JP2012014750A - Heat-assisted magnetic recording medium and magnetic storage device - Google Patents

Abstract

A heat-assisted recording medium in which exchange coupling between magnetic particles is sufficiently reduced and the cluster size is small, and a magnetic storage device using the same are provided.
And 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, at least one underlayer, Ru, Alternatively, a heat-assisted magnetic recording medium, which is an alloy having an HCP structure mainly composed of Ru, is used.
[Selection] Figure 1

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. When heat-assisted recording is used, even a 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, it becomes possible to use a material having high magnetocrystalline anisotropy Ku of 10 ⁶ J / m ³ for the recording layer, and the magnetic particle size can be reduced to 6 nm or less while maintaining the thermal stability. . Examples of such high Ku material, L1 ₀ type FePt alloy having a crystal structure ^{(Ku~7 × 10 6 J / m} 3) and, CoPt alloy ^{(Ku~5 × 10 6 J / m} 3) or the like is known ing.

The magnetic layer, when using the FePt alloy having an L1 ₀ type crystal structure, the FePt layer must have taken (001) orientation. This can be realized by using an appropriate material for the underlayer. For example, Patent Document 1 shows that the FePt magnetic layer exhibits (001) orientation by using an MgO underlayer. Non-Patent Document 1 describes that the FePt magnetic layer exhibits (001) orientation by using a RuAl underlayer.

JP-A-11-353648

J. et al. Appl. Phys. 97, 10H301 (2005)

In the heat-assisted recording medium, in order to reduce the medium noise, it is necessary to sufficiently reduce the exchange coupling between the magnetic particles and reduce the magnetic cluster size. In order to reduce exchange coupling, it is desirable to add a grain boundary segregation material such as SiO ₂ or C to the magnetic layer. However, the addition a large amount of grain boundary polarization析材fee is deteriorated rules of the FePt alloy having an L1 ₀ structure, Ku is lowered. For this reason, it is necessary to reduce the exchange coupling between the magnetic particles without adding a large amount of the grain boundary segregation material.

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, at least one underlayer, Ru, Alternatively, the problem can be solved by using a heat-assisted magnetic recording medium that is an alloy having an HCP structure mainly composed of Ru. That is, the present invention has the following configuration.

(1) a substrate, a plurality of base layer formed on the substrate, the thermally assisted magnetic recording medium comprising a magnetic layer mainly composed of an alloy having an L1 ₀ structure, at least one underlayer, Ru Or a heat-assisted magnetic recording medium characterized by being an alloy having an HCP structure mainly composed of Ru.
(2) The underlying layer containing Ru as a main component is any one of RuAl, RuCo, RuNi, RuMn, RuCr, RuV, RuMo, RuW, RuTi, RuTa, RuZr, RuCu, RuSi, and RuB. The heat-assisted magnetic recording medium according to (1).
(3) The heat-assisted magnetic recording medium according to (1) or (2), wherein the Ru or Ru alloy underlayer is oriented with the (11.0) plane parallel to the substrate surface.
(4) The heat-assisted magnetism according to any one of (1) to (3), wherein the Ru or Ru alloy underlayer is formed by a sputtering method in an Ar gas atmosphere of 5 Pa or more. recoding media.
(5) Any one of (1) to (4), wherein an MgO underlayer is formed on a Ru or Ru alloy underlayer, and a magnetic layer is formed on the MgO underlayer. 2. The heat-assisted magnetic recording medium according to item 1.
(6) Any of (1) to (5), wherein the Ru or Ru alloy underlayer is formed on an underlayer made of Cr or an alloy having a BCC structure mainly composed of Cr. 2. The heat-assisted magnetic recording medium according to item 1.
(7) The heat-assisted magnetic recording medium according to (6), wherein the alloy having a BCC structure mainly composed of Cr is one of CrTi, CrMo, CrV, CrMn, and CrW alloy.
(8) The heat described in any one of (1) to (5), wherein the Ru or Ru alloy underlayer is formed on a NiAl or RuAl alloy underlayer having a B2 structure. Assisted magnetic recording medium.
(9) The magnetic layer is mainly composed of FePt or CoPt alloy having an L1 ₀ structure, and SiO ₂ , TiO ₂ , Cr ₂ O ₃ , Al ₂ O ₃ , Ta ₂ O ₅ , ZrO ₂ , Y ₂ O ₍₃ ) The element according to any one of (1) to (8), which contains at least one kind of oxide or element selected from CeO ₂ , MnO, TiO, ZnO, and C Thermally assisted magnetic recording medium.
(10) A magnetic recording medium, a drive 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 Is a heat-assisted medium according to any one of (1) to (9).

