JP2010182386A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium used for a magnetic recording device of a thermally-assisted recording system in which signal writing is performed at a temperature higher than in a signal holding state. <P>SOLUTION: The magnetic recording medium comprises at least a soft magnetic lining layer 3, a magnetic recording layer 5, and a protection layer 6 in this order on a nonmagnetic substrate 1, and has a layer constitution in which two heat-radiation layers 2-1 and 2-2 sandwich the soft magnetic lining layer 3. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium mounted on various magnetic recording devices.

  As a technique for realizing a high recording density of magnetic recording, the “perpendicular magnetic recording method” has recently been put into practical use. This method replaces the conventional longitudinal magnetic recording method in which the recording magnetization is perpendicular to the in-plane direction of the recording medium and the conventional recording magnetization is parallel to the in-plane direction. The perpendicular magnetic recording medium used for magnetic recording mainly includes a magnetic recording layer of a hard magnetic material, an underlayer for orienting the recording magnetization of the magnetic recording layer in the vertical direction, a protective layer for protecting the surface of the magnetic recording layer, And it is comprised from main layers, such as a soft-magnetic underlayer which plays the role which concentrates the magnetic flux which the magnetic head used for recording to this recording layer concentrates.

  One of the guidelines for designing the medium for increasing the density is to increase the magnetic separation degree of the magnetic particles constituting the magnetic recording layer and reduce the magnetization reversal unit. Basically, since the film thickness of the magnetic recording layer is uniform in the in-plane direction of the medium, reducing the magnetization reversal unit corresponds to reducing the cross-sectional area with a constant magnetization reversal unit height. Therefore, when the magnetization reversal unit becomes smaller, the demagnetizing field acting on itself becomes smaller and the reversal magnetic field becomes larger. Since such a relationship exists in the shape and size of the magnetization reversal unit, a higher write magnetic field is required when the recording density is increased. On the other hand, for long-term stability of the recording signal, it is known that the value of the particle energy KuV with respect to the thermal energy kT needs to be sufficiently increased (where k is the Boltzmann constant and K is the absolute temperature). Ku is the magnetocrystalline anisotropy, V is the activation volume). The aforementioned reduction in the magnetization reversal unit size means a decrease in V, and this influence causes a problem of signal instability, so-called “thermal fluctuation”. In order to avoid this, it is necessary to increase Ku. However, since Ku and the switching magnetic field are generally in a proportional relationship, this also results in an increase in the write magnetic field.

  As a method for solving such a problem, a recording method called heat-assisted recording has been proposed. This utilizes the temperature dependence of Ku in the magnetic material, that is, the characteristic that Ku becomes smaller as the temperature increases. That is, the magnetic recording layer is heated to temporarily reduce Ku, that is, the switching magnetic field, and writing is performed during that time. After the temperature has returned (decreased), Ku returns to the original high value, so that the recording signal can be held stably.

  In this new recording method, for example, laser light or near-field light is irradiated to locally raise the temperature of the recording layer. In this case, the influence on adjacent tracks becomes a problem. This is because if the adjacent track is heated and demagnetized, the track density cannot be increased. On the other hand, reducing the heating spot, which is one of the countermeasures on the head side, has a limit, although the problem is alleviated as the heating spot is reduced. On the other hand, as a countermeasure on the medium side, there is a method of providing a heat dissipation layer which is a material having high thermal conductivity.

  Such a heat dissipation layer is generally a metal layer, and when the metal layer is formed below the recording layer as a material having high thermal conductivity, the thickness of the metal layer must be increased in order to improve heat dissipation. However, as the thickness of the heat dissipation layer increases, the surface of the heat dissipation layer tends to become rough and uneven in particle size, and the surface of the recording layer thereon also has an effect. There is a publicly known document that describes this (Patent Document 1).

