JP5294062B2 - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium in which the thermal changes in the backing layer characteristics is improved, in the magnetic recording medium used in a magnetic recording device to conduct signal writing at temperature higher than that at which signal is held. <P>SOLUTION: In the magnetic recording medium used in the magnetic recording device for conducting signal writing at the temperature higher than that at which the signal is held, the magnetic recording medium is constituted, by sequentially laminating at least a soft magnetic backing layer, a heat conduction preventing layer, an underlayer, a magnetic recording layer, and a protective layer on a non-magnetic substrate. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

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

  As a technique for realizing a high recording density of magnetic recording, a “perpendicular magnetic recording method” has recently been put into practical use. This is because the recording magnetization is performed in a direction perpendicular to the surface of the recording medium, which is replacing the conventional longitudinal magnetic recording method in which the recording magnetization is parallel to the surface.

  The perpendicular magnetic recording medium (abbreviated perpendicular medium) used in this perpendicular magnetic recording system mainly includes a magnetic recording layer made of a hard magnetic material, an underlayer for orienting the recording magnetization of the magnetic recording layer in the vertical direction, and a magnetic layer. It comprises a protective layer for protecting the surface of the recording layer, and a backing layer made of a soft magnetic material that plays a role of concentrating the magnetic flux generated by the magnetic head used for recording on the recording layer.

  One guideline for medium design for increasing the density of perpendicular magnetic recording is to increase the magnetic separation 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 means that the height of the magnetization reversal unit is constant and the cross-sectional area is reduced. To do. As a result, the demagnetizing field acting on itself decreases and the reversal field increases. Thus, when considering the shape of the magnetization reversal unit, increasing the recording density requires a larger write magnetic field.

  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, and V is the activation volume). The reduction in the magnetization reversal unit size described above 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 another approach to the problem of the writing ability, a recording method called heat-assisted recording considered in combination with a head 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. When such a new recording method is assumed, the magnetic recording medium needs to consider the effect of heat in addition to the conventional guidelines.

  A non-magnetic intermediate layer including a first backing layer formed of a soft magnetic material on a substrate, a second backing layer formed of a ferrimagnetic material, a dielectric layer made of nitride or oxide, and an uneven layer There is a proposal of a thermally assisted magnetic recording medium in which a magnetic recording layer and a protective layer are laminated in this order (see, for example, Patent Document 1).

  In Patent Document 1, the dielectric layer is made of nitride or oxide, but this dielectric layer prevents aluminum from diffusing uniformly when an uneven layer is formed of aluminum on the dielectric layer, This is used to make it easy to form irregularities.

JP 2006-164436 A

When the basic configuration of the current perpendicular medium is applied to heat-assisted recording, when the recording layer is heated, the underlying layer and the underlying soft magnetic backing layer are also heated by heat conduction. Since the magnetic material used for the soft magnetic underlayer usually has a property that the saturation magnetization Ms decreases with temperature, it means that the role of concentrating the magnetic flux of the magnetic head is reduced. If the backing layer is moved away from the outermost surface layer to alleviate the influence of heat, this also makes it difficult to attract the head magnetic field, which is contrary to the original purpose.
Thus, when the recording medium used in the heat-assisted recording method has a soft magnetic backing layer, a method for preventing a decrease in Ms due to heating of the backing layer is required.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a heat-resistant backing layer in a magnetic recording medium used in a magnetic recording apparatus that performs signal writing at a temperature higher than the signal holding state. It is to provide a magnetic recording medium with improved changes.

  In order to achieve the above object, the magnetic recording medium of the present invention is a magnetic recording medium used in a magnetic recording apparatus in which signal writing is performed at a temperature higher than the temperature at which the signal is held. The heat conduction preventing layer, the underlayer, the magnetic recording layer, and the protective layer are sequentially laminated.

  Since the magnetic recording medium of the present invention is provided with the heat conduction preventing layer, the temperature rise of the soft magnetic underlayer is suppressed, and the saturation magnetization Ms is not deteriorated at the time of heating writing. Therefore, it is possible to show better writing performance as compared with the case without the heat conduction preventing layer.

It is a cross-sectional schematic diagram which shows one embodiment of the magnetic recording medium of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram for explaining a configuration example of a magnetic recording medium according to the present invention, and is a cross-sectional view showing a configuration when a soft magnetic underlayer is provided. In the magnetic recording medium, a soft magnetic backing layer 2, a heat conduction preventing layer 3, a nonmagnetic underlayer 3, a magnetic recording layer 4, and a protective layer 5 are sequentially laminated on a nonmagnetic substrate 1. A lubricant layer may be further formed on the protective layer 5.

