JPH05128469A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To attain the overwrite property by more lowering coercive force of an underside magnetic layer than of an upperside magnetic layer when direction of a surface faced to a magnetic head from a substrate is regarded as upperside. CONSTITUTION:A magnetic layer 5, a Cr layer 6, a magnetic layer 7, a Cr layer 8 and a magnetic layer 9 are laminated with an under layer 4 on a substrate 3 in this order. In this case, each thickness of the magnetic layer 5, 7, 9 increases in proportion as the magnetic layer nears to the side of the under layer 4 from the surface side to weaken coercive force. In this way, as coercive force of the underside magnetic layer is made lower than of the upperside magnetic layer, a pattern is easily written on the underside magnetic layer and the overwrite property is improved.

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 such as a magnetic disk, and more particularly to a magnetic recording medium having a good overwriting characteristic.

[0002]

2. Description of the Related Art In recent years, a thin film (magnetic layer) of a Co alloy type ferromagnetic metal having uniaxial crystal magnetic anisotropy such as CoNiCr or CoCr has been formed on a non-magnetic substrate as the recording density of a magnetic recording medium is increased. A metal thin film type magnetic recording medium is used. In order to achieve high density recording in the magnetic recording medium, it is necessary to have a high coercive force, and it is necessary to promote thinning of the magnetic layer. However, when the thinning is promoted, the product Brδ of the residual magnetic flux density Br and the film thickness δ becomes small, and there is a problem that the reproduction output becomes small.

Therefore, as disclosed in Japanese Patent Application Laid-Open No. 1-217723, an underlayer made of Cr is provided on a non-magnetic substrate, and Co alloy magnetic layers and non-magnetic layers are alternately formed on the underlayer. Laminated magnetic recording media have been developed. In this medium, since a large number of thin-film magnetic layers with high coercive force are formed, the total sum of Brδ of each magnetic layer becomes a large value,
High-density recording has become possible without damaging the reproduction output.

[0004]

However, in the magnetic recording medium in which the magnetic layers are laminated, the overwrite characteristics (referred to as overwrite characteristics and O / W characteristics) are not taken into consideration, and the O / W characteristics are not taken into consideration. I had a problem with. That is, the magnetomotive force of the magnetic head decreases from the surface of the magnetic recording medium (head facing surface) downward (toward the substrate side), but the coercive force of the lower magnetic layer is high, so Along with the decrease, it is difficult to write a new pattern (information) to the lower layer, and there is a problem that the S / N of the new pattern deteriorates due to noise caused by the residual of the previous pattern.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a magnetic recording medium having a high recording density and a high reproduction output and having a good overwrite characteristic.

[0006]

In the magnetic recording medium of the present invention made in view of the above object, an underlayer made of Cr is formed on a nonmagnetic substrate, and a ferromagnetic Co alloy is formed on the underlayer. In a magnetic recording medium in which a magnetic recording layer in which magnetic layers and Cr layers are alternately laminated is formed, the coercive force of the lower magnetic layer is the upper side when the direction of the surface facing the magnetic head from the base is upward. It is an aspect of the invention that the magnetic field is smaller than the coercive force of the magnetic layer. At this time, in order to reduce the coercive force of the lower magnetic layer, the film thickness may be made larger than that of the upper magnetic layer.

[0007]

[Function] Since the coercive force of the lower magnetic layer is made smaller than that of the upper magnetic layer, the pattern can be easily rewritten even if the magnetomotive force from the magnetic head weakens with respect to the upper magnetic layer. Therefore, it is possible to prevent noise due to the residual pattern before writing.

In order to make the coercive force of the lower magnetic layer smaller than that of the upper magnetic layer, the layer thickness of the magnetic layer may be made larger than that of the upper magnetic layer. By controlling the film time, the desired magnetic recording layer can be easily formed.

[0009]

EXAMPLE FIG. 1 is a partial cross-sectional view of a magnetic recording medium according to an example. An underlayer 4 made of Cr is formed on a non-magnetic substrate 3, and a uniaxial crystal magnetic anisotropy is formed on the underlayer 4. Magnetic layers 5,7,9 and Cr layers made of ferromagnetic Co alloy having directionality
A magnetic recording layer 10 in which 6 and 8 are alternately laminated and the uppermost layer is a magnetic layer 9 is formed, and a protective layer 11 is further formed thereon.

The substrate 3 has an amorphous Ni-P plating layer 2 of about 10 to 20 μm formed on the Al alloy substrate 1 to ensure rigidity. The substrate 3 is not limited to this structure, and glass or ceramics may be used.
The upper surface of the Ni-P plated layer 2 is usually provided with a textured process called texture in order to reduce the contact resistance with the magnetic head.

The Cr underlayer 4 formed on the substrate 3 is
It is formed for in-plane orientation of the c-axis (crystal axis showing crystal magnetic anisotropy) of the ferromagnetic Co alloy (crystal structure hcp) of the magnetic layer 5 formed thereon, and usually 500- 20
It is formed to a thickness of about 00Å. The ferromagnetic Co alloy forming the magnetic layers 5, 7, 9 of the magnetic recording layer 10 may be any alloy having an hcp crystal structure, and examples thereof include CoNiCr, CoCrTa, and CoCrPt. The magnetic layers 5, 7, 9 are made thicker in order to weaken the coercive force from the surface side toward the underlayer side. However,
The total thickness of the magnetic layers 5, 7 and 9 is preferably 600 to 800Å, and the uppermost magnetic layer 9 is preferably 100Å or more. Total layer thickness 6
The reason why it is set to 00 to 800Å is that a magnetic recording medium having a Brδ of 450 to 600 G · μ is required to secure a reproduction output and reduce noise. If the thickness of the uppermost layer, which is the thinnest, is 100 Å or more, if it is less than 100 Å, alloy parts will be scattered like islands instead of a continuous film, superparamagnetism will appear, and coercive force will suddenly decrease. Because.
In the illustrated example, the magnetic layers 5, 7, 9 are three layers, but the number of layers can be set freely.