WO2004 / 038715 pamphlet (2 pages 23-24 lines of the specification)

  Although the heat dissipation layer requires a film thickness corresponding to the heating spot, as described above, the thicker the heat dissipation effect, the greater the effect. However, when the film thickness of the heat dissipation layer is increased, the surface irregularities generally increase. When the surface irregularities become large, the fine structure of the upper recording layer, particularly the crystal orientation and the size control of the magnetic crystal grains, are affected, the crystal orientation is deteriorated, and the particle size variation is increased. As a result, it becomes an obstacle to high density. Also, when the material of the heat dissipation layer is crystalline or microcrystalline, crystal growth is promoted by increasing the film thickness, so that it tends to be an obstacle to the higher density.

  In order to increase the effect of concentrating the head magnetic flux, which is the original role, the soft magnetic underlayer is preferably made thicker. However, as for the thickening of the soft magnetic backing layer, as with the heat dissipation layer, increasing the thickness causes a problem of increasing the surface unevenness. This problem can be avoided by making the crystal structure amorphous and selecting a material composition that suppresses crystal growth as much as possible. However, there is another adverse effect of increasing the thickness of the soft magnetic backing layer. Since the magnetization component of the soft magnetic backing layer is detected as noise in the reproduction signal of the magnetic head, when the film thickness is increased, the amount of magnetization of the soft magnetic backing layer increases and the noise component increases.

  Thus, replacing the conventional recording method with the heat-assisted recording method is preferable for increasing the density of the magnetic recording apparatus because there is a possibility that the limitations of the conventional recording method can be overcome. However, in order to cope with this heat-assisted recording method, there is a problem that a medium that can reduce the heating spot size and suppress the influence on adjacent tracks to have good recording performance and also has low noise is required. Newly occurs.

  The present invention has been made in view of the above-described new problems, and an object of the present invention is to a heat-assisted recording type magnetic recording apparatus that performs signal writing at a temperature higher than the signal holding state. It is to provide a magnetic recording medium to be used. Specifically, while suppressing surface irregularities and crystal growth, reducing the influence on the fine structure of the recording layer, etc., while maintaining the heat dissipation effect and writing performance equivalent to the conventional configuration, noise from the soft magnetic backing layer is reduced. It is to provide a magnetic recording medium that can be reduced.

  In order to achieve the above object, a magnetic recording medium according to the present invention is used in a magnetic recording apparatus that performs signal writing at a temperature higher than a signal holding state, and includes at least a soft magnetic backing layer, a magnetic recording layer, A magnetic recording medium having a protective layer in this order is characterized in that the two heat dissipation layers have a layer structure with the soft magnetic underlayer sandwiched therebetween. Preferably, the heat dissipation layer and the soft magnetic backing layer are both composed of a plurality of layers, and each heat dissipation layer and each soft magnetic backing layer of the plurality of layers have a layer structure in which the layers are alternately stacked. . More preferably, the heat dissipation layer and the soft magnetic backing layer are both composed of a plurality of layers, and each heat dissipation layer and each soft magnetic backing layer of the plurality of layers has a layer structure in which the layers are alternately laminated. To do.

Furthermore, it is also preferable that the magnetic recording medium has a higher heat conductivity of the heat dissipation layer than that of the soft magnetic backing layer.
Furthermore, it is also preferable that the thermal conductivity of the heat-dissipating layer at a room temperature of 300 K is greater than 100 (W / (m · K)).
Still further, the heat dissipation layer is a high thermal conductivity material made of any element selected from W, Ir, Mg, Mo, Re, Rh, Ru, Si, Zn, Al, Cu, Ag, Au, and C, or any of the above An alloy containing any of these elements can be used as a main component.

Furthermore, the soft magnetic backing layer may be a layer mainly containing any element selected from Fe, Co, and Ni, and may have an amorphous or microcrystalline structure.
In addition, the antiferromagnetic coupling layer is a metal composed of any element selected from V, Cr, Ru, Cu, Ir, Nb, Mo, Re, Rh, Ta, W, Re, Ir, or any of the above An alloy containing an element as a main component may be used.

  The heat dissipation layer and the soft magnetic backing layer are laminated with a thinner film thickness than in the past. This suppresses surface irregularities and crystal growth of the recording layer and reduces the influence on the fine structure of the recording layer, etc., while maintaining the same heat dissipation effect and writing performance as the conventional configuration, and derived from the soft magnetic backing layer Noise can be reduced. As a result, a medium suitable for the heat-assisted recording method is provided, and high-density recording is possible.

