurality of magnetic layers A, each magnetic layer A may independently have either a granular structure or a non-granular structure. Desirably, the magnetic layer A has a granular structure.

The magnetic recording layer of this embodiment may include at least one magnetic layer that does not include the ordered alloy described above. In other words, at least one of the plurality of magnetic layers other than the magnetic layer A may not include the ordered alloy described above. In the present embodiment, the magnetic layer that does not include the ordered alloy is referred to as “magnetic layer B”. The magnetic layer B may have a non-granular structure or a granular structure. When the magnetic recording layer includes a plurality of magnetic layers B, each magnetic layer B may independently have either a granular structure or a non-granular structure. The magnetic layer B includes, for example, at least one first element selected from the group consisting of Fe, Co, and Ni, and at least one second element selected from the group consisting of Pt, Pd, Au, and Ir. The ordered alloy may be included. In other words, the magnetic layer B may be a layer that does not include an ordered alloy having Ru. It ordered alloy can be a L1 ₀ type ordered alloy. Preferred L1 ₀ type ordered alloys include FePt, CoPt, FePd, and CoPd. A particularly preferable L1 ₀ type ordered alloy is FePt.

For example, the magnetic layer B may be a layer having a Curie temperature Tc different from that of the magnetic layer A and intended for Tc control. The magnetic layer B for the purpose of Tc control desirably has a granular structure. The magnetic crystal grains of the magnetic layer B having a granular structure can be formed of, for example, a magnetic material containing at least one of Co and Fe. The magnetic material preferably further includes at least one of Pt, Pd, Ni, Mn, Cr, Cu, Ag, and Au. For example, the magnetic layer B for the purpose of Tc control can be formed using a CoCr alloy, a CoCrPt alloy, a FePt alloy, a FePd alloy, or the like. The crystal structure of the magnetic material, L1 ₀ type, L1 ₁ type, ordered structure of L1 ₂ type or the like, hcp structure, it is possible to fcc structure or the like. The nonmagnetic crystal grain boundary may include an oxide selected from the group consisting of carbon, boron, SiO ₂ , TiO ₂ , and ZnO, or a nitride selected from the group consisting of SiN and TiN.

Alternatively, the magnetic layer B may be a cap layer. The cap layer can be a magnetically continuous layer within the magnetic layer. By disposing the continuous magnetic layer, magnetization reversal as a magnetic recording medium can be adjusted. The material constituting the continuous magnetic layer is preferably a material containing at least one of Co and Fe. Further, among the Pt, Pd, Ni, Mn, Cr, Cu, Ag, Au, and rare earth elements It is preferable to include at least one of them. For example, a CoCr alloy, a CoCrPt alloy, a FePt alloy, a FePd alloy, a CoSm alloy, or the like can be used. The continuous magnetic layer may be composed of either polycrystalline or amorphous. Crystal structure when configured in polycrystalline, L1 ₀ type, L1 ₁ type, L1 ordered structure of type _2, etc., hcp structure (hexagonal close-packed structure), be a fcc structure (face-centered cubic structure), etc. it can.

  In the magnetic recording layer of this embodiment, an exchange coupling control layer may be disposed between the magnetic layers in order to adjust the magnetic exchange coupling between the two magnetic layers. The reversal magnetic field can be adjusted by adjusting the magnetic exchange coupling at the recording temperature. The exchange coupling control layer may be either a magnetic layer or a nonmagnetic layer depending on the desired exchange coupling. In order to enhance the effect of reducing the switching field at the recording temperature, it is preferable to use a nonmagnetic layer.

  The magnetic layer B has a function of maintaining magnetization corresponding to information to be recorded (for example, information of 0, 1) in cooperation with the magnetic layer A at a temperature at which recording is stored, and / or at a recording temperature. 1 has the effect of facilitating recording in cooperation with the magnetic layer. In order to serve this purpose, other magnetic layers can be added instead of the magnetic layer and cap layer for Tc control described above or in addition to the magnetic layer and cap layer for Tc control. . For example, a magnetic layer for controlling magnetic characteristics, a magnetic layer for controlling the ferromagnetic resonance frequency for microwave-assisted magnetic recording, and the like may be added. Here, the magnetic characteristics to be controlled include a magnetic anisotropy constant (Ku), a reversal magnetic field, a coercive force Hc, a saturation magnetization Ms, and the like. Further, the magnetic layer to be added may be a single layer, or may have a configuration in which different layers having different compositions are laminated. A plurality of second magnetic layers having different configurations may be added.

