JP5923152B2 - Thermally assisted magnetic recording medium and magnetic recording / reproducing apparatus - Google Patents

Description

  The present invention relates to a heat-assisted magnetic recording medium used for a hard disk device (HDD) or the like and a magnetic recording / reproducing apparatus using the same.

In recent years, heat-assisted recording, in which a magnetic recording medium is irradiated with near-field light or the like to locally heat the surface and the coercive force of the magnetic recording medium is reduced to perform writing, is a 1 Tbit / inch ² class surface recording density. As a next-generation recording method that can realize

When this heat-assisted recording is used, even a magnetic recording medium having a coercive force of several tens of kOe at room temperature can be easily written by the recording magnetic field of the current head. For this reason, in the thermally assisted magnetic recording medium, it is possible to use a material having high crystal magnetic anisotropy (Ku) of 10 ⁶ J / m ³ for the magnetic layer, and while maintaining the thermal stability, The particle size can be reduced to 6 nm or less.

Examples of such high Ku material, L1 ₀ type FePt alloy having a crystal structure (Ku: about ^{7 × 10 6 J / m 3} ) and, CoPt alloy having an L1 ₀ type crystal structure (Ku: about 5 × 10 ⁶ J / m ³ ) and the like are known. Furthermore, the CoPt alloy having the L1 type ₁ crystal structure also shows a high Ku on the order of 10 ⁶ erg / cc. In addition, it is known that rare earth alloys such as CoSm alloys and NdFeB alloys also exhibit high Ku. In addition, since the Co / Pt multilayer film, the Co / Pd multilayer film, etc. exhibit a high anisotropic magnetic field (Hk) and at the same time, the Curie temperature is relatively easy to control, the magnetic layer of the heat-assisted magnetic recording medium It is being considered.

The magnetic layer of the current perpendicular magnetic recording medium has a granular structure in which a Co alloy is divided by an oxide such as SiO ₂ , and the magnetic exchange coupling between Co crystal grains is reduced by the oxide. An S / N ratio is obtained. However, in general, a magnetic layer having a granular structure has a large magnetization switching field (Hsw) dispersion. In order to realize a high surface recording density, it is necessary to reduce the Hsw dispersion of the magnetic recording medium. Therefore, the magnetic layer having a granular structure does not contain an oxide and is magnetically continuous in the in-plane direction of the film. A magnetic layer bonded to is formed. This is because uniform exchange coupling is introduced between the magnetic particles in the magnetic layer having a granular structure. Thereby, Hsw dispersion can be reduced. The continuous film containing no oxide is also called a Cap layer, and the laminated structure including a magnetic layer having a granular structure and a Cap layer is also called a CGC (Coupled Granular and Continuous) structure.

For thermally assisted magnetic recording medium, it is desirable that the magnetic layer using a material exhibiting high Ku of such FePt alloy having an L1 ₀ type crystal structure. However, also in this case, SiO ₂ , TiO ₂ , Cr ₂ O ₃ , Al ₂ O ₃ , Ta ₂ O ₅ , ZrO ₂ , Y ₂ O are used to reduce the magnetic particle size and reduce the exchange coupling between the magnetic particles. ₃ , oxides such as CeO ₂ , MnO, TiO, ZnO, and MgO, and C need to be added as a grain boundary segregation material. Further, in order to realize a fine particle size of 6 nm or less and sufficient exchange coupling reduction, the content of the grain boundary segregation material needs to be 30% by volume or more, preferably 40% by volume or more.

Non-Patent Document 1 below describes that the magnetic particle size can be reduced to 5.5 nm by adding 50 atomic% of C to the FePt alloy. Non-Patent Document 2 below describes that the magnetic particle diameter can be reduced to 5 nm by adding 20 vol% TiO ₂ to the FePt alloy. Further, Non-Patent Document 3 below describes that the magnetic particle size can be reduced to 2.9 nm by adding 50% by volume of SiO ₂ to the FePt alloy. In this case, however, the FePt alloy crystal grains do not have a column structure, but have a spherical structure divided in the direction perpendicular to the film surface.

Appl. Phys. Express, 101301, 2008 J. Appl. Phys. 104, 023904, 2008 IEEE. Trans. Magn., Vol. 45, 839-844, 2009

  As described above, in order to realize a high medium S / N ratio, it is necessary to reduce the Hsw dispersion at the same time as reducing the magnetic particle diameter. Since the Hsw dispersion has a correlation with the coercive force dispersion (ΔHc / Hc), it is usually possible to evaluate the Hsw dispersion by measuring ΔHc / Hc. In the case of a heat-assisted magnetic recording medium, it is necessary to heat the magnetic layer to 200 to 400 ° C. during recording, but the coercive force dispersion in this temperature region is significantly higher than that of the current granular medium. For this reason, reduction of coercive force dispersion is an extremely important issue in achieving higher density of the heat-assisted magnetic recording medium.

In the current granular medium, the coercive force dispersion is reduced by adopting a configuration called a CGC structure or an ECC structure in which a magnetic layer having a continuous structure is laminated on a magnetic layer having a granular structure. However, as a result of studies by the present inventors, even if a continuous film such as a CoCrPt alloy is formed on a magnetic layer having a granular structure composed of an FePt alloy and a grain boundary segregation material such as SiO ₂ , the coercive force is increased. It became clear that dispersion could not be reduced. The reason is as follows.