It is a cross-sectional schematic diagram of the magnetic recording medium of Example 1 which concerns on this invention. It is a cross-sectional schematic diagram of the magnetic recording media of Examples 2 to 4 according to the present invention. It is a cross-sectional schematic diagram of the magnetic recording medium of Example 5 which concerns on this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 to FIG. 3 are schematic cross-sectional views for explaining a magnetic recording medium having a different layer structure, each of which is the present invention. First, the layer structure will be described. The magnetic recording medium shown in FIG. 1 has a heat dissipation layer 2-1, a heat dissipation layer 2-2, an underlayer 4, a magnetic recording layer 5, and a protective layer 6 in this order on a nonmagnetic substrate 1 with a soft magnetic backing layer 3 interposed therebetween. It has a laminated structure. The material which comprises each layer is demonstrated in Example 1 mentioned later. The magnetic recording medium shown in FIG. 2 has a layer configuration in which a heat dissipation layer 2, a soft magnetic backing layer 3, an underlayer 4, a magnetic recording layer 5, and a protective layer 6 are laminated in this order on a nonmagnetic substrate 1. In particular, a layer structure in which the heat dissipation layer 2 and the soft magnetic backing layer 3 are alternately laminated at least twice or more is employed. A laminated structure in which the heat dissipating layer 2 and the soft magnetic backing layer 3 are alternately repeated 10 times, 5 times, and 2 times will be described in the following Example 2, Example 3, and Example 4. The magnetic recording medium shown in FIG. 3 has an anti-strength between the two soft magnetic backing layers 3-A and 3-B in addition to the laminated structure of FIG. 2 as described in Example 5 described later. It has a laminated structure in which the magnetic coupling layer 7 is inserted.

  Next, an embodiment of the magnetic recording medium of the present invention will be described with reference to FIG. In the magnetic recording medium of the present invention, as the nonmagnetic substrate 1, an Al alloy substrate, a tempered glass substrate, a crystallized glass substrate or the like subjected to NiP plating, which is used for a normal magnetic recording medium, can be used. In the case where the substrate temperature during film formation or recording can be suppressed to about 100 ° C. or less, a plastic substrate made of a resin such as polycarbonate or polyolefin can also be used. In addition, a Si substrate can also be used.

  For the heat dissipation layer 2, a material having high thermal conductivity is preferably used. In order to serve as a heat dissipation layer, it is preferable to have a higher thermal conductivity than the soft magnetic backing layer. The thermal conductivity is preferably greater than 100 [W / (m · K)] at a room temperature of 300 K, and more preferably greater than 200 [W / (m · K)]. As such a high thermal conductivity material, a metal such as W, Ir, Mg, Mo, Re, Rh, Ru, Si, Zn or an alloy containing these metals is preferably used, and Al, Cu, Ag, Au, Any metal material such as C, high thermal conductivity material such as graphite, or an alloy containing these materials as a main component is more preferably used.

  The soft magnetic underlayer 3 is a layer intended to improve the recording / reproducing characteristics by controlling the magnetic flux from the magnetic head, as in the current perpendicular magnetic recording system. The soft magnetic backing layer 3 is preferably made of a material mainly composed of Fe, Co, or Ni. The crystal structure may be any of amorphous, microcrystalline, and amorphous, and is preferably selected in consideration of the crystal orientation of the immediately underlayer. In order to reduce the influence on the crystal orientation of the underlayer, amorphous is preferable. When the soft magnetic underlayer also has a role of controlling crystal orientation, it is preferable to use a microcrystalline or crystalline material. It is also possible to make a multilayer structure using several kinds of soft magnetic layer materials. For example, NiFe alloy, CoFe alloy, CoNi alloy can be used as the crystalline material, and B, Si, C, Zr, Nb, P, Ta are added to the alloy for microcrystallization or amorphization. Those using a trace additive such as are also preferably used. In addition, for example, FeTaC or the like obtained by adding an additive to a single metal such as Fe, Co, or Ni can be used. In order to improve the recording ability, it is preferable that the saturation magnetization of the soft magnetic underlayer 3 is large. The optimum film thickness and total film thickness of the soft magnetic underlayer 3 vary depending on the structure and characteristics of the head used for recording, but are preferably 100 nm or less. As a film forming method, it can be formed by a commonly used sputtering method.

