JP4034485B2 - Magnetic recording medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium used in a magnetic recording apparatus.
[0002]
[Prior art]
Conventionally, in a perpendicular two-layer medium in which a magnetic recording layer having perpendicular anisotropy with respect to a substrate surface is laminated on a soft magnetic backing layer having a high magnetic permeability, the soft magnetic backing layer is formed from a magnetic head that has magnetized the magnetic recording layer. It plays a part of the function of the magnetic head that causes the recording magnetic field to flow back to the magnetic head side in the horizontal direction, and plays the role of improving the recording and reproducing efficiency.
[0003]
However, a stray magnetic field that leaks mainly from the spindle motor and voice coil motor is generated in the magnetic disk device, and the stray magnetic field is soft compared with the recording magnetic field by the magnetic head, but the stray magnetic field is soft in the magnetic disk. There is a problem that the recording magnetization of the perpendicular recording layer is demagnetized or demagnetized by being absorbed by the magnetic backing layer and concentrating on the tip of the main pole of the magnetic head.
[0004]
In order to prevent such demagnetization and demagnetization in the perpendicular double-layer medium, conditions such as the permeability and film thickness of the soft magnetic underlayer that are not easily affected by the stray magnetic field from the outside of the medium have been proposed.
[0005]
In addition, in order to improve the uniformity of the reproduced output waveform of the perpendicular double-layer medium, the hard magnetic layer and the antiferromagnetic layer are softened so that the easy axis of magnetization of the soft magnetic underlayer is aligned in the radial direction or the circumferential direction. When it is provided under the magnetic backing layer or used as an intermediate layer having a multilayer structure, it is considered that there is an effect of suppressing demagnetization and demagnetization because the movement of the domain wall is restricted.
[0006]
However, limiting the conditions such as the magnetic permeability and film thickness of the soft magnetic underlayer has the problem of limiting the recording / reproducing characteristics, and such conditions largely depend on the material and film forming conditions. Because it is easy to depend on, it can be difficult to handle practically. In addition, even when the easy magnetization axis of the soft magnetic underlayer is aligned, the magnetic state of the soft magnetic layer is high in the easy magnetization direction, so that the magnetization state fluctuates with a slight external magnetic field, thereby suppressing demagnetization and demagnetization. There was a problem that was not enough.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a magnetic recording medium in which demagnetization and demagnetization of recording magnetization of a magnetic recording layer due to an external stray magnetic field is suppressed.
[0009]
[Means for Solving the Problems]
The present invention provides a magnetic recording medium in which a soft magnetic backing layer and a magnetic recording layer having perpendicular anisotropy with respect to the surface of the nonmagnetic substrate are laminated on a nonmagnetic substrate, wherein the soft magnetic backing layer comprises two layers . It has a structure in which nonmagnetic intermediate layers are arranged between soft magnetic layers. When the external magnetic field is below a certain level, adjacent soft magnetic layers are antiferromagnetically coupled to each other through the nonmagnetic intermediate layer, and have a certain size. Provided is a magnetic recording medium characterized in that the magnetization directions of adjacent soft magnetic layers are parallel to each other through the nonmagnetic intermediate layer when an external magnetic field of more than 10 mm is applied.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
A magnetic recording medium according to a first aspect of the present invention has a soft magnetic backing layer and a magnetic recording layer having a perpendicular anisotropy with respect to the surface of the nonmagnetic substrate on a nonmagnetic substrate, and the soft magnetic backing layer Has a characteristic that the differential value of the magnetization curve when the magnetic field is applied in the in-plane direction and the magnetization is reversed from the saturated magnetization state to the opposite saturation state has two peaks.
