JP5150925B2 - Magnetic recording medium and magnetic recording / reproducing apparatus - Google Patents

Description

  The present invention relates to a magnetic recording medium, and more particularly to a so-called heat-assisted magnetic recording medium in which information is recorded by applying an external magnetic field while locally heating a part of the medium. More specifically, a thermally assisted magnetic recording medium in which information is recorded by applying an external magnetic field in a state where the coercive force of the recording film is reduced while performing local heating by laser light irradiation or near-field light irradiation, and The present invention relates to the magnetic recording / reproducing apparatus used.

  2. Description of the Related Art In recent years, magnetic recording apparatuses such as magnetic disk apparatuses have been required to improve the performance of thin film magnetic heads and magnetic recording media as the recording density increases.

  A magnetic recording layer of a magnetic recording medium mounted on a magnetic disk device is made of an aggregate of magnetic fine particles, and each magnetic fine particle has a single magnetic domain structure. For example, one piece of information (one recording bit) in the vertical direction is recorded using a plurality of magnetic fine particles. In a magnetic recording medium having such a structure, in order to increase the recording density, it is necessary to reduce irregularities between magnetic fine particles at the boundary of recording bits. Therefore, it is necessary to reduce the volume V of the magnetic fine particles.

  However, if the volume V of the magnetic fine particles is too small, the thermal stability deteriorates and the magnetization direction may be disturbed due to the influence of temperature or the like. Therefore, it is required to reduce the volume V of the magnetic fine particles without impairing the thermal stability.

By the way, the thermal fluctuation index, which is a measure of thermal stability, is given by _Ku V / K _B T. Here, K _u is the anisotropy energy constant of the magnetic fine particles, V is the volume of one magnetic particle, the K _B Boltzmann constant, T is the absolute temperature. If the volume of one magnetic fine particle is simply decreased in order to increase the recording density, the thermal fluctuation index decreases, the thermal stability is impaired, and the recording cannot be held.

In order to solve such a problem of thermal fluctuation, a magnetic material having a large anisotropic energy constant _Ku may be used. However, the coercive force Hc of the magnetic particles to become larger in proportion to the anisotropy energy constant K _u, disadvantageously no longer be recorded occur in ordinary head.

  In order to solve such a problem, a so-called Thermally Assisted Magnetic Recording (TAMR) system has been proposed. The heat-assisted magnetic recording method is a method of recording information by heating a minute area (recording bit) to be recorded on a magnetic recording medium with laser light, near-field light, or the like during recording, and reducing the Hc of magnetic fine particles. is there. Thereby, a magnetic material having Hc larger than the recording head magnetic field H at room temperature can be used. Therefore, the volume V of one magnetic fine particle can be reduced without reducing the thermal fluctuation index, which is a measure of thermal stability, and a high recording density is possible.

  However, when the magnetic recording layer is heated, the periphery of the recording bit becomes a high temperature of about 300 ° C., for example, and microscopic observation causes thermal expansion around the recording bit. When such thermal expansion occurs, the direction of the magnetic anisotropy axis is inclined as the medium is distorted. That is, the magnetization direction that should be perpendicular is inclined at random (a state during heating). On the other hand, the magnetization direction that entered the cooling process from a state in which the magnetization direction was randomly inclined and became a high Hc state after cooling, coupled with exchange coupling with adjacent magnetic grains, is fixed in a state in which the magnetization direction is randomly inclined. The In other words, in the cooling process (during cooling), even if the film stress constituting the magnetic recording layer is relaxed, the magnetization direction remains disordered due to exchange interaction (state during cooling). ).

  When the recorded information is reproduced using the reproducing head on the magnetic recording medium after such heating and cooling, if the degree of thermal expansion is large, the magnetization transition width of the magnetic information increases, and as a result, the SNR ( There arises a problem that the S / N ratio is reduced.

Furthermore, since the medium surface of the recording portion that is locally heated during recording protrudes, the distance between the head and the medium surface becomes narrow, and if the degree of thermal expansion is large, the head and the medium may collide. The problem can arise.
The following patent document 1 is mentioned as a prior art considered to be related to the present invention.

