JP2012221542A - Heat-assisted magnetic recording medium and magnetic storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a heat-assisted recording medium which is segmented by the uniform grain boundary width and has a magnetic layer comprising magnetic crystal grains grown with column, and to provide a magnetic storage device having a low error rate using the heat-assisted recording medium.SOLUTION: A magnetic recording medium comprises a substrate, a plurality of foundation layers formed on the substrate, and a magnetic layer containing an alloy having an L1structure as a main component. The magnetic layer has a two-layer structure constituted of a first magnetic layer comprising an FePt alloy having an L1structure and C, and a second magnetic layer comprising an FePt alloy having an L1structure, and CrO, YOor TaO. Moreover, a non-magnetic intermediate layer for controlling exchange coupling is provided between the first magnetic layer and the second magnetic layer.

Description

  The present invention relates to a heat-assisted magnetic recording medium and a magnetic storage device using the same.

Thermally assisted recording, in which writing is performed by irradiating the medium with near-field light to locally heat the surface and reducing the coercive force of the medium, the next-generation recording method that can realize a surface recording density of 1 Tbit / inch ² class It is attracting attention as. The thermally-assisted recording medium, the magnetic layer, and FePt alloy having an L1 ₀ type crystal structure, is also medium using CoPt alloy having an L1 ₀ type crystal structure is used. Ordered alloy having the L1 ₀ type crystal structure, because it has a 10 6 J ^/ m ³ units high magnetocrystalline anisotropy Ku, while maintaining the thermal stability can refining crystal grain size to less than about 6nm . Thereby, the medium noise can be greatly reduced while maintaining the thermal stability.

In order to reduce the medium noise of the heat-assisted recording medium, it is necessary to reduce exchange coupling between the magnetic particles in addition to miniaturization of the magnetic particle diameter. For this purpose, it is desirable to add a grain boundary material to the magnetic layer to form a granular structure in which the magnetic crystal grains are divided by the grain boundary material. Patent Document 1, the magnetic layer containing the L1 ₀ type FePt alloy, it is described that the addition of _{SiO 2, TiO 2, Ta 2} O 5 as a grain boundary material. Patent Document 2 describes that MgO, C, SiO ₂ , TiO ₂ , Ta ₂ O ₅ , Al ₂ O ₃ , BN, SiNx, and B ₄ C are added as grain boundary materials.

On the other hand, it has been proposed to form a continuous film on a magnetic film having a granular structure. For example, in Patent Document 3, writing characteristics are improved by forming a continuous film made of FePt or CoCrPtB alloy as a cap layer on a magnetic layer having a granular structure made of an L1 ₀ -FePt alloy and an oxide. It is disclosed. Further, Patent Document 4 discloses that by forming a TbFeCo film having an amorphous structure on a magnetic layer having a granular structure, a fine magnetic domain structure can be formed in the TbFeCo film and recording resolution can be improved. Has been.

JP 2009-158054 A JP 2010-176829 A JP 2009-158053 A JP 2008-159177 A

  In order to reduce exchange coupling between the magnetic particles, it is desirable to have a granular structure in which the magnetic particles are surrounded by a grain boundary phase made of an oxide or the like. However, the width of the grain boundary phase needs to be as uniform as possible. If the grain boundary width becomes non-uniform, the strength of exchange coupling between the magnetic grains becomes non-uniform and the switching field distribution SFD (Switching Field Distribution) increases.

  On the other hand, the magnetic crystal grains need to have a column structure in which the grain size is kept constant from the initial growth portion to the upper portion and is continuously grown. Currently, when the proposed grain boundary material is used alone, the above conditions cannot be satisfied. Realization of a structure in which magnetic grains are divided by a uniform grain boundary width and the magnetic grains are column-grown is an important issue for achieving a high recording density of the heat-assisted recording medium.

The above object includes a substrate, a plurality of base layer formed on the substrate, a magnetic recording medium comprising a magnetic layer mainly composed of an alloy having an L1 ₀ structure, the magnetic layer is an L1 ₀ structure A two-layer configuration including a first magnetic layer made of FePt alloy and C, a FePt alloy having an L1 ₀ structure and a _second magnetic layer made of Cr ₂ O ₃ , Y ₂ O ₃ or Ta ₂ O ₅ ; This can be solved. That is, the present invention relates to the following.

