JPH08306029A - Magnetic recording media - Google Patents

Abstract

PURPOSE: To obtain a magnetic recording medium ensuring low modulation noise and having a superior S-N ratio by regulating the ratio of the average grain diameter of magnetic grains constituting a magnetic layer to that of grains constituting an underlayer to a prescribed value. CONSTITUTION: An SiO2 , layer 2, a Cr layer 31, a Co75 Cr10 Pt15 alloy layer 41, an amorphous carbon film 5 and a lubricative layer 6 are formed on an amorphous olefin resin substrate 1 to obtain the objective magnetic disk. The SiO2 layer 2 is a layer for increasing the mechanical strength of the surface of the substrate 1. The Cr layer 31 is an underlayer and this underlayer 31 is columnar. The CoCrPt layer 41 covers the tops of the columnar crystals of the Cr underlayer 31. The ratio (Y/X) of the average grain diameter Y of magnetic grains constituting the magnetic layer 41 to that X of grains constituting the underlayer 31 is 0.4-0.9. The resultant medium ensures low modulation noise and has a superior S-N ratio, and high density recording is performed by using this medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium,
More specifically, it relates to a high-density magnetic recording medium having an alloy thin film as a magnetic layer.

[0002]

2. Description of the Related Art With the recent increase in the amount of information and the miniaturization of information-oriented devices, there is a demand for a magnetic recording medium capable of recording with even higher recording density in the field of magnetic recording. In order to meet such demands, a medium having an alloy thin film as a magnetic layer has been developed and is becoming the mainstream in the market in place of the conventional coating type medium. Since the alloy thin film medium can be manufactured by the plating method or the sputtering method, the thickness of the magnetic layer can be set to about 1/20 to 1/10 of the thickness of the coating medium. This has the advantage that the demagnetizing field of the minute magnetic domains is reduced and the output does not deteriorate even at high recording density.

[0003]

However, unlike the coating type medium, the alloy thin film medium has a drawback that the noise (modulation noise) in the vicinity of the writing frequency increases because the separation of the fine magnetic domains is not sufficient. FIG. 1 shows an enlarged view of the vicinity of the boundary of different magnetizations formed by minute magnetic domains of a conventional alloy thin film medium. As shown in FIG. 1, the magnetization boundary portion where different magnetizations face each other has a sawtooth shape along the width direction of the medium, and therefore appears as modulation noise during reproduction. Therefore, in order to further increase the recording density of the current alloy thin film medium, it is required to reduce the modulation noise due to insufficient magnetization division.

It is an object of the present invention to provide a magnetic recording medium capable of high density recording by reducing the modulation noise of the above-mentioned prior art alloy thin film medium.

[0005]

The present inventors have found that when a magnetic layer is grown on an underlayer having a grain or columnar structure,
It has been found that the noise can be reduced without deteriorating the signal strength by growing sufficiently large grains or columnar crystals of the underlayer and forming a magnetic layer made of fine magnetic grains on the grains. That is, according to the present invention, in a magnetic recording medium in which an underlayer and a magnetic layer are laminated on a substrate, the average particle size Y of the magnetic particles forming the magnetic layer is larger than the average particle size X of the particles forming the underlayer. Ratio of
There is provided the above magnetic recording medium, wherein / X is 0.4 ≦ Y / X ≦ 0.9.

The modulation noise of the magnetic recording medium can be effectively reduced by providing the magnetic layer having a grain size smaller than that of the underlayer according to the ratio Y / X. Y /
When X is less than 0.4 or when Y / X exceeds 0.9, the S / N ratio decreases, which is not preferable. Especially Y
When / X is less than 0.4, there is a problem of thermal fluctuation, which is not preferable.