That is, in order to reduce the magnetic particle size to 5 to 6 nm or less, it is necessary to add approximately 30% by volume or more of grain boundary segregation material such as SiO ₂ . However, when the grain boundary segregation material is added in an amount of 30% by volume or more, the column structure in which the magnetic layer is continuously grown in the direction perpendicular to the substrate surface is not taken. This is because if the grain boundary segregation material is added excessively, the grain boundary segregation material precipitates not only on the magnetic grain boundary but also on the surface of the magnetic crystal.

  In the non-patent document 3, as a result of cross-sectional TEM observation of the FePt magnetic layer added with 15% by volume of C, spherical FePt grows discontinuously on columnar FePt crystal grains. Have been described. In this case, even if a continuous Cap layer is formed on the magnetic layer having a granular structure, exchange coupling cannot be introduced between the FePt magnetic particles. In addition, the spherical magnetic crystal formed on the upper part of the magnetic layer is magnetically isolated and has a small reversal magnetic field, which is a major factor in expanding the coercive force dispersion. Therefore, in order to reduce the coercive force dispersion, it is necessary to suppress the generation of the spherical crystal grains and to make the magnetic layer have a column structure continuously grown in a direction perpendicular to the substrate surface.

The present invention has been proposed in view of such conventional circumstances, and includes a heat-assisted magnetic recording medium having a surface recording density of 1 Tbit / inch ² or more, and such a heat-assisted magnetic recording medium. An object of the present invention is to provide a large-capacity magnetic recording / reproducing apparatus.

The present invention provides the following means.
(1) at least on a substrate, and a first magnetic layer and the second magnetic layer are sequentially stacked, the first magnetic layer, FePt alloy having an L1 ₀ structure, L1 ₀ structure A crystal grain of either a CoPt alloy having a structure or a CoPt alloy having an L1 ₁ structure; and SiO ₂ , TiO ₂ , Cr ₂ O ₃ , Al ₂ O ₃ , Ta ₂ O ₅ , ZrO ₂ , Y ₂ O ₃ , It has a granular structure including at least one kind of grain boundary segregation material among CeO ₂ , MnO, TiO, ZnO, MgO, C,
A heat-assisted magnetic recording medium, wherein the content of the grain boundary segregation material in the first magnetic layer decreases from the substrate side toward the second magnetic layer side.
(2) a region in which the content of the grain boundary segregation material in the first magnetic layer is constant from the substrate side toward the second magnetic layer side, and the second magnetic layer from the substrate side The heat-assisted magnetic recording medium according to item (1), including a region that decreases toward the side.
(3) The thermally assisted magnetism according to (2) above, wherein the ratio of the region where the content of the grain boundary segregation material is constant is 70% or less of the thickness of the first magnetic layer. recoding media.
(4) In the region where the content of the grain boundary segregation material is constant, the content of the grain boundary segregation material is 30% by volume or more, as described in (2) or (3) above Thermally assisted magnetic recording medium.
(5) The above-mentioned item (2), wherein the second magnetic layer is an amorphous alloy containing Co and containing at least one of Zr, Ta, Nb, B, and Si. The heat-assisted magnetic recording medium according to any one of 1) to (4).
(6) The above-mentioned item (2), wherein the second magnetic layer is an amorphous alloy containing Fe and containing at least one of Zr, Ta, Nb, B, and Si. The heat-assisted magnetic recording medium according to any one of 1) to (4).
(7) The thermally-assisted magnetic recording according to any one of (1) to (4) above, wherein the second magnetic layer is an Fe-containing BCC structure or FCC structure alloy. Medium.
(8) The thermally-assisted magnetic recording medium according to any one of (1) to (4), wherein the second magnetic layer is an HCP-structure alloy containing Co.
(9) Any of (1) to (4) above, wherein the magnetocrystalline anisotropy constant of the second magnetic layer is lower than the magnetocrystalline anisotropy constant of the first magnetic layer. The heat-assisted magnetic recording medium according to one item.
(10) The heat-assisted magnetic recording medium according to any one of (1) to (9),
A medium drive unit for driving the heat-assisted magnetic recording medium in a recording direction;
A recording and reproducing operation for the thermally-assisted magnetic recording medium, comprising: a laser generating section for heating the thermally-assisted magnetic recording medium; and a waveguide for guiding the laser beam generated from the laser generating section to a tip section. A magnetic head to perform,
A head moving unit for moving the magnetic head relative to the heat-assisted magnetic recording medium;
A magnetic recording / reproducing apparatus comprising a recording / reproducing signal processing system for inputting a signal to the magnetic head and reproducing an output signal from the magnetic head.

As described above, according to the present invention, a heat-assisted magnetic recording medium having a surface recording density of 1 Tbit / inch ² or more is realized, and a large-capacity magnetic recording / reproducing apparatus including such a heat-assisted magnetic recording medium is provided. It is possible to provide.