JP 2007-26511 A

  In Patent Document 1 (Japanese Patent Application Laid-Open No. 2007-26511), the magnetic anisotropy induction auxiliary layer that is in close contact with the magnetic recording layer is locally concaved due to the negative thermal expansion coefficient due to local heating. Transforms into It is disclosed that the deformation of the concave shape generates a tensile stress at the interface between the magnetic anisotropy induction auxiliary layer and the magnetic recording layer, and the tensile stress induces magnetic anisotropy energy through magnetostriction. Yes. However, deformation of the magnetic recording layer due to heating stress causes disturbance of the magnetization direction after recording, and the SNR of the reproduction signal decreases. Moreover, since the magnetic anisotropy induction auxiliary layer is arranged directly below the magnetic recording layer, there is a problem that it is difficult to form a magnetic recording layer having sufficient magnetic characteristics. For this reason, the configuration of the magnetic recording medium described in Patent Document 1 cannot achieve a high SNR of the reproduction signal.

  Under such circumstances, the present invention has been invented, and its purpose is to suppress the thermal expansion due to heating and suppress the deformation of the magnetic recording layer, and the temperature around the recording bit during recording. An object of the present invention is to propose a magnetic recording medium capable of realizing a recording state with a high slope and a high SNR.

  In order to solve such a problem, the magnetic recording medium of the present invention includes a soft magnetic layer, a negative expansion layer made of a negative expansion material having a negative thermal expansion coefficient, an alignment layer, a magnetic layer, on a substrate. The orientation layer is disposed below the magnetic recording layer, and the soft magnetic layer and the negative expansion layer are disposed below the alignment layer, respectively. The thermal conductivity is configured to be larger than the thermal conductivity of the alignment layer.

  As a preferred embodiment of the magnetic recording medium of the present invention, the soft magnetic layer is disposed below the negative expansion layer.

  As a preferred embodiment of the magnetic recording medium of the present invention, the negative expansion layer is disposed below the soft magnetic layer.

  As a preferred embodiment of the magnetic recording medium of the present invention, the negative expansion layer has a thermal conductivity of 0.1 to 1.5 W / cm · K.

  Further, as a preferred embodiment of the magnetic recording medium of the present invention, the alignment layer is configured to have a thermal conductivity of 0.01 to 0.05 W / cm · K.

  As a preferred embodiment of the magnetic recording medium of the present invention, the negative expansion layer is made of manganese nitride.

  As a preferred embodiment of the magnetic recording medium of the present invention, the negative expansion layer is made of lithium oxide.

  A magnetic recording / reproducing apparatus according to the present invention includes the above-described magnetic recording medium and a magnetic head for recording / reproducing a magnetic signal to / from the magnetic recording medium.

  The magnetic recording medium of the present invention comprises, on a substrate, a soft magnetic layer, a negative expansion layer made of a negative expansion material having a negative thermal expansion coefficient, an alignment layer, and a magnetic recording layer. The layer is disposed below the magnetic recording layer, the soft magnetic layer and the negative expansion layer are respectively disposed below the alignment layer, and the thermal conductivity of the negative expansion layer is the thermal conductivity of the alignment layer. Because the thermal expansion due to heating is suppressed and deformation of the magnetic recording layer is suppressed, the temperature gradient around the recording bit at the time of recording is steep to realize a recording state with a high SNR. Can be made.

FIG. 1 is a cross-sectional view schematically showing a configuration example of a magnetic recording medium. FIG. 2 is a cross-sectional view schematically showing another configuration example of the magnetic recording medium. FIG. 3 is a perspective view showing a schematic configuration of the magnetic recording / reproducing apparatus.

  Hereinafter, embodiments of the magnetic recording medium of the present invention will be described in detail.

  FIG. 1 is a schematic cross-sectional view schematically showing the main structure of a magnetic recording medium 1 of the present invention. FIG. 2 is a cross-sectional view schematically showing a magnetic recording medium 2 as another configuration example.

  1 and 2, the direction in which the layers are stacked is referred to as “upper” or “upper”, and the opposite direction is referred to as “lower” or “lower”.

