JP2009059432A - Perpendicular magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain compatibility between reduction of medium noise and recording performance by forming a thin film, with respect to a perpendicular magnetic recording medium wherein a plurality of recording layers are layered and disposed via binder layers (interlayer bonding force control layer). <P>SOLUTION: The perpendicular magnetic recording medium has a non-magnetic substrate 1, a soft magnetic backing layer 10 formed on the non-magnetic substrate 1, an intermediate layer 20 formed on the soft magnetic backing layer 10 and a magnetic recording layer 30 (comprising a first recording layer 31, the interlayer bonding force control layer 32 and a second recording layer 33) formed on the intermediate layer 20, wherein a magnetic region which becomes in an anti-ferromagnetic bonding state is provided in an interface 34 between the interlayer bonding force control layer 32 and the first recording layer 31, and an interface 35 between the interlayer bonding force control layer 32 and the second recording layer 33. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a perpendicular magnetic recording medium, and more particularly to a perpendicular magnetic recording medium in which a plurality of recording layers are stacked via a coupling layer.

  Conventionally, an in-plane magnetic recording system in which the magnetization direction of a magnetic recording layer faces in-plane has been used as a magnetic recording apparatus. However, in the in-plane magnetic recording system, if the domain domain is made smaller for high density recording, the recorded information disappears due to thermal fluctuation.

  Therefore, a magnetic recording layer is placed on the soft magnetic underlayer, a magnetic field perpendicular to the surface of the magnetic recording layer is applied, and the perpendicular magnetic recording method is put into practical use with the magnetization direction perpendicular to the surface of the recording layer. Is being advanced. According to the perpendicular magnetic recording system, high density recording is possible. However, even in a perpendicular magnetic recording medium, it is not easy to keep both the heat-resistant fluctuation characteristics and the signal-to-noise ratio (SN ratio) good.

  As a perpendicular magnetic recording medium capable of solving this, Patent Document 1 proposes a configuration in which an intermediate layer is formed on a first magnetic layer and a second magnetic layer is formed thereon. The first and second magnetic layers are made of, for example, Co (66 at%) Pt (18 at%) Cr (16 at%), and the intermediate layer is made of a Ru—Ti alloy or Hf. It is explained that the noise generated in the first and second magnetic layers is independent and can improve the S / N ratio. The first and second magnetic layers are not divided magnetically and can obtain good thermal fluctuation resistance. Yes.

  In Patent Document 2, when the first and second magnetic layers are magnetically coupled by the coupling layer, the antiferromagnetic coupling and the ferromagnetic coupling are compared, and when the ferromagnetic coupling is performed, It is disclosed that as the exchange coupling energy increases, the thermal stability increases as in the case of antiferromagnetic coupling, and the ease of recording improves unlike in the case of antiferromagnetic coupling. Such a magnetically coupled recording medium is called an ECC (exchange coupled composite) medium.

This ECC medium has a magnetic recording layer having a configuration in which a magnetic film (Capping Layer) not containing SiO ₂ is laminated on a magnetic film containing SiO ₂ added to a Co-based alloy, and the magnetic film containing the SiO ₂ added Has proposed a laminated structure in which Co-based alloy magnetic grains have a film structure spatially separated from each other by SiO ₂ , and a Ru layer is disposed as an intermediate layer directly under the magnetic recording layer.

In this perpendicular magnetic recording medium, a CoCrPt or CoCrPt based alloy magnetic film to which such an oxide is not added is directly above the granular magnetic layer which is a CoCrPt magnetic film to which an oxide such as SiO ₂ or TiO ₂ is added. The cap layer is arranged to control the magnetic characteristics. In the conventional example, after forming a granular structure magnetic layer having a film thickness that provides Hc and Hs necessary for having sufficient thermal disturbance resistance, a cap layer is disposed for the purpose of facilitating magnetization reversal, and Hc ( The recording performance was ensured by reducing the coercive force) and Hs (saturation magnetic field).
JP 2003-157516 A JP 2006-48900 A

  However, in order to reduce the thickness of the granular structure magnetic layer, it is necessary to increase the Pt concentration in the CoCrPt alloy to obtain high perpendicular magnetic anisotropy (high Ku), and the medium noise required for high recording density There is a problem of inhibiting the reduction (increase in transition noise due to increase in grain size).