Cr layers 6, 8 formed between the magnetic layers 5, 7, 9
Is provided for in-plane orientation of the c-axis of the Co-based alloy of the magnetic layer and for weakening the magnetic interaction between the magnetic layers, and the layer thickness may be about 50 to 250 Å. Cr less than 50Å
Since the magnetic interaction between the magnetic layers sandwiching the layers is too strong, it is difficult to reduce the medium noise due to the multilayer structure. On the other hand, if it exceeds 250 Å, the medium noise becomes large and the electrical characteristics also deteriorate.

A non-magnetic protective layer 11 made of carbon or the like is formed on the magnetic recording layer 10 to a thickness of about 200 to 400 liters, and a lubricant such as fluorinated polyether or the like is further formed thereon.
You may apply about 50Å. The protective layer 11 and the lubricant coating layer may be formed as needed. As the means for forming the magnetic layer, the Cr layer, and the carbon-based protective layer on the substrate, sputtering is generally performed, but other physical vapor deposition methods can be used.

Next, specific examples will be given. (1) A Ni-P plated layer was formed on an Al substrate, and a substrate having a textured surface was used to form a 1000-liter Cr underlayer 4 on the Ni-P plated layer as shown in FIG.
On top of that, the magnetic layers 5, 7 and 9 having the film thicknesses shown in Table 1 are formed on the 100 Å Cr layer
Three layers were laminated via 8. In addition, a carbon layer on it
A 300Å laminated film was formed.

The RF magnetron sputtering method is used as the film forming method, and the film forming conditions are Ar gas pressure of 5 mmTorr and substrate temperature 2
It was set to 30 ° C. The Co alloy composition (composition of the magnetic layer) used as the target is Co ₈₆ Cr ₁₂ Ta ₂ . The relationship between the film thickness of the Co alloy and the coercive force Hc is shown in FIG. As shown in FIG. 2, the lower magnetic layer of the example has a larger film thickness, and thus has a lower coercive force.

[0016]

[Table 1]

(2) The coercive force, medium noise (SNm) and overwrite characteristic of the magnetic recording medium after film formation were examined.
The results are shown in Table 2. The overwrite characteristic is a value defined by the following formula after writing 1F data on the medium and then overwriting 2F data without erasing DC, measuring the frequency components of 1F and 2F with a spectrum analyzer. (O / W value) evaluated. O / W
A smaller value (larger absolute value) indicates that the pattern before writing is erased cleanly. The measurement conditions used a thin film head as the magnetic head, and the flying height was 0.13 μm and 1F.
Data: 1.75MHz, 2F data: 5.0MHz.

[0018]

[Equation 1]

[0019]

[Table 2]

(3) From Table 2, it can be seen that although the coercive force of the example is higher than that of the comparative example, the O / W value is greatly reduced, and the overwrite characteristic is improved. Be done.
It should be noted that although no remarkable improvement was observed in the medium noise, the result was equal to or better than that of the comparative example.

[0021]

As described above, in the magnetic recording medium of the present invention, since the plurality of magnetic layers are laminated with the Cr layer interposed, the recording density and the reproduction output can be improved.
Moreover, since the coercive force is made smaller toward the lower magnetic layer of the magnetic recording layer, new patterns can be easily written in the lower magnetic layer even if the magnetomotive force from the magnetic head decreases.
It is possible to improve the overwrite characteristic.

In this case, by lowering the thickness of the lower magnetic layer to be thicker than that of the upper magnetic layer, it is possible to easily reduce the nutritional support, and to easily overwrite by simply controlling the deposition conditions. It is possible to improve the characteristics.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of essential parts of a magnetic recording medium according to an example.

FIG. 2 is a graph showing the relationship between the film thickness and the coercive force of the Co alloy according to the example.

[Explanation of symbols]

 3 Substrate 4 Underlayer 5 Magnetic Layer 6 Cr Layer 7 Magnetic Layer 8 Cr Layer 9 Magnetic Layer 10 Magnetic Recording Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Zenzo Okumura 5-10 Okuhata, Itami City, Hyogo Prefecture Kubota Amagasaki Plant, Itamibu Plant (72) Inventor Yoshiki Takemura 5-10 Okubata, Itami City, Hyogo Stock Company Kubota Amagasaki Factory Itamibu Factory

Claims (2)

[Claims] 1. An underlayer made of Cr is formed on a non-magnetic substrate, and a magnetic recording layer in which magnetic layers made of a ferromagnetic Co alloy and Cr layers are alternately laminated is formed on the underlayer. In the magnetic recording medium, the coercive force of the lower magnetic layer is smaller than the coercive force of the upper magnetic layer when the direction of the surface facing the magnetic head from the substrate is upward. 2. The magnetic recording medium according to claim 1, wherein the film thickness of the lower magnetic layer is thicker than the film thickness of the upper magnetic layer.