  As shown in the embodiment of FIGS. 1 and 2, the magnetic recording medium 1 of the present invention includes a soft magnetic layer 20 on a substrate 10 and a negative expansion layer made of a negative expansion material having a negative thermal expansion coefficient. 30, an alignment layer 40, and a magnetic recording layer 50. In the present invention, the alignment layer 40 is disposed below the magnetic recording layer 50, and the soft magnetic layer 20 and the negative expansion layer 30 are disposed below the alignment layer 40, respectively.

  More specifically, FIG. 1 shows an example in which the magnetic recording medium 1 is configured in the stacking order of the substrate 10 / soft magnetic layer 20 / negative expansion layer 30 / alignment layer 40 / magnetic recording layer 50. .

  As a modification, as shown in FIG. 2, the magnetic recording medium 2 is configured in the order of lamination of the substrate 10 / the negative expansion layer 30 / the soft magnetic layer 20 / the orientation layer 40 / the magnetic recording layer 50. Also good.

  In each of these configurations, in the present invention, the order of arrangement of the layers and the setting specifications of the thermal conductivity are important. In particular, it is important that the thermal conductivity of the negative expansion layer 30 is larger than the thermal conductivity of the alignment layer 40. Requirements.

  In addition, although the layers are in contact with each other in the magnetic recording media 1 and 2 stacked in the form shown in FIG. 1 and FIG. 2, a range that does not impair the operational effects of the present invention between the layers in the magnetic recording media 1 and 2. Thus, various intermediate layers such as a base layer may be appropriately interposed. For example, Ru, Cr, Rh, Pd, Pt, etc. are mentioned.

Hereinafter, each layer constituting the magnetic recording medium 1 will be described in detail.
[Description of Substrate 10]
For the substrate 10 in the present invention, glass, aluminum, silicon, plastic, or the like can be used. A composite substrate in which metal, ceramics, or the like is deposited on a substrate made of a hard material can also be used. Although there is no restriction | limiting in particular about the thickness of such a board | substrate 10, For example, it shall be about 0.5-1.0 mm.

  The substrate 10 is generally in the form of a disk.

[Description of Magnetic Recording Layer 50]
The magnetic recording layer 50 in the present invention is configured as a so-called perpendicular magnetization film, and is made of a material such as FePt, CoPt, FePd, CoPd, CoCrPr, Co / Pd laminated film, CoB / Pd laminated film, Co / Pt laminated film, CoB. A / Pt laminated film or the like is preferably used.

  It is particularly preferable to use a so-called granular recording material in which a nonmagnetic material such as O, SiOx, TiOx, TaOx, B, or C is interposed at the grain boundary between magnetic particles made of the above materials.

The film thickness of the magnetic recording layer 50 is, for example, 10 to 20 nm.
The thermal conductivity of the magnetic recording layer 50 is, for example, about 0.5 to 1.5 W / cm · K.
Various protective films are usually formed on the magnetic recording layer 50.

[Description of Orientation Layer 40]
The alignment layer 40 in the present invention is disposed below the magnetic recording layer 50.

  The alignment layer 40 functions as an alignment base film for facilitating the vertical alignment of the magnetic particles of the magnetic recording layer 50. Due to the presence of the alignment layer 40, a magnetic recording layer with good magnetic properties can be formed. The thermal conductivity of the alignment layer 40 is smaller than the thermal conductivity of the magnetic recording layer 50, and a heat insulating layer for efficiently raising the temperature of the magnetic recording layer 50 by irradiation with laser light, near-field light, or the like during recording. Functions as a (thermal barrier layer).

  Accordingly, the material of the alignment layer 40 should be selected in consideration of the relationship with the magnetic recording layer 50 to be used, and the thermal conductivity in the alignment layer 40 is, for example, 0.01 to 0.05 W / cm. -Within the range of K.

Examples of the material of the alignment layer 40 used include MgO, TiO, ZnO, and CrO.
The thickness of the alignment layer 40 is, for example, about 2 to 4 nm.

[Description of Negative Expansion Layer 30]
The negative expansion layer 30 used in the present invention is configured to be disposed below the alignment layer 40.