  Further, in order to obtain a sufficient holding force Hc and saturation magnetic field Hs reduction effect, it is necessary to increase the saturation magnetization Ms of the cap layer or to increase the film thickness, which also inhibits the reduction of medium noise (recording magnetic field gradient). There was a problem of slowing down.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a perpendicular magnetic recording medium capable of realizing both reduction in medium noise and recording performance by thinning.

From the first aspect of the present invention, the above problem is
A non-magnetic substrate;
A soft magnetic backing layer formed above the non-magnetic substrate;
A nonmagnetic intermediate layer formed on the soft magnetic backing layer;
A first recording layer formed on the intermediate layer and having perpendicular magnetic anisotropy; an interlayer coupling force control layer formed on the first recording layer; and a perpendicular magnetic layer formed on the interlayer coupling force control layer. A perpendicular magnetic recording medium having a magnetic recording layer including a second recording layer having anisotropy,
This is solved by a perpendicular magnetic recording medium having magnetic regions in an antiferromagnetic coupling state at the interface between the interlayer coupling force control layer and the first recording layer and at the interface between the interlayer coupling force control layer and the second recording layer. be able to.

  In the above invention, it is desirable that the magnetic recording layer as a whole has a ferromagnetic coupling state.

  In the above invention, it is desirable that the first ferromagnetic recording layer has a perpendicular magnetic anisotropy greater than that of the second ferromagnetic recording layer.

  In the above invention, it is desirable that the first recording layer is formed of a granular magnetic layer containing at least a CoPt alloy, and the second magnetic recording layer is formed of a magnetic alloy containing CoCr.

  In the above invention, the interlayer coupling force control layer is preferably made of a nonmagnetic material.

  In the above invention, the interlayer coupling force control layer is preferably made of a magnetic material.

  In the above invention, palladium can be used as the interlayer cohesion control layer.

  Further, in the above invention, the film thickness of the interlayer coupling force control layer is a saturation magnetic field that becomes a minimum among the vibration change of the saturation magnetic field of the magnetic recording layer that occurs with the film thickness change of the interlayer coupling force control layer. It is desirable to select the corresponding film thickness.

  According to the present invention, since there is a magnetic region in an antiferromagnetic coupling state at the interface between each recording layer and the interlayer coupling force control layer, fluctuations in magnetization in the interlayer coupling region are suppressed and medium noise is suppressed. Can be reduced.

  In addition, since there is a magnetic region in an antiferromagnetic coupling state at the interface between each recording layer and the interlayer coupling force control layer, the effect of effectively increasing the magnetic anisotropy can be obtained. Thus, it is not necessary to increase the Ku concentration by increasing the Pt concentration in the CoCrPt alloy, and the medium noise can be reduced.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic sectional view showing the basic configuration of a perpendicular magnetic recording medium having an ECC structure according to the present invention. As shown in the figure, a perpendicular magnetic recording medium having an ECC structure includes a soft magnetic backing layer 10 and a nonmagnetic intermediate layer 20 on a nonmagnetic substrate 1 made of a nonmagnetic material such as glass, aluminum, or Si. The magnetic recording layer 30 and the protective layer 40 are stacked.

  The magnetic recording layer 30 has a configuration in which the ferromagnetic recording layers 31 and 33 are coupled by a nonmagnetic or magnetic (nonmagnetic in this embodiment) interlayer coupling force control layer 32. The soft magnetic backing layer 10 is a magnetic layer for forming a magnetic closed circuit together with the magnetic head, and for example, an amorphous Co alloy such as CoZrNb, CoZrTa or the like can be used. The soft magnetic backing layer 10 may be configured by laminating a plurality of layers including a nonmagnetic layer. For example, a configuration in which each of the FeCoB layer, the Ru layer, and the FeCoB layer is stacked may be employed.