In the above-mentioned magnetic recording medium of the present invention, the particles forming the underlayer are generally in the form of particles or columnar crystals, and the average particle size X is preferably X ≧ 15 nm. If the average grain size X of the underlayer is less than 15 nm, the crystallinity of the grains or columnar crystals of the underlayer is lowered, so that it becomes difficult for the magnetic layer to grow thereon, and the crystal orientation of the grown magnetic layer deteriorates. As a result, the signal strength decreases. The range of the grain size Y of the magnetic layer is determined by the Y / X ratio between the grain size Y of the magnetic layer and the grain size X of the underlayer and the lower limit of the grain range of the underlayer X.

The magnetic recording medium having the above structure can be formed by a sputtering method. An underlayer is formed on a non-magnetic substrate under conditions of low sputtering gas pressure and high substrate temperature, and an upper magnetic layer is formed under high sputtering gas pressure. It can be formed under a substrate temperature condition lower than that at the time of forming the underlayer, and a negative bias voltage may be applied or oxygen or nitrogen gas as a sputtering gas may be added. These methods may be used alone or in combination. Ratio Y / X of the average particle size of the magnetic layer and the underlayer
Can be within the scope of the present invention by appropriately adjusting the flow rate and gas pressure of the sputtering gas.

The material used for the underlayer is, for example, Cr, CrTi, CrW, CrTa, CrAl, C.
Examples thereof include Cr-based alloys such as rAg, Ti and Ti-Ta, but various materials that can be used for the underlayer of the magnetic recording medium are not particularly limited to these. As the magnetic material, for example, CoCr, CoCrTa, CoCrPt, CoCr
PtTa, CoPt, CoPd, CoCrPtSi, C
Examples thereof include Co-based alloys such as oCrPtB, composite materials in which Co and Fe are sputtered at the same time as SiO ₂ , and Co and Fe particles are dispersed, but are not particularly limited thereto. The magnetic layer may be made of a material other than the CoNi-based alloy. The underlayer and the magnetic layer can be easily formed by the sputtering method, the vacuum deposition method or the like as described above.

The substrate used in the magnetic recording medium of the present invention is, for example, Al, NiP-plated Al, glass, ceramics, carbon, a polymeric material such as polycarbonate, amorphous polyolefin, epoxy, polyamide, polyimide, polyethylene terephthalate. , Nylon, etc. can be used.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

[0012]

【Example】

Example 1 In this example, a continuous sputtering apparatus was used to obtain SiO ₂ /
A magnetic disk is manufactured in which four recording layers of Cr / CoCrPt / carbon are laminated on both sides of a substrate. A four-layer recording film was formed on an amorphous polyolefin substrate using a continuous sputtering apparatus capable of simultaneously sputtering both surfaces of the substrate as shown in FIG. This sputtering apparatus includes a preliminary exhaust chamber 7, a SiO ₂ film forming chamber 8, a Cr film forming chamber 9, and CoCrP.
The t film forming chamber 10 and the carbon film forming chamber 11 are connected in this order through the gate valve 13. By closing the gate valve 13 during film formation, each film formation chamber is isolated from the adjacent film formation chamber. A cryopump 12 is attached to each film forming chamber, and argon gas and a mixed gas thereof are introduced as a sputtering atmosphere gas. The amorphous polyolefin substrate is sequentially transferred to each film forming chamber by a dedicated tray. Si target in the SiO ₂ film forming chamber,
A Cr target is set in the Cr film forming chamber, a Co ₇₅ Cr ₁₀ Pt ₁₅ alloy target is set in the CoCrPt film forming chamber, and two carbon targets are installed in the carbon film forming chamber so that they face each other across the substrate passing position. This is 2
A film is formed on both surfaces at the same time by passing the substrate between the targets. Before the substrate was put into this sputtering apparatus, all the film forming chambers were evacuated until the ultimate vacuum reached 1 × 10 ⁻⁵ Pa.