  The thermal conductivity of the negative expansion layer 30 is larger than the thermal conductivity of the alignment layer 40. The thermal conductivity of the negative expansion layer 30 is preferably in the range of 0.1 to 1.5 W / cm · K, for example.

  By providing such a negative expansion layer 30 having a higher thermal conductivity than that of the alignment layer 40, the thermal expansion of the magnetic recording medium due to heating is suppressed to suppress deformation of the magnetic recording layer 50, and the thermal conductivity is reduced. Since the large negative expansion layer 30 quickly releases the heat of the magnetic recording layer 50 downward after recording, the temperature gradient around the recording bit at the time of recording can be made steep and a recording state with high SNR can be realized.

  As the negative expansion material constituting the negative expansion layer 30, a material exhibiting a negative coefficient of thermal expansion in a temperature range from room temperature (25 ° C.) to the highest temperature achieved by heating is used. For example, it is preferable to use manganese nitride, lithium oxide, or the like. The maximum temperature reached by the negative expansion layer 30 is, for example, 100 ° C. to 200 ° C. Therefore, it is desirable to provide a physical property showing a negative coefficient of thermal expansion in a temperature range from room temperature to 200 ° C.

The manganese nitride is preferably a Mn nitride having an inverted perovskite structure, and specifically includes a material that can be expressed as a general formula Mn ₃ XN. Here, X is at least one element selected from a group such as Cu, Ge, and Sn. Usually, Cu—Ge system is represented as Mn ₃ (Cu _1−x Ge _x ) N, and Cu—Sn system is represented as Mn ₃ (Cu _1−x Sn _x ) N. The element ratio x is preferably in the range of 0.4 to 0.6. In addition, a material such as (Mn ₃ CuS) N is also included.

Examples of the lithium oxide include Li ₂ O—Al ₂ O ₃ —nSiO ₂ (n is preferably in the range of 0 to 2.0).

  In particular, it is desirable to have physical properties that can always provide a negative coefficient of thermal expansion in the temperature range from room temperature to the highest temperature reached. For example, when the maximum temperature reached by the negative expansion layer 30 is 100 ° C., it is desirable to have physical properties that can always provide a negative coefficient of thermal expansion in the temperature range from room temperature to 100 ° C.

  As the thickness of the negative expansion layer 30 made of such a negative expansion material, an optimum film thickness may be appropriately set according to the material system to be used. For example, it is selected from the range of 3 to 20 nm.

[Description of Soft Magnetic Layer 20]
The soft magnetic layer 20 in the present invention is configured to be disposed below the alignment layer 40.

  The soft magnetic layer 20 is provided to generate a steep and large vertical magnetic field by magnetic interaction with the recording head.

  Examples of the material used include soft magnetic materials such as NiFe alloy and FeCo alloy.

  The thickness of the soft magnetic layer 20 is, for example, 25 to 50 nm. When this thickness is less than 25 nm, there is a tendency that a head magnetic field intensity sufficiently high for obtaining a magnetization transition having a high SNR cannot be obtained. On the other hand, when it exceeds 50 nm, there is a tendency that a disadvantage that the DC noise increases.

  The thermal conductivity of the soft magnetic layer 20 is larger than the thermal conductivity of the alignment layer 40, and is, for example, in the range of 0.5 to 1.5 W / cm · K.

  With respect to the magnetic recording medium of the present invention described above, in the embodiment shown in FIG. 1, the soft magnetic layer 20 is disposed below the negative expansion layer 30. On the contrary, in the embodiment shown in FIG. 2, the negative expansion layer 30 is disposed below the soft magnetic layer 20. In any aspect, the effect of the present invention can be exhibited. However, in the embodiment shown in FIG. 2, the distance between the negative expansion layer 30 and the magnetic recording layer 50 is long. 1 is required to be set slightly thicker than the thickness of the negative expansion layer 30 in the embodiment of FIG. In the embodiment of FIG. 2, since the distance between the recording head and the soft magnetic layer 20 can be reduced, the recording magnetic field applied to the magnetic recording layer 50 can be increased.