  In order to suppress a noise component derived from the soft magnetic backing layer 3, the soft magnetic backing layer 3 can be made into two layers, and the nonmagnetic antiferromagnetic coupling layer 7 can be inserted between the two layers. Soft magnetic backing layers 3-A and 3-B disposed above and below the antiferromagnetic coupling layer 7 are magnetically antiparallel coupled via the antiferromagnetic coupling layer 7 and cancel out the magnetization component output to the outside. By doing so, noise can be suppressed. Therefore, it is preferable that the upper and lower soft magnetic underlayers 3-A and 3-B have the same amount of magnetization, that is, the product of the saturation magnetization Ms and the film thickness. The material of the antiferromagnetic coupling layer 7 is an element selected from V, Cr, Ru, Cu, Ir, Nb, Mo, Re, Rh, Ta, W, Re, and Ir, or at least one of them. An alloy containing one element as a main component is preferably used. The film thickness is preferably set in consideration of the antiferromagnetic coupling and the relatively large exchange coupling energy, and the optimum value varies depending on the material used, but is usually preferably 2 nm or less.

  The underlayer 4 is primarily used to control the crystal grain size and crystal orientation of the material of the upper magnetic recording layer 5, and secondly, the magnetic coupling between the soft magnetic backing layer 3 and the magnetic recording layer 5 is performed. It is a layer used for the purpose of prevention. Therefore, it is preferably non-magnetic, and the crystal structure needs to be appropriately selected according to the material of the upper magnetic recording layer 5, but it can also be used with an amorphous structure. For example, when a magnetic recording layer material mainly composed of Co having a hexagonal close-packed (hcp) structure is used for the magnetic recording layer 5 immediately above, the material having the same hcp structure or face-centered cubic (fcc) structure is preferable. Used. Specifically, Ru, Re, Rh, Pt, Pd, Ir, Ni, Co or an alloy material containing these is preferably used. The thinner the film thickness, the better the writeability. However, considering the first and second objects, a certain film thickness is required, and it is preferably within the range of 3 to 30 nm.

  For the magnetic recording layer 5, a crystalline magnetic layer material can be used. It is preferable to take a structure in which columnar crystal particles having a diameter of several nanometers mainly composed of a magnetic element such as Co, Fe, and Ni are separated by a nonmagnetic material having a thickness of about sub-nm. For example, a magnetic crystal grain is a material obtained by adding a metal such as Cr, B, Ta, W, or Cu to a CoPt alloy or FePt alloy, and a non-magnetic material is an oxidation of Si, Cr, Co, Ti, Ta, or B. A material added with an oxide or nitride, or C or carbide is also preferably used. Examples of the film forming method include a magnetron sputtering method. A structure may be adopted in which magnetic crystal grains are epitaxially grown on the crystal portion on the underlayer 4 and the nonmagnetic material is arranged on the grain boundary portion of the underlayer 4 so as to perform one-to-one crystal growth. In addition to this, it is also possible to use an amorphous material such as TbFeCo used in magneto-optical recording, or a multilayer film in which Co and Pt, or Co and Pd are alternately laminated with a thin film thickness of 2 nm or less. It is. Further, it can be used as a laminated structure combined with the crystal system. The magnetic recording layer 5 may have a physically processed structure. In other words, for example, in the case of a disk-shaped recording medium used in a hard disk, a discrete track medium in which the recording layer is physically separated for each track in the circumferential direction, and a bit pattern medium in which the recording layer is divided in the bit direction. The layer structure of the present invention can be applied.