It is sectional drawing which shows the layer structure of the magnetic recording medium produced in the 1st Example. It is a graph of the pattern which shows the content rate of C in a 1st magnetic layer in a 1st Example. It is a graph which shows the relationship between the heating temperature of a 1st magnetic layer, and Hc in a 1st Example. It is a graph which shows the relationship between the heating temperature of a 1st magnetic layer and (DELTA) Hc / Hc in a 1st Example. 6 is a graph showing the relationship between Hc of the first magnetic layer and ΔHc / Hc in the first example. 6 is a graph showing the relationship between Hc of the second magnetic layer and ΔHc / Hc in the first example. It is sectional drawing which shows the layer structure of the magnetic recording medium produced in the 2nd Example. It is a graph of the pattern which shows the content rate of TiO2 in a 1st magnetic layer in a _2nd Example. It is sectional drawing which shows the layer structure of the magnetic recording medium produced in the 3rd Example. It is a perspective view which shows the structure of the magnetic recording / reproducing apparatus used in the 4th Example. It is sectional drawing which shows typically the structure of the magnetic head with which the magnetic recording / reproducing apparatus shown in FIG. 10 is provided.

  Hereinafter, a thermally assisted magnetic recording medium and a magnetic recording / reproducing apparatus to which the present invention is applied will be described in detail with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent.

Thermally assisted magnetic recording medium according to the present invention, on at least a substrate, and a first magnetic layer and the second magnetic layer are sequentially stacked, the first magnetic layer, L1 ₀ structure Any of the crystal grains of a FePt alloy having a structure, a CoPt alloy having an L1 ₀ structure, or a CoPt alloy having an L1 ₁ structure, and SiO ₂ , TiO ₂ , Cr ₂ O ₃ , Al ₂ O ₃ , Ta ₂ O ₅ , Grains having a granular structure including at least one kind of grain boundary segregation material among ZrO ₂ , Y ₂ O ₃ , CeO ₂ , MnO, TiO, ZnO, MgO, and C, and grains in the first magnetic layer The content of the field segregation material decreases from the substrate side toward the second magnetic layer side.

  Among these, for the substrate, a crystallized glass substrate having excellent heat resistance, a chemically strengthened glass, or a silicon (Si) substrate having a high thermal conductivity can be used.

The first magnetic layer, FePt alloy having an L1 ₀ structure, the grain boundary of the L1 ₀ CoPt alloy having a structure, or L1 ₁ or grain of CoPt alloy having a structure (magnetic _particles), SiO 2, TiO ₂ , grain boundary segregation materials (non-magnetic materials) such as Cr ₂ O ₃ , Al ₂ O ₃ , Ta ₂ O ₅ , ZrO ₂ , Y ₂ O ₃ , CeO ₂ , MnO, TiO, ZnO, MgO, and C These mixed materials have a segregated granular structure.

  In the present invention, by reducing the content (concentration) of the grain boundary segregation material in the first magnetic layer from the substrate side toward the second magnetic layer side, the excess grain boundary segregation material is FePt alloy, or It is possible to prevent the grain growth from being separated in the vertical direction by precipitating on the upper part of the crystal grains of the CoPt alloy. Further, this makes it possible to form FePt alloy or CoPt alloy crystal grains having a fine grain size and continuously grown in a direction perpendicular to the substrate surface.

  In order to reduce the grain boundary segregation material in the first magnetic layer, for example, in simultaneous sputtering using an FePt target and a grain boundary segregation material target, the discharge power ratio of the grain boundary segregation material target to the FePt target is continuously set. Alternatively, it may be lowered step by step. Thereby, the 1st magnetic layer which consists of a several layer (multilayer film) in which the content rate of the grain boundary segregation material fell continuously or in steps can be formed.

  In addition, by using a composite target of FePt and grain boundary segregation material having different contents of grain boundary segregation material, the content of grain boundary segregation material can also be formed by multi-stage film formation in order of decreasing grain boundary segregation material content. Thus, a first magnetic layer composed of a plurality of layers (multilayer film) having a stepwise decrease can be formed.

  The first magnetic layer includes a region where the content (concentration) of the grain boundary segregation material in the first magnetic layer is constant from the substrate side to the second magnetic layer side, and a second region from the substrate side. And a region that decreases toward the magnetic layer side. That is, the content of the grain boundary segregation material in the first magnetic layer may be reduced from the initial stage during the sputtering film formation, or may be reduced from the middle during the sputtering film formation.

  For example, when the thickness of the first magnetic layer is 10 nm, the content of the grain boundary segregation material is constant up to 5 nm, and thereafter the content of the grain boundary segregation material is gradually reduced to 10 nm. Good. In this case, the ratio of the region where the content of the grain boundary segregation material is constant is preferably 70% or less of the thickness of the first magnetic layer. If this ratio exceeds 70%, column growth may be hindered by an excessive grain boundary segregation material, which is not preferable.

  In the region where the content of the grain boundary segregation material is constant, the content of the grain boundary segregation material is preferably 30% by volume or more, more preferably 40% by volume or more. As a result, the crystal grain size of the FePt alloy or CoPt alloy can be reduced to 6 nm or less, and at the same time, the grain boundary width can be set to 1 nm or more, and exchange coupling between magnetic particles can be sufficiently reduced.

  The thickness of the first magnetic layer is desirably 1 nm or more and 20 nm or less. If it is less than 1 nm, sufficient reproduction output cannot be obtained, and if it exceeds 20 nm, the crystal grains are remarkably enlarged.

  The second magnetic layer is desirably a magnetically coupled continuous film in order to introduce exchange coupling between FePt crystal grains or CoPt crystal grains in the first magnetic layer. Thereby, coercive force dispersion can be effectively reduced. The second magnetic layer preferably has a lower magnetocrystalline anisotropy than the first magnetic layer. Thereby, the magnetization reversal of the first magnetic layer can be assisted.