  In the magnetic recording medium of the present invention, the nonmagnetic substrate (nonmagnetic substrate) 1 may be an Al alloy plated with NiP, tempered glass, or crystallized glass, which is used for ordinary magnetic recording media. . When the substrate temperature during film formation or recording is kept within about 100 ° C., a plastic substrate made of a resin such as polycarbonate or polyolefin may be used. In addition, a Si substrate can also be used.

  The soft magnetic backing layer 2 is preferably formed in order to improve the recording / reproducing characteristics by controlling the magnetic flux from the magnetic head, as in the current perpendicular magnetic recording method, but this layer is omitted. Is also possible. As the soft magnetic underlayer, for example, crystalline NiFe alloy, Sendust (FeSiAl) alloy, CoFe alloy, or the like, microcrystalline FeTaC, CoFeNi, CoNiP, or the like can be used. In order to improve the recording ability, it is preferable that the saturation magnetization of the soft magnetic underlayer is large. Note that the optimum value of the thickness of the soft magnetic backing layer 2 varies depending on the structure and characteristics of the magnetic head used for magnetic recording. The thickness is desirably 100 nm or less in view of deterioration of flatness due to an increase in film thickness and balance with productivity.

  As a film forming method, a commonly used sputtering method is used. When the thickness of the soft magnetic underlayer is increased to about 50 nm or more, in addition to forming a domain wall, magnetization in the vertical component may occur due to fluctuations in the magnetization in the vicinity of the recording layer, which may be a noise source. In order to suppress this, it is preferable to make the soft magnetic underlayer a single magnetic domain. When an antiferromagnetic layer or a hard magnetic layer is provided and a soft magnetic layer is disposed so as to be in contact with these layers, the soft magnetic layer is antiferromagnetic or hard magnetic when the external magnetic field is removed by exchange coupling at the interface. Magnetization is aligned with the spin direction of the layer surface. By aligning the spin on the antiferromagnetic layer surface or the spin on the hard magnetic layer surface in one direction, the soft magnetic layer can have a single magnetic domain.

  The antiferromagnetic layer or the hard magnetic layer may be provided immediately below, immediately above, or in the middle of the soft magnetic layer, or may be provided immediately below, immediately above, or in the middle of the soft magnetic layer. In addition, it is also possible to use a configuration in which a soft magnetic backing layer is laminated with a nonmagnetic layer. In particular, by controlling the film thickness of the nonmagnetic layer and using antiferromagnetic coupling via the nonmagnetic layer, it is possible to suppress perpendicular component magnetization. That is, a structure in which a nonmagnetic layer is inserted between soft magnetic layers, that is, a structure of soft magnetic layer / nonmagnetic layer / soft magnetic layer, and when the nonmagnetic layer is controlled to a predetermined film thickness of several nm or less, The upper and lower soft magnetic layers have anti-parallel magnetization due to the coupling called RKKY coupling. For example, when the upper and lower soft magnetic layer material compositions and film thicknesses are the same, the overall magnetization is apparently zero because the magnetizations of both layers cancel each other.

The heat conduction preventing layer 3 is used for the purpose of blocking heat transferred from the recording layer side to the backing layer. Specific examples of these compounds in which oxide, nitride, or carbide having a low thermal conductivity is used as the material constituting the heat conduction preventing layer 3 include SiO ₂ , TiO ₂ , Y ₂ O ₃ , Al _2. Examples thereof include O ₃ , SiN, TiN, AlN, TiC, and SiC. The crystal structure is not particularly limited, and may be an amorphous structure. When a crystalline material is used, the bcc, fcc, and hcp structures can be selected as appropriate in consideration of the crystal orientation of the underlying layer immediately above. The material for the heat conduction preventing layer 3 may be magnetic or non-magnetic. However, if it is made magnetic, it can be integrated with the soft magnetic backing layer directly below and can serve as a backing layer. The film thickness of the heat conduction preventing layer 3 is preferably thinner in consideration of the distance between the head and the backing layer, and is preferably 30 nm or less.

  The underlayer 4 is a layer used for 1) controlling the crystal grain size and crystal orientation of the upper recording layer material, and 2) preventing magnetic coupling between the soft magnetic backing layer and the recording layer. Therefore, it is preferably nonmagnetic, and the crystal structure needs to be appropriately selected according to the material of the upper magnetic recording layer, 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 layer immediately above, a material having the same hcp structure or face-centered cubic (fcc) structure is preferably used. . Specifically, Ru, Re, Rh, Pt, Pd, Ir, Ni, Co, Cu or an alloy material containing these is preferably used. The thinner the film thickness, the better the writeability. However, considering the guidelines 1) and 2) above, a certain film thickness is required, and it is preferably within the range of 3 to 30 nm. Since heat diffusion in the downward direction is suppressed by the lower heat conductivity prevention layer, it is preferable to perform heat diffusion in the in-plane direction of the underlayer, and higher heat conductivity is preferable. The underlayer portion can be multilayered, and the upper layer can be shared with the crystal orientation layer, and the lower layer can be shared with the heat dissipation layer. Specific materials can be adjusted to characteristics suitable for each by adjusting the composition ratio of the elements.