The protective layer 6 may be a conventionally used protective film, for example, a protective film mainly composed of carbon. Instead of a single layer, for example, a double-layer carbon having different properties, a metal film and a carbon film, or a laminated film of an oxide film and carbon can be used.
Examples of the method for manufacturing a magnetic recording medium of the present invention will be described in detail below. These examples are merely representative examples for suitably explaining the method of manufacturing the magnetic recording medium of the present invention, and the present invention is not limited to these examples.

Example 1
A magnetic recording medium described in Example 1 is shown in a schematic cross-sectional view of FIG. A disk-shaped glass substrate having a smooth surface is used as the nonmagnetic substrate 1. After cleaning this glass substrate, it is introduced into a sputtering apparatus, and Cu is formed to a thickness of 30 nm as a heat dissipation layer 2-1 under an Ar gas pressure of 5 mTorr (133.322 Pa) using a Cu target. Subsequently, using a Co ₄₄ Fe ₃₉ Zr ₈ Ni ₅ Zr ₄ target, an FeCoZrNiNb film having a thickness of 50 nm is formed as the soft magnetic backing layer 3 under an Ar gas pressure of 5 mTorr (133.322 Pa). Subsequently, using a Cu ₇₉ C ₂₀ Cr ₁ target and under an Ar gas pressure of 5 mTorr (133.322 Pa), a CuCCr film having a thickness of 20 nm is formed as the heat dissipation layer 2-2, and the heat dissipation layer 2-1 is Cu / CoFeZrNiNb / CuCCr. / Soft magnetic backing layer 3 / Heat dissipation layer 2-2 was formed.

Subsequently, the Ru underlayer 4 is formed with a film thickness of 20 nm under an Ar gas pressure of 30 mTorr (133.322 Pa) using a Ru target. Thereafter, using a (Co ₇₅ Pt ₂₀ Ni ₅ ) ₉₁ (TiO ₂ ) ₉ target, a CoPtNi—TiO ₂ magnetic layer having a thickness of 15 nm is formed at an Ar gas pressure of 60 mTorr (133.322 Pa), thereby forming the magnetic recording layer 5. did. Next, the protective layer 6 made of carbon was formed to a thickness of 3 nm by the CVD method, and then taken out from the vacuum apparatus. Thereafter, a film thickness of 2 nm of a liquid lubricant layer made of perfluoropolyether was formed by a dip method to obtain a magnetic recording medium. In sputtering, pulsed DC magnetron sputtering was used for forming the magnetic layer, and DC magnetron sputtering was used for the other layers.

(Example 2)
A magnetic recording medium described in Example 2 is shown in a schematic cross-sectional view of FIG. [Cu / Co ₄₄ Fe ₃₉ Zr ₈ Ni] is formed 10 times on the nonmagnetic substrate 1 by repeatedly forming Cu as a heat dissipation layer 2 with a thickness of 5 nm and subsequently forming a soft magnetic backing layer 3 with a thickness of 5 nm as CoFeZrNiNb. ₅ Zr ₄ ] ₁₀ heat dissipation layer 2 / soft magnetic backing layer 3 is formed 10 times repeatedly. In Example 1, the heat dissipation layer 2-1 which is Cu / CoFeZrNiNb / CuCCr is replaced with the above-mentioned 10 times repeating layer, and only the other layers are the examples. 1 was used as a magnetic recording medium.

(Example 3)
A magnetic recording medium described in Example 3 is shown in a schematic cross-sectional view of FIG. [Cu / Co ₄₄ Fe ₃₉ Zr ₈ Ni ₅ Zr ₄ ] _{5 is} formed five times on the nonmagnetic substrate 1 by forming Cu as a heat dissipation layer 2 with a thickness of 10 nm and subsequently forming eCoZrNiNb with a thickness of 10 nm. 5 layers of heat dissipation layer 2 / soft magnetic backing layer 3 are formed. Only the portion of the heat dissipation layer 2-1 / soft magnetic backing layer 3 / heat dissipation layer 2-2 which is Cu / CoFeZrNiNb / CuCCr in Example 1 is replaced with the above-mentioned five-time repeating layer, and all other layers are in Example 1. In the same manner as described above, a magnetic recording medium was obtained.