  The second magnetic layer has an amorphous alloy or a microcrystalline structure close thereto, specifically, Co, and at least one of Zr, Ta, Nb, B, and Si Or an alloy containing Fe and containing at least one of Zr, Ta, Nb, B, and Si can be used. When these alloys are used for the second magnetic layer, the flatness of the surface of the magnetic recording medium is improved, and the flying characteristics of the magnetic head are improved.

In the case of using the FePt alloy having an L1 ₀ type crystal structure into the first magnetic layer, a second magnetic layer, alloys of BCC structure or FCC structure mainly composed of Fe, specifically, FeNi, FeCr, FeV, FePt, etc. can be used. These alloys, because epitaxially grown on FePt alloy having an L1 ₀ type crystal structure, as compared with the case of using an amorphous alloy in the second magnetic layer, a high Hc is obtained.

On the other hand, when a CoPt alloy having a L1 ₁ type crystal structure into the first magnetic layer, a second magnetic layer, Co alloy having a HCP structure, specifically, CoCr, CoCrPt, CoPt, CoCrTa CoCrB, CoCrPtTa, CoCrPtB, CoCrPtTaB, or the like can be used. These alloys, because epitaxially grown on CoPt alloy having a L1 ₁ type crystal structure, as compared with the case of using an amorphous alloy in the second magnetic layer, a high Hc is obtained.

  The layer thickness of the second magnetic layer is preferably 0.5 nm or more and 10 nm or less. If the thickness of the second magnetic layer is less than 0.5 nm, the flatness of the surface deteriorates, which is not preferable. On the other hand, if the thickness of the second magnetic layer exceeds 10 nm, the spacing with the magnetic head becomes too large, which is not preferable.

  In the heat-assisted magnetic recording medium to which the present invention is applied, a plurality of underlayers are provided under the first magnetic layer for the purpose of controlling the orientation of the first magnetic layer, controlling the particle size, improving adhesion, and the like. Can be provided.

For example, when using a FePt alloy having an L1 ₀ structure in the first magnetic layer, since assume a (001) orientation on the FePt alloy, preferably provided a base layer made of (100) -oriented MgO. In order to make MgO take (100) orientation, for example, a Ta layer may be formed on a substrate, and MgO may be formed on the Ta layer. In addition to the Ta layer, a (100) orientation can be obtained in this MgO by forming an MgO layer on an amorphous alloy layer such as a Ni-40 at% Ta layer or a Cr-50 at% Ti layer. Can be made.

  In addition, by forming a Cr layer on a substrate heated to 150 ° C. or higher, the Cr layer can be (100) oriented. By forming an MgO layer on the (100) -oriented Cr layer, the (100) orientation can be made to MgO.

When a (100) -oriented Cr underlayer is used, the first magnetic layer may be formed directly on the Cr layer without using an MgO layer. Thereby, it is possible to assume a (001) oriented FePt alloy having an L1 ₀ structure of the first magnetic layer.

In the case of using a CoPt alloy having a L1 ₁ structure in the first magnetic layer preferably assume a (111) orientation on the CoPt alloy. In this case, for example, a (111) -oriented Pt layer can be used as the underlayer. Underlayer this case, the CoPt alloy having a L1 ₁ structure, (111) as long as the material can assume an orientation, it is not particularly limited.

  In the thermally assisted magnetic recording medium to which the present invention is applied, a soft magnetic underlayer can be provided under the first magnetic layer. As the soft magnetic underlayer, for example, a CoFeTaZr alloy, a CoFeTaSi alloy, a CoFeTaB alloy, or a CoTaZr alloy that are antiferromagnetically coupled to each other via a Ru layer can be used. Moreover, what used these alloys by the single layer is good also as a soft-magnetic underlayer.

  In the heat-assisted magnetic recording medium to which the present invention is applied, a heat sink layer is provided between the substrate and the magnetic layer so that the magnetic layer heated by the near-field light at the time of recording is cooled quickly after recording. It can also be provided. Further, the position of the heat sink layer is not particularly limited as long as it is between the substrate and the magnetic layer. For this heat sink layer, Cu, Ag, Al, or a material having high thermal conductivity containing these as a main component can be used.

  As described above, in the thermally-assisted magnetic recording medium to which the present invention is applied, the content of the grain boundary segregation material in the first magnetic layer is decreased by decreasing from the substrate side toward the second magnetic layer side. Therefore, it is possible to prevent the grain boundary segregation material from being deposited on the upper part of the FePt alloy or CoPt alloy crystal grains and dividing the grain growth in the vertical direction. Further, this makes it possible to form FePt alloy or CoPt alloy crystal grains having a fine grain size and continuously grown in a direction perpendicular to the substrate surface.

  According to the present invention, since the coercive force dispersion (ΔHc / Hc) can be reduced, a heat-assisted recording medium having a surface recording density of 1 Tbit / inch 2 or more can be realized, and a large-capacity magnetic recording / reproducing apparatus using the same Can be provided.

  Hereinafter, the effects of the present invention will be made clearer by examples. In addition, this invention is not limited to a following example, In the range which does not change the summary, it can change suitably and can implement.

