JPH0754574B2 - Perpendicular magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a perpendicular magnetic recording medium having a two-layer film structure having a perpendicular recording layer and a soft magnetic layer such as a CoCr / permalloy laminated film capable of high density magnetic recording.

[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 Japanese Patent Publication No. 58-91, Japanese Patent Publication No. 58-10764, etc.,
The recording medium is such that the easy axis of magnetization is perpendicular to the film surface and the remanent magnetization is oriented perpendicular to the film surface. The higher the signal density, the smaller the demagnetizing field inside the medium. 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, a perpendicular magnetic recording medium provided with a soft magnetic layer such as a permalloy alloy as an underlayer of a Co-based alloy thin film proposed in JP-B-58-91 can improve recording efficiency and obtain a large reproduction output. It is attracting attention because it is used.

However, some problems that have newly occurred due to the provision of the soft magnetic layer have been reported. For example, JP-A-60-3
Japanese Patent No. 8718 describes a phenomenon in which the reproduction output differs depending on the running direction of the magnetic head in one medium due to the magnetic characteristics of the soft magnetic layer. It is disclosed that the sex should be reduced. In addition, IEICE technical report MR84-6 (vol.84, N
o.61, 1984), it is stated that pulse-like noise generated during signal reproduction is caused by the soft magnetic layer, and as a solution to this problem, Hc of the soft magnetic layer can be set larger than 5 Oersted (Oe). It is stated that it is good.

As described above, a perpendicular magnetic recording medium having a double-layer film structure of a soft magnetic layer and a recording layer (hereinafter referred to as a double-layer film medium) has an excellent feature that the reproduction output is large, and is most expected to be put into practical use. However, there are various problems resulting from the instability of the soft magnetic layer, and there is a long-awaited solution to these problems.

[Object of the Invention] The present invention provides a perpendicular magnetic recording medium having a double-layered film structure having a recording layer and a soft magnetic layer, which has excellent reproduction output stability, that is, smooth output envelope. It is a proposal.

[Structure and Effect of the Present Invention] In the process of studying a two-layer film medium using an organic polymer film having a thickness of about 50 μm as a support, the present inventors have prepared a two-layer film having a soft magnetic layer. It has been found that the reproduction output of the film medium is wavy or / and the reproduction output envelope has protrusions. Example 5
It is shown in Fig. 6 and Fig. 6. The inventors believe that such an inconvenient phenomenon is related to the magnetostriction of the soft magnetic layer and partially caused by the sliding of the head at the time of recording / reproducing to partially change the magnetic characteristics of the soft magnetic layer. The present invention has been achieved through repeated research.

That is, according to the present invention, in a perpendicular magnetic recording medium having a recording layer and a soft magnetic layer, the magnetostriction constant (λ) measured in the film surface of the soft magnetic layer is larger than -1 × 10 ^-6 and 1 × 10 ⁶ or less. A soft magnetic layer with a coercive force (Hc) of 30 Oersted (Oe) or less (however, the easy axis of magnetization is almost perpendicular to the film surface, or even if in-plane, a soft magnetic layer is used when recording / reproducing with a ring-shaped magnetic head. The perpendicular magnetic recording medium is characterized in that it is a soft magnetic layer that is oriented almost at right angles to the magnetic force lines flowing through the magnetic layer).

Hereinafter, the details of the present invention will be described.

FIG. 1 shows the constitution of a preferable perpendicular magnetic recording medium of the present invention. In the figure, F is a support material, and a non-magnetic metal or non-metal sheet is usually used. For applications such as magnetic tapes, floppy disks, still electronic cameras, and image files, polyethylene terephthalate, polyethylene-
An organic polymer film having a thickness of about 4 μm to 120 μm such as 2,6-naphthalene dicarboxylate or polyimide is preferably used. In particular, the effect of the present invention is great when a soft organic polymer film having a large strain generated by sliding with the magnetic head is used as the support.

S in the drawing is a soft magnetic layer which is a feature of the present invention, and the details will be described later. Thickness Hc of about 50 Oe or less 0.1 μm to 0.7 μm
Those of about m are usually used. Various materials can be applied, and examples thereof include CoZr-based amorphous alloy film and NiFe-based alloy (permalloy) thin film. Particularly, permalloy is preferable because the raw material cost is low, the material is easily available, and it has suitable magnetic properties. For Permalloy
Not only NiFe alloys but also various types such as Mo permalloy, CuMo permalloy, corrosion resistant permalloy, and high hardness permalloy, all of which are applicable. Examples of the production method include vacuum vapor deposition, sputtering, ion plating, plating, etc., but the sputtering method is most preferable because it has good soft magnetic properties, film strength, and film adhesion strength, and the composition of the alloy can be easily controlled. Applied.