Example 4
A magnetic recording medium described in Example 4 is shown in a schematic cross-sectional view of FIG. [Cu / Co ₄₄ Fe ₃₉ Zr ₈ Ni ₅ Zr ₄ ] _{2 is} formed twice on the nonmagnetic substrate 1 by repeatedly forming Cu as the heat dissipation layer 2 with a thickness of 25 nm and subsequently forming FeCoZrNiNb with a thickness of 25 nm. The heat-radiating layer 2 / soft magnetic backing layer 3 is repeatedly formed twice. Only the part of the heat radiation layer 2-1 / soft magnetic backing layer 3 / heat radiation layer 2-2 which is Cu / CoFeZrNiNb / CuCCr in Example 1 is replaced with the above-mentioned twice repeated layer, and all other layers are in Example 1. In the same manner as described above, a magnetic recording medium was obtained.

(Example 5)
A magnetic recording medium described in Example 5 is shown in a schematic cross-sectional view of FIG. On the nonmagnetic substrate 1, Cu is 25 nm thick as the heat dissipation layer 2, Co ₄₄ Fe ₃₉ Zr ₈ Ni ₅ Zr ₄ is 25 nm thick as the soft magnetic backing layer 3, and Cu is 25 nm thick as the heat dissipation layer 2, soft magnetic Co ₄₄ Fe ₃₉ Zr ₈ Ni ₅ Zr ₄ is formed to a thickness of 12.5 nm as the backing layer 3-A. Subsequently, a Ru antiferromagnetic coupling layer 7 is formed with a film thickness of 0.8 nm under an Ar gas pressure of 5 mTorr (133.322 Pa) using a Ru target, and Fe ₄₄ Co ₃₈ Zr ₈ Ni ₆ is formed as a soft magnetic backing layer 3-B. Zr ₄ is deposited to a thickness of 12.5 nm. Only the portion of the heat dissipation layer 2-1 / soft magnetic backing layer 3 / heat dissipation layer 2-2 that is Cu / CoFeZrNiNb / CuCCr in Example 1 is replaced with the above-mentioned plural layers, and all other layers are the same as in Example 1. Thus, a magnetic recording medium was obtained. Of the plurality of replacement layers described above, the continuous layer of the heat dissipation layer 2 and the soft magnetic backing layer 3 may be a plurality of repeated layers.

(Comparative Example 1)
On the non-magnetic substrate, Cu is formed with a thickness of 50 nm as a heat dissipation layer, and subsequently FeCoZrNiNb is formed with a thickness of 50 nm as a soft magnetic backing layer, and the heat dissipation layer / soft layer is Cu / Co ₄₄ Fe ₃₉ Zr ₈ Ni ₅ Zr _4. A magnetic backing layer is formed. Only the part of the heat dissipation layer 2-1 / soft magnetic backing layer 3 / heat dissipation layer 2-2 which is Cu / CoFeZrNiNb / CuCCr in Example 1 is replaced with the above heat dissipation layer and the soft magnetic backing layer, and all other layers are A magnetic recording medium was prepared in the same manner as in Example 1.

(Comparative Example 2)
On the nonmagnetic substrate, a CuCCr film having a thickness of 50 nm is formed as a heat dissipation layer, and subsequently a FeCoZrNiNb film having a thickness of 50 nm is formed as a soft magnetic backing layer, and Cu ₇₉ C ₂₀ Cr ₁ / Co ₄₄ Fe ₃₉ Zr ₈ Ni ₅ Zr ₄ is formed. A heat dissipation layer / soft magnetic backing layer is formed. Only the part of the heat dissipation layer 2-1 / soft magnetic backing layer 3 / heat dissipation layer 2-2 which is Cu / CoFeZrNiNb / CuCCr in Example 1 is replaced with the above heat dissipation layer and the soft magnetic backing layer, and all other layers are A magnetic recording medium was prepared in the same manner as in Example 1.