(First embodiment)
An example of the layer structure of the thermally-assisted magnetic recording medium produced in the first example is shown in FIG.
In producing the thermally-assisted magnetic recording medium in the first embodiment, an underlayer 102 made of a Cr-50 at% Ti alloy with a layer thickness of 100 nm and a Co-27 at% Fe- with a layer thickness of 30 nm are formed on a glass substrate 101. A single-layer soft magnetic underlayer 103 made of a 5 at% Zr-5 at% B alloy was sequentially formed. Thereafter, the glass substrate 101 is heated to 250 ° C., and an underlying layer 104 made of Cr having a thickness of 10 nm and an underlying layer 105 made of MgO having a thickness of 5 nm are sequentially formed thereon, and then the glass substrate 101 is made 450 The first magnetic layer 106 made of an (Fe-55 at% Pt) -C alloy having a layer thickness of 10 nm and the first magnetic layer 106 made of a Co-26 at% Fe-10 at% Ta-2 at% B alloy having a layer thickness of 3 nm were heated to 2 magnetic layers 107 and a protective layer 108 made of carbon (C) having a thickness of 3 nm were sequentially formed.

  Here, the first magnetic layer 106 was formed by simultaneously sputtering an Fe-55 at% Pt target and a C target. Further, by gradually reducing the discharge power ratio of the C target to the Fe-55 at% Pt target, the content of C (grain boundary segregation material) in the first magnetic layer 106 is gradually increased in the layer thickness direction. Reduced. As a result, thermally assisted magnetic recording media having three C concentration profiles (P-1 to P-3) shown in FIGS. As a comparative example, as shown in FIG. 2D, a thermally assisted magnetic recording medium having a C concentration profile (P-4) in which the C content in the first magnetic layer 106 is constant at 40 at%. Was made.

When the X-ray diffraction measurement was performed on the heat-assisted magnetic recording medium having the four types of C concentration profiles (P-1 to P-4) manufactured as described above, the first magnetism was measured from any medium. A strong L1 ₀ -FePt (001) diffraction peak was observed from the layer 106. In addition, a mixed peak of the L1 ₀ -FePt (002) diffraction peak and the FCC-Fe (002) diffraction peak was also observed. Also, the integrated intensity ratio of the former diffraction peak for the latter mixed peak was 1.7, it was found that a high regularity of L1 ₀ type FePt alloy crystal is formed.

  FIG. 3 shows the change in coercive force (Hc) when the heat-assisted magnetic recording medium having the four types of C concentration profiles (P-1 to P-4) is heated from 280 ° C. to 360 ° C. The change in magnetic dispersion (ΔHc / Hc) is shown in FIG. ΔHc / Hc was measured by the method described in “IEEE Trans. Magn., Vol. 27, pp4975-4977, 1991”. Specifically, in the major loop and the minor loop, the magnetic field when the magnetization value is 50% of the saturation value is measured, and ΔHc / Hc is calculated from the difference between the two assuming that the Hc distribution is a Gaussian distribution. Calculated.

  As shown in FIGS. 3 and 4, the heat-assisted magnetic recording media having the above four types of C concentration profiles (P-1 to P-4) all have a decrease in Hc with an increase in temperature and an increase in ΔHc / Hc. You can see that In the heat-assisted magnetic recording medium, recording is performed by locally heating the recording portion and sufficiently reducing the Hc of the portion. Therefore, the above result shows that ΔHc / Hc at the time of recording is higher than the value at room temperature. It shows a significant increase.

  Since it is necessary to compare ΔHc / Hc with the same Hc, ΔHc / Hc shown in FIG. 4 is shown in FIG. 5 as a function of Hc shown in FIG.

  As shown in FIG. 5, for example, when compared with the case where Hc is 5 kOe, the P-1 to P-3 heat-assisted magnetic recording media manufactured by applying the present invention are P- manufactured as a comparative example. Compared with the thermally assisted magnetic recording medium of No. 4, ΔHc / Hc is about 0.1 to 0.4 lower. Moreover, (DELTA) Hc / Hc is falling in order of P-1, P-2, and P-3, and it turns out that coercive force dispersion | distribution improves as the area | region where the content rate of C decreases increases.

  Next, as a comparative example, a heat-assisted magnetic recording medium in which the second magnetic layer 107 was not provided on the first magnetic layer 106 was produced. The magnetic recording medium shown as the comparative example has four types of C concentration profiles (P-1 to P-4) similar to the magnetic recording medium shown as the above-described example. The film forming process is also the same as that of the magnetic recording medium shown as the above-described embodiment. For these heat-assisted magnetic recording media, the coercive force (Hc) and coercive force dispersion (ΔHc / Hc) when heated from 280 ° C. to 360 ° C. were measured, and the relationship between them was shown in FIG.

  As shown in FIG. 6, the plot showing the relationship between Hc and ΔHc / Hc is on the same line regardless of the C concentration profile, and ΔHc / Hc when Hc is 5 kOee is 0.8-0. It is extremely high as about 9.

  From the above results, it is clear that even if the C content in the first magnetic layer 106 is decreased stepwise, the coercive force distribution cannot be improved if the second magnetic layer 107 is not provided. became. In other words, in the present invention, the content of C in the first magnetic layer 106 is reduced stepwise, and the second magnetic layer 107 is provided on the first magnetic layer 106, so that the coercive force dispersion is achieved. Can be reduced.