  In the magnetic recording layer of this embodiment, it is desirable that at least one of the plurality of magnetic layers has a granular structure. The layer having a granular structure may be the magnetic layer A or the magnetic layer B. Moreover, when two magnetic layers having a granular structure are adjacent to each other, it is desirable that the materials forming the nonmagnetic crystal grain boundaries of these magnetic layers are different. By forming nonmagnetic grain boundaries between adjacent magnetic layers using different materials, the columnar growth of magnetic grains in the magnetic layer is promoted, the degree of ordering of the ordered alloy is improved, and the magnetic grains It is possible to improve the magnetic separation.

  Of the plurality of magnetic layers constituting the magnetic recording layer of the present embodiment, the layer that does not include an ordered alloy is an arbitrary layer known in the art such as sputtering (including DC magnetron sputtering) and vacuum deposition. It can form using the method of. In the formation of a layer having a granular structure without including an ordered alloy, as described in the first embodiment, the material forming the magnetic crystal grains and the material forming the nonmagnetic crystal grain boundaries have a predetermined ratio. Sputtering using a target mixed in (1) may be used. Alternatively, the layer having a granular structure may be formed by sputtering using a target made of a material that forms magnetic crystal grains and a target made of a material that forms nonmagnetic crystal grain boundaries. On the other hand, as described in the first embodiment, the layer including the ordered alloy among the plurality of magnetic layers is preferably formed by a sputtering method that involves heating the substrate.

  In one configuration example of the magnetic recording medium according to the second embodiment, the magnetic recording layer includes a first magnetic layer and a second magnetic layer. The second magnetic layer is formed on the first magnetic layer. For example, in the configuration example shown in FIG. 2, the magnetic recording medium includes a nonmagnetic substrate 10, a magnetic recording layer 30 including a first magnetic layer 31 and a second magnetic layer 32, and an optional protective layer 40. Including.

The first magnetic layer 31 has a granular structure including magnetic crystal grains and nonmagnetic crystal grain boundaries. The magnetic crystal grains of the first magnetic layer 31 do not include an FePtRu ordered alloy that satisfies the formulas (i) to (v) described in the first embodiment. Specifically, the magnetic crystal grains of the first magnetic layer 31 are selected from the group consisting of at least one first element selected from the group consisting of Fe, Co, and Ni, and Pt, Pd, Au, and Ir. And an ordered alloy composed of at least one second element. It ordered alloy can be a L1 ₀ type ordered alloy. Preferred L1 ₀ type ordered alloys include FePt, CoPt, FePd, and CoPd. A particularly preferable L1 ₀ type ordered alloy is FePt.

  Further, the nonmagnetic crystal grain boundary of the first magnetic layer 31 contains carbon. Preferably, the nonmagnetic crystal grain boundary of the first magnetic layer 31 is made of carbon. In the case of using the above-mentioned ordered alloy, carbon is a material having excellent diffusibility, and moves quickly from the position of the magnetic crystal grain to the nonmagnetic portion as compared with oxide, nitride, and the like. As a result, the magnetic crystal grains are well separated from carbon and the degree of ordering of the ordered alloy constituting the magnetic crystal grains is improved. Moreover, it is easy to form homogeneous magnetic crystal grains.

  The first magnetic layer 31 desirably has a thickness of 0.5 to 4 nm, preferably 1 to 2 nm. By using a film thickness in this range, it is possible to achieve both improvement in the degree of order of magnetic crystal grains and improvement in magnetic separation. In order to suppress the diffusion of carbon to the top surface of the magnetic crystal grains, it is desirable that the first magnetic layer 31 has a film thickness within the above-described range.