(1) FePt having a substrate, a plurality of base layer formed on the substrate, a magnetic recording medium comprising a magnetic layer mainly composed of an alloy having an L1 ₀ structure, the magnetic layer is an L1 ₀ structure A magnetic recording comprising: a first magnetic layer made of an alloy and C; and a second magnetic layer made of a FePt alloy having an L1 ₀ structure and Cr ₂ O ₃ , Y ₂ O ₃ or Ta ₂ O _5. Medium.
(2) The magnetic recording medium according to (1), wherein the thickness of the first magnetic layer is 6 nm or less.
(3) The magnetic recording medium according to (1) or (2), wherein a nonmagnetic intermediate layer for controlling exchange coupling is provided between the first magnetic layer and the second magnetic layer. .
(4) The magnetic recording according to any one of (1) to (3), wherein the magnetic layer further includes a third magnetic layer not having a granular structure composed of crystal grains and a grain boundary phase. Medium.
(5) The third magnetic layer has an amorphous structure or a microcrystalline structure containing Fe or Co as a main component and containing at least one element selected from Nd, Sm, Gd, Tb, and Dy. The magnetic recording medium according to (4), which is an alloy.
(6) The third magnetic layer has an amorphous structure or a microcrystalline structure containing Fe or Co as a main component and containing at least one element selected from Ta, Nb, Zr, Si, and B. The magnetic recording medium according to (4), which is an alloy.
(7) In any one of (4) to (6), a nonmagnetic intermediate layer for controlling exchange coupling is provided between the second magnetic layer and the third magnetic layer. The magnetic recording medium described.
(8) A magnetic recording medium, a driving unit for rotating the magnetic recording medium, a laser generating unit for heating the magnetic recording medium, and a laser beam generated from the laser generating unit for guiding the laser light to the head tip. In a magnetic storage device comprising a waveguide, a magnetic head having a near-field light generating unit attached to the tip of the head, a driving unit for moving the magnetic head, and a recording / reproducing signal processing system, the magnetic recording medium A magnetic storage device according to any one of (1) to (7).

  According to the present invention, it is possible to obtain a heat-assisted magnetic recording medium in which the magnetic particles in the magnetic layer are divided at a uniform grain boundary width and the magnetic particles are column-grown. As a result, a heat-assisted recording medium having a narrow switching field dispersion SFD is realized, and a magnetic storage device having a low error rate using the medium can be provided.

The figure showing an example of the laminated constitution of the magnetic recording medium of this invention Schematic representation of grain growth in the magnetic layer The figure showing an example of the laminated constitution of the magnetic recording medium of this invention The figure showing the magnetic head of this invention The perspective view of the magnetic storage device of the present invention

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments.

The present invention relates to a magnetic recording medium including a substrate, a plurality of underlayers formed on the substrate, and a magnetic layer mainly composed of an alloy having an L1 ₀ structure, wherein the magnetic layer has an FePt alloy having the L1 ₀ structure. And a second magnetic layer comprising an FePt alloy having an L1 ₀ structure and Cr ₂ O ₃ , Y ₂ O ₃ or Ta ₂ O ₅ . FIG. 1 shows an example of an embodiment of the present invention. A first underlayer 102, a second underlayer 103, a third underlayer 104, a first magnetic layer 105, and a second magnetic layer are shown on a substrate 101. A layer 106 and a protective film 107 are formed.

In the manufacture of magnetic recording medium of the present invention, since assume a good L1 ₀ ordered structure in FePt alloy used in the magnetic layer, it requires heating the substrate above 450 ° C.. Therefore, it is desirable to use a heat-resistant glass substrate having a softening temperature of 500 ° C. or higher as the substrate.

  It is desirable to use an amorphous alloy for the first underlayer. Specifically, Co-50 at% Ta, Co-50 at% Ti, Ni-50 at% Ta, Ni-50 at% Ti, Cr-50 at% Ti alloy, or the like can be used. If the film thickness of the seed layer is less than 10 nm, it is difficult to raise the substrate temperature by infrared heating. Therefore, the film thickness is desirably 10 nm or more.

  For the second underlayer, RuAl or NiAl having a B2 structure can be used. By forming the base layer having the B2 structure on the amorphous alloy base layer heated to 150 ° C. or higher, the base layer can be made to have B2 (100) orientation. Thereby, the (100) orientation can be made to the 3rd underlayer mentioned later. Further, Cr or an alloy having a BCC structure containing Cr as a main component and containing at least one of Ti, V, Mo, W, Mn, and Ru may be used for the second underlayer. These alloys can also be (100) oriented by forming on an amorphous alloy underlayer heated to 150 ° C. or higher.