R in the figure is the recording layer, and the saturation magnetization (Ms) is 200 to 900 emu /
An alloy thin film of Co and Cr of about cc is preferably used. other
Co and Cr to which several wt% of third elements such as Re, W, Mo and Ta are added, CoV alloy thin film, FeCr alloy thin film, and further Co
It may be a CoO vapor deposition film. The point is a moderate Ms and Hc of several hundred Oe.
A thin film having perpendicular magnetic anisotropy and a thickness of about 0.1 μm to 0.5 μm is used.

P in the figure is a protective layer provided for the purpose of durability and the like provided as necessary. For example, a thin film of SiO ₂ , hard carbon, SiN or the like having a thickness of about 0.01 μm to 0.03 μm is provided to ensure durability.

Further, other intermediate layers, base layers, adhesive layers, etc. may be provided between the layers F, S, R, P. Further, in a disk-shaped medium such as a floppy disk, it is usual that each layer of the same structure is formed on both surfaces of the support F.

The soft magnetic layer which is a feature of the present invention will be described below.

In the present invention, in order to stabilize the reproduction output,
The λ measured in the film plane is in the range of -1 × 10 ^-6 or more and 1 × 10 ^-6 or less. That is, a soft magnetic film of λ whose absolute value is smaller than 1 × 10 ⁻⁶ is used. However, when Hc of the soft magnetic film is larger than 30 Oe, the soft magnetic film is stable against the disturbance of the soft magnetic characteristics (for example, Hc and magnetic permeability), and it is meaningless to define λ.

When the absolute value of λ of the film is larger than 1 × 10 ^-6 , the soft magnetic property of the film is unstable, and when the magnetic head slides on the medium, the soft magnetic property changes, causing waviness in the reproduction output envelope. It was found that convex parts and protrusions were generated.

To further improve the recording and reproducing sensitivity, the soft magnetic layer
Hc needs to be about 15 Oe or less, and in order to reduce noise as described above or to reduce modulation (see JIS C 6291) in the disk-shaped medium, the in-plane magnetic anisotropy of the soft magnetic layer is required. However, Hc needs to be about 3 Oe or more for this purpose. In a soft magnetic film having such Hc, its λ is −7 ×
A range of 10 ^-7 or more and 7 × 10 ^-7 or less, that is, a small Hc means that the soft magnetic characteristics are unstable. In such a case, it was found that λ with a smaller absolute value is required. did.

2 to 6 show Co having a soft magnetic film having various Hc and λ.
The reproduction output envelope for a fixed length of a bilayer film medium composed of Cr / Permalloy is shown. In the figure, the vertical axis is the output, and the horizontal axis is the time, in other words, the sample position. The manufacturing conditions of the medium and the method of measuring the electromagnetic conversion characteristics will be described in Examples below.

FIG. 7 shows various Permalloy films having different magnetostriction constants (λ) and coercive forces (Hc) as soft magnetic layers, and recording layers made of CoCr alloy films formed thereon, as in Examples and Comparative Examples described later. The result of evaluation of the reproduction output of the provided two-layer medium is shown, and the quality of the reproduction output envelope with respect to the absolute values of Hc and λ is shown by four grades from ⊚ to ×. When a good envelope waveform with no noise as shown in Fig. 2 is shown, it is indicated by ⊚. Is indicated by a triangle, and the time when a long-period wave with large convex portions and protrusions as shown in FIGS. 5 and 6 is also observed is indicated by a cross. In the case of Δ, an envelope with a good shape may be obtained depending on the recording / reproducing system and the method of mounting the head. From FIG. 7, it is understood that | λ | ≦ 1 × 10 ⁻⁶ , preferably | λ | ≦ 7 × 10 ⁻⁷ is required to obtain a stable and uniform reproduction output.

Next, a method of measuring the magnetostriction constant (λ) will be described with reference to FIGS. 8 to 12 by taking as an example the case where one side of the support film F has one soft magnetic layer (S) with positive λ. The magnetostriction constant (λ) measured in the film plane according to the present invention is a value obtained by the following method.

(1) When the soft magnetic film (S) has an easy axis (easy) and a hard axis (hard), a sample is cut into a width of m with the easy axis as the longitudinal direction as shown in FIG. Then, as shown in the drawing, the soft magnetic film (S) is left in the m × m square, and the other portions are removed. Although m may be appropriately selected depending on the sensitivity of the measuring device for the magnetization characteristics, m = 7 mm in the present invention. Such a shape is convenient for measuring the saturation magnetization characteristic (MH curve) while applying the tension f to the film (S) as described later.