The present invention has a high L1 ₀ ordering parameter, and heat-assisted recording medium is realized in which the exchange coupling between the magnetic particles comprise sufficiently reduced magnetic particles, to provide a magnetic storage apparatus using the same Can do.

The figure showing an example of the laminated constitution of the magnetic recording medium of this invention 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 figure showing the relationship between Ar gas pressure and SNR of the magnetic recording medium of the present invention The perspective view of the magnetic storage device of the present invention

Thermally assisted magnetic recording medium of the present invention includes a substrate, a plurality of base layer formed on the substrate, comprising a magnetic layer mainly composed of an alloy having an L1 ₀ structure, at least one underlayer, It is characterized by being an alloy having an HCP structure mainly composed of Ru or Ru.

  The Ru underlayer is widely used as an underlayer for a granular magnetic layer made of a CoCrPt alloy and an oxide. In this case, the Ru underlayer has a (00 · 1) orientation. The CoCrPt alloy has the same HCP structure as Ru and has a relatively close lattice constant. Therefore, by forming a CoCrPt alloy on the (00 · 1) oriented Ru underlayer, the CoCrPt alloy exhibits good (00 · 1) orientation by epitaxial growth. This is the reason why the Ru underlayer is widely used in current perpendicular recording media using a CoCrPt alloy magnetic layer.

Meanwhile, the alloy having an L1 ₀ structure in the magnetic layer, for example, when using a FePt alloy, has been considered to be difficult to use the Ru underlying layer. This is because the (00 · 1) plane of the L1 ₀ -FePt alloy is a four-fold symmetric square, and therefore it was considered that epitaxial growth does not occur on the six-fold Ru (00 · 1) plane.

Here, by forming the Ru underlayer at a high gas pressure of 5 Pa or more by using a sputtering method, dome-shaped Ru crystal grains in which the upper layer part (tip part) is thinner than the initial growth part of the Ru crystal grains. Can be formed. This is due to the self-shading effect, but as a result, deep grooves are formed between adjacent Ru crystal grains, and the unevenness of the Ru underlayer surface becomes large. The present inventor has a magnetic layer mainly composed of an alloy having an L1 ₀ structure, by forming the previous period Ru underlying layer, grooves are also formed between the magnetic grains, thereby reducing the exchange coupling between grains I found what I could do. Thereby, the magnetic cluster size is reduced, and a low noise heat assist medium can be obtained.

  The Ru underlayer may contain elements such as Al, Co, Ni, Mn, Cr, V, Mo, W, Ti, Ta, Zr, Cu, Si, and B. As long as the Ru alloy can maintain the HCP structure, the content of the element is not particularly limited. However, in order to form more prominent irregularities, the addition amount is desirably 30 at% (atomic%) or less.