(Second embodiment)
An example of the layer structure of the heat-assisted magnetic recording medium produced in the second example is shown in FIG.
When producing a heat-assisted magnetic recording medium in the first embodiment, after forming an underlayer 202 made of a Ni-40 at% Ta alloy with a layer thickness of 30 nm on a glass substrate 201, the glass substrate 201 is heated to 280 ° C. A base layer 203 made of Cr having a thickness of 10 nm was formed thereon by heating. Thereafter, a heat sink layer 204 made of Ag with a layer thickness of 100 nm and an underlayer 205 made of MgO with a layer thickness of 10 nm were sequentially formed, and then the glass substrate 201 was heated to 420 ° C. a first magnetic layer 206 made of Fe-55at% Pt) -TiO ₂ alloy, a second magnetic layer 207 were sequentially formed a protective layer 208 made of carbon having a thickness of 3.5 nm (C).

As shown in Table 1, the combination of the concentration profile of TiO ₂ (grain boundary segregation material) in the first magnetic layer 206 and the second magnetic layer 207 was changed. Heat-assisted magnetic recording media of 2-1 to 2-13 were produced.

The first magnetic layer 206 was formed by simultaneously sputtering an Fe-55 at% Pt target and a TiO ₂ target. Further, by reducing the discharge power ratio of the TiO ₂ target with respect to the Fe-55 at% Pt target stepwise or continuously, six types of TiO ₂ concentration profiles (P-5) shown in FIGS. ~ P-10). As a comparative example, a thermally assisted magnetic recording medium in which the content of TiO ₂ in the first magnetic layer 106 was constant (20 mol%) was manufactured (NO. 2-1 to 2-13). The layer thickness of the second magnetic layer 207 was 2 to 4 nm.

The NO. When X-ray diffraction measurement was performed on the heat-assisted magnetic recording media 2-1 to 2-13, strong BCC (200) diffraction peaks were observed from the Cr underlayer 203 and the Ag heat sink layer 204 in any of the media. It was. In addition, a strong L1 ₀ -FePt (001) diffraction peak was observed from the first magnetic layer 206. Further, from the first magnetic layer 206, a mixed peak of L1 ₀ -FePt (002) diffraction peak and FCC-Fe (200) diffraction peak was also observed. Of the first diffraction peaks observed from the magnetic layer 206, the integrated intensity ratio of the former diffraction peak for the latter mixed peak was 1.6, regular high degree of L1 ₀ type FePt alloy crystals formed I found out.

Next, NO. When planar TEM observation was performed on the heat-assisted magnetic recording media 2-1 to 2-12, the first magnetic layer 206 had a granular structure in which the FePt alloy crystal grains were surrounded by TiO _2. Met. Moreover, the average particle diameter of the crystal grains of the FePt alloy was about 5 to 6 nm.

  Furthermore, NO. When the cross-sectional TEM observation was performed on the heat-assisted magnetic recording media of 2-1 to 2-12, as for the first magnetic layer 206, the FePt alloy was continuously grown in the direction perpendicular to the substrate surface for each of the media. It was found that the column structure was taken. On the other hand, NO. When the cross-sectional TEM observation was performed on the heat-assisted magnetic recording medium 2-13, the first magnetic layer 206 had a two-layer structure including a columnar FePt crystal and a spherical FePt crystal formed thereon. I found out.

  In addition, clear lattice fringes were not observed from the alloy used for the second magnetic layer 207. From this, it can be seen that the second magnetic layer 207 used in this example has an amorphous structure.

  Next, NO. For the heat-assisted magnetic recording media of 2-1 to 2-13, the coercive force (Hc) and coercive force dispersion (ΔHc / Hc) when heated from 280 ° C. to 360 ° C. were measured, and when Hc was 5 kOe ΔHc / Hc at temperature was estimated. The results are shown in Table 1.

As shown in Table 1, NO. The heat-assisted magnetic recording media Nos. 2-1 to 2-12 are NO. Compared with the heat-assisted magnetic recording medium of 2-13, ΔHc / Hc when Hc is 5 kOe is about 0.3 to 0.6 lower.
As described above, this is because NO. In the heat-assisted magnetic recording medium 2-13, the first magnetic layer 206 has a two-layer structure including a columnar FePt crystal and a spherical FePt crystal formed on the first magnetic layer 206. In the heat-assisted magnetic recording media of 2-1 to 2-12, it is considered that the cause is that the first magnetic layer has a column structure in which an FePt alloy is continuously grown in a direction perpendicular to the substrate surface.

From the above, in the present invention, the content of TiO ₂ in the first magnetic layer 206 is reduced stepwise, so that the first magnetic layer 206 is continuously grown in a direction perpendicular to the substrate surface. It has become clear that the column structure can be taken, which can reduce coercive force dispersion.

  Further, ΔHc / Hc can be further reduced by increasing the thickness of the second magnetic layer 207 or increasing the saturation magnetic flux density (Bs). However, in any case, since the medium noise increases due to an increase in exchange coupling between FePt crystal grains in the first magnetic layer 206, the thickness and Bs of the second magnetic layer 207 are as follows. It is necessary to design so as to suppress such an increase in medium noise.

  As the second magnetic layer 207, in addition to the above, a BCC or FCC alloy such as FeNi, FeCr, FeV, FePt, or the like can be used.