(2) The MH curve is measured while applying the tension f to the film F as shown in FIG. FIG. 9 is a schematic configuration diagram of a known AC MH tracer, and the sample holder is devised so that measurement can be performed while applying tension.

In the figure, 1 is a Helmholtz coil, 2 is a detection coil, 3 is a free roll, and S is a soft magnetic film. The chuck 4 fixes one end of the film F and applies tension f to the other end. This figure is designed to measure the MH curve in the direction in which the tension f is applied. However, in the case of λ> 0, the MH curve in the direction perpendicular to the direction in which the tension is applied (width direction of the sample). Is preferably measured.

(3) Fig. 10 shows ha measured with tension f = 0.4 kgf.
It is an MH curve in the direction of the rd axis. A tangent line is drawn from the origin to the magnetization curve to find the intersection with the saturation magnetization (Ms) line, and the magnetic field indicated by the intersection is Hk.

Figure 11 shows MH in the hard axis direction when tension f = 1kgf is applied.
It is an axis. When the tension is increased, λ> 0 when the magnetic anisotropy (Hk) having the hard axis in the direction perpendicular to the direction in which the tension is applied increases.

(4) FIG. 12 is a plot of the value of Hk measured by the method shown in FIGS. 10 and 11 above against the tension f.

From FIG. 12, the gradient (b / a) of the relationship between Hk and f can be found, and the change width of Hk per unit tension can be found. The width of change in Hk (hereinafter referred to as ΔHk) is related to the magnitude of λ, and is used in the formula for calculating λ shown in item (6) below.

In the above item (1), the easy axis direction is used as the length direction for sampling, but when λ <0, it is preferable to sample from the hard axis direction and measure the hard axis direction with the configuration of FIG. Further, when the anisotropy (Hk) is very large under no tension, the reduction amount of Hk by applying tension may be calculated. Moreover, when it has an isotropic magnetic property in the plane, it may be measured in any direction.

The calculation formula of λ is shown below.

(5) In FIG. 8, the thickness of the film F is Df, the Young's modulus is Ef, the thickness of the soft magnetic film (S) is Ds, and the Young's modulus is Es.
And The stress (σ) acting on the film (S) due to the tension of f is given by the following formula.

Stress (σ) = (f · Es) / (Es · Df · m + Ef · Df · m) The above is an example of finding the stress (σ) acting on the film (S), using a strain gauge or the like. The stress (σ) may be obtained.

(6) The magnetostriction constant (λ) is calculated by the following equation.

Magnetostriction constant (λ) = (Is / 3) × (ΔHk / σ ′) where Is is saturation magnetization [wb / m ² ] and σ ′ is stress applied to the film (S) per unit tension [(N / m ² ) / kgf], ΔHk is the change in Hk per unit tension [(A / m) / kgf].

The method described above is suitable for a soft support material, that is, an organic polymer film. For a rigid support, λ can be determined according to the principles disclosed in the above method. Further, even in the state where the recording layers are laminated, it can be obtained by knowing the Young's modulus of the recording layers according to the principle described in the above item (5). The Young's modulus of the soft magnetic layer (S) and the recording layer (R) has a small error given to λ, and therefore an approximate value can be known.

To obtain a soft magnetic layer whose magnetostriction constant (λ) is smaller than 1 × 10 ^{−6 in} absolute value, first, the composition of the constituent elements of the soft magnetic layer may be selected. However, as is known, λ usually differs depending on the direction of the crystal axis, and is affected by the crystal lattice structure of the soft magnetic film and the crystal orientation of the film.

Therefore, it is necessary to select the composition in consideration of the method of manufacturing the soft magnetic film and the film microstructure derived from the manufacturing conditions. Thirteenth
The figure shows the relationship between the Ni content and the magnetostriction constant (λ) in NiFeMo (Mo permalloy) containing 5 wt% of Mo. FIG. 13 shows a 0.25 μm to 0.50 μm vertically oriented with weak <111> axis having a face-centered cubic crystal structure produced by sputtering.
This is an example of the Mo permalloy thin film, and does not limit this patent in any way.

Examples will be shown below.

Example A film of biaxially oriented polyethylene terephthalate having a thickness of 50 μm was used as a support F, and a permalloy thin film S and a CoCr alloy thin film R were formed on the support F under the following conditions using a DC bipolar magnetron sputtering device. The layers were 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 placed and modified to enable sputtering of a ferromagnetic target with a thickness of 4 mm. Furthermore, the board mounting part was modified so that the following conditions were possible.

