JP2785276B2 - Magnetic recording media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium such as a magnetic disk, a magnetic drum, and a magnetic tape.

(Prior Art) Recently, a method of performing perpendicular magnetic recording on a magnetic thin film having perpendicular magnetic intention has been studied in order to meet a demand for higher recording density in a magnetic recording medium, and a high recording density has been obtained. .

As a magnetic thin film having perpendicular magnetic anisotropy, cobalt chromium alloy by sputtering or vacuum evaporation method,
An alloy magnetic thin film such as a cobalt-chromium-platinum alloy (JP-A-59-11605) is known.

(Problems to be Solved by the Invention) However, the perpendicular coercive force of these alloy magnetic thin films is insufficient, and the coercive force in the vertical direction is reduced by heating the substrate during sputtering or vacuum deposition.
It has been improved to more than 0 Oersted. For this reason, variations in magnetic properties due to uneven heating are unavoidable, and there are drawbacks that cannot be applied to substrates having low heat resistance such as plastic substrates. SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium which has a stable high perpendicular magnetic anisotropy and a high perpendicular coercive force without such defects.

(Means for Solving the Problems) In order to achieve the above object, the present inventor has made various studies on the composition of the cobalt-chromium-platinum alloy and the method of undercoating the magnetic thin film.

As a result, the content of cobalt was 86 atomic% or less, and the content of chromium was 8 to 24%.
It has been found that a magnetic thin film consisting of 6 at.% And 6 to 25 at.% Of platinum has a particularly high perpendicular magnetic anisotropy and does not require heating the substrate during sputtering or vacuum deposition.

Further, by providing a layer mainly composed of chromium on the substrate and forming a magnetic thin film composed mainly of cobalt, chromium and platinum on the layer, the magnetic thin film has a particularly perpendicular magnetic anisotropy. It has been found that it is not necessary to heat the substrate during sputtering or vacuum deposition.

That is, the present invention relates to a method for preparing a non-magnetic
A layer containing chromium as a main component having a thickness of not more than 00 ° is provided, and on this layer, the main components are 86 at% or less of cobalt, 8 to 17 at% of chromium, and 6 to 25 at% of platinum. A magnetic recording medium in which a magnetic thin film is formed, and a carbonaceous protective film is provided on the surface of the magnetic thin film.

 Hereinafter, the present invention will be described in detail.

The nonmagnetic substrate of the present invention is a hard molded product such as an aluminum plate, a glass plate, a synthetic resin, or a soft film such as an aluminum foil or a polyester film. It is necessary that the surface of the substrate has sufficiently small undulations and irregularities. If necessary, a hard layer or a high magnetic permeability soft magnetic layer made of a nickel-phosphorus alloy may be provided on the surface of the base.

The magnetic thin film composed of cobalt, chromium and platinum is deposited by either sputtering or vacuum evaporation. In the first aspect of the present invention, the composition ratio of cobalt, chromium and platinum is important.

The composition ratio is 86 atomic% or less for Co, 8 to 24 atomic% for Cr,
Pt must be in the range of 6 to 25 atomic%. If Cr is less than 8 atomic%, good vertical alignment cannot be obtained, and Pt is 6 atomic%.
If it is less than 1, a magnetic recording medium having a high coercive force cannot be obtained. When Cr exceeds 24 atomic%, Pt exceeds 25 atomic%, or Co is less than 86 atomic%, not only does the coercive force not particularly increase, but also the residual magnetic flux decreases and the perpendicular magnetic anisotropy decreases. Become smaller.

In the present invention, a layer containing chromium as a main component is provided as an underlayer of a magnetic thin film made of cobalt, chromium, and platinum. The thickness of the chromium layer is preferably 100 to 10,000Å. If it is less than 100 °, the height of the perpendicular coercive force is insufficient, and even if it exceeds 10,000 °, the perpendicular coercive force does not increase particularly. The chromium layer is provided by a sputtering method or a vacuum evaporation method. A magnetic thin film made of cobalt, chromium, and platinum is deposited on the surface of the underlayer by sputtering or vacuum evaporation. The objective of improving the perpendicular coercive force is achieved regardless of the ratio of cobalt, chromium and platinum. However, the ratio according to the present invention makes the improvement of the perpendicular coercive force more remarkable.

The protective film is particularly preferably made of carbonaceous material. Since the carbonaceous protective film has an appropriate lubricity and an appropriate hardness, the reliability is ensured for a long period without damaging the magnetic head.

The protective film made of carbonaceous material is applied to the surface of the magnetic thin film by a coating method, a vapor deposition method, a sputtering method or the like. It becomes crystalline like graphite, etc. by the deposition method, and becomes amorphous like glassy carbon, etc.
The effect as the protective film is the same in all cases. The thickness of the protective film sensitively affects the durability and reproduction output of the magnetic thin film. The thickness of the protective film is preferably 100 to 1000 mm.

If the thickness of the protective film is less than 100 mm, the durability of the magnetic thin film, particularly the still life, becomes very short. Also, if the thickness of the protective layer exceeds 1000 mm, the reproduction output will decrease and the reproduction signal
Since the S / N ratio is deteriorated, an error occurs in digital recording and reproduction, and noise is generated in analog recording and reproduction.