  For the magnetic recording layer 5, a crystalline magnetic layer material is preferably used. The magnetic recording layer 5 has a structure in which columnar crystal grains having a diameter of several nm mainly composed of magnetic elements such as Co, Fe, and Ni are separated by a non-magnetic material having a thickness of about sub nm. Is preferred. The magnetic recording layer 5 having such a structure can be obtained, for example, by sputtering using a synthetic target of a magnetic element and a nonmagnetic material that easily phase separates, or by simultaneous sputtering. Examples of the sputtering method include a magnetron sputtering method. More preferably, the structure of the underlayer is controlled so that one-to-one crystal growth in which the magnetic crystal grains are epitaxially grown on the crystal portion on the underlayer and the nonmagnetic material is arranged on the grain boundary portion of the underlayer. A structure is preferred. Thereby, a desired structure (granular structure) can be obtained. For example, as the magnetic crystal particles, a material obtained by adding a metal such as Cr, B, Ta, or W to a CoPt alloy, or a material obtained by adding Ni, Cu, or the like to an FePt alloy can be used. As the nonmagnetic material, a material added with an oxide or nitride of Si, Cr, Co, Ti or Ta is preferably used.

Of the magnetic layers included in the magnetic recording layer 5, at least one layer is preferably a material having a large magnetocrystalline anisotropy constant, at least 5.0 × 10 6 erg / cm ³ or more, more preferably 1.0 × 10 7 erg / cm ³ or more. It is preferable that The film thickness is preferably 20 nm or less. Moreover, it can also be set as the structure which laminated | stacked two layers. At least one has the structure or Ku value as described above, the other can be a structure not separated by a non-magnetic material, can be an amorphous material, and has a relatively low Ku value. Is also possible. As the amorphous material, a TbCo or TbFe-based ferrimagnetic material that exhibits perpendicular anisotropy even when amorphous can be used.

  As the protective layer 6, a protective film conventionally used for a protective layer of a magnetic recording medium can be used. For example, a protective film mainly composed of carbon can be used. 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 a metal oxide film and a carbon film may be used.

  The perpendicular magnetic recording medium of the present invention will be described below using examples. These examples are merely representative examples for suitably explaining the magnetic recording medium of the present invention, and are not limited thereto.

<Example 1>
A disc-shaped glass substrate having a smooth surface is used as the non-magnetic substrate 1, which is cleaned, introduced into a sputtering apparatus, and CoNbZr is deposited to a thickness of 80 nm under a Ar gas pressure of 5 mTorr using a Co88Nb7Zr5 target. A soft magnetic backing layer 2 was formed.

Subsequently, the SiO ₂ target was used to form the thermal conduction preventing layer 3 made of SiO ₂ with a film thickness of 10 nm under an Ar gas pressure of 30 mTorr.

  Next, a Cu layer was formed using a Cu target at an Ar gas pressure of 10 mTorr, and subsequently a Ru layer was formed using an Ru target at an Ar gas pressure of 60 mTorr to form a Cu / Ru underlayer 4.

Subsequently, using a (Co73Pt27) 92 (SiO ₂ ) 8 target, a magnetic layer made of CoPt—SiO ₂ was formed to a thickness of 12 nm under an Ar gas pressure of 30 mTorr, thereby forming a magnetic recording layer 4.

  Next, the protective layer 5 made of carbon was formed with a thickness of 4 nm by the CVD method, and then taken out from the vacuum apparatus. Thereafter, a liquid lubricant layer 2 nm made of perfluoropolyether was formed by a dip method to obtain a magnetic recording medium. In the sputtering, RF magnetron sputtering was used for the formation of the heat conduction preventing layer and the magnetic recording layer, and the DC magnetron sputtering method was used for the other layers.

When a hysteresis loop of the recording layer of the magnetic recording medium obtained above was obtained using a Kerr effect measuring apparatus, the coercive force Hc = 10.4 kOe and S = 1.0.
We have also measured the XRD diffraction, in the embodiment 1 is broad peak of SiO ₂ is observed, it was found that SiO ₂ is amorphous structure.

  Table 1 shows the results of electromagnetic conversion characteristics of the obtained magnetic recording medium. The electromagnetic conversion characteristics were evaluated by a spin stand tester using a thermal assist head in which a laser spot heating mechanism was mounted on a perpendicular magnetic recording head. The laser power was set so that the recording layer temperature was 200 ° C., the laser power was turned on during recording or overwriting, 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.