The second magnetic layer 32 has a granular structure including magnetic crystal grains and nonmagnetic crystal grain boundaries. The magnetic crystal grains of the second magnetic layer 32 are made of the ordered alloy described in the first embodiment. Specifically, the ordered alloy includes Fe, Pt, and Ru, and has a composition that satisfies the above-described formulas (i) to (v). It ordered alloy may have an L1 ₀ ordered structure.

The nonmagnetic crystal grain boundary of the second magnetic layer 32 includes a mixture of carbon and boron, or SiO ₂ . Preferably, the nonmagnetic crystal grain boundary of the second magnetic layer 32 is composed of a mixture of carbon and boron, or SiO ₂ . That is, the nonmagnetic crystal grain boundary of the second magnetic layer 32 is formed of a material different from the nonmagnetic crystal grain boundary of the first magnetic layer 31. By forming the nonmagnetic crystal grain boundaries of the first magnetic layer 31 and the second magnetic layer 32 with different materials, the magnetic crystal grains of the second magnetic layer 32 are formed on the magnetic crystal grains of the first magnetic layer 31. Columnar growth is possible. By forming the magnetic crystal grains of the second magnetic layer 32 on the magnetic crystal grains of the first magnetic layer 31, magnetic crystal grains penetrating the film thicknesses of the first magnetic layer 31 and the second magnetic layer 32 are formed. The Such magnetic crystal grain formation reduces exchange interaction between adjacent magnetic crystal grains. This effect enables high-density magnetic recording on the magnetic recording medium.

  The second magnetic layer 32 desirably has a thickness of 0.5 to 10 nm, preferably 3 to 7 nm. By using a film thickness in this range, it is possible to improve the order of magnetic crystal grains. In addition, by using a film thickness in this range, the magnetic crystal grains of the second magnetic layer 32 can be prevented from coalescing to form huge crystal grains, and the magnetic crystal grains of the second magnetic layer 32 can be magnetized. The target separation can be improved.

  The magnetic recording medium described in this specification is selected from the group consisting of an adhesion layer, a heat sink layer, a soft magnetic backing layer, an underlayer, and a seed layer 20 between the nonmagnetic substrate 10 and the magnetic recording layer 30. One or more layers may further be included. The magnetic recording medium described in this specification may further include a protective layer 40 on the magnetic recording layer 30. Furthermore, the magnetic recording medium described in this specification may further include a liquid lubricant layer on the magnetic recording layer 30 or the protective layer 40.

  The adhesion layer that may be optionally provided is used to enhance 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 metals such as Ni, W, Ta, Cr, Ru, and alloys containing the aforementioned metals. Alternatively, an adhesion layer may be formed between two constituent layers other than the nonmagnetic substrate 10. The adhesion layer may be a single layer or may have a laminated structure of a plurality of layers.

  The soft magnetic backing layer 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 underlayer 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. Includes amorphous material. The optimum value of the thickness of the soft magnetic underlayer depends on the structure and characteristics of the magnetic head used for magnetic recording. When the soft magnetic backing layer is formed by continuous film formation with other layers, the soft magnetic backing layer preferably has a thickness in the range of 10 nm to 500 nm (including both ends) in consideration of productivity.

  When the magnetic recording medium described in this specification is used in the heat-assisted magnetic recording method, a heat sink layer may be provided. The heat sink layer is a layer for effectively absorbing excess heat of the magnetic recording layer 30 generated during the heat-assisted magnetic recording. The heat sink layer can be formed using a material having high thermal conductivity and specific heat capacity. Such a material includes Cu simple substance, Ag simple substance, Au simple substance, or an alloy material mainly composed of them. Here, “mainly” means that the content of the material is 50 wt% or more. Further, from the viewpoint of strength and the like, the heat sink layer can be formed using an Al—Si alloy, a Cu—B alloy, or the like. Further, a heat sink layer is formed using Sendust (FeSiAl) alloy, soft magnetic CoFe alloy, etc., and the function of the soft magnetic backing layer (the function of concentrating the perpendicular magnetic field generated by the head on the magnetic recording layer 30). Can also be given. The optimum value of the heat sink layer thickness varies depending on the amount of heat and heat distribution during heat-assisted magnetic recording, the layer configuration of the magnetic recording medium, and the thickness of each component layer. In the case of forming by continuous film formation with other constituent layers, the film thickness of the heat sink layer is preferably 10 nm or more and 100 nm or less in consideration of productivity. The heat sink layer can be formed by using any method known in the art such as sputtering (including DC magnetron sputtering) and vacuum deposition. Usually, the heat sink layer is formed using a sputtering method. The heat sink layer can be provided between the nonmagnetic substrate 10 and the adhesion layer, between the adhesion layer and the underlayer, etc. in consideration of characteristics required for the magnetic recording medium.