  The nonmagnetic intermediate layer 20 is a layer for improving the crystallinity of the magnetic recording layer 30 and is formed of a single layer or a plurality of layers. The intermediate layer 20 can be formed by, for example, an amorphous Ta layer, a NiFeCr layer, a Ru layer, a NiFeCr layer, a Ru layer, or the like. The amorphous Ta layer has a function of improving the orientation of the crystalline metal layer formed thereon.

  The ferromagnetic recording layers 31 and 33 can be formed of a CoCrPt magnetic alloy such as CoCrPt or CoCrPtB, or a ferromagnetic material such as CoCrTa or CoPt.

  The interlayer coupling force control layer 32 is a layer for realizing a good ECC structure. In the present invention, an attempt was made to use Pd, which is a nonmagnetic material, as the interlayer coupling force control layer 32. However, it is also possible to use a magnetic material such as Pt for the interlayer coupling force control layer 32.

  Next, a perpendicular magnetic recording medium having an ECC structure according to an embodiment of the present invention will be described with reference to FIG. In the following description, an example of the configuration of a sample actually manufactured will be described.

  In order to manufacture the perpendicular magnetic recording medium according to this example, first, a 25 nm thick FeCoB film to be the soft magnetic backing layer 10 is formed on the glass substrate 1 with an Ar gas pressure of 0.5 Pa and a sputtering power of 1 kW. In this embodiment, the soft magnetic backing layer 10 is a single magnetic backing layer.

  Next, the intermediate layer 20 is formed on the soft magnetic backing layer 10. As the intermediate layer 20, a 3 nm thick (amorphous) Ta layer 21 is formed by sputtering with an argon gas pressure of 0.5 Pa and a sputtering power of 0.4 kW, and a 3 nm thick NiFe layer is formed thereon with an Ar gas pressure of 0. A film is formed by sputtering at 5 Pa and sputtering power of 0.1 kW, and a Ru layer having a thickness of 20 nm is formed thereon by sputtering at an Ar gas pressure of 4.0 Pa and 0.4 kW. As described above, in this embodiment, the Ta layer, the NiFeCr layer, and the Ru layer constitute the intermediate layer 20 having a three-layer structure.

When the intermediate layer 20 is manufactured as described above, the magnetic recording layer 30 is formed on the intermediate layer 20. In order to manufacture the magnetic recording layer 30, first, a 10 nm thick CoCrPt—SiO ₂ film serving as the first recording layer (granular layer) 31 is sputtered on the intermediate layer 20 with an Ar gas pressure of 4 Pa and a sputtering power of 0.4 kW. The film was formed.

  Next, Pd was deposited as an interlayer bonding force control layer 32 to 1.8 nm in increments of 0.1 nm. Film formation conditions at this time were formed by sputtering with an Ar gas pressure of 0.5 Pa and a sputtering power of 0.1 kW. Next, a CoCrPtB layer having a thickness of 8 nm as the second recording layer 33 was formed at an Ar gas pressure of 0.5 Pa and a sputtering power of 0.4 kW.

  The first recording layer 31, the interlayer cohesive force control layer 32, and the second recording layer 33 constitute the recording layer 30 having an ECC structure. The first recording layer 31 and the second recording layer 33 have a ferromagnetic coupling state without applying an external magnetic field. The perpendicular magnetic anisotropy (Ku1) of the first recording layer 31 of the granular ferromagnetic layer is larger than the perpendicular magnetic anisotropy (Ku2) of the second recording layer 33 of the non-granular ferromagnetic layer (Ku1> Ku2). .

  Finally, a C layer having a thickness of 3 nm was formed as a protective layer 40 on the recording layer 30. When actually used, it is preferable to further apply a liquid lubricant layer on the protective layer 40. Since the layer above the amorphous Ta layer has an fcc or hcp structure, excellent crystallinity and orientation can be obtained, and an epitaxial layer can be obtained. In addition, each layer 10-40 on the above-mentioned glass substrate 1 formed into a film continuously, without breaking a vacuum.

  The characteristics of the perpendicular magnetic recording medium manufactured as described above are shown in FIGS.