(Examples) Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

Examples 9 to 16 and Comparative Example 2 As a substrate, a substrate made of an aluminum disk having an outer diameter of 90 mm, an inner diameter of 25 mm, and a thickness of 1.2 mm was prepared. After lapping the substrate surface, a 30 μm thick hard layer made of nickel / phosphorus was provided by electroless plating. After the hard layer is mirror-polished, the substrate is magnetron sputtered (Tokuda Seisakusho)
(CFS-8ES type). First, a chromium film was deposited using chromium metal as a target under the conditions of an argon gas pressure of 1 × 10 ^-2 Torr, a sputter power of 4 W / cm ² , and a DC sputter. The deposition rate of the chromium film was 1000 l / min. By changing the chromium spatter time stepwise, eight substrates having various thicknesses of the chromium film having a thickness of 100 to 10,000 ° were produced. As Comparative Example 2, a substrate without chromium spatter was also manufactured. Next, set the degree of vacuum to 2 × 10−7T.
After adjusting the pressure to orr, introduce argon gas to reduce the pressure to 1
× 10−3 Torr. Operate the magnetron sputtering device to produce a magnetic thin film of 80 atomic% of Co, 10 atomic% of Cr, and 10 atomic% of Pt with a target power of 6 W / cm2 and a thickness of 25 under RF sputtering conditions.
00 ° formed. The temperature of the substrate during the formation of the magnetic thin film is approximately
60 ° C. Then, using a graphite as a target, an argon gas pressure of 8 × 10 −3 Torr, a sputtering power of 5 W / cm 2,
Sputtering was performed for 6 minutes under the conditions of DC sputtering at a sputtering rate of 50 ° / min, and a protective film made of carbonaceous material having a thickness of 300 ° was provided on the magnetic thin film to obtain a magnetic disk.

The above magnetic recording medium is repeatedly manufactured, and in this case, eight magnetic recording media having various thicknesses from 100 to 10,000 mm in thickness of the chromium film are manufactured by changing the spatter time of chromium stepwise. did. In Comparative Example 2 only, chromium spatter was not performed. For these magnetic recording media, the perpendicular coercive force and the half width of a rocking curve were measured. As shown in Table 3, the provision of the chromium layer significantly improved the perpendicular coercive force without lowering the vertical alignment.

The thickness of the protective film was confirmed as follows.
That is, after cutting out a sample of 7 × 14 mm from the magnetic disk and embedding the periphery of the sample with epoxy resin,
The sample was trimmed. Then, ultrathin sections were prepared with a diamond knife, observed with a transmission electron microscope, and the thickness of the protective film was measured.

The coercive force was measured for these magnetic recording media. The coercive force was measured using a vibrating sample magnetometer (model BH
V-55) with an external magnetic field of 15K Gauss. The vertical orientation was determined by the half value Δθ ₅₀ of the rocking curve of the X-ray diffraction spectrum.
Were compared. As the vertical orientation of the value of the Δθ ₅₀ is small is good. Generally, it is considered that Δθ ₅₀ is preferably 10 degrees or less. The X-ray diffraction apparatus recorded a diffraction spectrum in the θ direction using a Cu-Kα target.

Next, recording and reproduction of the magnetic disks of Examples 10 and 13 and Comparative Example 2 were performed under the same conditions as in the previous example.
The C / N ratio and frequency characteristics were measured. Table 4 shows the results of these measurements. From this result, it is clear that the chromium-adhered layer as the underlayer has a high C / N ratio, has a high reproduction output at a high frequency, and enables high-density recording / reproduction. The C / N ratio was measured by first writing a 7 MHz signal to the magnetic disk with a magnetic head, then reading the written signal with a magnetic head and passing it through a spectrum analyzer.The signal voltage at 7 MHz and the noise voltage at 4 MHz were measured. It was measured and the ratio was expressed in dB.

Table 3 shows the results obtained by measuring the perpendicular coercive force and the half width of the rocking curve of the magnetic disk thus obtained. From this table, it can be seen that the chromium layer provided below the magnetic thin film has a higher perpendicular coercive force.

Next, the recording and reproducing frequency characteristics of the magnetic disks of Examples 10 and 13 and Comparative Example 2 were measured.
The measurement conditions are as described above. As shown in Table 4, in the case where the chromium layer was provided under the magnetic thin film, the output voltage was high over the entire range of 0.5 to 12 MHz.

(Effect of the Invention) The magnetic recording medium of the present invention has a high perpendicular coercive force and is stable. Further, since the recording / reproducing C / N ratio is high and the frequency characteristics are excellent, it is particularly suitable for high-density recording / reproducing.

Claims (1)

(57) [Claims] A chromium-based layer having a thickness of more than 400 ° and not more than 10,000 ° is provided on a non-magnetic substrate. On the layer, 86% by atom or less of cobalt as a main component and 8 to 8% of chromium are contained. A magnetic recording medium in which a magnetic thin film comprising 17 at% and 6 to 25 at% of platinum is formed, and a carbonaceous protective film is provided on the surface of the magnetic thin film.