For the third underlayer, TiN, TiC, MgO, NiO or the like having a NaCl structure can be used. When these alloys are formed on a (100) -oriented base layer of B2 structure or a (100) -oriented base layer of BCC structure, (100) orientation is exhibited by epitaxial growth. As a result, the (001) orientation can be taken in the L1 ₀ -FePt alloy formed on the third underlayer. The material used for the third underlayer also functions as a thermal barrier layer because of its low thermal conductivity. For this reason, the magnetic layer can be heated to a higher temperature. However, when the medium heating capacity of the recording head is sufficient, the third underlayer is not necessarily provided.

The magnetic layer includes a first magnetic layer composed of an FePt alloy having an L1 ₀ structure and a C grain boundary phase, an FePt alloy having an L1 ₀ structure and a Cr ₂ O ₃ , Y ₂ O ₃ , or Ta ₂ O ₅ grain boundary. A two-layer structure including a second magnetic layer made of a phase is preferable. By forming a magnetic layer after heating the substrate temperature above 450 ° C., to assume a high L1 ₀ structure regularity degree FePt alloy in the magnetic layer, and (001) can assume an orientation. The amount of C added to the first magnetic layer is desirably 30 at% or more. Thereby, the L1 ₀ -FePt alloy crystal grains can have a granular structure divided by a C grain boundary phase having a uniform width. However, the thickness of the first magnetic layer is desirably 6 nm or less. If it exceeds 6 nm, the FePt crystal grains in the first magnetic layer 105 do not take the column structure continuously grown in the direction perpendicular to the film surface, and the initial growth portion 201 and the upper portion thereof as schematically shown in FIG. In addition, a two-stage structure composed of secondary growth portions (secondary growth grains) 203 grown in a spherical shape via the C grain boundary phase 202 is adopted. Note that the lower limit of the thickness of the first magnetic layer is preferably 1 nm. When the thickness of the first magnetic layer is less than 1 nm, the first magnetic layer is less likely to have the column structure described above.

  The FePt crystal in the secondary growth portion indicated by reference numeral 203 in FIG. 2 is randomly oriented and has a low degree of order. For this reason, the reversed magnetic field dispersion SFD is remarkably widened, and the medium SNR is remarkably lowered. In order to obtain a high SNR, it is necessary to set the reproduction output of the medium high. Therefore, the total film thickness of the magnetic layer is desirably 8 nm or more. However, as described above, it is difficult to set the film thickness to 8 nm or more with a single magnetic layer composed of FePt magnetic grains and a C grain boundary phase.

Therefore, the thickness of the first magnetic layer is set to 6 nm or less, and an FePt alloy having an L1 ₀ structure and Cr ₂ O ₃ , Y ₂ O ₃ , or Ta ₂ O ₅ are formed on the first magnetic layer. The second magnetic layer is preferably formed so that the total thickness of the magnetic layer is 8 nm or more. The second magnetic layer is formed on the first magnetic layer, whereby the FePt crystal is separated by a uniform grain boundary phase made of Cr ₂ O ₃ , Y ₂ O ₃ , or Ta ₂ O _5. Take the structure. Further, FePt alloy of the second magnetic layer is on the _L1 0 -FePt alloy of the first magnetic layer epitaxially grown (001) takes the orientation, and take a high degree of order L1 ₀ structure. As a result, a magnetic layer having a thickness of 8 nm or more and magnetic crystal grains separated by a uniform grain boundary width can be formed. By using the magnetic layer having the two-layer structure, a heat assist medium having a narrow switching field dispersion SFD and a high medium SNR can be obtained.

  Ag, Cu, or the like may be added to the FePt alloy in the first magnetic layer or the second magnetic layer. Thereby, the degree of order can be improved and the magnetic anisotropy can be increased. Ni may also be added. Thereby, the Curie temperature is lowered and the recording temperature can be set low.

Even if the C concentration in the first magnetic layer and the Cr ₂ O ₃ , Y ₂ O ₃ , or Ta ₂ O ₅ concentration in the second magnetic layer are changed continuously or stepwise in the film thickness direction. Good. That is, the first magnetic layer may be composed of a plurality of layers having different C concentrations, and the second magnetic layer may be composed of a plurality of Cr ₂ O ₃ , Y ₂ O ₃ , or Ta ₂ O ₅ concentrations. It may be composed of layers. Further, the concentration of additive elements such as Ag, Cu, and Ni may be changed in the thickness direction of the magnetic layer. The recording / reproducing characteristics can be further improved by changing the magnetic characteristics in the magnetic layer, the strength of exchange coupling, and the like in the film thickness direction according to the distance from the head.