  FIG. 5 is a diagram showing the coercive force Hc and the saturation magnetic field Hs with respect to the thickness of the interlayer coupling force control layer 32 measured with the produced perpendicular magnetic recording medium. In FIG. 5, the thickness of the interlayer coupling force control layer 32 is changed from 0 nm to 2.0 nm in increments of 0.1 nm, and the coercive force Hc and the saturation magnetic field Hs with respect to the thickness of each interlayer coupling force control layer 32 are shown. It is shown. The horizontal axis indicates the thickness of the interlayer bonding force control layer 32 in the unit of nm, and the vertical axis indicates Hs and Hc in the unit of kOe. However, when the thickness is 1.9 nm or more, the lower layer and the upper layer of the granular magnetic layer are in a decoupled state, and each exhibits magnetic properties of a single layer, and thus the following illustration and description are omitted.

  The value of the coercive force Hc as a magnetic characteristic indicates resistance to rewriting of magnetic recording due to an unintended cause, and represents thermal fluctuation and barrier height against a leakage magnetic field caused by writing in an adjacent area (recording holding force). Larger is preferable. Further, the value of the saturation magnetic field Hs represents a magnetic field necessary for writing and is preferably as low as possible.

  FIG. 6 shows a change in dynamic Hc with respect to the film thickness of the interlayer bonding force control layer 32 (Pd film) (dynamic Hc corresponds to a recording magnetic field, expressed as Hc0). The horizontal axis indicates the thickness of the Pd film as the interlayer bonding force control layer 32 in the unit of nm, and the vertical axis indicates the dynamic Hc0 in the unit of kOe.

  FIG. 7 shows the dependence of the overwrite (OW) characteristic on the film thickness of the interlayer bonding force control layer 32. The horizontal axis indicates the thickness of the Pd layer in the unit of nm, and the vertical axis indicates OW in the unit of dB.

  The OW characteristic is a kind of writing characteristic, and has a recording characteristic when recording is performed once after recording. The OW characteristic is an overwrite OW that indicates how much the high-density recording previously recorded is attenuated when high-density recording with a short bit length is performed and low-density recording with a long bit length is performed thereon. (DB) is often measured. In OW, if the attenuation factor is increased, the effective write core width WCw tends to increase.

  As shown in FIG. 5, when Pd is used as the interlayer coupling force control layer 32, the interlayer coupling force control layer 32 has a layer coercivity Hc and a saturation magnetic field Hs that are 0 compared to the coercivity Hc and the saturation magnetic field Hs. Compared to a double-layer recording layer medium (recording medium in which the interlayer cohesion control layer 32 (Pd film) does not exist) that shows a minimum value in the vicinity of a film thickness of 1.3 nm to 1.5 nm and does not have an ECC structure. It was confirmed that the coercive force Hc and the saturation magnetic field Hs were lowered. In the experiment, it was also confirmed that the film thickness margin was the widest when Pd was used as the interlayer bonding force control layer 32 (region indicated by II in FIG. 5).

  Further, as shown in FIG. 6, even in the dynamic Hc (Hc0) that is a standard of the recording magnetic field, the Hc0 is higher than that of the two-layer recording layer medium that does not have the ECC structure (the recording medium having the interlayer coupling force control layer 32 of zero thickness). It was confirmed that the recording magnetic field can be reduced by about 5 kOe (specifically, 12.3 kOe can be reduced to 7.2 kOe).

  Furthermore, as shown in FIG. 7, it is shown that the attenuation of OW2 increases as the thickness of the Pd layer increases. From the read / write evaluation by a spin stand (depending on the measurement head), it was confirmed that OW2 can be improved by 5 dB or more when the thickness of the Pd film as the interlayer bonding force control layer 32 is 1.5 nm.

  Here, the present inventor paid attention to the dependency of the saturation magnetic field Hs shown in FIG. 5 on the Pd film thickness. As shown by the arrow in FIG. 5, the saturation magnetic field Hs has a constant period as the Pd film thickness changes. It was confirmed that it was vibrating.

  According to the experiment of the present inventor, from the minor loop evaluation by the Kerr effect, a magnetization curve having a phase opposite to that of a normal loop can be confirmed, and since it is not due to optical interference, this is due to the presence of a diamagnetic component of magnetization. Estimated. Therefore, this vibration is presumed to be due to RKKY interaction (RKKY: Ruderman-Kittel-Kasuya-Yosida).