  The underlayer is a layer for controlling the crystallinity and / or crystal orientation of the seed layer 20 formed above. The underlayer may be a single layer or a multilayer. The underlayer is formed of Cr metal or an alloy in which at least one metal selected from the group consisting of Mo, W, Ti, V, Mn, Ta, and Zr is added to Cr as a main component. A magnetic film is preferred. The underlayer can be formed using any method known in the art such as sputtering.

  The function of the seed layer 20 is to ensure the adhesion between the magnetic recording layer 30 and an underlying layer such as an underlayer, and to change the grain size and crystal orientation of the magnetic recording layer 30 of the upper magnetic recording layer 30. Is to control. The seed layer 20 is preferably nonmagnetic. In addition, when the magnetic recording medium described in this specification is used in the heat-assisted magnetic recording method, it is preferable that the seed layer 20 controls the temperature rise and temperature distribution of the magnetic recording layer 30 as a thermal barrier. . In order to control the temperature rise and temperature distribution of the magnetic recording layer 30, the seed layer 20 has a function of rapidly raising the temperature of the magnetic recording layer 30 when the magnetic recording layer 30 is heated during the heat-assisted recording, Before the heat transfer in the in-plane direction of the recording layer 30 occurs, it is preferable to achieve both the function of guiding the heat of the magnetic recording layer 30 to the lower layer such as the underlayer by the heat transfer in the depth direction.

In order to achieve the above function, the material of the seed layer 20 is appropriately selected according to the material of the magnetic recording layer 30. More specifically, the material of the seed layer 20 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 30 is formed by L1 ₀ type ordered alloy, it is preferable to form the seed layer using a Pt metal or NaCl-type compounds. Particularly preferably, the seed layer 20 is formed using an oxide such as MgO or SrTiO ₃ or a nitride such as TiN. Alternatively, the seed layer 20 can 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 30 and improving the productivity, the seed layer 20 preferably has a thickness of 1 nm to 60 nm, preferably 1 nm to 20 nm. The seed layer 20 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 protective layer 40 can be formed using a material conventionally used in the field of magnetic recording media. Specifically, the protective layer 40 can be formed using a non-magnetic metal such as Pt, a carbon-based material such as diamond-like carbon, or a silicon-based material such as silicon nitride. The protective layer 40 may be a single layer or may have a laminated structure. The laminated protective layer 40 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 40 can be formed using any method known in the art such as sputtering (including DC magnetron sputtering), CVD, and vacuum deposition.

  The liquid lubricant layer can be formed using a material conventionally used in the field of magnetic recording media (for example, a perfluoropolyether lubricant). The liquid lubricant layer can be formed using, for example, a coating method such as a dip coating method or a spin coating method.

[Example]
A (001) MgO single crystal substrate having a smooth surface was washed to prepare a nonmagnetic substrate 10. The nonmagnetic substrate 10 after cleaning was introduced into the sputtering apparatus. After heating the nonmagnetic substrate 10 to 350 ° C., a 20 nm-thick Pt seed is formed by RF magnetron sputtering using a Pt target placed at a distance of 320 mm from the nonmagnetic substrate 10 in Ar gas at a pressure of 0.44 Pa. Layer 20 was formed.

