JP3308239B2 - Perpendicular magnetic recording medium and magnetic recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a perpendicular magnetic recording medium suitable for high-density magnetic recording and a magnetic recording / reproducing apparatus using the same.

[0002]

2. Description of the Related Art A magnetic disk drive currently in practical use employs an in-plane magnetic recording system, and an in-plane magnetic domain parallel to the substrate is provided on an in-plane magnetic recording medium which is easily magnetized in a direction parallel to the disk substrate surface. It is a technical problem to form a high density. In order to increase the areal recording density, particularly the linear recording density, by this method, it is necessary to improve the coercive force of the longitudinal magnetic recording medium and to reduce the thickness of the recording magnetic film. When the coercive force of the magnetic film exceeds 4 kOe, recording with a magnetic head becomes difficult, and when the thickness of the magnetic film is less than 15 nm in the case of a Co alloy-based magnetic film, the recording magnetization intensity elapses due to thermal fluctuation. The problem that the number decreases as a result occurs. The in-plane recording method has an essential problem that the magnetizations of adjacent recording bits face each other and a magnetic transition region having a width is formed at the boundary. Technical difficulties are expected to achieve a surface recording density of ² or more.

[0003] The perpendicular magnetic recording system is a system in which magnetization is formed perpendicularly to the film surface of a thin film medium, and the recording principle and medium noise generation mechanism are different from those of the conventional longitudinal magnetic recording medium. The perpendicular magnetic recording method has attracted attention as a method suitable for high-density magnetic recording because adjacent magnetizations are antiparallel, and a medium structure suitable for perpendicular magnetic recording has been proposed. The perpendicular magnetic recording method includes a method using a single-layer perpendicular magnetic film and a method in which a backing magnetic film is provided on the perpendicular magnetic film. A technique using a two-layer perpendicular magnetic recording medium having a backing magnetic film is disclosed in, for example, IEEE Transaction on Magnetics, Vol.MAG.
-20, No.5, September 1984, pp.657-662, "Perpendicu
lar Magnetic Recording-Evolution and Future ". As a perpendicular magnetic recording medium of this type, Co-Cr is formed on a backing layer made of a soft magnetic film layer such as permalloy.
A medium provided with a perpendicular magnetization film made of an alloy has been studied.

[0004]

In order to put into practical use a magnetic recording / reproducing apparatus capable of high-density magnetic recording of 30 Gb / in ² or more by a perpendicular magnetic recording system using a two-layer perpendicular magnetic recording medium, medium noise must be reduced. Reduction and flattening of the medium surface are essential. The medium noise is generated from both the perpendicular magnetization film and the backing magnetic film, and spike noise generated from the backing magnetic film has been a problem. Examples of such noise are, for example, IEEE Transaction on Magnetics, Vo
l.MAG-20, No.5, September 1984, pp.663-668, "Cruci
al Points in Perpendicular Recording ".

In order to solve such a problem, a method of forming an in-plane magnetized film below the backing magnetic film is described in, for example, Journal of the Japan Society of Applied Magnetics, Vol. 21, Supplement No. S1, pp. 104-108, " 3
Higher S / N ratio of layer-perpendicular medium and stability of recording signal "have been proposed in order to put into practical use a magnetic recording / reproducing apparatus capable of high-density magnetic recording of 30 Gb / in ² or more. Further, almost no effective method has been proposed for flattening the surface, which is a condition required as a medium for high-density recording.The purpose of the present invention is to provide 30 Gb / in ² or more. Another object of the present invention is to provide a perpendicular magnetic recording medium having a low noise characteristic and a flat surface for realizing a high density recording density, and to facilitate realization of a high density recording / reproducing apparatus.

[0006]

In order to realize a perpendicular magnetic recording medium having a low noise characteristic and a flat surface, the present invention provides a perpendicular magnetic film on a non-magnetic substrate via a backing magnetic film layer.
In a perpendicular magnetic recording medium provided with a protective lubricating film, the backing magnetic film layer is formed of at least one soft magnetic film and at least one soft magnetic film.
It consists of two or more layers of a multilayer film composed of a hard magnetic film having a granular structure comprising magnetic material species L1 ₀ type crystal.
The soft magnetic film is, for example, a film of several tens Oe or less, as defined by coercive force, and the hard magnetic film is a film of several hundred Oe or more.

In order to reduce the noise caused by the backing magnetic film, it is necessary to make the magnetic domain structure of the magnetic film finer and to fix the domain wall existing in the magnetic film so as not to move easily. This is because the backing magnetic film is a multilayer film composed of at least one kind of soft magnetic film and at least one kind of hard magnetic film, and the soft magnetic film is an amorphous film and the hard magnetic film is a film having a granular structure. This is made possible by configuring from.