<Comparative Example 1>
A magnetic recording medium was manufactured in the same manner as in Example 1 except that the SiO ₂ heat conduction preventing layer was not formed.
When a hysteresis loop of the recording layer of the magnetic recording medium obtained above was obtained using a Kerr effect measuring apparatus, the coercive force Hc = 10.4 kOe, S = 1.0, and the loop shape was also Example 1. It was consistent with that obtained in

Further, the peak positions and intensities of Cu, Ru, and CoPt coincided with the respective peak positions and intensities in Example 1.
Table 1 shows the results of electromagnetic conversion characteristics of the obtained magnetic recording medium together with the results of Example 1.

<Comparative example 2>
A magnetic recording medium was manufactured in the same manner as in Example 1 except that a Ta layer was formed with a thickness of 10 nm using a Ta target instead of the SiO ₂ heat conduction preventing layer.
When a hysteresis loop of the recording layer of the magnetic recording medium obtained above was obtained using a Kerr effect measuring apparatus, the coercive force Hc = 10.4 kOe, S = 1.0, and the loop shape was also Example 1. It was consistent with that obtained in

Further, when XRD diffraction was evaluated, a broad peak of Ta was observed, and it was found that Ta has an amorphous structure. Further, the peak positions and intensities of Cu, Ru, and CoPt coincided with the respective peak positions and intensities in Example 1.
Table 1 shows the results of electromagnetic conversion characteristics of the obtained magnetic recording medium together with the results of Example 1.

From the results of studying the hysteresis loop and XRD diffraction of the recording layers of the magnetic recording media of Example 1 and Comparative Examples 1 and 2 using the Kerr effect measurement device, the presence or absence of the SiO ₂ thermal conduction prevention layer or the Ta layer was confirmed. It was found that there was no effect on the crystal structure and microstructure.

  From Table 1, it can be seen that the magnetic recording medium obtained in Example 1 has the highest SNR value as an index of recording density, compared with the magnetic recording media obtained in Comparative Examples 1 and 2. In the head used this time, if the OW value is 35 [-dB] or more, it is considered that the medium has sufficient writing performance. However, in the first embodiment, the magnetic recording medium is further 4 [- dB] was higher than that, and the MWW was slightly smaller than the design value of the head.

  On the other hand, in Comparative Example 1, OW is slightly inferior, SNR is low, and MWW is also large. The OW is inferior because the magnetic spacing between the head and the soft magnetic backing layer is narrow, but since there is no thermal conduction preventing layer as compared with Example 1, the soft magnetic backing layer is saturated during recording. This is because the magnetization has decreased. In addition, the SNR is deteriorated, and noise in the soft magnetic underlayer is picked up and the laser power is increased to raise the temperature of the recording layer, so that the amount of writing blur increases.

In Comparative Example 2, OW is inferior to that of Comparative Example 1 as compared with Comparative Example 1.
Since the thermal conductivity of the Ta layer formed in place of the SiO ₂ thermal conduction preventing layer of Example 1 is high, the heat during heating diffuses into the soft magnetic layer as in Comparative Example 1, and the soft magnetic backing The saturation magnetization of the layer is lowered, and OW is lowered due to the influence. Further, since the magnetic spacing is larger than that of Comparative Example 1, the value of OW is worse than that of Comparative Example 1. The MWW increases as in Comparative Example 1, but this is also because the laser power must be increased to raise the temperature of the recording layer. The SNR is better than that of Comparative Example 1 because the noise of the soft magnetic underlayer is reduced. However, since the OW is inferior, the saturation recording characteristics are slightly deteriorated, so that the SNR is inferior to that of Example 1.
As described above, the effect of providing the heat conduction preventing layer between the soft magnetic underlayer and the underlayer as in the present invention has been clarified.

  According to the present invention, a magnetic recording medium showing good writing performance can be obtained.

1: Nonmagnetic substrate 2: Soft magnetic backing layer 3: Thermal conduction prevention layer 4: Underlayer 5: Magnetic recording layer 6: Protective layer

Claims (5)

In a magnetic recording medium used in a magnetic recording apparatus that performs signal writing at a temperature higher than the temperature at which the signal is held, at least a soft magnetic backing layer, a heat conduction preventing layer, an underlayer, a magnetic recording layer, and a protective layer are provided on a nonmagnetic substrate. Ri Na are sequentially stacked, the underlying layer is the heat dissipation layer, a magnetic recording medium which the crystal orientation layer, characterized in Rukoto in this order.   2. The magnetic recording medium according to claim 1, wherein the heat conduction preventing layer is made of any one of oxide, nitride, and carbide.   3. The magnetic recording medium according to claim 1, wherein the magnetic recording layer has magnetic anisotropy in a direction perpendicular to the nonmagnetic substrate surface.   4. The magnetic recording medium according to claim 1, wherein the heat dissipation layer is made of Cu.   5. The magnetic recording medium according to claim 1, wherein the crystal orientation layer is made of Ru.

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