[0011]
The magnetic recording medium according to the second invention is an example of the configuration of the magnetic recording medium according to the first invention. The soft magnetic backing layer and the surface of the nonmagnetic substrate on the nonmagnetic substrate. The soft magnetic backing layer has a multilayer structure in which a nonmagnetic intermediate layer is arranged between a plurality of soft magnetic layers, and the nonmagnetic intermediate layer has a perpendicular magnetic anisotropy layer. Adjacent soft magnetic layers are antiferromagnetically coupled to each other through the magnetic intermediate layer, and the magnetization direction of the adjacent soft magnetic layers becomes parallel in an external magnetic field of a certain magnitude or more.
[0012]
According to the first invention, by using the soft magnetic underlayer having a differential value of the magnetization curve when the magnetization is reversed with two peaks, the magnetic permeability is originally high with respect to a slight stray magnetic field. However, in the backing layer in which the magnetization state is likely to fluctuate greatly, the change in the magnetization state with respect to the magnetic field only in the vicinity where the external magnetic field between the two peaks becomes zero can be suppressed to a small level. Thereby, demagnetization and demagnetization of the recording magnetization of the perpendicular recording layer due to the external stray magnetic field can be prevented.
[0013]
Preferably, by the extent to which the two peaks appear lower than the recording magnetic field, upon application of a recording magnetic field, the backing layer is that Do allow Rukoto refluxed magnetic flux from the magnetic head. Preferably, by adjusting the range in which these two peaks appear to be an external magnetic field of approximately the stray magnetic field, the change in the magnetization state of the soft magnetic layer is suppressed and the recording magnetization of the perpendicular recording layer by the external stray magnetic field is suppressed. Can be prevented from demagnetizing and demagnetizing.
[0014]
Further, according to the second invention, the soft magnetic backing layer is formed into a multilayer structure with the nonmagnetic intermediate layer, and the adjacent soft magnetic layers are antiferromagnetically coupled to each other in an external magnetic field of a certain size or less. A soft magnetic underlayer is obtained in which the differential value of the magnetization curve when the saturated magnetization state is reversed to the opposite saturation state has two peaks. Thereby, demagnetization and demagnetization of the recording magnetization of the perpendicular recording layer due to the external stray magnetic field can be prevented.
[0015]
Further, when the range in which these two peaks appear is less than the recording magnetic field and is adjusted to be an external magnetic field of approximately the stray magnetic field, when the recording magnetic field is applied to the adjacent soft magnetic layers, the directions of magnetization are mutually different. When the stray magnetic field is parallel and less than the recording magnetic field, the magnetic field can be coupled antiferromagnetically, so that recording can be prevented and the influence of the external stray magnetic field can be prevented. By suppressing the change in the magnetization state of the soft magnetic underlayer in this way, it is possible to prevent demagnetization and demagnetization of the recording magnetization of the perpendicular recording layer due to the external stray magnetic field.
[0016]
In the second invention, the magnetic moment of each soft magnetic layer is preferably approximately the same, the magnetic moment of the soft magnetic layers are different, collapses symmetry of the magnetization curve, the value of the residual magnetization increases, soft Leakage magnetic flux as the entire magnetic backing layer is likely to occur.
[0017]
FIG. 1 is a diagram showing the configuration of an example of a magnetic recording medium according to the first invention.
[0018]
As shown in the figure, this recording medium has a structure in which a soft magnetic backing layer 2 and a magnetic recording layer 3 are laminated on a nonmagnetic glass substrate 1.
[0019]
FIG. 2 is a diagram showing the configuration of an example of the magnetic recording medium according to the second invention.
[0020]
As shown in the figure, this recording medium has a structure in which a first soft magnetic layer 12, a nonmagnetic intermediate layer 13, a second soft magnetic layer 14, and a magnetic recording layer 15 are laminated on a nonmagnetic glass substrate 1. Have.