Next, after heating the nonmagnetic substrate 10 on which the seed layer 20 is formed to 350 ° C., an FePtRu magnetic film having a thickness of 10 nm is formed by RF magnetron sputtering using an FePt target and an Ru target in an Ar gas having a pressure of 0.60 Pa. A recording layer 30 was formed to obtain a magnetic recording medium having the structure shown in FIG. Here, the FePt target and the Ru target were arranged at a distance of 320 mm from the nonmagnetic substrate 10. In addition, Fe content x (atomic%) and Pt content y (atomic%) of the magnetic recording layer were adjusted using FePt targets having various compositions. Further, the power applied to the FePt target was fixed at 300 W, and the power applied to the Ru target was changed from 0 to 240 W to adjust the Ru content z (atomic%) of the magnetic recording layer 30. The compositions of the obtained magnetic recording layer 30 are shown in Tables 2-6. Further, the XRD of the magnetic recording layer 30 of each sample obtained, the magnetic recording layer 30 was confirmed to consist of L1 ₀ type ordered alloy.

Using a vibrating sample magnetometer (VSM), the saturation magnetization Ms of the obtained magnetic recording medium was measured. The obtained magnetic recording medium was heated to room temperature (25 ° C.) to 400 ° C., and the saturation magnetization Ms (T) at each temperature T was measured using a vibrating sample magnetometer (VSM). The measurement temperature T and the saturation magnetization square Ms ² (T) were plotted, and a regression line was obtained by the least square method. The obtained regression line was extrapolated to the point of Ms ² = 0, and the Curie temperature Tc was obtained. Tables 2 to 6 show the Curie temperature Tc of each sample.

  Furthermore, the magnetic anisotropy constant Ku of the obtained magnetic recording layer 30 was determined using the anomalous Hall effect. Specifically, a magnetic torque curve was measured under an external magnetic field of 7 T at room temperature (25 ° C.), and a magnetic anisotropy constant Ku (RT) at room temperature was calculated by fitting the obtained torque curve. The abbreviation “RT” means room temperature (25 ° C.).

  Subsequently, the magnetic anisotropy constant Ku (T) at a desired temperature T was determined using the formula (1).

      Ku (T) = Ku (RT) × [Tc−T] / [Tc−RT] (1)

  Furthermore, the anisotropic magnetic field Hk (T) at the temperature T was obtained from the saturation magnetization Ms (T) at the desired temperature T and the magnetic anisotropy constant Ku (T) using the equation (2).

      Hk (T) = 2 × Ku (T) / Ms (T) (2)

  Finally, the gradient dHk / dT of the anisotropic magnetic field with respect to the temperature change was obtained from the value of Hk (T) in the vicinity of the reference temperature. In this example, as the reference temperature, a temperature 60 ° C. lower than the Curie temperature, a temperature 40 ° C. lower than the Curie temperature, and a temperature 20 ° C. lower than the Curie temperature were used. Tables 2 to 6 show the gradient dHk / dT of the anisotropic magnetic field with respect to the temperature change of each sample. Moreover, Hk at room temperature of each sample is shown in Tables 2-6.

  In FIG. 3, the change in the Curie temperature Tc with respect to the composition of the magnetic recording layer is shown by contour lines. 4 to 6, the change in dHk / dT with respect to the composition of the magnetic recording layer is shown by contour lines. 4 shows the change in dHk / dT at a temperature 60 ° C. below the Curie temperature, FIG. 4 shows the change in dHk / dT at a temperature 40 ° C. below the Curie temperature, and FIG. 4 is 20 ° C. below the Curie temperature. The change of dHk / dT with temperature is shown. In FIG. 7, the change of the anisotropic magnetic field Hk with respect to the composition of the magnetic recording layer at room temperature is shown by contour lines. The black circles in FIG. 3 to FIG. 7 indicate the compositions of the samples described in Tables 2 to 6.

(Evaluation)
As shown in FIG. 3, the Curie temperature Tc of the magnetic recording layer 30 tends to decrease as the Ru content in the magnetic recording layer 30 increases. Further, when the same level of Ru is used, the maximum value of the Curie temperature Tc of the magnetic recording layer 30 exists in the vicinity of x / y of about 1.15. Even if the Fe content x increases from the maximum composition, or the Pt content y increases, the Curie temperature Tc decreases. It can be seen that the change in the Curie temperature Tc is smaller when Pt is replaced with Ru than when Fe in the ordered alloy is replaced with Ru.