In the above Examples 1 to 5 and Comparative Examples 1 and 2, the total thickness of the soft magnetic backing layer and the heat dissipation layer is 100 nm, and the total thickness of the soft magnetic backing layer and the heat dissipation layer film are provided for easy comparison. The ratio of the total thickness is set to be 1: 1.
Hereinafter, the performance evaluation results of the magnetic recording media of Examples 1 to 5 and Comparative Examples 1 to 1 will be described. Table 1 below shows the results of surface roughness (Ra), electromagnetic conversion characteristics (overwriting (OW) and signal-to-noise ratio (SNR)), and influence on adjacent tracks (signal attenuation ratio) of each example and comparative example. Are shown together.

なお、Ｒａの評価にはＡＦＭ（原子間力顕微鏡）を用い、電磁変換特性評価は、レーザースポット加熱機構を搭載したスピンスタンドテスターにて、ＧＭＲヘッドを用いて行った。レーザーパワーは記録層温度２００℃となるように設定し、記録時にレーザーパワーをＯＮし、読み出し時はレーザーパワーＯＦＦで行った。ヘッドは、記録トラック幅１４０ｎｍ、再生トラック幅９０ｎｍのものを用いた。隣接トラックへの影響は、読み出しトラックに隣接する両側のトラックにそれぞれ書き込みを行った後の信号出力減衰割合を評価した。

Ra was evaluated using an AFM (Atomic Force Microscope), and electromagnetic conversion characteristics were evaluated using a GMR head with a spin stand tester equipped with a laser spot heating mechanism. The laser power was set so that the recording layer temperature was 200 ° C., the laser power was turned on during recording, and the laser power was turned off during reading. A head having a recording track width of 140 nm and a reproducing track width of 90 nm was used. As for the influence on the adjacent track, the signal output attenuation ratio after writing on both tracks adjacent to the read track was evaluated.

  By comparing the comparative example 1 and the comparative example 2, the materials of the heat dissipation layer 2 can be compared. Although Comparative Example 1 has a large and poor surface roughness as compared with Comparative Example 2, the output attenuation of the adjacent track is small and excellent. This result shows that the heat dissipation layer (Cu) used in Comparative Example 1 has higher thermal conductivity than the heat dissipation layer (CuCCr) used in Comparative Example 2, but it is easy to grow crystals and has large surface irregularities. ing. In addition, reflecting the difference in surface irregularities between Comparative Examples 1 and 2, Comparative Example 2 having a lower Ra may have a higher SNR (signal-to-noise ratio).

  Based on this fact, Example 1 is compared with Comparative Examples 1 and 2. In Example 1 in which the heat dissipation layer 2 is divided into two layers, Ra (surface roughness) is significantly smaller than those of Comparative Examples 1 and 2, and the SNR is greatly improved reflecting the result. Since Cu and CuCCr of the heat dissipation layer immediately below the base layer 4 of Example 1 are divided into two layers, the heat dissipation layers 2-1 and 2-2 are thinner than the film thickness of 50 nm of Comparative Examples 1 and 2. The effect has appeared.

OW (overwriting) is slightly deteriorated because the magnetic spacing (distance between the outermost surface of the soft magnetic backing layer 3 and the magnetic head) is larger than that of Comparative Examples 1 and 2, while the heat dissipation layer 2 is magnetically recorded. It can be seen that by approaching the layer 5, the distribution of heat distribution is suppressed, and the influence on the adjacent track is reduced.
Overall, the magnetic recording medium shown in FIG. 1 described in the first embodiment has a very large noise reduction effect due to an increase in SNR, and can be a magnetic recording medium suitable for the above-described heat-assisted recording method. .