[0021]
In a thin film in which a ferromagnetic transition metal and a nonmagnetic metal are multilayered as in the magnetic recording medium according to the second aspect of the invention, the ferromagnetic and antiferromagnetic coupling between the ferromagnetic layers with respect to the thickness of the nonmagnetic layer Appearing periodically, in many multilayer films ((Fe, Co) / (V, Cr, Cu, Mo, Ru, Rh, Re)), adjacent ferromagnetic layers are opposite to each other. It is known that the period of ferromagnetic coupling (or ferromagnetic coupling) is about 1 nm ( A. Heinlich and JAC Bland, Ultrathin Magnetic Structures II, Springer-Verlag (1994) ). In addition, the thickness of the nonmagnetic layer in which the antiferromagnetic coupling, that is, the state in which the magnetization of the adjacent ferromagnetic layer is antiparallel, first appears is approximately 1 nm or less, and thereafter, the nonmagnetic layer is spaced at approximately 1 nm intervals. As the layer thickness increases, the antiferromagnetic coupling becomes weaker. Therefore, the coupling strength can be selected by setting the nonmagnetic layer to an appropriate thickness. Therefore, when the magnetic field is applied from the head during recording by selecting the coupling strength, that is, the nonmagnetic layer thickness, so that the magnetization is parallel to the external magnetic field of the recording magnetic field applied from the head, it is excellent. While it functions as a soft magnetic underlayer, the change in the magnetization state is suppressed for stray magnetic fields other than during recording, so the recording magnetization of the magnetic recording layer can be demagnetized by an external stray magnetic field without hindering recording. And demagnetization can be prevented. The nonmagnetic intermediate layer thickness is preferably 0.5 nm or more and less than 1.5 nm.
[0023]
In the magnetic recording medium of the present invention, since the easy axis of magnetization of the soft magnetic backing layer is aligned in the circumferential direction or the radial direction, an antiferromagnetic layer such as FeMn or CoSm is provided between the nonmagnetic substrate and the soft magnetic backing layer. A hard magnetic layer may be formed.
[0024]
A nonmagnetic underlayer such as Ru, Ti or a nonmagnetic CoCr alloy may be formed between the soft magnetic underlayer and the perpendicular recording layer.
[0025]
As a material for the soft magnetic layer, a soft magnetic alloy having a high magnetic permeability such as FeSi alloy, FeCo alloy, NiFe alloy such as permalloy, and CoZr alloy such as CoZrNb can be used in addition to Sendust. In order to make the soft magnetic underlayer multi-layered, it is considered that the soft magnetic layer is preferably a material having a crystal structure similar to that of the nonmagnetic intermediate layer and having a close lattice constant or an amorphous material.
[0026]
As the nonmagnetic intermediate layer, V, Cr, Cu, Mo, Ru, Rh, and Re are preferably used, and Ru is more preferable.
[0027]
As a combination of the soft magnetic layer and the nonmagnetic intermediate layer, Cu, Ru, Rh, and Re are considered preferable for V, Cr, Mo, and NiFe alloys for Sendust, FeSi, and FeCo alloys. Therefore, an amorphous material such as CoZrNb is considered preferable for any nonmagnetic interlayer material.
[0028]
Examples of the magnetic material used for the magnetic recording layer having perpendicular anisotropy include CoPt alloys such as CoPtO and CoPtB in addition to CoCr alloys such as CoCrPt and CoCrTa.
[0029]
In the magnetic recording medium of the present invention, a magnetic recording layer having perpendicular anisotropy with respect to the substrate is laminated directly or via a nonmagnetic underlayer on the soft magnetic underlayer as described above.
[0030]
【Example】
First, the magnetic properties of the soft magnetic underlayer according to the present invention were examined.
[0031]
As the non-magnetic substrate, a glass substrate satisfying the standard specification of a 2.5 inch magnetic disk was used, and all layers were produced by DC magnetron sputtering.
[0032]
First, Sendust having a thickness of about 27 nm was formed as a first soft magnetic layer on a nonmagnetic substrate.
[0033]
Next, a Ru layer having a thickness of about 1 nm was formed as a nonmagnetic intermediate layer.