Further, in order to make the L1 ₀ -FePt alloy take the (001) orientation, it is desirable that the Ru underlayer has the (11.0) orientation. In order to make Ru have (11.0) orientation, for example, a Cr underlayer is formed at a high temperature of 150 to 300 ° C., and a Ru underlayer is formed on the Cr underlayer. Since the Cr underlayer formed at a high temperature has a (100) orientation, the Ru underlayer is formed on the Cr underlayer so that the Ru underlayer exhibits (11.0) orientation by epitaxial growth. Instead of the Cr underlayer, a Cr alloy having a BCC structure such as CrTi, CrMo, CrV, CrMn, or CrW may be used. Hereinafter, the Cr or Cr alloy underlayer for allowing the Ru underlayer to take (11.0) orientation is referred to as an orientation control layer. When a Cr alloy is used for the orientation control layer, the content of additive elements such as Ti, Mo, V, and W contained in the Cr alloy is preferably approximately 40 at% or less. If it exceeds 40 at%, the (100) orientation of the orientation control layer deteriorates, which is not preferable.

  Further, a NiAl alloy having a B2 structure or a RuAl alloy may be used as the orientation control layer. When a NiAl alloy or a RuAl alloy is formed at a high temperature of approximately 150 ° C. or higher, (100) orientation is exhibited. Therefore, by forming Ru on the orientation control layer made of the NiAl alloy or RuAl alloy, it is possible to make the Ru take (11.0) orientation.

A misfit mitigation layer for mitigating lattice misfit may be formed between the orientation control layer and the Ru or Ru alloy underlayer. Thereby, the orientation of the magnetic layer is improved, and Hc can be further increased. For the misfit mitigating layer, an alloy having a BCC structure or an HCP structure can be used. When an alloy having a BCC structure is used for the misfit relaxation layer, the lattice constant a _BCC of the BCC alloy is a ₁ , Ru, or the a-axis lattice constant of the Ru alloy is a ₂ . It is desirable that a ₁ <a _BCC <1.22a ₂ . In addition, when an HCP structure alloy is used for the misfit mitigating layer, the a-axis lattice constant a _HCP of the HCP alloy is preferably a ₁ <1.22a _HCP <1.22a ₂ . For the orientation control layer, for example, a BCC alloy such as MoCr, MoV, WCr, WV, or WMo, or an HCP alloy such as RuCo or RuCr can be used.

The magnetic layer made of the L1 ₀ -FePt alloy may be formed directly on the Ru or Ru underlayer, but the MgO underlayer is formed on the Ru or Ru underlayer, and is formed on the MgO underlayer. May be. By introducing MgO between the Ru underlayer and the magnetic layer, the elements in the underlayer can be prevented from diffusing into the magnetic layer. However, if the MgO layer is too thick, the surface unevenness is lowered, so the MgO film thickness is 5 nm or less, preferably 3 nm or less.

The magnetic layer can be used for FePt alloy or CoPt alloy, having an L1 ₀ type crystal structure. The magnetic layer is at least one selected from SiO ₂ , TiO ₂ , Cr ₂ O ₃ , Al ₂ O ₃ , Ta ₂ O ₅ , ZrO ₂ , Y ₂ O ₃ , CeO ₂ , MnO, TiO, ZnO, and C. It is desirable to contain an oxide or an element. By adopting a granular structure in which the oxide or element divides the magnetic crystal grains, exchange coupling between the magnetic grains can be reduced and the magnetic crystal grains can be made finer.

  An adhesion layer for improving adhesion may be provided between the Cr or Cr alloy underlayer (orientation control layer) and the substrate. Further, as the heat sink layer, Cu, Ag, Au, Al, or an alloy layer thereof having high thermal conductivity may be provided. Further, a soft magnetic underlayer (SUL) may be formed to improve the writing ability. As SUL, CoTaZr, CoFeZrTa, CoFeTaSi, CoFeZrB, FeTaC, FeAlSi, NiFe, or the like can be used. The SUL may be a single soft magnetic alloy layer or a laminated film antiferromagnetically coupled via Ru.