After the substrate was placed on the tray in the preliminary evacuation chamber 7, the preliminary evacuation chamber 7 was evacuated until the degree of vacuum reached 1 × 10 ^-4 Pa. Next was 100nm deposited SiO ₂ by RF reactive sputtering in Cupid Foss polyolefin substrate transferred tray SiO ₂ film formation chamber 8. The film forming conditions at this time are Ar flow rate 50 sccm and O ₂ flow rate 20 sccc.
m, gas pressure 0.5 Pa, and input power 3 Kw. Next, the tray was transported to the next Cr film forming chamber 9, and a Cr layer was formed to 100 nm by DC sputtering. The film forming conditions at this time were Ar 50 sccm, gas pressure 0.4 Pa, input power 3 Kw, and substrate setting temperature 50 ° C. Even at this temperature, the maximum temperature of the substrate during sputtering was 100 ° C., and the problem of melting the substrate did not occur. This tray is sent to the next CoCrPt film forming chamber 10,
A film having a thickness of 30 nm was formed by DC sputtering. The sputtering conditions at this time are Ar gas flow rate 100 scc
m, gas pressure 0.8 Pa, input power 3 Kw. CoCr
The substrate was not heated when the Pt film was formed. The maximum temperature during sputtering was 50 ° C. Finally, the tray is moved into the carbon film forming chamber 11 and the carbon protective film 10 is removed.
A film having a thickness of nm was formed by the DC sputtering method. The film forming conditions at this time are Ar gas flow rate of 50 sccm and gas pressure of 0.4.
Pa and input power 3 Kw. Then, the laminated substrates were taken out of the apparatus, and a perfluoropolyether-based lubricant was applied to both surfaces of the uppermost carbon protective film by a dip method.

FIG. 2 is a schematic sectional view of the magnetic disk having a four-layer structure of the present embodiment obtained in this way. This magnetic disk consists of an amorphous polyolefin resin substrate 1 with Si
An O ₂ layer 2, a Cr layer 3, a Co ₇₅ Cr ₁₀ Pt ₁₅ alloy layer 4, an amorphous carbon film 5 and a lubricant layer 6 are formed. S
The iO ₂ layer 2 is a layer for increasing the mechanical strength of the surface of the substrate, and the Cr layer 3 formed thereon corresponds to the underlayer in the present invention.

When the cross section of the obtained magnetic disk was observed with a transmission microscope, the underlayer 31 was columnar and the CoCrPt layer 41 covered the upper surface of each columnar crystal of the Cr underlayer as shown in FIG. I found out that

Example 2 The CoCrPt film was formed under the following conditions: Ar gas flow rate 200 scc
A magnetic disk was produced in the same manner as in Example 1 except that m and gas pressure were set to 1.6 Pa.

Example 3 The condition of the CoCrPt film was set to an Ar gas flow rate of 300 sccc.
A magnetic disk was produced in the same manner as in Example 1 except that m and gas pressure were set to 2.4 Pa.

Example 4 The CoCrPt film was formed under the Ar gas flow rate of 400 sccc.
A magnetic disk was produced in the same manner as in Example 1 except that m and gas pressure were 3.2 Pa.

Comparative Example 1 The CoCrPt film was formed under the Ar gas flow rate of 50 scc.
A magnetic disk was produced in the same manner as in Example 1 except that m and gas pressure were 0.4 Pa. The magnetic disk of Comparative Example 1 is the same as the conventionally used magnetic disk.

Comparative Example 2 The CoCrPt film was formed under the following conditions: Ar gas flow rate 500 sccc.
A magnetic disk was produced in the same manner as in Example 1 except that m and gas pressure were 4 Pa.