When an amorphous soft magnetic film and a hard magnetic film constituting a backing magnetic film are formed through a contact or an extremely thin non-magnetic film, a magnetic interaction exists between the two types of magnetic films. . For this reason, even if a domain wall exists in the soft magnetic film, the movement of the domain wall is suppressed even in an external magnetic field due to the interaction. Further, by forming a soft magnetic film on the hard magnetic film composed granular type of a non-magnetic material such as an oxide and a ferromagnetic material having an L1 ₀ structure, domain structure entering into the soft magnetic film is miniaturized Tend. Further, the surface flatness of the granular type film is superior to the flatness of a polycrystalline type magnetic film such as a Co-Cr-Pt alloy having the same thickness. Also, L1 granular type hard magnetic anisotropy energy of the magnetic film composed of non-magnetic material such as ₀ oxide and a ferromagnetic material having a structure magnetic anisotropy of the Co-based alloy film, such as Co-Cr-Pt Since it is about 10 times larger than the coercive energy, a high coercive force can be realized even with a thinner film thickness. Generally, as the film thickness increases, the surface flatness of the film deteriorates. Therefore, the granular hard magnetic film is effective in achieving a certain coercive force and reducing the film thickness. When a soft magnetic film having an amorphous structure is formed on this hard magnetic film directly or via an extremely thin non-magnetic film, a backing magnetic film having excellent surface flatness can be realized.

[0009] As the ferromagnetic material having an L1 ₀ structure, C
o-Pt _x or Fe-Pt _y alloy, or material obtained by adding other elements in these alloys are suitable.
Here, L1 ₀ values of both x and y stoichiometric composition of the ferromagnetic material having the structure is a 50at%, since generally have some solid solubility range, 20at% <x <60a
The range of t%, 20 at% <y <60 at% is possible. Further, B, Si, about several at%
It is also possible to add C, Nd, Sm, Cr and the like. As the nonmagnetic material for forming the granular structure, oxides such as SiO ₂ , ZrO ₂ and Al ₂ O ₃ and mixed crystal oxides thereof are suitable.

The soft magnetic film is made of Co-Nb, an amorphous material having higher electric resistance than Fe-Ni permalloy film or the like.
-X (X = Zr, Ti, Hf, Mo, W), Ni-Co
-Y (Y = Zr, Ti, Hf, Mo, W), Fe-Si
A -Z (Z = B, Al) alloy film is desirable. Since these magnetic films generally have an amorphous fine structure, they are suitable for obtaining a film having a flat surface.

In order to flatten the medium surface, it is essential to flatten the surface of the backing magnetic film. Generally, in order to increase the recording efficiency of the head in perpendicular magnetic recording, it is considered that the thickness of the backing magnetic film is preferably as thick as 1 μm or more. When such a thick film is formed of the same material, the structural fluctuation of the film increases in the process of forming the film as the film thickness increases, so that the roughness Ra of the surface increases. This tendency is particularly remarkable in a film having a polycrystalline structure. Although this problem can be solved to some extent by using an amorphous film and a granular magnetic film as described above, a more flat film can be obtained by making these films multilayer.

In order to achieve a surface recording density of 30 Gb / in ² or more, it is necessary to keep the distance between the magnetic head and the surface of the magnetic recording medium in the magnetic recording apparatus at 15 nm or less. For this purpose, the undulation Ra of the medium surface must be 3 nm or less in consideration of clearance, and for this purpose, the undulation Ra of the backing magnetic film must be equal to or less than this value. Although the total thickness of the backing magnetic film can be 10 μm or more in principle, the roughness Ra of the medium surface is 3 n
m or less, the total thickness of the backing magnetic film should be at most 1
μm, preferably 200 nm or less. Also. The smaller the film thickness is, the better the surface is. When the above-mentioned granular type film is used, the thickness of the hard magnetic film constituting the backing magnetic film can be reduced to about 20 nm even when a non-magnetic film for controlling the film orientation is included. Further, the thickness of the soft magnetic film needs to be at least 10 nm in order to obtain the advantage of the backing magnetic film in perpendicular magnetic recording. Therefore, in the case of the present invention, the range of the backing magnetic film thickness can be 30 nm or more and 1 μm or less. In consideration of the process conditions such as the time for film formation, a more desirable film thickness range is 30 nm or more and 200 nm or less.