Example 1
FIG. 1 shows an example of the layer structure of the magnetic recording medium produced in this example. Glass substrate 101, Co-50at% Ti seed layer 102, Co-3at% Nb-5at% Zr soft magnetic underlayer (SUL) 103, Cr-20at% V underlayer 104, Ru or Ru alloy underlayer 105, An Fe-45 at% Pt) -12 mol% TiO ₂ magnetic layer 106, an Fe-30 at% Ni cap layer 107, and a DLC protective film 108 are sequentially formed. A sputtering method was used for film formation from the seed layer to the cap layer, and an ion beam method was used for the DLC protective film. As the Ru alloy, RuAl, RuCo, RuNi, RuMn, RuCr, RuV, RuMo, RuW, RuTi, RuTa, and RuZr alloy were used. In order to promote the (100) orientation of the CrV alloy underlayer, it is desirable to heat the substrate at 150 to 300 ° C. before the formation of the underlayer, but in this example, the substrate was heated at 280 ° C. In order to improve the degree of order of the magnetic layer, the substrate was heated at 400 ° C. or higher before forming the magnetic layer. The Ru or Ru alloy underlayer is preferably formed in an Ar gas atmosphere of 5 Pa or more, desirably 10 Pa or more, but in this example, it was formed at 12 Pa.
Further, as a comparative example 1, a medium having the same layer configuration as that of the medium and having no Ru or Ru alloy underlayer (w / o Ru) was produced.

When X-ray diffraction measurement was performed on the medium of this example, the BCC (100) orientation of the CrV underlayer, the HCP (11.0) orientation of the Ru or Ru alloy underlayer, and the L1 ₀ (001) orientation of the magnetic layer were found. It could be confirmed. Table 1 shows the coercive force Hc, the average particle diameter <D> of the magnetic layer, and the cluster size Dn of the medium of this example. Here, the average particle diameter was estimated by TEM observation. In addition, the cluster size is IEEE Trans. Magn. , Vol. 27, pp 4975-4777, 1991, and measured at room temperature. Specifically, the cluster size was calculated as Dn = tmag × √Nd using the demagnetizing field coefficient Nd estimated from the minor loop analysis and the magnetic film tmag. The table also shows the values of comparative media in which the Ru underlayer was not formed but the MgO underlayer was formed directly on the CrV underlayer. All of the media of this example showed high Hc of 15 kOe or more. On the other hand, Hc of the comparative example medium was as low as 10.2 kOe. The average particle size was approximately 6 to 6.5 nm in both Examples and Comparative Examples, and no significant difference was observed. On the other hand, Dn of the example medium was 30 nm or less, whereas Dn of the comparative example medium was 56 nm, which was significantly larger than the example medium. Since the average particle sizes of the example medium and the comparative example medium were approximately the same, the reason why the cluster size of the example medium is small is considered that exchange coupling is further reduced.

  From the above, it has been clarified that exchange coupling is reduced and the cluster size can be reduced by forming an underlayer made of Ru or a Ru alloy. In addition, when RuCo, RuNi, and RuCr were used for the Ru alloy underlayer, the cluster size was particularly small, and it was found that the exchange coupling can be remarkably reduced by using these underlayers.

(Example 2)
FIG. 2 shows an example of the layer structure of the magnetic recording medium manufactured in this example. Glass substrate 201, Ti-50at% Al seed layer 202, Cu-2at% Zr heat sink layer 203, Ru-50at% Al underlayer 204, Mo-20at% V underlayer 205, Ru-2at% Cu underlayer 206, MgO An underlayer 207, a (Fe-50 at% Pt) -45 mol% C magnetic layer 208, a CoCrPt cap layer 209, and a DLC 210 are sequentially formed. A sputtering method was used for film formation from the seed layer to the cap layer, and an ion beam method was used for the DLC protective film. Here, the MoV underlayer is a misfit relaxation layer for improving the lattice matching between the NiAl underlayer and the RuCu underlayer. In order to make the RuAl underlayer take (100) orientation, the substrate was heated to about 200 ° C. before the RuAl underlayer was formed. In order to improve the degree of order of the magnetic layer, the substrate was heated at 450 ° C. before forming the magnetic layer. In this example, the Ar gas pressure during RuCu underlayer film formation was changed from 3 Pa to 22 Pa.