  As shown in FIG. 3, the magnetic recording medium 1 or 2 described above and a magnetic head 5 for recording / reproducing magnetic signals on the magnetic recording medium 1 or 2 are provided. Composed. The magnetic recording medium 1 or 2 is rotationally driven by, for example, a spindle motor 6. In order to read / write data from / to the magnetic recording medium, a rotating arm 4 extending from the outer side of the medium toward the inner side of the medium is provided. Is provided with a magnetic head 5 for recording / reproducing. The rotating arm 4 is rotated by, for example, a voice coil motor 3 and can position the magnetic head 5 on a predetermined track based on, for example, a servo signal detected by the magnetic head 5. .

  Hereinafter, specific experimental examples relating to the magnetic recording medium of the present invention described above will be shown, and the present invention will be described in more detail.

[Experimental Example I]
(Example I-1 sample)
As shown in FIG. 1, Example I-1 Sample of Magnetic Recording Medium of the Present Invention Sequentially Formed in the Laminate Order of Substrate 10 / Soft Magnetic Layer 20 / Negative Expansion Layer 30 / Orientation Layer 40 / Magnetic Recording Layer 50 Was made.

The specific materials, physical properties, etc. of each laminated film were as follows.
・Board 10
Material: Glass Thickness: 0.8mm

・Soft magnetic layer 20
Material: NiFe alloy Film thickness: 50 nm Thermal conductivity: 0.5 W / cm · K

-Negative expansion layer 30
Material: (Mn ₃ CuS) N
Film thickness: 7 types: 1 nm, 3 nm, 5 nm, 7 nm, 9 nm, 11 nm, 13 nm
Thermal conductivity: 0.5 W / cm · K

-Orientation layer 40
Material: MgO Film thickness: 2 nm Thermal conductivity: 0.01 W / cm · K

Magnetic recording layer 50
Material: FePt-granular Film thickness: 10 nm
Thermal conductivity: 0.5 W / cm · K

(Example I-2 sample)
In the above Example I-1 sample, the specification of the negative expansion layer 30 was changed as follows. Example I-2 sample was prepared in the same manner as the above Example I-1 sample.

-Negative expansion layer 30
Material: Li ₂ O—Al ₂ O ₃ —SiO ₂ (n = 1)
Film thickness: 5 types: 1 nm, 3 nm, 5 nm, 7 nm, 9 nm
Thermal conductivity: 0.1 W / cm · K

(Comparative Example I-1 sample)
In the above Example I-1 sample, the specification of the negative expansion layer 30 was changed as follows. Other than that, the Comparative Example I-1 sample was produced in the same manner as the Example I-1 sample.

-Negative expansion layer 30
Material: ZrW ₂ O ₈
Film thickness: 7 types: 1 nm, 3 nm, 5 nm, 7 nm, 9 nm, 11 nm, 13 nm
Thermal conductivity: 0.008 W / cm · K

  About each sample produced in such a way, the recording signal of 1000 kFCI was recorded and reproduced, and the SNR was measured, and the improvement amount (dB) of SNR was obtained. That is, the improvement amount (dB) of the SNR with respect to the reference was determined on the basis of the case where no negative expansion layer was present.

  The results are shown in Table 1 below.

[Experimental Example II]
(Example II-1 sample)
Example II-1 of the magnetic recording medium of the present invention formed in the order of lamination of substrate 10 / negative expansion layer 30 / soft magnetic layer 20 / alignment layer 40 / magnetic recording layer 50 as shown in FIG. Produced.

  Specific materials and physical properties of the laminated film were as follows.

・Board 10
Material: Glass Thickness: 0.8mm

-Negative expansion layer 30
Material: (Mn ₃ CuS) N
Film thickness: 7 types of 5 nm, 7 nm, 9 nm, 11 nm, 13 nm, 15 nm and 17 nm
Thermal conductivity: 0.5 W / cm · K

・Soft magnetic layer 20
Material: NiFe alloy Film thickness: 50 nm Thermal conductivity: 0.5 W / cm · K

-Orientation layer 40
Material: MgO Film thickness: 2 nm Thermal conductivity: 0.01 W / cm · K

Magnetic recording layer 50
Material: FePt-granular Film thickness: 10 nm
Thermal conductivity: 0.5 W / cm · K

(Example II-2 sample)
In the sample of Example II-1 above, the specifications of the negative expansion layer 30 were changed as follows. Example II-2 sample was prepared in the same manner as the above Example II-1 sample except for that.