(Third embodiment)
An example of the layer structure of the heat-assisted magnetic recording medium produced in the third example is shown in FIG.
When producing a heat-assisted magnetic recording medium in the third embodiment, an underlayer 302 made of a Co-50 at% Ti alloy with a layer thickness of 10 nm and a heat sink layer 303 made of Cu with a layer thickness of 200 nm are formed on a glass substrate 301. Then, a soft magnetic underlayer 304 made of a CoFeTaZrB alloy antiferromagnetically coupled to each other via Ru and an underlayer 305 made of Pd having a layer thickness of 10 nm were sequentially formed. Thereafter, the glass substrate 301 is heated to 350 ° C., and a first magnetic layer 306 having a layer thickness of 13 nm and a second magnetic layer 307 made of an Fe-27 at% Co-10 at% Ta alloy having a layer thickness of 5 nm are formed thereon. Then, a protective layer 308 made of carbon (C) having a layer thickness of 3 nm was sequentially formed.

Further, the first magnetic layer 306, after forming the (Co-50at% Pt) -20mol % SiO 2 layer having a thickness of 5 nm, the thickness 2nm (Co-50at% Pt) -15mol% SiO 2 layer A (Co-50 at% Pt) -10 mol% SiO2 layer having a thickness of 2 nm, a (Co-50 at% Pt) -5 mol% SiO ₂ layer having a thickness of 2 nm, and a Co-50 at% Pt layer having a thickness of 2 nm are successively formed. did.

The above respective layers, SiO ₂ content using different CoPt-SiO ₂ composite target was formed by different film forming chambers. In this embodiment, the CoPt—SiO ₂ multilayer film having the five-layer structure is regarded as the first magnetic layer 306.

As a comparative example, a heat-assisted magnetic recording medium (NO. 3-2) using a single layer film of (Co-50 at% Pt) -20 mol% SiO 2 having a layer thickness of 13 nm as the first magnetic layer 306; A heat-assisted magnetic recording medium (NO.3-3) using a single layer film of (Co-50 at% Pt) -5 mol% SiO ₂ with a layer thickness of 13 nm was produced. Except for the difference in the first magnetic layer 306, the layer structure and film formation process of the comparative example medium are the same as those of the example medium (NO.3-1).

NO. For thermally assisted magnetic recording medium of 3-1 to 3-3, was subjected to X-ray diffraction measurement, in either medium, and the first magnetic layer 306 _L1 1 -CoPt (111) diffraction peak, L1 ₁ A -CoPt (333) diffraction peak was observed. This revealed that the CoPt alloy has a good L1 ₁ ordered structure.

In addition, NO. For the heat-assisted magnetic recording media of 3-1 to 3-3, the coercive force (Hc) and coercive force dispersion (ΔHc / Hc) when heated from 280 ° C. to 360 ° C. are measured, and when Hc is 5 kOe ΔHc / Hc at temperature was estimated. Furthermore, the dynamic coercive force Hc0 was measured at a temperature at which Hc was 5 kOe. Here, Hc ₀ was calculated using Sharrock's equation from the magnetic field application speed dependence of Hc. In general, Hc / Hc ₀ represents the strength of exchange coupling between magnetic particles, and becomes lower as the exchange coupling is stronger. Table 2 shows NO. ΔHc / Hc and Hc / Hc ₀ of the heat-assisted magnetic recording media of 3-1 to 3-3 are shown.

As shown in Table 2, NO. In the heat-assisted magnetic recording medium of 3-1, ΔHc / Hc was 0.37. Further, Hc / Hc ₀ is also 0.32 with relatively high, it can be seen that the exchange coupling is reduced.

In contrast, NO. In the heat-assisted magnetic recording medium 3-2, Hc / Hc ₀ is NO. Although it is almost the same as the heat-assisted magnetic recording medium of 3-1, ΔHc / Hc is remarkably high at 1.01. This is because NO. In the heat-assisted magnetic recording medium 3-2, the exchange coupling between the magnetic particles is NO. Although it is as low as the heat-assisted magnetic recording medium of 3-1, the coercive force dispersion is remarkably large.

On the other hand, NO. In the heat-assisted magnetic recording medium of No. 3-3, ΔHc / Hc is NO. Although the 3-1 of the thermally assisted magnetic recording medium is reduced to approximately the same extent, Hc / Hc ₀ is significantly lower and 0.12. This indicates that the exchange coupling between the magnetic particles is remarkably increased by reducing the addition amount of SiO ₂ (grain boundary segregation material), although the coercive force dispersion is reduced. Therefore, it is difficult to reduce the coercive force dispersion without increasing the exchange coupling between the magnetic particles simply by reducing the grain boundary segregation material.

  From the above, in order to reduce the coercive force dispersion without increasing the exchange coupling between the magnetic particles, the content of the grain boundary segregation material in the first magnetic layer 306 is made of glass as in the present invention. It has been found that it is effective to reduce the distance from the substrate 301 side toward the second magnetic layer 307 side.

  In addition to the FeCoTa alloy, a CoCr alloy having a HCP structure, a CoCrPt alloy, a CoCrPtTa alloy, a CoCrPtB alloy, or the like may be used as the second magnetic layer 307.

Example 4
In Example 4, after applying a perfluoropolyether lubricant to the surface of the heat-assisted magnetic recording medium produced in the first to third examples, it was incorporated into the magnetic recording / reproducing apparatus shown in FIG. It is. This magnetic recording / reproducing apparatus includes a heat-assisted magnetic recording medium 501, a medium driving unit 502 for rotating the heat-assisted magnetic recording medium, and a magnetic head that performs a recording operation and a reproducing operation on the heat-assisted magnetic recording medium 501. 503, a head drive unit 504 for moving the magnetic head 503 relative to the heat-assisted magnetic recording medium 501, and recording / reproduction for performing signal input to the magnetic head 503 and reproduction of output signals from the magnetic head 503 And a signal processing system 505. Although not shown in FIG. 10, the magnetic recording / reproducing apparatus is provided with a laser generator for generating laser light and a waveguide for transmitting the generated laser light to the magnetic head 503. .