As the perpendicular magnetic film formed on the backing magnetic film having such a structure, Co-Cr, Co-Cr-
Co-based alloy perpendicular magnetization film such as Ta, Co-Cr-Pt, Co-Cr-Pt-Ta, Pt / Co, Pd / Co, P
Any of a multilayer perpendicular magnetic film such as a t / Co alloy and a Pd / Co alloy, and an amorphous or microcrystalline perpendicular magnetic film such as Tb-Fe-Co and Fe-Pt are possible. It is also possible to introduce an intermediate layer for controlling the film structure between the backing magnetic film and the perpendicular magnetization film, if necessary. In addition, 30Gb
In order to realize a surface recording density of / in ² or more, the maximum linear recording density used is desirably 300 kFCI or more, and in this case, the shortest bit length is 80 nm. The thickness of the perpendicular magnetization film for realizing a bit length of less than this is less than half the bit length, that is, 4
It is necessary that the thickness be 0 nm or less. However, if the film thickness is 1
When the thickness is less than 0 nm, there arises a problem that the recording magnetization intensity decreases with time due to thermal fluctuation. Therefore, it is desirable that the film thickness is at least 10 nm or more.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. [Embodiment 1] A perpendicular magnetic recording medium having a sectional structure shown in FIG. 1 was manufactured by a magnetron sputtering method using a glass substrate having a diameter of 2.5 inches. On a substrate 11, a seed layer 12 having a thickness of 3 nm, an underlayer 13 having a thickness of 10 nm, a hard magnetic film layer 14 having a thickness of 10 nm, and a thickness of 200 nm
A backing magnetic film composed of the soft magnetic film layer 15 was formed, on which a perpendicular magnetic film 16 and a protective film 17 were formed in a thickness of 25 nm and a thickness of 5 nm in this order. MgO target for seed, Cr target for underlayer, C for hard magnetic film layer
A composite target having a surface area ratio of SiO ₂ pellets of 7: 3 on an o-35 at% Pt target, a Co-5 at% Zr-6 at% Nb target for a soft magnetic film, and a Co-20 at% Cr for a perpendicular magnetization film -8 at% Pt-4a
A t% Ta target and a carbon target for the protective film were used. The sputtering was performed under the conditions of an Ar gas pressure of 3 mTorr, a sputtering power of 10 W / cm ² , and a substrate temperature of 300 ° C. For film formation using an MgO target and a composite target, a high-frequency magnetron sputtering method was used, and for other targets, a DC magnetron sputtering method was used.

Under the same conditions, Co-35a is used for a hard magnetic film.
On a t% Pt target, ZrO ₂ pellets, Al ₂ O ₃
The pellets and the Si ₃ N ₄ pellets were each in a surface area ratio of 7:
A perpendicular magnetic recording medium was prepared in the same manner as described above, except that the composite target No. 3 was used. Further, under the same conditions, SiO 2 was deposited on a Fe-45 at% Pt target for a hard magnetic film.
₂ pellets, ZrO ₂ pellets, Al ₂ O ₃ pellets, Si
A perpendicular medium was prepared in the same manner as described above, except that a composite target in which the surface area ratio of each of the ₃ N ₄ pellets was 7: 3 was used.

As a result of examining the structure of each of the hard magnetic film and the Co-5 at% Zr-6 at% Nb film by X-ray diffraction and electron microscopy, the former was found to be composed of a magnetic metal phase having a crystal grain size of 8 to 25 nm and an oxide. It has a granular structure in which physical phases are mixed,
The latter was confirmed to be amorphous.

As a comparative sample 1, a sample having a thickness of 2
A backing magnetic film consisting of a single layer of a Co-5 at% Zr-6 at% Nb film having a thickness of 00 nm, and a perpendicular magnetic film consisting of Co-20 at% Cr-8 at% Pt-4 at% Ta having a thickness of 25 nm formed thereon; A sample on which a protective film made of carbon having a thickness of 5 nm was formed was prepared under the same sputtering conditions.
As Comparative Sample 2, a 15 nm thick Cr
Underlayer, 30 nm thick Co-20at% Cr-10a
t-5 Pt hard magnetic film, 200 nm thick Co-5 at% Z
A backing magnetic film made of an r-6 at% Nb film is formed, and a Co-20 at% Cr-8 at% 25 nm thick is formed thereon.
A sample having a perpendicular magnetization film made of Pt-4 at% Ta and a protective film made of carbon having a thickness of 5 nm was formed under the same sputtering conditions.