-Negative expansion layer 30
Material: Li ₂ O—Al ₂ O ₃ —SiO ₂ (n = 1)
Film thickness: 5 types: 5 nm, 7 nm, 9 nm, 11 nm, and 13 nm
Thermal conductivity: 0.1 W / cm · K

(Comparative Example II-1 sample)
In the sample of Example II-1 above, the specifications of the negative expansion layer 30 were changed as follows. Other than that, Comparative Example II-1 sample was produced in the same manner as Example II-1 sample.

-Negative expansion layer 30
Material: ZrW ₂ O ₈
Film thickness: 7 types of 5 nm, 7 nm, 9 nm, 11 nm, 13 nm, 15 nm and 17 nm
Thermal conductivity: 0.008 W / cm · K

  About each sample produced in such a way, the improvement (dB) of SNR was calculated | required in the same way as the case of the said experiment example I. That is, the improvement amount (dB) of the SNR with respect to the reference was determined on the basis of the case where no negative expansion layer was present.

  The results are shown in Table 2 below.

  In the form shown in FIG. 2, the SNR generally tends to be slightly larger than the form shown in FIG. It can be considered that this is because the distance between the soft magnetic layer 20 and the recording head is short.

  Moreover, in Comparative Example I-1 sample and Comparative Example II-1 sample, the thermal conductivity of the negative expansion layer 30 is smaller than the thermal conductivity of the alignment layer 40. Therefore, the heat of the magnetic recording layer 50 is lowered after recording. It can be considered that the amount of improvement in SNR is small as a result of not being able to escape quickly and the temperature gradient around the recording bit during recording not being steep.

  From the above results, the effects of the present invention are clear. That is, the magnetic recording medium of the present invention has a soft magnetic layer, a negative expansion layer made of a negative expansion material having a negative thermal expansion coefficient, an orientation layer, and a magnetic recording layer on a substrate. The alignment layer is disposed below the magnetic recording layer, the soft magnetic layer and the negative expansion layer are respectively disposed below the alignment layer, and the thermal conductivity of the negative expansion layer is the heat of the alignment layer. Since it is configured to be larger than the conductivity, recording with a high SNR can be achieved by suppressing the thermal expansion due to heating and suppressing deformation of the magnetic recording layer, while also steepening the temperature gradient around the recording bit during recording. A state can be realized.

  The magnetic recording medium of the present invention can be used in various technical fields such as the electronic equipment industry including a magnetic recording apparatus.

DESCRIPTION OF SYMBOLS 1, 2 ... Magnetic recording medium 10 ... Substrate 20 ... Soft magnetic layer 30 ... Negative expansion layer 40 ... Orientation layer 50 ... Magnetic recording layer

Claims (8)

On the substrate, there is a soft magnetic layer, a negative expansion layer made of a negative expansion material having a negative thermal expansion coefficient, an orientation layer, and a magnetic recording layer,
The alignment layer is disposed below the magnetic recording layer,
The soft magnetic layer and the negative expansion layer are each disposed below the orientation layer,
The magnetic recording medium, wherein the negative expansion layer has a thermal conductivity larger than that of the alignment layer.   The magnetic recording medium according to claim 1, wherein the soft magnetic layer is disposed below the negative expansion layer.   The magnetic recording medium according to claim 1, wherein the negative expansion layer is disposed below the soft magnetic layer.   The magnetic recording medium according to claim 1, wherein the negative expansion layer has a thermal conductivity of 0.1 to 1.5 W / cm · K.   The magnetic recording medium according to claim 1, wherein the alignment layer has a thermal conductivity of 0.01 to 0.05 W / cm · K.   The magnetic recording medium according to claim 1, wherein the negative expansion layer is manganese nitride.   The magnetic recording medium according to claim 1, wherein the negative expansion layer is lithium oxide.   A magnetic recording / reproducing apparatus comprising: the magnetic recording medium according to any one of claims 1 to 7; and a magnetic head for recording / reproducing a magnetic signal on the magnetic recording medium. .

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