  An intermediate layer for controlling exchange coupling may be formed between the first magnetic layer and the second magnetic layer. In this case, the intermediate layer is preferably made of a material that is epitaxially grown on the first magnetic layer. Thereby, the second magnetic layer can be epitaxially grown on the intermediate layer. The intermediate layer is preferably a non-magnetic material, but may be a magnetic material as long as it has a weak magnetization of 100 emu / cc or less. Specifically, a Cr alloy such as CrTi, CrW, or CrMo, a material used for the second underlayer or the third underlayer, such as MgO, TiN, or TiC, can be used. However, the material for the intermediate layer is not particularly limited as long as the lattice misfit with the first magnetic layer and the second magnetic layer is approximately 10% or less. By providing the intermediate layer and optimizing the interlayer coupling between the first magnetic layer and the second magnetic layer, the switching field dispersion SFD can be further reduced.

FIG. 3 shows another example of the embodiment of the present invention. A third magnetic layer 301 is further formed on the second magnetic layer. The third magnetic layer preferably does not contain an oxide such as C or Cr ₂ O ₃ and is a continuous film that is magnetically and structurally uniform and does not have a granular structure. Here, magnetically and structurally uniform means that there is no composition unevenness in the film and there is no local unevenness of magnetization and magnetic anisotropy. By introducing the magnetically uniform third magnetic layer, uniform exchange coupling can be introduced between the FePt magnetic grains in the first and second magnetic layers, and the switching field dispersion can be further reduced. The third magnetic layer is preferably an amorphous alloy. A crystalline alloy is not preferred because it has a large magnetic and structural non-uniformity due to lattice defects, compositional segregation, random direction of easy magnetization axis, etc., and uniform exchange coupling cannot be introduced. Specifically, amorphous alloys such as CoZrTa, CoZrNb, CoFeB, CoFeTa, CoFeTaZr, CoFeTaB, CoFeTaSi, and CoFeTaZr can be used. Further, an amorphous alloy containing a rare earth element such as TbFeCo or SmCo may be used.

  By introducing the third magnetic layer, uniform exchange coupling can be introduced and the SFD can be narrowed. However, in this case, the second magnetic layer needs to have a granular structure that is divided by a uniform grain boundary phase and column-grown. If the separation of crystal grains in the second magnetic layer is insufficient, uniform exchange coupling cannot be introduced even if the third magnetic layer is introduced. Therefore, the reversal magnetic field dispersion SFD cannot be reduced, and good recording / reproduction characteristics cannot be obtained. In addition, the magnetic cluster size increases due to the introduction of exchange coupling. In order to achieve good recording / reproduction characteristics, particularly high medium SNR, it is necessary to narrow the SFD and simultaneously reduce the magnetic cluster size. Therefore, it is necessary to design the magnetization and film thickness of the third magnetic layer in consideration of an appropriate balance between the SFD and the magnetic cluster size.

  An intermediate layer for controlling exchange coupling may be formed between the second magnetic layer and the third magnetic layer. In this case, the intermediate layer may be crystalline or amorphous. Further, a non-magnetic material may be used, and a magnetic material may be used as long as it has a weak magnetization of 100 emu / cc or less. By optimizing the interlayer coupling between the second magnetic layer and the third magnetic layer by the intermediate layer, the reversal magnetic field can be reduced and the overwrite characteristic can be improved.

Hereinafter, the effects of the present invention will be made clearer by examples. The present invention is not limited to the following examples.

Example 1
On the glass substrate, 50 nm Co-50 at% Ti as the first underlayer and 10 nm Cr-10 at% Ru as the second underlayer are formed. After heating the substrate at 250 ° C., the third underlayer is formed. A TiN underlayer having a thickness of 10 nm was sequentially formed as a base layer. Thereafter, the substrate is heated again at 520 ° C. to form 5 nm (Fe-50 at% Pt) -40 at% C as the first magnetic layer, and 5 nm (Fe-45 at% Pt) as the second magnetic layer. -15mol% _Cr 2 _{O 3} (example 1.1), (Fe-50at% Pt-3at% Cu) -9.5mol% Y 2 O 3 ( example 1.2), or (Fe-45at% Pt −5 at% Ag) -8 mol% Ta ₂ O ₅ (Example 1.3) was formed, and a DLC protective film of 3 nm was further formed.

As a comparative example, a medium in which the magnetic layer is a single layer film was produced. As the monolayer film, 10 nm of (Fe-50 at% Pt) -40 at% C (Comparative Example 1.1), (Fe-45 at% Pt) -15 mol% Cr ₂ O ₃ (Comparative Example 1.2), ( Fe-50 at% Pt-3 at% Cu) -9.5 mol% Y ₂ O ₃ (Comparative Example 1.3) or (Fe-45 at% Pt-5 at% Ag) -8 mol% Ta ₂ O ₅ (Comparative Example 1) .4) was used.