When X-ray diffraction measurement was performed on the medium of this example, it was found that the RuAl underlayer had a B2 (100) orientation, the MoV underlayer had a BCC (100) orientation, and a RuCu alloy, regardless of the Ar gas pressure during RuCu underlayer formation. The HCP (11.0) orientation of the underlayer and the L1 ₀ (001) orientation of the magnetic layer were confirmed.

  The recording / reproducing characteristics of the medium produced in this example were evaluated using the head shown in FIG. The head includes a main magnetic pole 301, an auxiliary magnetic pole 302, a coil 303 for generating a magnetic field, a laser diode LD304, and a waveguide 307 for transmitting laser light 305 generated from the LD to the near-field generating element 306. The reproducing head 311 includes a reproducing element 310 sandwiched between a head 308 and a shield 309. Recording can be performed by heating the medium 312 with near-field light generated from the near-field light element, and reducing the coercive force of the medium to a head magnetic field or less. In addition, a heating mechanism 313 including an LD, a waveguide, and a near-field generating element may be disposed between the main magnetic pole and the auxiliary magnetic pole. However, in this case, since the leading side of the main magnetic pole needs to be heated, the traveling direction of the medium is on the right side contrary to the figure.

  FIG. 4 shows the relationship between the SNR of the medium of this example evaluated by the head and the Ar gas pressure when forming the RuCu underlayer. As the gas pressure increases, the SNR increases, and a high SNR of 14 dB or more is obtained at 5 Pa or more. The SNR further increases with an increase in gas pressure, and a value of 15 dB or more is obtained at 10 Pa or more.

  When the average particle diameter of the magnetic layer of the medium in which the RuCu underlayer was formed at an Ar gas pressure of 3 Pa and the medium formed at 10 Pa was estimated by planar TEM observation, the average particle diameter of both was 6.1 nm and 6. It was almost the same at 3 nm. The planar TEM observation was performed by producing a medium on which no CoCrPt cap layer was formed in order to accurately estimate the average particle diameter of the magnetic layer. Further, when the cluster size of both was estimated by the same method as described in Example 1, the cluster size of the medium in which the RuCu underlayer was formed at an Ar gas pressure of 3 Pa was 62 nm. On the other hand, the cluster size of the medium in which the RuCu underlayer was formed at 10 Pa was as small as 22 nm. This indicates that the exchange interaction between magnetic particles is further reduced in the latter medium. Moreover, when cross-sectional TEM observation of both was performed, the tip of the RuCu underlayer formed at 10 Pa was narrower and deep grooves were formed between the particles. This is considered to be why the exchange interaction is reduced. From the above, it has been found that by increasing the Ar gas pressure during the formation of the RuCu underlayer, the exchange interaction between the magnetic particles is reduced and the SNR can be improved. Even if the Ar gas pressure during RuCu formation is further increased from 10 Pa, the SNR does not change greatly. However, if the gas pressure is excessively increased, the HDI performance such as the flying characteristics of the head deteriorates, so the Ar gas pressure is 40 Pa. The following is desirable.

(Example 3)
A perfluoropolyether-based lubricant was applied to the medium shown in Example 1 (Example mediums 1.1 to 1.12), and then incorporated into the magnetic storage device shown in FIG. This magnetic storage device includes a magnetic recording medium 501, 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 A magnetic head having the same structure as the head shown in FIG. 3 was used. Table 2 shows the SNR and the recording track width MWW when a 1400 kFCI signal was recorded and the recording / reproduction characteristics were evaluated. Here, the recording track width is defined as the half width of the track profile. All of the example media exhibited a high SNR of 15 dB or more and a narrow MWW of 60 nm or less. Among them, the example medium 1.3, the example medium 1.4, and the example medium 1.6, in which the cluster size was particularly small, exhibited high SNR. Further, Example Medium 1.5, Example Medium 1.9, and Example Medium 1.11 using RuMn, RuW, and RuTa underlayers showed particularly narrow MWW. Therefore, it was found that it is desirable to use a RuW, RuMo, or RuSi underlayer when increasing the track density.