  FIG. 2 is an enlarged view of the magnetic recording layer 30, and FIGS. 3 and 4 schematically show the magnetization state of the interface 34 between the first recording layer (granular layer) 31 and the interlayer coupling force control layer 32. FIG. 3 shows an example using a nonmagnetic material (Pd or the like) as the interlayer coupling force control layer 32, and FIG. 4 shows an example using a magnetic material (CoPt alloy or the like) as the interlayer coupling force control layer 32.

  As shown in FIG. 2, the first recording layer 31 and the second recording layer 33 of the magnetic recording layer 30 are in a ferro-coupling (ferromagnetic coupling) state via the interlayer coupling force control layer 32. That is, the first recording layer 31 and the second recording layer 33 are in a combined state similar to the ECC structure.

  As for the magnetization state of the recording layer interface of the interface 34 between the first recording layer 31 and the interlayer coupling force control layer 32, as shown in FIG. 3, when the interlayer coupling force control layer 32 is a non-magnetic material, the unevenness of the interface 34 It is estimated that an antiferromagnetic coupling component (indicated by a black arrow in the figure) exists partially due to the energy balance of. In addition, when the interlayer coupling force control layer 32 is a magnetic material as shown in FIG. 4, not only the first recording layer 31 but also the interior of the interlayer coupling control layer 32 has an antiferromagnetic component (indicated by black coating in the figure). It is presumed that there is an arrow).

  The above phenomenon also occurs at the interface 34 between the interlayer bonding force control layer 32 and the second recording layer 33 in the same manner. Further, the antiferromagnetic coupling at the interfaces 34 and 35 is controlled by the interface state. As a control method thereof, for example, the film forming gas pressure (process control) and the recording layer and the interlayer coupling force control layer material are appropriately selected. It is presumed that this can be realized by taking such a method.

  Next, the present inventor performed electromagnetic conversion measurement with an SPT (single pole) head with a trailing shield by a spin stand. The measurement conditions were a single pole (SPT) head with a trailing shield and 450 kBPI as the F2 recording frequency (kBPI) (the shortest recording density was F1: 900 kBPI). FIG. 8 shows the result.

  As a sample, based on the magnetic characteristics shown in FIG. 5, an interlayer coupling force control layer 32 suitable for use as a perpendicular magnetic recording medium has a thickness of 0.7 nm to 1.2 nm (referred to as a medium selection region). A film having a minimum value of the saturation magnetic field Hs oscillating at a constant period (indicated by an arrow II-A in FIG. 5) is an embodiment of the present invention. The film thickness of the saturation magnetic field Hs oscillating at a constant period (shown by the arrow II-B in FIG. 5) is Comparative Example 1, and the interlayer bonding force control layer 32 has a film thickness of zero. The (two-layer recording layer) was set as Comparative Example 2.

  From FIG. 8, when selecting the film thickness of the interlayer coercivity control layer 32, selecting the film thickness at which the saturation magnetic field Hs takes the minimum value by selecting the film thickness at which the saturation magnetic field Hs takes the minimum value in the medium region. It was confirmed that the R / W characteristics were better than Furthermore, while the Wcw of Comparative Example 1 was 0.171 μm and the Wcw of Comparative Example 2 was 0.177 μm, it was confirmed that Wcw of the Example of the present invention was 0.171 μm and Wcw did not spread.

  From the above results, according to the perpendicular magnetic recording medium according to the embodiment of the present invention, the interface 34 between the interlayer coupling force control layer 32 and the first recording layer 31 and the interface between the interlayer coupling force control layer 32 and the second recording layer 33. By providing the magnetic region 35 in the antiferromagnetic coupling state 35, it is possible to reduce both medium noise and recording performance.