When X-ray diffraction measurement of Examples 1.1 to 1.3 was performed, the L1 ₀ -FePt (001) diffraction peak, the L1 ₀ -FePt (002) diffraction peak, and the FCC from the magnetic layer in all the media. Only a mixed peak of -FePt (200) peak was observed. Further, no clear diffraction peak was observed from the CoTi underlayer, but only the (200) peak was observed from the CrRu underlayer and TiN underlayer. From this, it can be seen that the CoTi underlayer is amorphous, the CrRu underlayer formed thereon has a (100) orientation, and the TiN underlayer thereon has also a (100) orientation by epitaxial growth. It was. The reason why the magnetic layer has the above-mentioned orientation is considered to be due to epitaxial growth on the TiN underlayer.

  Next, a planar TEM observation of the medium of this example was performed, and a granular structure in which the magnetic grains were divided at the grain boundary phase was taken. Table 1 shows the average particle size <D> of the medium of this example and the particle size dispersion σ / <D> normalized by the average particle size. The average particle size of all of the media of this example was 6 nm or less, and the particle size dispersion was 20% or less. Further, when a cross-sectional TEM observation of the medium of this example was performed, it was found that the magnetic crystal grains had a column structure continuously grown in the direction perpendicular to the film surface.

  On the other hand, when a plane TEM observation was performed on the comparative example medium 1.1 using C as the grain boundary phase, the granular material in which crystal grains having a grain size of about 5 to 7 nm were divided at the grain boundaries as in the example medium. It had a structure. However, in addition to the crystal grains, a large number of extremely fine crystal grains having a grain size of 2-3 nm or less were observed at the grain boundaries or within the grains. When the cross-sectional TEM observation of Comparative Example 1.1 was performed, the magnetic layer had a dome-shaped initially grown crystal grain that stopped growing at a height of 5-6 nm, and a spherical shape grown on the dome-shaped crystal grain via the grain boundary. It has a two-stage structure composed of secondary grown crystal grains. Therefore, the fine crystal grains of 2-3 nm or less observed in the planar TEM image are considered as the secondary grown crystal grains.

Next, when plane TEM observation was performed on the comparative example media 1.2 to 1.4 using Cr ₂ O ₃ , Y ₂ O ₃ , and Ta ₂ O ₅ as the grain boundary phase, the magnetic grains were in the grain boundary phase. Many portions where adjacent magnetic particles were connected were observed without being completely divided.

  Table 2 shows the average particle size <D> of the comparative example medium and the particle size dispersion σ / <D> normalized by the average particle size. Note that adjacent particles connected to each other in the TEM image are regarded as one particle. The average particle diameter of Comparative Example Medium 1.1 was 5.4 nm, which was almost the same as that of the Example Medium, but the normalized particle diameter dispersion showed a remarkably high value. This is considered to be due to the presence of a large number of secondary growth grains having a remarkably fine grain size. Comparative media 1.2 to 1.4 were significantly higher in average particle size and particle size dispersion than the example media. This is presumably because there are many adjacent particles connected to each other.

From the above, consisting of a first magnetic layer, FePt alloy having an L1 ₀ structure and the _{Cr 2 O 3, Y 2 O} 3, or _Ta 2 _{O 5} grain boundary phase composed of the magnetic layer from FePt alloy and C grain boundary phase By adopting a two-layer structure composed of the second magnetic layer, a column structure in which the magnetic crystal grains are completely divided by the grain boundary phase and the magnetic crystal grains are continuously grown in the direction perpendicular to the film surface is adopted. I found out that It was also found that this can reduce the particle size dispersion to 20% or less of the average particle size.

  Table 3 shows the coercive force Hc and the normalized coercive force dispersion ΔHc / Hc of the above example medium and the comparative example medium. Here, Hc was measured at room temperature by applying a 7T magnetic field by PPMS. ΔHc / Hc was measured by the method described in “IEEE Trans. Magn., Vol. 27, pp 4975-4777, 1991”. Specifically, in the major loop and the minor loop measured at room temperature by applying a maximum magnetic field of 7T, the magnetic field when the magnetization value is 50% of the saturation value is measured, and the Hc distribution is calculated from the difference between the two. ΔHc / Hc was calculated on the assumption that is a Gaussian distribution. ΔHc / Hc is a parameter corresponding to reversal magnetic field dispersion, and a lower value is desirable because a higher medium SNR can be obtained.