[0034]
On top of that, Sendust having a thickness of about 27 nm was again laminated as the second soft magnetic layer. 10 nm of C was formed as a protective layer on the soft magnetic backing layer having the three-layer structure.
[0035]
Further, as a comparative example, lamination was performed in the same manner except that the thickness of the Ru layer as the nonmagnetic intermediate layer was set to about 1.5 nm.
[0036]
With respect to the obtained soft magnetic backing layer, a magnetization curve when a magnetic field is applied in the in-plane direction by a vibrating sample magnetometer (VSM) and a graph showing the result of differentiating the magnetization curve with respect to the magnetic field are shown in FIG. As shown in FIG. FIG. 5 and FIG. 6 show the magnetization curve and differential value when the thickness of the Ru layer is about 1.5 nm, respectively. 4 and 6, the solid line corresponds to the case where the applied magnetic field is changed from negative to positive, and the dotted line corresponds to the case where the magnetic field is changed from positive to negative.
[0037]
As shown in FIG. 3, the magnetization curve of the soft magnetic underlayer used in the present invention shows that the upper and lower soft magnetic layers are antiferromagnetically coupled by setting the nonmagnetic intermediate layer to an appropriate thickness. Since the change in which the magnetizations of the upper and lower soft magnetic layers are aligned in the same direction as the magnetic field in the vicinity of the magnetic field 0 is suppressed, the change in magnetization with respect to the magnetic field mainly in the vicinity of the magnetic field 0 is suppressed to be small. I understand.
[0038]
Here, the applied magnetic field is suppressed small values of magnetization in the vicinity of 0, the magnetization curve is in the approximate origin for symmetry is because the magnetic moments of the upper and lower non-magnetic intermediate layer is equal to, the upper and lower soft When the magnetic moments of the layers is different, collapses symmetry of the magnetization curve, the value of the residual magnetization increases, since the leakage flux of the entire soft magnetic backing layer is likely to occur, the magnetic moments of the upper and lower soft magnetic layer is approximately It is desirable that they are the same.
[0039]
On the other hand, in the comparative example, as shown in FIG. 5, the magnetization curve of the soft magnetic backing layer when the thickness of the Ru layer is about 1.5 nm indicates that the nonmagnetic intermediate layer thickness is the upper and lower soft magnetic layers. Since the thickness is not suitable for antiferromagnetic coupling, it is basically the same as that of a general soft magnetic layer, and since the magnetic permeability is high, even when an external magnetic field of about 20 Oe is applied. It can be seen that the magnetization state varies greatly.
[0040]
From the magnetization curve of FIG. 5, when the thickness of the Ru layer is 1.5 nm, it is considered that the soft magnetic layers above and below the nonmagnetic intermediate layer are ferromagnetically coupled. When the thickness is less than this Ru layer thickness, the thickness of the ferromagnetically coupled layer is expected to be less than 0.5 nm due to its periodicity, and the Ru layer thickness at which antiferromagnetic coupling appears is 0.5 nm to 1.5 nm. It is considered that the Ru intermediate layer thickness that can most effectively suppress the change in the magnetization state with respect to the external stray magnetic field is within this range.
[0041]
3 and 5 can be seen as a difference in the number of peaks in the differentiated curve. That is, when the magnetization is reversed by changing the applied magnetic field from negative to positive or from positive to negative, the comparative example has one peak as shown in FIG. Two peaks can be seen as shown in FIG. Although the peak position differs by about 20 Oe between the solid line and the dotted line, if the magnitude of the magnetic field that takes these peaks is set as a threshold value, in the embodiment, the change in the magnetization state is suppressed between the magnetic field from 0 to the threshold value. It can be seen that such a region does not exist in the comparative example while the region exists.
[0042]
On the soft magnetic underlayer, a Ru layer having a thickness of 20 nm was formed as a nonmagnetic underlayer by a DC magnetron sputtering method.