After recording a sample signal on the magnetic disks obtained in Examples 1 to 4 and Comparative Examples 1 and 2, S was recorded.
The / N ratio was measured. Further, for each magnetic disk, the average grain size of the crystal grains of the underlayer and the magnetic layer was examined. The S / N ratio is MIG with a track width of 8 μm and a gap length of 0.4 μm.
Using the head, linear velocity 7 m / S, head flying height 0.1
After recording a sample signal with a line recording density of 50 μm and a linear recording density of 50 kfci, the track width is 5 μm and the gap length is 0.2 μm.
Was reproduced at a linear velocity of 7 m / S and the flying height of the head was 0.1 μm, and the reproduced signal was taken into a spectrum analyzer for examination. The average grain size of the crystal grains of the underlayer and the magnetic film was obtained by making ultra-thin sections of a section of the disc obtained in the above example using a microtome and observing them with a transmission microscope. The average value was calculated. The results are shown in Table 1. When the cross section of each disk is observed with a microscope, the underlayer is the magnetic disk of Example 1
It was found that the magnetic disk had a columnar structure as shown in FIG. 4 similarly to the magnetic disk obtained in the above, and had magnetic particles grown on it.

[0022]

[Table 1]

As can be seen from Table 1, the magnetic disks obtained according to the examples of the present invention had an average particle size ratio Y / X of the magnetic layer to the underlayer within the range of 0.4 to 0.9, Y
It can be seen that the S / N ratio is superior to that of the comparative example in which / X is outside this range. It is considered that the improvement of the S / N ratio is mainly because the particle size of the magnetic particles is reduced and the separation of the magnetic particles is improved, thereby lowering the modulation noise.

S / N of average particle size of particles constituting the underlayer
In order to investigate the influence on the ratio, C
When the film formation conditions for the r layer are Ar gas flow rate 100 sccm and gas pressure 0.8 Pa, and Ar gas flow rate 100 sccc
m, a gas pressure of 0.8 Pa, and a substrate temperature of 25 ° C., a magnetic disk was produced. The average particle diameter of the constituent particles of the underlayer of the magnetic disk thus obtained was 13 nm and 10 nm, respectively, and the respective S / N ratios were lower than in the case of Example 1. Therefore, it is preferable to maintain the average particle size of the underlayer particles at 15 nm or more.

[0025]

The magnetic recording medium of the present invention has a low modulation noise and an excellent S / N ratio. High density recording is possible by using the magnetic recording medium of the present invention.

[Brief description of drawings]

FIG. 1 is a partially enlarged plan view of a conventional alloy thin film recording medium, conceptually showing boundaries of different magnetizations formed by minute magnetic domains.

2 is a schematic sectional view of the magnetic disk of the present invention obtained in Example 1. FIG.

FIG. 3 is a schematic configuration diagram of a continuous sputtering apparatus used in Examples.

FIG. 4 is an enlarged cross-sectional view of the magnetic disk of the present invention obtained in Example 1.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Substrate 2 SiO ₂ layer 3 Cr layer 4 CoCrPt alloy layer 5 Carbon layer 6 Lubricant layer 7 Preliminary exhaust chamber 9 Cr deposition chamber 12 Cryopump 13 Gate valve 31 Columnar underlying layer 41 Magnetic particles of magnetic layer

Claims (4)

[Claims] 1. A magnetic recording medium in which an underlayer and a magnetic layer are laminated on a substrate, and a ratio Y of an average particle size Y of magnetic particles forming the magnetic layer to an average particle size X of particles forming the underlayer. / X is
The magnetic recording medium described above, wherein 0.4 ≦ Y / X ≦ 0.9. 2. The magnetic recording medium according to claim 1, wherein X ≧ 15 nm. 3. The underlayer is Cr, CrTi, CrW, Cr
The magnetic layer is composed of one kind selected from the group consisting of Ta, Ti, and Ti-Ta, and the magnetic layer is CoCr, CoCrTa, Co.
CrPt, CoCrPtTa, CoPt, CoPd, C
3. The magnetic recording medium according to claim 1, which is composed of one kind selected from the group consisting of oCrPtSi, CoCrPtB, Co grain dispersion composite material, and Fi grain dispersion composite material. 4. The magnetic recording medium according to claim 1, wherein the magnetic layer is made of a material excluding a CoNi-based alloy.