  All of the media of Examples 1.1 to 1.3 showed a high coercive force of 32 kOe or more, and the coercive force dispersion was 0.29 or less. On the other hand, for the comparative example medium, the coercive force of the comparative example medium 1.1 was almost the same as that of the example, but the coercive force of the comparative example mediums 1.2 to 1.4 was significantly larger than that of the example. It was low. This is considered because the exchange coupling between magnetic particles is strong. Further, the coercive force dispersion of the comparative example medium was remarkably wide as compared with the example medium. As described above, this is considered to be due to the fact that the particle size dispersion of the comparative example medium is significantly larger than that of the example medium. From the above, it was found that the medium of this example had a narrow particle size dispersion and a narrow coercive force dispersion.

(Example 2)
A heat sink layer made of a 50 nm Cu-12.5 at% Pd alloy and a soft magnetic underlayer made of a 50 nm Co-15 at% Ta-10 at% Zr alloy were formed on a glass substrate, and the substrate was heated at 550 ° C. Thereafter, a Ru-50 at% Al underlayer of 25 nm was formed. Next, a 4 nm TiN underlayer is formed, 3 nm (Fe-45 at% Pt-5 at% Ni) -45 at% C as the first magnetic layer, and 8 nm (Fe-50 at% Pt) as the second magnetic layer. -12mol% _Cr 2 _{O 3} (example 2.1), (Fe-50at% Pt) -7mol% Y 2 O 3 ( example 2.2), or (Fe-50at% Pt) -6.5mol % Ta ₂ O ₅ (Example 2.3) was formed, and a 2.5 mn DLC protective film was formed. In addition, as a comparative example, the second magnetic layer has 8 nm of (Fe-50 at% Pt) -12 mol% SiO ₂ (Comparative Example 2.1), (Fe-50 at% Pt) -17.5 mol% TiO ₂ (Comparison A medium using Example 2.2) was prepared.

  Table 4 shows the coercive force Hc and the normalized coercive force dispersion ΔHc / Hc of Example Media 2.1 to 2.3. Here, Hc and ΔHc / Hc were obtained in the same manner as in Example 1. In all of the media of this example, Hc was 36 kOe or more, and ΔHc / Hc was 0.24 or less. On the other hand, Hc of Comparative Example Media 2.1 to 2.2 was as low as 24 kOe or less, and ΔHc / Hc was 0.35 or more.

  When planar TEM observation of the media of Examples 2.1 to 2.3 was performed, a granular structure in which magnetic particles having an average particle size of 5.5 to 6.3 nm were divided by a grain boundary phase was taken. On the other hand, when plane TEM observation of Comparative Example Media 2.1 to 2.2 was performed, grain separation due to the grain boundary phase was insufficient, and many adjacent particles connected to each other were observed. This is considered to be the reason why ΔHc / Hc of the comparative example medium was large.

From the above, the second magnetic layer, by using the FePt alloy and _Cr 2 _{O 3,} Y 2 _O consists of ₃ or _Ta 2 _{O 5} material having an L1 ₀ structure, it .DELTA.Hc / Hc is low medium is obtained I understood.

(Example 3)
With the same underlayer structure as in Example 2, the first magnetic layer was (Fe-45 at% Pt-5 at% Ni) -40 at% C, and the second magnetic layer was (Fe-50 at% Pt) -5 mol% Ta ₂ O. ₅ was used. Here, the thickness of the first magnetic layer was set to 1 nm, 3 nm, and 5 nm, and the total thickness of the first magnetic layer and the second magnetic layer was set to 10 nm. As a comparative example, a medium in which the thickness of the first magnetic layer was 9 nm, 7 nm, and 5 nm was manufactured.

  As a result of cross-sectional TEM observation of this example medium and the comparative example medium, column-grown crystal grains were observed in the magnetic layer of the example medium, whereas in the magnetic layer of the comparative example medium, magnetic properties were observed. Many spherical crystal grains secondary grown near the surface of the layer were observed. Table 5 shows Hc and ΔHc / Hc of the medium of this example and the comparative medium. Although ΔHc / Hc tends to increase as the thickness of the first magnetic layer increases, ΔHc / Hc is as low as 0.27 or less in this example medium in which the thickness of the first magnetic layer is 5 nm or less. The value is suppressed. This is considered because the production | generation of a secondary growth grain is suppressed as mentioned above. From the above, it was found that the thickness of the first magnetic layer is preferably 6 nm or less in order to grow magnetic crystal grains in a column and to suppress ΔHc / Hc to a low value.