(2) Substrate The film is stretched and attached to a circular metal frame with a diameter of 16 cm,
It was rotated at 18 rpm during film deposition. A direct current potential (Vb; bias voltage) can be applied from the outside (for the bias sputtering method, see, for example, FIG. 4 of JP-A-57-34324).

(3) Sputtering conditions (3-1) Permalloy thin film S; Mo5.0wt%, Mn0.02wt%, Fe16.1wt%, balance Ni (99.9% purity) was used as the substrate and the target. Interval 55.5mm, argon gas pressure 0.8Pa,
Sputtering was performed with an applied power of 300 watt for 10 minutes and 37 seconds while applying a Vb voltage of −100 volt to the substrate.

The λ of the permalloy thin film obtained under these sputtering conditions
Was 5.2 × 10 ⁻⁷ .

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

(4) Evaluation result Radius 45m from the center of the obtained CoCr / permalloy bilayer film medium
The static characteristics at m were as follows.

CoCr film: 0.20 μm Coercive force in the vertical direction (Hcv)… 680 Oe Effective anisotropic magnetic field (Hk)… (4.3 ± 0.1) kOe Permalloy film: Film thickness… 0.53 μm Coercive force… (9 ± 1) Oe (A CoCr film and a permalloy film were laminated and evaluated using an MH tracer.) A rectangular sample centered at a radius of 45 mm and having a width of 0.5 inch and a length of 60 mm from two directions, the radial direction and the circumferential direction, was used. Sampling was performed, the tape was 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 below. Table of measurement results
Shown in 2.

FIG. 2 described above shows the reproduction output envelope at the recording density of 2 KBPIK in the radial direction of this embodiment. It should be noted that FIGS. 2 to 6 are all the portions of each sample at a measurement length of about 40 mm of the envelope at 2 KBPI.

[Comparative Example] Similar to the example, except that Cu4.51 wt%, Mo3.82 wt%, Mn0.52 wt%, Fe13.64 wt%, as a permalloy target,
A CuMo permalloy consisting of the balance Ni was used to fabricate a two-layer film medium. The λ of this CuMo permalloy thin film was 1.2 × 10 ⁻⁶ , and the Hc was 4.5 ± 3 Oe. The characteristics of the CoCr film were almost the same as those of the example.

Table 3 shows the results of electromagnetic conversion characteristics evaluated in the same manner as in the example.

As described above, the two-layer film medium having the soft magnetic layer according to the present invention has excellent reproduction output stability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a typical constitution of the perpendicular magnetic recording medium of the present invention. F is a support, S is a soft magnetic layer, R is a recording layer, and P is a protective layer. 2 to 6 show typical shapes of the reproduction output envelope. When FIG. 2 is good, FIG. 5 and FIG. 6 are bad, and FIG. 3 and FIG. The figure is something in between. FIG. 7 shows the quality of the reproduction output envelope of the two-layer film medium having the soft magnetic layer with respect to the coercive force Hc and the absolute value | λ | of the magnetostriction constant of various soft magnetic layers. 8 to 11 are explanatory views of the method for obtaining the magnetostriction constant λ, FIG. 8 is the shape of the measurement sample, FIG. 9 is the state in which the sample is set on the MH tracer, FIG. 10 and FIG. The figure shows how to obtain the MH loop and the Hk value in the hard axis direction measured while applying tension. FIG. 12 is a plot of the change in Hk with tension f. FIG. 13 shows the magnetostriction constant λ with respect to the Ni content in Mo permalloy.

Claims (3)

[Claims] 1. In a perpendicular magnetic recording medium having a two-layer film structure having a soft magnetic layer and a recording layer on a support, a magnetostriction constant (λ) measured in the film plane of the soft magnetic layer is -1 ×. 10 ^-6 or more 1
× 10 ^-6 or less and a coercive force (Hc) of 30 Oersted (Oe) or less in the soft magnetic layer (however, if the easy axis of magnetization is almost perpendicular to the film surface or in-plane, the ring-shaped magnetic head A perpendicular magnetic recording medium characterized in that the soft magnetic layer is oriented in a direction substantially perpendicular to the magnetic field lines flowing through the soft magnetic layer when recording / reproducing). 2. A soft magnetic layer having a coercive force (Hc) of 15 Oe or less and a magnetostriction constant (λ) of −7 × 10 ⁻⁷ or more and 7 × 10 ⁻⁷ or less. ) The perpendicular magnetic recording medium according to the item. 3. The perpendicular magnetic recording medium according to claim 1, wherein the soft magnetic layer is permalloy.