DESCRIPTION OF SYMBOLS 101 ... Glass substrate 102 ... CoTi seed layer 103 ... CoNbZr soft magnetic underlayer 104 ... CrV underlayer 105 ... Ru or Ru alloy underlayer 106 ... FePt-TiO2 magnetic layer 107 ... FeNi cap layer 108 ... DLC protective film 201 ... Glass Substrate 202 ... TiAl seed layer 203 ... CuZr heat sink layer 204 ... RuAl underlayer 205 ... MoV underlayer 206 ... RuCu underlayer 207 ... MgO underlayer 208 ... FePtC magnetic layer 209 ... CoCrPt cap layer 2010 ... DLC protective film 301 ... main magnetic pole 302 ... auxiliary magnetic pole 303 ... coil 304 ... semiconductor laser diode 305 ... laser beam 306 ... near-field light generator 307 ... waveguide 308 ... recording head 309 ... shield 310 ... reproducing element 311 ... reproducing head 501 ... magnetic recording medium 502 ... Body drive unit 503 ... magnetic head 504 ... head driving unit 505 ... recording signal processing system

Claims (10)

A substrate, a plurality of base layer formed on the substrate, the thermally assisted magnetic recording medium comprising a magnetic layer mainly composed of an alloy having an L1 ₀ structure, at least one underlayer, Ru or Ru, A heat-assisted magnetic recording medium, characterized by being an alloy having an HCP structure mainly composed of The underlayer comprising Ru as a main component is any one of RuAl, RuCo, RuNi, RuMn, RuCr, RuV, RuMo, RuW, RuTi, RuTa, RuZr, RuCu, RuSi, and RuB alloy. 2. The heat-assisted magnetic recording medium according to 1. 3. The heat-assisted magnetic recording medium according to claim 1, wherein the Ru or Ru alloy underlayer is oriented with the (11.0) plane being parallel to the substrate surface. The heat-assisted magnetic recording medium according to any one of claims 1 to 3, wherein the Ru or Ru alloy underlayer is formed by a sputtering method in an Ar gas atmosphere of 5 Pa or more. 5. The MgO underlayer is formed on the Ru or Ru alloy underlayer, and the magnetic layer is formed on the MgO underlayer. 6. Thermally assisted magnetic recording medium. The Ru or Ru alloy underlayer is formed on an underlayer made of Cr or an alloy having a BCC structure containing Cr as a main component, according to any one of claims 1 to 5. Thermally assisted magnetic recording medium. 7. The heat-assisted magnetic recording medium according to claim 6, wherein the alloy having a BCC structure mainly composed of Cr is any one of CrTi, CrMo, CrV, CrMn, and CrW alloys. The heat-assisted magnetic recording medium according to claim 1, wherein the Ru or Ru alloy underlayer is formed on a NiAl or RuAl alloy underlayer having a B2 structure. The magnetic layer is mainly composed of FePt or CoPt alloy having an L1 ₀ structure, and SiO ₂ , TiO ₂ , Cr ₂ O ₃ , Al ₂ O ₃ , Ta ₂ O ₅ , ZrO ₂ , Y ₂ O ₃ , CeO. 9. The heat-assisted magnetic recording medium according to claim 1, comprising at least one oxide or element selected from ₂ , MnO, TiO, ZnO, and C. 10. . 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 storage device according to any one of 1 to 9, wherein the magnetic storage device is the heat-assisted medium.

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