Example 4
In the same layer configuration as in Example 1, (Fe-50 at% Pt) -8 mol% Ta ₂ O ₅ of 5 nm was formed as the _second magnetic layer, and a third magnetic layer was further formed. The third magnetic layer has 4 nm of Co-20 at% Nb-5 at% Zr (Example 4.1), Co-27 at% Fe-5 at% Zr-5 at% Si (Example 4.2), Fe- 10 at% Ta-10 at% B (Example 4.3), Fe-10 at% Ta-10 at% C (Example 4.4), Fe-28 at% Tb-12 at% Co (Example 4.5), Co An alloy of −20 at% Sm (Example 4.6) was used. Further, as a comparative example, a medium in which 4 nm of Co-12 at% Cr-14 at% Pt-8 at% B (Comparative Example 4.1) was formed on the third magnetic layer was produced. Furthermore, as a comparative example, 5 nm of (Fe-50 at% Pt) -16 mol% SiO ₂ (Comparative Example 4.2) or 5 nm of (Fe-50 at% Pt) -21.5 mol% TiO ₂ was used for the second magnetic layer. (Comparative Example 4.3) and a medium using 4 nm Co-20 at% Nb-5 at% Zr (Comparative Example 4.2) (Comparative Example 4.2, 4.3) for the third magnetic layer Was made.

  When cross-sectional TEM observation of the media of Examples 4.1 to 4.6 was performed, clear lattice fringes were not observed from the third magnetic layer. Therefore, these alloys are considered to have an amorphous or microcrystalline structure. On the other hand, it was confirmed that the CoCrPtB alloy used for the third magnetic layer of Comparative Example Medium 4.1 had an HCP structure.

  Table 6 shows the coercive force Hc and the normalized coercive force dispersion ΔHc / Hc of the medium of this example. Here, Hc and ΔHc / Hc were obtained in the same manner as in Example 1. In all of Examples 4.1 to 4.6, Hc was 25 kOe or more, and ΔHc / Hc was 0.25 or less. By comparing this result with the medium of Example 1 shown in Table 3, it can be seen that ΔHc / Hc can be further reduced by forming the third magnetic layer. Example media 4.1 to 4.4 in which an alloy containing Fe or Co as a main component and containing Ta, Nb, Zr, Si, B, and C is used for the third magnetic layer among the example media. A particularly low ΔHc / Hc of 0.22 or less was exhibited. In addition, Examples Media 4.5 to 4.6 using an amorphous alloy containing a rare earth alloy such as FeTeCo or CoSm for the third magnetic layer showed a high Hc of 28 kOe or more.

On the other hand, Comparative Example Medium 4.1 had a lower Hc than the Example Medium, and ΔHc / Hc was significantly larger than the Example Medium. From this, it can be seen that using an amorphous alloy for the third magnetic layer is more effective in reducing ΔHc / Hc than a Co alloy having an HCP structure. However, even when a CoNbZr alloy, which is an amorphous alloy, is used for the third magnetic layer, the comparative example medium 4.2 using FePt—SiO ₂ or FePt—TiO ₂ for the second magnetic layer, the comparative example The ΔHc / Hc of the medium 4.3 is higher than that of the example medium. This is because, as shown in Example 2, when FePt—SiO ₂ or FePt—TiO ₂ is used for the second magnetic layer, the separation of the magnetic crystal grains is insufficient and non-uniform exchange coupling occurs. This is probably because it has been introduced. Therefore, in order to effectively reduce ΔHc / Hc by forming the third magnetic layer, the grain boundary phase material added to the second underlayer is Cr ₂ O ₃ , Y ₂ O ₃ or Ta ₂ O ₅ . I found it desirable.

(Example 5)
A perfluoroether-based lubricant was applied to the medium shown in Example 4, and the RW characteristics were evaluated using a heat-assisted recording head. As shown in FIG. 4, the used head transmits a main magnetic pole 401, an auxiliary magnetic pole 402, a coil 403 for generating a magnetic field, a laser diode LD404, and a laser beam 405 generated from the LD to a near-field generating element 406. The recording head 408 is composed of a waveguide 407, and the reproducing head 411 is composed of a reproducing element 410 sandwiched between shields 409. Recording can be performed by heating the medium 412 with near-field light generated from the near-field light element and reducing the coercivity of the medium to a head magnetic field or less.

  Table 7 shows the medium SNR and the track width MWW measured by recording an all-one pattern signal with a linear recording density of 1400 kFCI using the head. Here, the track width is defined as the half width of the track profile. Each of the example media 4.1 to 4.6 showed a high SNR of 15 dB or more and a narrow track width of 80 nm or less. In particular, the example media 4.1 to 4.3 using Co for the third magnetic layer exhibited a high SNR of 16 dB or more. This is considered to be because ΔHc / Hc is low. On the other hand, the track widths of the example media 4.4 to 4.6 were particularly narrow. On the other hand, the SNRs of the comparative example media 4.1 to 4.3 were extremely low and the track width was widened. From this, it was found that a heat-assisted recording medium having a high SNR and a narrow track width can be obtained by using an amorphous alloy for the third magnetic layer.

