JP5267938B2 - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium for which the characteristics of a soft magnetic backing layer suitable for thermal assist recording are improved. <P>SOLUTION: In the magnetic recording medium used in a magnetic recording device to conduct signal writing at temperature higher than that at which a signal is held and a signal is reproduced; and the magnetic recording medium is constructed by sequentially laminating at least a soft magnetic backing layer, an underlayer, a magnetic recording layer, and a protective layer on a non-magnetic substrate, wherein the soft magnetic backing layer is constituted of at least three layers of a first soft magnetic layer, a temperature characteristic control layer, and a second soft magnetic layer. <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 a new approach to the problem of such writing ability, a recording method called heat-assisted recording has been proposed (for example, see Patent Document 1). 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.

  On the other hand, the soft magnetic backing layer also plays an important role in the writing capability of current perpendicular magnetic recording media, and generally has a larger film thickness and saturation magnetic flux density (or saturation magnetization) than the recording layer. Large magnetic material is selected to aid recording.

  However, such a backing layer means that the total amount of magnetization is large, and acts as a noise source during reproduction, although the distance from the reproducing head is farther than that of the recording layer. As a method of optimization in such a trade-off, there is a method of controlling the film thickness of the nonmagnetic intermediate layer inserted between the recording layer and the backing layer, and the film thickness / saturation magnetization of the backing layer. In addition, a method for applying an antiferromagnetic layer and a method using AFC coupling have been proposed. However, these effects are also reduced in nature by increasing the thickness of the soft magnetic underlayer.

  When diverting the basic configuration of the perpendicular magnetic recording medium to the heat-assisted recording medium as it is, the above-described soft magnetic underlayer is also made of a magnetic material, so that its magnetic characteristics are also affected by temperature. For example, it is conceivable that the saturation magnetization Ms decreases with increasing temperature in currently used alloys mainly composed of Fe, Co, and Ni. In Patent Document 1, a first soft magnetic backing layer made of a conventional soft magnetic material on a substrate, a second backing layer made of ferrimagnetic material, a nonmagnetic intermediate layer including a dielectric layer and an uneven layer, a recording layer, a protective layer A heat-assisted magnetic recording medium in which layers are stacked in this order has been proposed.

  In the above configuration in Patent Document 1, the second backing layer is set to a compensation temperature (temperature at the time of signal reproduction) near normal temperature. Therefore, it apparently functions as a non-magnetic material at room temperature, and functions as part of the backing layer because it is not a compensation temperature during recording. That is, since the distance between the magnetic head and the backing layer is shortened at the time of recording compared to the time of reproduction, the writing ability is excellent. On the contrary, the distance is increased at the time of reproduction.

JP 2006-164436 A

  In the conventional perpendicular recording medium concept, the film thickness of the backing layer is in a trade-off relationship between the effect during recording and the noise source during reproduction. Further, as shown in Patent Document 1, thermal assist recording has an advantage of noise reduction caused by the backing layer, and is effective as a means for breaking the trade-off relationship. However, in Patent Document 1, since a ferrimagnetic material is used as the backing layer on the side close to the head, there is a problem that the magnetic flux density is smaller than the current backing layer material due to material characteristics. That is, in this configuration, there is a problem that it is difficult to concentrate the head magnetic flux and the magnetic field gradient cannot be made steep.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a magnetic recording medium having improved characteristics of a soft magnetic backing layer suitable for heat-assisted recording.

  In order to solve the above problems, 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, and at least a soft magnetic backing is provided on a nonmagnetic substrate. A layer, an underlayer, a magnetic recording layer, and a protective layer are laminated in this order, and the soft magnetic backing layer is composed of at least a first soft magnetic layer, a temperature characteristic control layer, and a second soft magnetic layer. It is characterized by.

  In the present invention, the temperature characteristic control layer is preferably made of a ferrimagnetic material, and the compensation temperature of the ferrimagnetic material is preferably near the reproduction temperature (the temperature when reproducing magnetic recording, usually around room temperature). . Further, it is preferable that the saturation magnetic flux density during recording of the second soft magnetic layer is larger than the saturation magnetic flux density of the temperature characteristic control layer. Of the layers constituting the soft magnetic backing layer, the three layers are laminated in order of the first soft magnetic layer, the temperature characteristic control layer, and the second soft magnetic layer from the non-magnetic substrate side. The thickness of the soft magnetic layer is preferably smaller than the thickness of the first soft magnetic layer.