  That is, during reproduction, the presence of antiferromagnetic coupling components at the interfaces 34 and 35 between the recording layers 31 and 33 and the interlayer coupling force control layer 32 suppresses fluctuations in magnetization in the interlayer coupling region, thereby reducing medium noise. Reduction (S / N improvement) can be achieved. In addition, since an antiferromagnetic component is present, an effect of effectively increasing the magnetic anisotropy can be obtained, so that it is not necessary to increase the Ku with an increased Pt concentration. Further, at the time of recording, the recording magnetic field can be reduced by adjusting the film thickness and magnetic energy balance of the interlayer coupling force control layer 32.

  In FIGS. 5 to 7, the symbol I indicates the heat that maximizes the bonding force between layers (direct coupling), and the symbol II indicates the interlayer coupling control region (including the RKKY coupling component). The reference numeral III indicates an interlayer coupling control region (film thickness that minimizes the recording magnetic field), and the reference symbol IV indicates a region having a weak interlayer coupling force (decoupled region: The magnetic layer operates independently).

  The perpendicular magnetic recording medium according to the present invention can be widely applied to perpendicular magnetic recording media having an ECC structure. Further, it can be widely applied to a magnetic recording / reproducing apparatus such as an HDD.

FIG. 1 is a cross-sectional view schematically showing the configuration of a perpendicular magnetic recording medium having an ECC structure according to this embodiment. FIG. 2 is an enlarged cross-sectional view showing the magnetic recording layer of the perpendicular magnetic recording medium according to this example. FIG. 3 is a cross-sectional view schematically showing a magnetization state between the second recording layer and the interlayer coupling force control layer. FIG. 4 is a cross-sectional view schematically showing a magnetization state between the first recording layer and the interlayer coupling force control layer. FIG. 5 is a diagram illustrating changes in the coercive force Hc and the saturation magnetic field Hs with respect to changes in the thickness of the interlayer coupling force control layer (Pd). FIG. 6 is a diagram showing a change in the recording magnetic field Hc ₉₉ with respect to the thickness of the interlayer coupling force control layer (Pd). FIG. 7 is a diagram showing recording characteristics. FIG. 8 is a diagram for explaining the effect of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nonmagnetic substrate 10 Soft magnetic backing layer 20 Intermediate layer 30 Magnetic recording layer 31 First recording layer (granular layer)
32 Interlayer bonding force control layer 33 Second recording layer 40 Protective layer

Claims (8)

A non-magnetic substrate;
A soft magnetic backing layer formed above the non-magnetic substrate;
A nonmagnetic intermediate layer formed on the soft magnetic backing layer;
A first recording layer formed on the intermediate layer and having perpendicular magnetic anisotropy; an interlayer coupling force control layer formed on the first recording layer; and a perpendicular magnetic layer formed on the interlayer coupling force control layer. A perpendicular magnetic recording medium having a magnetic recording layer including a second recording layer having anisotropy,
A perpendicular magnetic recording medium having a magnetic region in an antiferromagnetic coupling state at an interface between the interlayer coupling force control layer and the first recording layer and at an interface between the interlayer coupling force control layer and the second recording layer.   The perpendicular magnetic recording medium according to claim 1, wherein the magnetic recording layer has a ferromagnetic coupling state as a whole.   The perpendicular magnetic recording medium according to claim 1, wherein the first ferromagnetic recording layer has a perpendicular magnetic anisotropy greater than that of the second ferromagnetic recording layer.   4. The perpendicular magnetic recording medium according to claim 3, wherein the first recording layer is formed of a granular magnetic layer containing at least a CoPt alloy, and the second magnetic recording layer is formed of a magnetic alloy containing CoCr.   The perpendicular magnetic recording medium according to claim 1, wherein the interlayer coupling force control layer is made of a nonmagnetic material.   The perpendicular magnetic recording medium according to claim 1, wherein the interlayer coupling force control layer is made of a magnetic material.   The perpendicular magnetic recording medium according to claim 5, wherein the interlayer coupling force control layer is palladium.   As the film thickness of the interlayer coupling force control layer, a film thickness corresponding to the minimum saturation magnetic field is selected from the change in the saturation magnetic field vibration of the magnetic recording layer that occurs with the film thickness variation of the interlayer coupling force control layer. The perpendicular magnetic recording medium according to any one of claims 1 to 6.

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