[0043]
Next, a CoPtCrO magnetic layer was formed on the nonmagnetic underlayer.
[0044]
Thereafter, a 10 nm C layer was formed as a protective layer.
[0045]
The obtained magnetic recording medium was evaluated stability of the reproduced signal output by the head utilizing the magnetoresistance effect in an external magnetic field in which is generated by the Helmholtz coils.
[0046]
As a result, when an external magnetic field of 20 Oe was applied, a decrease in reproduction output and a change in reproduction waveform were observed in the comparative example, whereas such a change was not observed in the example. The difference in change with respect to the external magnetic field of 20 Oe corresponds well with the above-described magnetization curve.
[0047]
The perpendicular magnetic recording medium according to the present invention has a structure in which a perpendicular recording layer is laminated directly or via a nonmagnetic underlayer on a soft magnetic underlayer as mentioned in the examples.
[0048]
The soft magnetic backing layer in this magnetic recording medium has a function of returning the recording magnetic field to the magnetic head side by setting the above threshold value to be smaller than the recording magnetic field by the magnetic head and about the stray magnetic field in the magnetic disk device. However, the fluctuation of the magnetization state is sufficiently suppressed with respect to the stray magnetic field. In addition, since the soft magnetic underlayer has a multilayer structure as in the embodiment, demagnetization and demagnetization of the recording magnetization of the perpendicular recording layer by an external stray magnetic field without impairing the freedom of design such as permeability and film thickness. Can be obtained.
[0049]
In each of the above embodiments, a glass substrate is used as the nonmagnetic substrate. However, an Al-based alloy substrate, a Si single crystal substrate whose surface is oxidized, ceramics, plastic, or the like can also be used. Furthermore, the same effect is expected even when the surfaces of these nonmagnetic substrates are plated with NiP alloy or the like. Further, although only the sputtering method has been taken up as the film formation method of the soft magnetic backing layer, the same effect can be obtained by a vacuum evaporation method or the like.
[0050]
【The invention's effect】
According to the magnetic recording medium of the present invention, demagnetization and demagnetization of the recording magnetization of the magnetic recording layer can be prevented because the magnetic recording medium is hardly affected by the external stray magnetic field.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating an example of a magnetic recording medium according to the first invention. FIG. 2 is a schematic diagram illustrating an example of a magnetic recording medium according to the second invention. FIG. 3 is a soft magnetic backing used in the present invention. derivative of the graph [6] Figure 5 represents the magnetization curve of the soft magnetic underlayer for graph Figure 5 comparison representing a differential value of the graph [4] FIG. 3 represents an example magnetization curves of the layers Graph diagram showing values

Claims (5)

In a magnetic recording medium in which a soft magnetic backing layer and a magnetic recording layer having perpendicular anisotropy with respect to the surface of the nonmagnetic substrate are laminated on a nonmagnetic substrate, the soft magnetic backing layer is interposed between two soft magnetic layers. It has a structure in which a nonmagnetic intermediate layer is arranged, and when the external magnetic field is below a certain magnitude, the adjacent soft magnetic layers are antiferromagnetically coupled to each other via the nonmagnetic interlayer, and the external area exceeds a certain magnitude. A magnetic recording medium characterized in that, when a magnetic field is applied, the magnetization directions of adjacent soft magnetic layers are parallel to each other through the nonmagnetic intermediate layer . The magnetic recording medium of claim 1 in which the magnetic moment of the soft magnetic layer adjacent via the non-magnetic intermediate layer has a substantially identical der Rukoto. The non-magnetic intermediate layer is a magnetic recording medium according to claim 1 or 2, characterized in Ru Tona Rukoto. The magnetic recording medium according to any one of claims 1 to 3 wherein the non-magnetic intermediate layer is characterized by a 1.5nm less der Rukoto than 0.5 nm. The magnetic recording medium according to any one of claims 1 to 4 SUL is characterized to Rukoto and mainly composed of Fe.

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