The surface undulations Ra of these samples were measured using an atomic force microscope, and the recording / reproducing characteristics were measured using a recording / reproducing separation type magnetic head. The recording head is a single pole type thin film head, with a track width of 0.5 μm, a pole thickness of 0.2 μm,
The reproducing head is a giant magnetoresistive (GMR) head with a shield interval of 0.15 μm, a track width of the reproducing element of 0.45 μm, and a spacing of 0.015 at the time of measurement.
μm. S / N of the medium when subjected to magnetic recording of 300kFCI as a relative value to the S / N of the comparative sample, the recording resolution reproduction output of low linear recording density was measured as a recording density to half (D ₅₀ kFCI) . Table 1 shows the results.

[0019]

[Table 1]

As can be seen from Table 1, the perpendicular magnetic recording medium of the present embodiment has a significantly improved surface undulation Ra and a higher medium S / N than the comparative example, and has a high density magnetic recording medium. Desirable as a medium. Using the magnetic recording medium manufactured in the present embodiment, a magnetic recording / reproducing apparatus having a disk diameter of 2.5 inches was manufactured. FIG.
As shown in a schematic plan view in (a) and a cross-sectional view along AA in FIG. 3 (b), a magnetic recording medium 51, a magnetic recording medium driving unit 52 for rotating the magnetic recording medium 51, a recording head and a reproducing head are provided. This is a magnetic recording / reproducing apparatus having a known configuration including a magnetic head 53, a magnetic head driving unit 54, a signal processing unit 55 for processing a recording / reproducing signal of the magnetic head, and the like. When a GMR head is used as the reproducing element of the reproducing head, the error rate is 10 ^{−9 under} the condition of the areal recording density of 35 Gb / in ^2.
It was confirmed that any of the samples could be secured and that the device operated as an ultra-high density recording / reproducing apparatus.

[Embodiment 2] Using a silicon substrate having a diameter of 2.5 inches, a magnetron sputtering method is used.
A perpendicular magnetic recording medium having the cross-sectional structure shown in FIG. 2 was manufactured. On a substrate 21, a seed layer 22 having a thickness of 5 nm
3 was formed to a thickness of 5 nm, and the hard magnetic film layer 24 was formed to a thickness of 10 nm.
On top of this, four laminated films of a nonmagnetic film 25 having a thickness of 1 nm and a soft magnetic film 26 having a thickness of 50 nm were formed. Further, the perpendicular magnetization film 27 was formed with a thickness of 25 nm, and the carbon protection film 28 was formed with a thickness of 6 nm. MgO target for seed layer, Cr for underlayer
Target, the hard magnetic film ZrO ₂ pellets area ratio placed thereon and Fe-50at% Pt targets for layer 8: 2. The term composite target, for non-magnetic film Hf target, the soft magnetic film Co- 6at% Zr-3at% Ti
Co-20at% Cr-1 for target and perpendicular magnetization film
A 2 at% Pt-2 at% Ta-1 at% Nb target was used, and a carbon target was used for a protective film. The sputtering was performed under the conditions of an Ar gas pressure of 2.5 mTorr, a sputtering power of 10 W / cm ² , and a substrate temperature of 310 ° C.
The structure of the hard magnetic film examined by X-ray diffraction and electron microscope observation was a granular structure in which a magnetic material and a non-magnetic material were mixed.

Here, the material of the soft magnetic layer is Co-6 at%.
Nb-3at% Hf, Co-5at% Nb-4at% T
i, Co-5 at% Nb-4 at% Hf, Co-5 at
% Nb-2at% W, Ni-10at% Co-3at%
Zr, Ni-29 at% Co-3 at% Ti, Ni-5
at% Co-6 at% Hf, Ni-9 at% Co-2a
t% Mo, Ni-12at% Co-2at% W, Fe-
4 at% Si-2 at% B, Fe-4 at% Si-3a
A similar perpendicular magnetic recording medium was produced under the same conditions as above, except that t% Al was used.

As a comparative sample, the backing magnetic film was a single Co-6 at% Zr-3 at% T having a thickness of 200 nm.
i, Co-6 at% Nb-3 at% Hf, Co-5 at
% Nb-4at% Ti, Co-5at% Nb-4at%
Hf, Co-5at% Nb-2at% W, Ni-10a
t% Co-3at% Zr, Ni-29at% Co-3a
t% Ti, Ni-5at% Co-6at% Hf, Ni-
9at% Co-2at% Mo, Ni-12at% Co-
2 at% W, Fe-4 at% Si-2 at% B, Fe-
A perpendicular magnetic recording medium was prepared in the same manner as described above except that 4 at% Si and 3 at% Al were used.

The surface flatness Ra of these magnetic recording media,
Medium S / N, recording resolution (D ₅₀ kFCI) was measured under the same conditions as in the first embodiment. For each soft magnetic film material, the perpendicular magnetic recording medium of the present invention and a comparative example,
The above characteristics were compared. As for the medium S / N,
The S / N of the perpendicular magnetic recording medium of the present invention is shown as a relative value to the S / N of each comparative sample. Table 2 shows the results.

[0025]

[Table 2]

As shown in Table 2, the perpendicular magnetic recording medium of the present embodiment has a surface flatness Ra, medium S / N, and recording resolution (D ₅₀ kFC) which are smaller than those of the comparative examples.
I) was greatly improved overall, and it was found that it was desirable as a high-density magnetic recording medium.

[0027]

According to the present invention, the surface flatness of the perpendicular magnetic recording medium, the medium S / N, and the recording resolution can be improved, and as a result, a magnetic disk drive capable of high-density magnetic recording can be obtained. Can be. In particular, high-density magnetic recording of 30 Gb / in ² or more becomes possible, and it is easy to reduce the size and capacity of the device.

[Brief description of the drawings]

FIG. 1 is a sectional view of an example of a perpendicular magnetic recording medium according to the present invention.

FIG. 2 is a sectional view of another example of the perpendicular magnetic recording medium according to the present invention.

FIG. 3 is a schematic diagram of a magnetic recording / reproducing apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 ... board | substrate, 12 ... seed layer, 13 ... base layer, 14 ... hard magnetic film, 15 ... soft magnetic film, 16 ... perpendicular magnetization film, 17 ... protective film, 21 ... substrate, 22 ... seed layer, 23 ... base film , 2
4: hard magnetic film, 25: non-magnetic film, 26: soft magnetic film, 27
... perpendicular magnetic film, 28 ... protective film, 51 ... magnetic recording medium, 5
2: magnetic recording medium driving unit, 53: magnetic head, 54: magnetic head driving unit, 55: signal processing unit

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Atsushi Kikukawa 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (56) References JP-A-59-63026 (JP, A) JP-A-9 −320847 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G11B 5/62-5/858 H01F 10/08

Claims (8)

(57) [Claims] 1. A perpendicular magnetic recording medium having a perpendicular magnetic film provided on a nonmagnetic substrate with a backing magnetic film layer interposed therebetween, wherein the backing magnetic film layer has a hard magnetic structure having a granular structure.
Film and at least one layer of soft magnetism formed on the hard magnetic film
A perpendicular magnetic recording medium, comprising: a conductive film . 2. A perpendicular magnetic recording medium according to claim 1, wherein the hard magnetic film is a perpendicular magnetic recording medium which comprises a magnetic material of L1 ₀ type crystal. 3. A perpendicular magnetic recording medium according to claim 2, wherein the magnetic material of the L1 ₀ type crystal is perpendicular magnetic recording medium, which is a Fe-Pt alloy or Co-Pt alloy. 4. The perpendicular magnetic recording medium according to claim 1, wherein the hard magnetic film contains a non-magnetic material. 5. The perpendicular magnetic recording medium according to claim 1, wherein the soft magnetic film is an amorphous film. 6. The perpendicular magnetic recording medium according to claim 5, wherein the soft magnetic film is made of Co—Nb—X (X
= Zr, Ti, Hf, Mo, W), Ni-Co-Y (Y
= Zr, Ti, Hf, Mo, W) or Fe-Si-Z
(Z = B, Al) The perpendicular magnetic recording medium characterized by the above-mentioned. 7. The perpendicular magnetic recording medium according to claim 1, wherein the thickness of the backing magnetic film layer is 30 nm or more and 500 nm.
Hereinafter, the thickness of the perpendicular magnetization film is 10 nm or more and 40 nm or less, and the undulation Ra measured on the surface of the perpendicular magnetization film is 3 nm.
A perpendicular magnetic recording medium characterized by the following. 8. A magnetic recording medium having a perpendicular magnetization film provided on a non-magnetic substrate with a backing magnetic film layer interposed therebetween, a magnetic recording medium driving unit for rotating the magnetic recording medium, a recording head and a reproducing head. A magnetic head comprising: a magnetic head driving unit that drives the magnetic head; and a signal processing unit that processes a recording / reproducing signal of the magnetic head. There, Gras
Hard magnetic film having a nuclear structure and formed on the hard magnetic film
A perpendicular magnetic recording medium comprising at least one soft magnetic film , wherein the recording head is a thin film head, and the reproducing head is a GMR.
And a surface recording density of 30 Gb / m under conditions adjusted so that the distance between the magnetic head and the perpendicular magnetic recording medium is 20 nm or less.
a magnetic recording / reproducing apparatus which achieves in ² or more.