  At the time of recording the heat assist signal, the temperature characteristic control layer is also magnetized, and the first soft magnetic layer, the temperature characteristic control layer, and the second soft magnetic layer are magnetized together, so that the head magnetic flux can be concentrated and drawn. it can. Further, since the second soft magnetic layer having a large saturation magnetization is closest to the head, a steep magnetic field gradient can be realized. On the other hand, if the temperature during recording / reproduction is near the compensation temperature, the magnetization of the temperature characteristic control layer is apparently zero during reproduction. Therefore, the magnetization that can be a noise source is only the first soft magnetic layer and the second soft magnetic layer. Therefore, the magnetic flux of the head can be concentrated during signal recording, a steep magnetic field gradient can be realized, and the magnetic recording medium can be reduced in noise during reproduction.

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

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram for explaining a configuration example of a magnetic recording medium of the present invention. The magnetic recording medium includes a soft magnetic backing layer in which a first soft magnetic layer 3, a temperature characteristic control layer 4, and a second soft magnetic layer 5 are formed in this order on the nonmagnetic substrate 1 from the nonmagnetic substrate 1 side. 2, the underlayer 6, the magnetic recording layer 7, and the protective layer 8 are sequentially laminated. A lubricant layer may be further formed on the protective layer 8.

  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. . 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.

  The soft magnetic layer backing layer 2 is formed for the purpose of improving the recording performance by controlling the magnetic flux from the magnetic head, as in the current perpendicular magnetic recording system. Since the soft magnetic backing layer 2 has a three-layer structure of the first soft magnetic layer 3, the temperature characteristic control layer 4, and the second soft magnetic layer 5, a total of three layers at the time of heat-assisted recording and at the time of reproduction are obtained. It has the characteristic that performance of changes. That is, at the time of recording the heat assist signal, the temperature characteristic control layer is magnetized together with the first soft magnetic layer 3 and the second soft magnetic layer 5, and the first soft magnetic layer, the temperature characteristic control layer, and the second soft magnetic layer are magnetized. Are magnetized as a unit, so that the head magnetic flux can be concentrated and drawn.

  On the other hand, during reproduction, the magnetization of the temperature characteristic control layer is apparently zero. Therefore, the magnetization that can be a noise source is only the first soft magnetic layer and the second soft magnetic layer. Therefore, the magnetic flux of the head can be concentrated during signal recording, a steep magnetic field gradient can be realized, and the magnetic recording medium can be reduced in noise during reproduction. In order to realize such a feature, the first soft magnetic layer 3 and the second soft magnetic layer 5 are made of the same material as that constituting the soft magnetic layer in the current perpendicular magnetic recording medium, and the temperature characteristic control layer 3 is made of a ferrimagnetic material and has a temperature characteristic such that the temperature during reproduction is a compensation temperature (a temperature at which positive and negative magnetization are just canceled). Examples of ferrimagnetic materials having temperature characteristics such that the temperature during reproduction is the compensation temperature include TbFe, DyFe, TbCo, TbFeCo, etc., so that the compensation temperature and the temperature during reproduction are equal depending on the respective composition ratios. Can be controlled.

  In the present invention, it is preferable that the saturation magnetization of the second soft magnetic layer 5 is larger than that of the temperature characteristic control layer 4. When the saturation magnetization of the second soft magnetic layer 5 closest to the head among the soft magnetic backing layers is large, a steep magnetic field gradient can be realized. Examples of such temperature characteristic control layer 4 and second soft magnetic layer 5 include, for example, temperature characteristic control layer 4 made of TbFe, DyFe, TbCo, and TbFeCo having a saturation magnetization Ms of less than 400 emu / cc during recording. For example, a combination of the second soft magnetic layer 5 made of FeCo alloy, FeNi alloy, or CoNi alloy whose saturation magnetization during recording is 400 emu / cc or more can be exemplified.

  As the first soft magnetic layer 3 or the second soft magnetic layer 5, a material used for the current perpendicular magnetic recording medium can be applied. For example, crystalline NiFe alloy, Sendust (FeSiAl) alloy, CoFe alloy, etc., microcrystalline FeTaC, CoFeNi, CoNiP, etc. can be used. In order to improve the recording ability, it is preferable that the soft magnetic layer has a larger saturation magnetization. Note that the optimum value of the thickness of the soft magnetic layer varies depending on the structure and characteristics of the magnetic head used for magnetic recording, but considering the noise during reproduction, the second soft magnetic layer 5 close to the head has a thickness. It is preferable to set it thin, and it is preferably 50 nm or less, more preferably 30 nm or less. On the other hand, the total film thickness is desirably 100 nm or less in view of the deterioration of flatness due to the increase in film thickness and the balance with productivity. As a film forming method, a commonly used sputtering method is used.