(Example 6)
The medium shown in Example 1 (Example Medium 1.1 to 1.3, Comparative Example Medium 1.1 to 1.4) and the medium shown in Example 2 (Example Medium 2.1 to 2.3) Comparative Examples Media 2.1 to 1.2) were coated with a perfluoroether lubricant and incorporated into the magnetic storage device shown in FIG. This magnetic storage device includes a magnetic recording medium 412, a driving unit 502 for rotating the magnetic recording medium, a magnetic head 503, a driving unit 504 for moving the head, and a recording / reproducing signal processing system 505. The As the magnetic head, the heat-assisted recording head described in Example 5 was used.

Table 8 shows the result of evaluating the bit error rate BER by recording with the magnetic storage device under the conditions of a linear recording density of 1600 kFCI and a track density of 400 kFCI (surface recording density of 640 Gbit / inch ² ). Magnetic storage devices incorporating the example media 1.1 to 1.3 and the example media 2.1 to 2.3 showed a low error rate of 1 × 10 ⁻⁶ units. On the other hand, the error rate of Comparative Example Medium 1.1 to 1.4 and Comparative Example Medium 2.1 to 1.2 was 1 × 10 ⁻⁴ or more, which was worse than that of Example Medium.

As described above, the magnetic layer is the first magnetic layer made of FePt alloy having the L1 ₀ structure and C, the FePt alloy having the L1 ₀ structure and Cr ₂ O ₃ , Y ₂ O ₃ or Ta ₂ O ₅ . It was found that a magnetic memory device with a low error rate can be realized by using a medium composed of two magnetic layers.

DESCRIPTION OF SYMBOLS 101 ... Glass substrate 102 ... 1st base layer 103 ... 2nd base layer 104 ... 2nd base layer 105 ... 1st magnetic layer 106 ... 1st magnetic layer 107 ... DLC protective film 201 ... Initial growth part 202 ... Grain boundary phase 203 ... Secondary growth part (secondary growth grains)
301 ... third magnetic layer 401 ... main magnetic pole 402 ... auxiliary magnetic pole 403 ... coil 404 ... semiconductor laser diode 405 ... laser light 406 ... near-field light generator 407 ... waveguide 408 ... recording head 409 ... shield 410 ... reproducing element 411 ... reproducing head 412 ... magnetic recording medium 502 ... medium driving unit 503 ... magnetic head 504 ... head driving unit 505 ... recording / reproducing signal processing system

Claims (8)

A substrate, a plurality of base layer formed on the substrate, a magnetic recording medium comprising a magnetic layer mainly composed of an alloy having an L1 ₀ structure, the magnetic layer is, FePt alloy and C having an L1 ₀ structure And a second magnetic layer comprising a FePt alloy having an L1 ₀ structure and Cr ₂ O ₃ , Y ₂ O ₃ or Ta ₂ O ₅ . The magnetic recording medium according to claim 1, wherein the thickness of the first magnetic layer is 6 nm or less. 3. The magnetic recording medium according to claim 1, further comprising a nonmagnetic intermediate layer for controlling exchange coupling between the first magnetic layer and the second magnetic layer. 4. The magnetic recording medium according to claim 1, wherein the magnetic layer further includes a third magnetic layer not having a granular structure composed of crystal grains and a grain boundary phase. 5. The third magnetic layer is an alloy having an amorphous structure or a microcrystalline structure containing Fe or Co as a main component and containing at least one element selected from Nd, Sm, Gd, Tb, and Dy. The magnetic recording medium according to claim 4. The third magnetic layer is an alloy having an amorphous structure or a microcrystalline structure containing Fe or Co as a main component and containing at least one element selected from Ta, Nb, Zr, Si, and B The magnetic recording medium according to claim 4. 7. The magnetic recording medium according to claim 4, further comprising a nonmagnetic intermediate layer for controlling exchange coupling between the second magnetic layer and the third magnetic layer. . A magnetic recording medium, a driving unit for rotating the magnetic recording medium, a laser generating unit for heating the magnetic recording medium, a waveguide for guiding laser light generated from the laser generating unit to the head tip, In a magnetic storage device comprising a magnetic head having a near-field light generating unit attached to the tip of the head, a driving unit for moving the magnetic head, and a recording / reproducing signal processing system, the magnetic recording medium is claimed. A magnetic recording device according to any one of 1 to 7, wherein the magnetic storage device is a magnetic recording device.

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