  FIG. 11 schematically shows the structure of the magnetic head 503 incorporated in the magnetic recording / reproducing apparatus. The magnetic head 503 includes a recording head 601 and a reproducing head 602. The recording head 601 includes a main magnetic pole 603, an auxiliary magnetic pole 604, and a PSIM (Planar Solid Immersion Mirror) 605 sandwiched therebetween. . The PSIM 605 having a structure as described in, for example, “Jpn., J. Appl. Phys., Vol 145, no. 2B, pp 1314-1320 (2006)” can be used. The recording head 601 irradiates the grating portion 606 of the PSIM 605 with laser light L having a wavelength of 440 nm from a laser light source 607 such as a semiconductor laser, and heats the heat-assisted magnetic recording medium 501 with near-field light NL generated from the front end portion of the PSIM 605. While recording. On the other hand, the reproducing head 602 includes a TMR element 610 sandwiched between an upper shield 608 and a lower shield 609.

  The heat-assisted magnetic recording medium 501 was heated by the magnetic head 503, recorded at a linear recording density of 21800 kFCI (kilo Flux changes per inch), and the electromagnetic conversion characteristics were measured. As a result, a high medium SN ratio of 15 dB or more and good overlay were obtained. Writing characteristics were obtained.

DESCRIPTION OF SYMBOLS 101 ... Glass substrate 102 ... Underlayer 103 ... Soft-magnetic underlayer 104 ... Underlayer 105 ... Underlayer 106 ... First magnetic layer 107 ... Second magnetic layer 108 ... Protective layer 201 ... Glass substrate 202 ... Underlayer 203 ... Underlayer 204 ... Heat sink layer 205 ... Underlayer 206 ... First magnetic layer 207 ... Second magnetic layer 208 ... Protective layer 301 ... Glass substrate 302 ... Underlayer 303 ... Heat sink layer 304 ... Soft magnetic underlayer 305 ... Underlayer 306 ... First magnetic layer 307 ... Second magnetic layer 308 ... Protective layer 501 ... Thermally assisted magnetic recording medium
502: Medium drive unit
503: Magnetic head
504 ... Head drive unit
505. Recording / reproduction signal processing system
601. Recording head
602 ... Reproducing head
603 ... Main pole
604 ... Auxiliary magnetic pole
605 ... PSIM (Planar Solid Immersion Mirror)
606: Grating section
607 ... Laser light source
608 ... Upper shield
609 ... Bottom shield
610 ... TMR element
L ... Laser light
NL ... Near-field light

Claims (9)

At least on the substrate, and a first magnetic layer and the second magnetic layer are sequentially stacked, the first magnetic layer, FePt alloy having an L1 ₀ structure, CoPt having an L1 ₀ structure a alloy, or with any of the crystal grains of CoPt alloy having a L1 ₁ structure, a granular structure including a C forming the grain boundary polarization析材fees,
And the content rate of C in the first magnetic layer is decreasing from the substrate side toward the second magnetic layer side, and the content rate of C in the first magnetic layer is A heat-assisted magnetic recording comprising: a region that is constant from the substrate side toward the second magnetic layer side; and a region that decreases from the substrate side toward the second magnetic layer side. Medium. Thermally assisted magnetic recording medium according to claim 1, the content of the C is the percentage of the area becomes constant, wherein the first 70% or less of the thickness of the magnetic layer. In the region where the content of the C is constant, the content of this C is thermally assisted magnetic recording medium according to claim 1 or 2, characterized in that 30% by volume or more. Said second magnetic layer contains a Co, and, Zr, Ta, Nb, B, according to claim 1 to 3, characterized in that an amorphous alloy containing at least one or more of Si The heat-assisted magnetic recording medium according to any one of the above. Said second magnetic layer contains a Fe, and, Zr, Ta, Nb, B, according to claim 1 to 3, characterized in that an amorphous alloy containing at least one or more of Si The heat-assisted magnetic recording medium according to any one of the above. It said second magnetic layer is thermally assisted magnetic recording medium according to any one of claim 1 to 3, characterized in that an alloy of BCC structure, or FCC structure containing Fe. Said second magnetic layer is thermally assisted magnetic recording medium according to any one of claim 1 to 3, characterized in that an alloy of HCP structure containing Co. The magnetocrystalline anisotropy constant of the second magnetic layer is heat according to any one of claim 1 to 3, wherein a lower than the crystalline magnetic anisotropy constant of the first magnetic layer Assisted magnetic recording medium. The heat-assisted magnetic recording medium according to any one of claims 1 to 8 ,
A medium drive unit for driving the heat-assisted magnetic recording medium in a recording direction;
A recording and reproducing operation for the thermally-assisted magnetic recording medium, comprising: a laser generating section for heating the thermally-assisted magnetic recording medium; and a waveguide for guiding the laser beam generated from the laser generating section to a tip section. A magnetic head to perform,
A head moving unit for moving the magnetic head relative to the heat-assisted magnetic recording medium;
A magnetic recording / reproducing apparatus comprising a recording / reproducing signal processing system for inputting a signal to the magnetic head and reproducing an output signal from the magnetic head.

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