  When the soft magnetic layer has a thickness exceeding about 50 nm, a domain wall is formed, and the magnetization in the vicinity of the recording layer fluctuates to generate perpendicular component magnetization, which may be a noise source. . In order to suppress this, the soft magnetic underlayer is preferably made into a single magnetic domain, and an antiferromagnetic layer or a hard magnetic layer can be provided. It is possible to apply any of the soft magnetic layer directly below, directly above, or in the middle, and the lamination of both layers is also possible. 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, it is possible to suppress perpendicular component magnetization by controlling the film thickness of the nonmagnetic layer and using antiferromagnetic coupling via the nonmagnetic layer.

  The temperature characteristic control layer 3 can use a transition-rare earth metal having ferrimagnetism. It is necessary to adjust the composition so that the compensation temperature is near the regeneration temperature. The film thickness should be optimized as appropriate depending on the head to be used, but is preferably 5 nm or more in order to exhibit sufficient temperature characteristics.

  The underlayer 6 is used for 1) controlling the crystal grain size and crystal orientation of the magnetic material constituting the magnetic recording layer 7 formed thereon, and 2) magnetizing the soft magnetic backing layer 2 and the magnetic recording layer 7. This layer is used to prevent general bonding. Therefore, it is preferably nonmagnetic, and the crystal structure needs to be appropriately selected according to the magnetic material of the magnetic recording layer, but it can also be used with an amorphous structure. For example, when a magnetic material mainly composed of Co having a hexagonal close-packed (hcp) structure is used for the magnetic recording layer 7 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), a certain film thickness is required, and it is preferably within the range of 3 to 30 nm.

  For the magnetic recording layer 7, a crystalline magnetic material is preferably 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, as the magnetic crystal grains, 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. Examples of the film forming method include a magnetron sputtering method. Preferably, a structure in which one-to-one crystal growth is performed such that magnetic crystal grains are epitaxially grown on a crystal portion on the underlayer and the nonmagnetic material is arranged on a grain boundary portion of the underlayer.

Of the magnetic layers included in the magnetic recording layer 7, 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 is preferable. 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 protective layer 8, a conventionally used protective film 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 an oxide film and carbon can 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 sputtered under a Ar gas pressure of 5 mTorr using a Co ₈₆ Nb ₅ Zr ₉ target. A first soft magnetic layer 3 made of CoNbZr having a thickness of 50 nm was formed.

Subsequently, the Tb ₂₄ Fe ₅₀ Co ₂₄ target was sputtered under an Ar gas pressure of 5 mTorr to form a temperature characteristic control layer 4 made of TbFeCo with a film thickness of 30 nm.

Subsequently, using a Co ₈₆ Nb ₅ Zr ₉ target, sputtering was performed under an Ar gas pressure of 5 mTorr to form CoNbZr with a thickness of 20 nm, thereby forming a second soft magnetic layer 5 made of CoNbZr.

  Next, a Ta layer is formed by sputtering with an Ta target under an Ar gas pressure of 5 mTorr, and then a Ru layer is formed by sputtering with an Ar gas pressure of 60 mTorr to form a Ru layer with a thickness of 20 nm. / Ru underlayer 6 was formed.

Subsequently, using a (Co ₇₃ Pt ₂₇ ) ₉₀ (SiO ₂ ) ₁₀ target, sputtering was performed under an Ar gas pressure of 30 mTorr to form a CoPt—SiO ₂ magnetic layer having a thickness of 15 nm, thereby forming a magnetic recording layer 7.

  Next, the protective layer 8 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 made of perfluoropolyether and having a thickness of 2 nm was formed by a dipping 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 = 14.8 kOe and S = 1.0.
Further, when XRD diffraction was evaluated, it was found that in Example 1, CoNbZr, TbFeCo, and Ta have an 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 250 ° 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 120 nm and a reproducing track width of 80 nm was used. In this table, numerical values performed at a constant write current are shown.