  Next, Example 2, Example 3, Example 4, and Comparative Example 1 are compared. The magnitude of Ra (surface roughness) is Example 2 = Example 3 <Example 4 <Comparative Example 1, and SNR (Signal Noise Ratio) is Example 2, Example 3, Example 4, Comparative Example. Since it is high in order of 1, it is low. The signal output attenuation of the adjacent track also decreases in this order. OW (overwriting) was a comparable value. From this result, it can be seen that by reducing the film thickness per heat dissipation layer, the writing performance and the heat dissipation effect are maintained while suppressing the increase in surface roughness and preventing the characteristic deterioration of the recording layer. Further, when Example 2 and Example 3 are compared, the SNR of Example 2 is higher in spite of equal Ra, so that Example 2 is derived from the soft magnetic backing layer as compared to Example 3. It can be seen that the noise is small. From the above, the magnetic recording medium of FIG. 2 described in the second, third, and fourth embodiments can be a magnetic recording medium suitable for the above-described heat-assisted recording method.

  Subsequently, when Example 4 and Example 5 are compared, the influence on Ra and adjacent tracks is the same, but Example 5 is superior in SNR. This is because the noise of the soft magnetic underlayer is suppressed. Although OW is somewhat worse, it can be applied to the heat-assisted recording method because the influence on adjacent tracks is suppressed and the SNR is high overall. From the above, the magnetic recording medium of FIG. 3 described in the fifth embodiment can be a magnetic recording medium suitable for the above-described heat-assisted recording method.

  As described above, when the structure of the soft magnetic underlayer and the heat dissipation layer of the present invention is used, the increase in surface unevenness and crystal growth due to the thick film can be suppressed, and the influence on the fine structure of the recording layer can be reduced. It is also possible to obtain an effect of reducing noise derived from the soft magnetic underlayer while maintaining the heat radiation effect and the writing performance equivalent to the above configuration. As a result, a magnetic recording medium suitable for the above-described heat-assisted recording method can be obtained, and a medium is provided, enabling high-density recording.

DESCRIPTION OF SYMBOLS 1 Nonmagnetic board | substrate 2 Heat dissipation layer 2-1 Heat dissipation layer 2-2 Heat dissipation layer 3 Soft magnetic backing layer 3-A Soft magnetic backing layer 3-B Soft magnetic backing layer 4 Underlayer 5 Magnetic recording layer 6 Protective layer 7 Antiferromagnetic Bonding layer

Claims (8)

In a magnetic recording medium that is used in a magnetic recording device that performs signal writing at a temperature higher than the signal holding state, and includes a soft magnetic underlayer, a magnetic recording layer, and a protective layer in this order on a nonmagnetic substrate, two heat dissipation layers are provided. A magnetic recording medium having a layer structure sandwiching the soft magnetic backing layer. 2. The heat dissipation layer and the soft magnetic backing layer are both composed of a plurality of layers, and each heat dissipation layer and each soft magnetic backing layer of the plurality of layers have a layer configuration that is alternately stacked. The magnetic recording medium described. A two-layer soft magnetic backing layer sandwiching a nonmagnetic antiferromagnetic coupling layer is disposed on the uppermost heat dissipation layer of the heat dissipation layer, and the two soft magnetic backing layers are interposed via the antiferromagnetic coupling layer. 3. The magnetic recording medium according to claim 2, wherein the magnetic recording medium is magnetically coupled to each other. 2. The magnetic recording medium according to claim 1, wherein the heat dissipation layer has a thermal conductivity higher than that of the soft magnetic backing layer. 5. The magnetic recording medium according to claim 4, wherein the heat dissipation layer has a thermal conductivity at a room temperature of 300 K of greater than 100 (W / (m · K)). The heat dissipation layer is a high thermal conductivity material composed of any element selected from W, Ir, Mg, Mo, Re, Rh, Ru, Si, Zn, Al, Cu, Ag, Au, and C, or any of the above elements 6. A magnetic recording medium according to claim 5, wherein an alloy containing is used as a main component. 2. The magnetic recording medium according to claim 1, wherein the soft magnetic underlayer is a layer mainly composed of any element selected from Fe, Co, and Ni and has an amorphous or microcrystalline structure. . The antiferromagnetic coupling layer is formed of a metal composed of any element selected from V, Cr, Ru, Cu, Ir, Nb, Mo, Re, Rh, Ta, W, Re, and Ir, or any one of these elements. 4. The magnetic recording medium according to claim 3, wherein the magnetic recording medium is an alloy having a main component.

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