  On the other hand, as shown in FIG. 7, the value of the anisotropic magnetic field Hk increases as the Ru content z decreases and the ratio x / y of the Fe content to the Pt content approaches 1.0. I understand that It can also be seen that the change in the value of the anisotropic magnetic field Hk is smaller when Pt is replaced with Ru than when Fe in the ordered alloy is replaced with Ru.

  4 to 6 show the relationship between the composition of the magnetic recording layer 30 and the gradient dHk / dT of the anisotropic magnetic field with respect to temperature change. 4 shows a value at a temperature 60 ° C. lower than the Curie temperature Tc, FIG. 5 shows a value at a temperature 40 ° C. lower than the Curie temperature Tc, and FIG. 6 shows a value at a temperature 20 ° C. lower than the Curie temperature Tc. Moreover, the area | region which satisfy | fills Formula (i)-(v) was shown in FIGS. 4-6 with the broken hexagon.

  The value of dHk / dT at each temperature shows the same tendency. Specifically, when z is about 12 and x / y is about 0.9 to 1.15, the value of dHk / dT at each temperature is maximized. Even at a temperature lower by 60 ° C. than the Curie temperature Tc at which magnetic recording is most difficult as shown in FIG. 4, the composition of the region satisfying the formulas (i) to (v) is required, so that 170 Oe necessary for reducing the bit transition width is obtained. It was found that dHk / dT greater than / ° C. (13.5 A / mm · ° C.) can be achieved.

10 nonmagnetic substrate 20 seed layer 30 magnetic recording layer 31 first magnetic layer 32 second magnetic layer 40 protective layer

Claims (7)

A non-magnetic substrate, a seed layer, and a magnetic recording layer;
The magnetic recording layer is formed on the seed layer, and the magnetic recording layer includes an ordered alloy containing Fe, Pt, and Ru. The ordered alloy is based on the total number of atoms of Fe, Pt, and Ru. , X atomic% Fe, y atomic% Pt, and z atomic% Ru, wherein x, y and z are represented by the following formulas (i) to (v):
(I) 0.85 ≦ x / y ≦ 1.3;
(Ii) x ≦ 53;
(Iii) y ≦ 51;
(Iv) 0.6 ≦ z ≦ 20; and (v) x + y + z = 100
The filling,
The heat-assisted magnetic recording medium, wherein the seed layer is formed of a material selected from the group consisting of Pt metal, MgO, SrTiO ₃ , and TiN.   A heat sink layer is further included, and the heat sink layer is made of Cu alone, Ag alone, Au alone, an alloy containing 50 wt% or more of Cu, Ag, or Au, an Al—Si alloy, a Cu—B alloy, a FeSiAl alloy, and a soft magnetic CoFe alloy. The heat-assisted magnetic recording medium according to claim 1, wherein the heat-assisted magnetic recording medium is made of a material selected from the group consisting of: The ordered alloy, heat-assisted magnetic recording medium according to claim 1, characterized in that the L1 ₀ type ordered alloy.   The magnetic recording layer has a granular structure including magnetic crystal grains including the ordered alloy and nonmagnetic crystal grain boundaries, and the nonmagnetic crystal grain boundaries include carbon, boron, carbide, oxide, and nitride. The heat-assisted magnetic recording medium according to claim 1, comprising at least one material selected from the group consisting of:   The thermally assisted magnetic recording medium according to claim 1, wherein the magnetic recording layer includes a plurality of magnetic layers, and at least one of the plurality of magnetic layers is a magnetic layer including the ordered alloy. The ordered alloy, heat-assisted magnetic recording medium according to claim 5, characterized in that the L1 ₀ type ordered alloy.   The magnetic layer containing the ordered alloy has a granular structure including magnetic crystal grains and nonmagnetic crystal grain boundaries, and the nonmagnetic crystal grain boundaries are made of carbon, boron, carbide, oxide, and nitride. The heat-assisted magnetic recording medium according to claim 5, comprising at least one material selected from the group consisting of: