JPH0630136B2 - Perpendicular magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention is capable of high-density magnetic recording and has a two-layer film structure having a perpendicular magnetic recording layer represented by a CoCr / permalloy laminated film and a soft magnetic layer, particularly a floppy disk. Relates to a perpendicular magnetic recording medium suitable for.

[Prior Art] In recent years, a perpendicular magnetic recording system has been proposed as a magnetic recording system having excellent high-density recording characteristics. This method is
As known in JP-A-58-91 and JP-B-58-10764, a recording medium having an easy axis of magnetization perpendicular to the film surface is used, and the residual magnetization is oriented perpendicular to the film surface. The higher the signal density, the smaller the demagnetizing field in the medium and the more excellent recording and reproduction can be performed.
A Co-based alloy thin film (especially CoCr alloy thin film) is known as a recording medium suitable for this system. In particular, Japanese Examined Japanese Patent Sho 58-91
The perpendicular magnetic recording medium having a Co-based alloy thin film provided with a soft magnetic layer such as a permalloy alloy as an underlayer, which has been proposed in Japanese Patent Laid-Open Publication No. 1993-52, has been noted for its improved recording efficiency and high read output. .

Further, as a measure for increasing the recording / reproducing sensitivity, it has been proposed to provide a non-magnetic Ti thin film between the recording layer and the soft magnetic layer.

For example, JP-A-55-163630 discloses the effect of using a non-magnetic intermediate layer having a thickness of about 1000Å or more.

In addition, IEICE technical research report MR80-43 (vol.
0, No. 287, 1980) describes a Ti intermediate layer having a thickness of 500Å.

In addition, the 7th Japan Society for Applied Magnetic Science Academic Lectures 7aA-
B, p8 (1983), experiments with Ti underlayer of 70 Å or more and 70
The effect of a 0Å Ti intermediate layer is stated.

Proceedings of the 32nd Joint Lecture on Applied Physics, 29
p-G-7, p358 (1985) describes an experiment of a 200 liter Ti intermediate layer, and 29p-G-8, p358 of the same paper has about 1
Experiments of Ti intermediate layer of 00 Å or more and improvement of electromagnetic conversion characteristics in the Ti intermediate layer of 400 Å are described.

Furthermore, IEICE technical research report MR84-51 (vo
l. 84, No. 293, 1985), in the case of a soft magnetic layer having an inner surface magnetic anisotropy of 1400Å thickness, the improvement of the reproducing output and the recording / reproducing resolution by the Ti intermediate layer of about 30Å to 100Å are described. Has been.

As described above, the comparatively thick Ti has been studied in the past.
The effect has been recognized when it is an intermediate layer and the soft magnetic layer has a relatively small coercive force and in-plane magnetic anisotropy. That is, in such a structure, even if the magnetic head can be a magnetic tape that travels in one direction of the medium, the in-plane magnetic anisotropy of the soft magnetic layer deteriorates the reproduction output modulation like a floppy disk (for example, JP 60-3871
This is inconvenient. In addition, a high reproduction output is required for the disk medium from the viewpoint of reliability, and the thickness of the soft magnetic layer is required to be about 3000 Å or more, but in such a thickness, the effect of the non-magnetic intermediate layer was confirmed. Therefore, the above-mentioned conventional technique has a negative effect.

[Object of the Invention] The object of the present invention is to improve the electromagnetic conversion characteristics by providing a non-magnetic intermediate layer between the recording layer and the soft magnetic layer.

[Configuration and Operation and Effect of the Present Invention] The above-mentioned object is achieved by the following present invention.

That is, the present invention has a two-layer film structure of a perpendicular magnetic recording layer (hereinafter referred to as a recording layer) and a soft magnetic layer, and the soft magnetic layer has a coercive force having in-plane isotropic magnetic characteristics. Is a soft magnetic thin film having a thickness of 3 Oersted (Oe) or more and a thickness of 0.3 μm or more, and a non-magnetic intermediate layer having a thickness of 5 Å or more and 30 Å or less is arranged between the two layers.

The present inventors have conducted research on a perpendicular magnetic recording medium having a two-layer film structure of a recording layer and a soft magnetic layer for the purpose of disk use such as a floppy disk. The characteristics of the soft magnetic film necessary for this purpose are, first of all, to have isotropic magnetic characteristics. The isotropic means, for example, as disclosed in the above-mentioned Japanese Patent Laid-Open No. 60-38718, a saturation magnetization curve (M-H loop) measured in a plane with a small difference due to the measuring direction. Specifically, it means that the reproduction output modulation on the medium described later is 10% or less. For this purpose, a permalloy film having perpendicular magnetic anisotropy (rotational magnetic anisotropy) or a coercive force (Hc) of 3 to 4 Oersted (O) is generally used for this purpose.
e) Higher coercive force permalloy films may be used. Furthermore, in a two-layer film medium having a soft magnetic film having too small Hc, it is already known that spike noise accompanying the domain wall movement of the soft magnetic film appears at the time of reproduction (at the time of reading a signal). Also, the coercive force Hc of the soft magnetic film is 3 to 4
Oe or higher is required. However, in the case of such Hc, the required thickness of the soft magnetic layer is 0.3 μm or more, preferably about 0.5 μm from the reproduction output surface.

The present inventors have studied to provide a Ti thin film as a non-magnetic intermediate layer between the CoCr alloy thin film and the permalloy thin film in a state where the requirement for the soft magnetic film is satisfied. Then, in the medium under such a constraint, the present inventors have found that the very thin non-magnetic intermediate layer of 5Å to 30Å, which has been ignored in the prior art, has the effect of improving the recording density, and reached the present invention.

The present invention will be described in detail below with reference to the drawings and examples.

FIG. 1 shows the structure of a typical perpendicular magnetic recording medium of the present invention. Reference character F in FIG. 1 is a support member, and a non-magnetic metal or non-metal sheet is preferably used. For use in floppy disks, still electronic cameras, and the like, organic polymer films having a thickness of about 30 to 120 μm, such as polyethylene terephthalate, polyethylene-2,6-naphthalenedicarboxylate, and polyimide, are preferably used.

S in FIG. 1 is a soft magnetic layer, and in the present invention, it has isotropic magnetic characteristics and has a thickness of about 0.3 μm or more, preferably 0.4 μm.
A ferromagnetic metal thin film having a coercive force of 30 m or more and 50 Oe or less is used. For example, NiFe alloy (Mo permalloy, CuMo permalloy, corrosion resistant permalloy, high hardness permalloy) thin film, CoZr, CoZrMo, CoN
Amorphous alloy thin films such as bZr can be used.

It is to be understood that isotropic does not have in-plane magnetic anisotropy such that the reproduction output modulation (see JIS C 6291) when a magnetic disk is made is 10% or more. The influence of the in-plane magnetic anisotropy of the soft magnetic layer S on the modulation, and the degree thereof vary depending on the shape, material and configuration of the magnetic head and cannot be uniformly defined. As an example of the soft magnetic layer S having such isotropic magnetic characteristics, the above-mentioned Japanese Patent Laid-Open No.
-Measured in the plane disclosed in Japanese Patent No. 38718-
Examples of the H-curve include a soft magnetic layer having a small difference depending on the measuring direction and a permalloy thin film having perpendicular magnetic anisotropy. In particular, a permalloy thin film having a Ni composition of about 80 wt% is preferably used, which can obtain the cost, moderate saturation magnetization, coercive force, and low magnetostriction. The coercive force of the permalloy thin film is preferably 3 to 4 Oe or more, and particularly preferably 50 e or more from the viewpoint of noise and uniformity of reproduction output envelope.

T in FIG. 1 is a non-magnetic intermediate layer having a thickness of 5 Å or more and 30 Å or less, and its effect will be described later. Although a Ti thin film was used in the examples, other oxides such as iron oxide, cobalt oxide, and chromium oxide, and organic thin films can also be used. That is, the present invention is not intended to improve the crystal orientation of the CoCr alloy thin film formed on the intermediate layer by the intermediate layer as in the prior art, and if the intermediate layer of the present invention is non-magnetic, Any material may be used as long as it does not deteriorate the adhesion between the layers.

R in FIG. 1 is a recording layer. Saturation magnetization 200-900emu / cc
An alloy thin film of Co and Cr to a degree is preferably used. Alternatively, CoCr to which several wt% of Re, W, Mo, or Ta is added, a CoV alloy thin film, a FeMn alloy thin film, or the like may be used. The point is to use a thin film having a thickness of 0.1 μm to 0.5 μm, which has an appropriate saturation magnetization, a coercive force of several hundred Oersteds, and perpendicular magnetic anisotropy.

Although P in FIG. 1 is a protective layer, it is not always necessary. However, normally, with a disk medium, playback of millions of times or more,
That is, since it is required to withstand sliding with a magnetic head, the thickness of SiO ₂ , hard carbon, Co oxide, etc.
It is preferable to provide a protective layer P having a thickness of about 01 μm to 0.03 μm.

Although FIG. 1 illustrates a double-sided medium, in the present invention, a medium in which a soft magnetic layer S, an intermediate layer T and a recording layer R are sequentially formed on a support F is an essential constituent element, and only one side of the support F is formed. The present invention can also be applied to those having the soft magnetic layer S, the intermediate layer T, and the recording layer S (for example, a single-sided medium).

Each of the soft magnetic layer S, the intermediate layer S, and the recording layer R is formed by a sputtering method, a vacuum evaporation method, a plating method, or the like. In particular, in order to improve the adhesion between the layers, it is preferable to successively form the three layers in the same vacuum chamber by a sputtering method or a vacuum evaporation method.

Hereinafter, the effects of the present invention will be described in detail with reference to Examples.

Example A film of biaxially oriented polyethylene terephthalate having a thickness of 50 μm was used as a support F, and a soft magnetic layer S was formed on the support as a soft magnetic layer S under the following conditions using the following DC bipolar magnetron sputtering device. As the intermediate layer T, the thin film was a Ti thin film, and as the recording layer R, a CoCr alloy thin film was sequentially laminated.

(1) Device A model SPF-430H manufactured by Nichiden Anelva Co., Ltd. was used.
It has three 4-inch targets and is capable of stacking three layers in vacuum.

In addition, a powerful permanent magnet was arranged and modified so that a ferromagnetic target with a thickness of 4 mm could be sputtered. Furthermore, the board mounting part was modified so that the following conditions were possible.

(2) Substrate The film was spread on a circular metal frame having a diameter of 16 cm and rotated at 18 rpm around the center of the metal frame during the deposition of the attached film. Also, a DC potential (Vb: Vb:
Bias voltage) can be applied. (For the bias sputtering method, see, for example, FIG. 4 of JP-A-57-34324.) (3) Sputtering conditions (3-1) Permalloy thin film of soft magnetic layer S; Mn0.05wt
%, Fe 15.4 wt%, balance Ni (99.9% purity) is used, the distance between the substrate and the target is 55.5 mm, argon gas pressure is 0.8 Pa, input power is 300
Sputtering was performed for 10 minutes and 37 seconds at a watt while applying a Vb voltage of -10001 volt to the substrate.

(3-2) Ti thin film of the intermediate layer T: Sputtering was performed with a target of Ti and an argon gas pressure of 1.3 Pa and an input power of 10 watt. The film thickness was controlled by the sputtering time. Deposition rate is 1.23Å / at a radius of 45 mm on a rotating substrate
It was min.

(3-3) CoCr alloy thin film for recording layer R; CoCr consisting of Cr 20 wt% and balance Co (99.9% purity)
Using alloy target, distance between substrate and target
2 at 55.5mm, argon gas pressure 0.4Pa, input power 500watt
Sputtering was performed for 17 minutes. A voltage (Vb) of -70 volt was applied during sputtering.

(4) Evaluation Results Seven samples were prepared, in which the thickness of the Ti thin film was OÅ (blank) of the conventional example, 5Å, 10Å, 15Å, 30Å of the example, and 50Å, 500Å of the comparative example, and a radius of 45 mm was evaluated. .

The measurement results of the film thickness and the magnetic properties are as follows, and the results are shown by the average value of 7 samples and the change width for those that are almost constant regardless of the Ti film thickness.

CoCr alloy film: film thickness 0.20 ± 0.01 μm Perpendicular coercive force In FIG. 2, the Ti film thickness (DT) is plotted against (Hcv).

Effective anisotropic magnetic field (H _K ) 4.3 ± 0.1 kOe Permalloy film: Film thickness 0.53 ± 0.02 μm Coercive force 10 ± 10 e (CoCr film / Ti film / Permalloy film laminated state, evaluated using MH tracer .) Also, with a radius of 45 mm as the center, 2 in the radial direction and the circumferential direction.
A rectangular sample having a width of 0.5 inch and a length of 60 mm from the direction was sampled, connected to a commercially available VTR tape having a width of 0.5 inch, and the electromagnetic conversion characteristics were measured under the conditions shown in Table-1. The results are shown in FIGS. 3 and 4. The difference in reproduction output between the two directions depending on the sampling direction is within a relative error of ± 3%, and the figure shows the average value of both.

FIG. 3 shows the reproduction output (Ep) when the recording density is 2 _K BPI with respect to the Ti film thickness (DT).
When T = O and DT = 5, 10, 15, 30 (Å) of the embodiment, the output is constant or tends to be slightly larger in the embodiment. When DT = 50,500 (Å) of the comparative example, the output is lower than that of the conventional example, and when DT> 40Å, the output is lower than that of the conventional example. It is considered that the performance of the output is caused by the reduction of the coercive force of the COCr film shown in FIG. 2 and the spacing loss due to the increase of the distance between the main magnetic pole and the soft magnetic film.

FIG. 4 is a plot of recording density (D ₅₀ ; _k BPI) 0 at which the reproduction output value becomes half of the reproduction output at the recording density of 2 _k BPI, with respect to the Ti film thickness (DT). Note that D ₅₀ was obtained from the satiety line obtained by connecting the peaks of the peaks derived from the thickness of the main pole in the recording density characteristics. From the figure, it is clear that the D ₅₀ was improved at DT = 5 to 30Å of the example.

From the above, in the two-layer film medium having the isotropic soft magnetic film having a relatively large coercive force and film thickness, the low-density reproduction output is constant in the non-magnetic intermediate layer having a thickness of 5 to 30 Å of the present invention. ,
It was confirmed that the effect was improved slightly and the D ₅₀ was increased, which is a preferable effect for high density recording and reproduction.

The reason for this is not clear, but by having a non-magnetic layer, COC is generated by the action of the magnetic charge generated on the back surface of the CoCr film.
It is considered that the slight increase in the in-plane magnetization component of the r film contributes to the increase in the reproduction output at high density.

[Brief description of drawings]

FIG. 1 is a sectional view showing a typical constitution of the present invention,
F is a support, S is a soft magnetic layer, T is a non-magnetic intermediate layer, R is a recording layer, and P is a protective layer. 2 to 3 are graphs showing respective characteristics of the embodiment, the conventional example, and the comparative example. FIG. 2 shows the relationship between the film thickness (DT) of the Ti layer and the coercive force (H _cv ) of the CoCr film, FIG. 3 shows the relationship between the thickness of the Ti layer (DT) and the reproduction output (Ep) of 2 _k BPI, and FIG. 4 shows the thickness of the Ti layer (DT).
And D ₅₀ .

Claims (3)

[Claims] 1. A perpendicular magnetic recording medium having a perpendicular magnetic recording layer and a soft magnetic layer on a support, wherein the soft magnetic layer has in-plane isotropic magnetic characteristics and has a coercive force of 3 oersteds (Oe). As described above, the soft magnetic thin film has a thickness of 0.3 μm or more, and the thickness is 5Å between the soft magnetic layer and the perpendicular magnetic recording layer.
A perpendicular magnetic recording medium having a non-magnetic intermediate layer of 30 Å or less. 2. The perpendicular magnetic recording medium according to claim 1, wherein the soft magnetic thin film is a permalloy thin film. 3. The perpendicular magnetic recording medium according to claim 1, wherein the non-magnetic intermediate layer is a titanium thin film.