<Comparative Example 1>
A magnetic recording medium was manufactured in the same manner as in Example 1 except that the TbFeCo temperature characteristic control layer 3 was not formed.
When the hysteresis loop of the recording layer of the magnetic recording medium obtained above was obtained using the Kerr effect measuring apparatus, the coercive force Hc = 14.8 kOe, S = 1.0, and the loop shape was also Example 1. It was consistent with that obtained in
Further, CoNbZr, TbFeCo, and Ta had an amorphous structure as in Example 1, and 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 instead of the TbFeCo temperature characteristic control layer 3, a Co ₈₆ Nb ₅ Zr ₉ target was used to form CoNbZr with a thickness of 30 nm under an Ar gas pressure of 5 mTorr.
When the hysteresis loop of the recording layer of the magnetic recording medium obtained above was obtained using the Kerr effect measuring apparatus, the coercive force Hc = 14.8 kOe, S = 1.0, and the loop shape was also Example 1. It was consistent with that obtained in
Further, CoNbZr, TbFeCo, and Ta had an amorphous structure as in Example 1, and the peak positions and intensities of Cu, Ru, and CoPt coincided with the respective peak positions and intensities in Example 1.
The results of electromagnetic conversion characteristics of the obtained magnetic recording medium are shown in Table 1 together with the results of Example 1 and Comparative Example 1.

<Comparative Example 3>
A magnetic recording medium was manufactured in the same manner as in Example 1 except that the thickness of the TbFeCo temperature characteristic control layer 3 was 50 nm and the second soft magnetic CoZrNb layer was not formed.
When the hysteresis loop of the recording layer of the magnetic recording medium obtained above was obtained using the Kerr effect measuring apparatus, the coercive force Hc = 14.8 kOe, S = 1.0, and the loop shape was also Example 1. It was consistent with that obtained in
Further, CoNbZr, TbFeCo, and Ta had an amorphous structure as in Example 1, and the peak positions and intensities of Cu, Ru, and CoPt coincided with the respective peak positions and intensities in Example 1.
The results of electromagnetic conversion characteristics of the obtained magnetic recording medium are shown in Table 1 together with the results of Example 1 and Comparative Examples 1 and 2.

  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 measuring device, the structure of the soft magnetic backing layer can be changed even if the configuration of the soft magnetic backing layer is changed. It was found that the structure and microstructure were not affected.

  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. Further, 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 5 [- dB] is a high value, indicating high write performance.

  In Comparative Examples 1 and 2, the OW characteristics are relatively good and sufficient writing performance is obtained, but the SNR is significantly inferior to Example 1. This is because the noise from the backing layer during reproduction is large. This is supported by the inferior SNR of Comparative Example 2 having a thick CoZrNb film when Comparative Examples 1 and 2 are compared.

  Comparative Example 3 is superior to Comparative Examples 1 and 2 in SNR, but inferior in OW characteristics. This is considered to be a little inferior in writing performance because TbFeCo having a low magnetic flux density is arranged in a portion close to the head during recording, but has a large SNR because noise due to the backing layer is reduced during reproduction. When this Comparative Example 3 is compared with Example 1, both OW and SNR are lower. Since OW exceeds 35 [−dB], saturation recording is performed, and it is considered that the small SNR is caused by a difference in magnetic field gradient due to the head. That is, in Example 1 in which a magnetic material having a high magnetic flux density is thinly formed on the surface of the backing layer, the noise component is small due to the thin film while reducing transition noise between bits formed with a steep magnetic field gradient. It is considered to be suppressed.

  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: First soft magnetic layer 4: Temperature characteristic control layer 5: Second soft magnetic layer 6: Underlayer 7: Magnetic recording layer 8: Protective layer

Claims (4)

In a magnetic recording medium used in a magnetic recording apparatus that performs signal writing during recording at a temperature higher than that during signal holding and signal reproduction, at least a soft magnetic backing layer, an underlayer, a magnetic recording layer, and a nonmagnetic substrate protective layer stacked in this order, the soft magnetic backing layer is at least a first soft magnetic layer, the temperature characteristic control layer, Ri Do three layers of the second soft magnetic layer, the temperature characteristic control layer ferrimagnetic the magnetic recording medium characterized Rukoto such material.   The magnetic recording medium according to claim 1, wherein a compensation temperature of the ferrimagnetic material is around a temperature during reproduction. 3. The magnetic recording medium according to claim 1, wherein a saturation magnetic flux density of the second soft magnetic layer at the time of recording is larger than a saturation magnetic flux density of the temperature characteristic control layer.   Of the layers constituting the soft magnetic backing layer, the three layers are laminated in the order of the first soft magnetic layer, the temperature characteristic control layer, and the second soft magnetic layer from the non-magnetic substrate side. The magnetic recording medium according to claim 1, wherein the magnetic layer has a thickness smaller than that of the first soft magnetic layer.

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