JPH05120662A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve an overwriting characteristic by using a ferromagnetic Co alloy contg. Co, Ta or Nb at prescribed % and setting the concn. of the Ta or Nb in a lower magnetic layer lower than in an upper magnetic layer. CONSTITUTION:A substrate layer 4 consisting of Cr is formed on a nonmagnetic base body 3. A magnetic recording layer 10 which is alternately laminated with magnetic layers 5, 7, 9 consisting of the CoCrTa alloy or CoCrNb alloy having uniaxial crystalline magnetic anisotropy and Cr layers 6, 8 and is formed with a magnetic layer 9 as the uppermost layer is formed thereon. Further, a protective layer 11 is formed thereon. The CoCrTa alloy or CoCrNb alloy contg. 80 to 93at.% Co and 1 to 6at.% Ta or Nb is used as the ferromagnetic Co alloy for the respective magnetic layers forming the recording layer 10. The concn. of the Ta or Nb of the lower magnetic layer 5 is set lower than the concn. of the same components of the upper magnetic layer 9. The recording density and reproduced output are improved in this way and the overwriting characteristic 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 Laid-Open No. 1-217723, an underlayer made of Cr is provided on a non-magnetic substrate, and a Co alloy magnetic layer and a non-magnetic layer are formed on the under layer by sputtering. A magnetic recording medium having alternating layers has been developed. In this medium, since a large number of thin-film magnetic layers having a high coercive force are formed, the sum of Brδ of each magnetic layer becomes a large value, and high density recording can be achieved without impairing 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, there is a problem that a new pattern (information) is difficult to be heavily loaded into the lower layer, and the S / N of the new pattern is deteriorated 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 non-magnetic 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, Co: 80 to 93 at% as a ferromagnetic Co alloy, Ta or Nb: 1 to 6 at%
When using a CoCrTa alloy or a CoCrNb alloy containing Al, and the direction of the surface facing the magnetic head from the substrate is upward, the Ta or Nb concentration of the lower magnetic layer is lower than the same component concentration of the upper magnetic layer. Is the constitution of the invention.

[0007]

The CoCrTa alloy or the CoCrNb alloy is a ferromagnetic Co alloy having an hcp crystal structure exhibiting uniaxial magnetocrystalline anisotropy (crystal axis exhibiting anisotropy: c axis). A good magnetic recording effect is achieved. Co
It is less than 80 at% or the concentration is defined as 80-93 at%.
If it exceeds 93 at%, the C axis of the Co alloy shifts to random orientation instead of in-plane orientation, which causes deterioration of coercive force and squareness S (Br / Bs), resulting in deterioration of electrical characteristics. Because it is not preferable.

Ta or Nb is contained to promote the segregation of Cr in the CoCr alloy (film) and improve the coercive force. If it is less than 1 at%, such an effect is too small. On the other hand, if it exceeds 6 at%, the Co alloy film formed is not crystalline and becomes amorphous, resulting in a decrease in coercive force. Further, by making the Ta or Nb concentration of the lower magnetic layer lower than the same component concentration of the upper magnetic layer, the coercive force of the lower magnetic layer can be made smaller than the coercive force of the upper magnetic layer. Even if the magnetomotive force from the magnetic head is weakened, the pattern can be easily rewritten, and noise due to the residual pattern before writing can be prevented.

[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. A magnetic recording layer 10 in which magnetic layers 5, 7 and 9 and Cr layers 6 and 8 made of a CoCrTa alloy or CoCrNb alloy having directionality are alternately laminated and the uppermost layer is the magnetic layer 9 is formed. A protective layer 11 is formed on top.

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
C-axis of ferromagnetic Co alloy of magnetic layer 5 formed on it
(Crystal axis showing crystal magnetic anisotropy) is formed for in-plane orientation, and is usually formed to a thickness of about 500 to 2000Å. The magnetic layers 5, 7, and 9 of the magnetic recording layer 10 have a lower Ta or Nb content because the coercive force is weakened from the surface side toward the underlayer side. Incidentally, FIG. 2 shows CoCrTa.
It is a graph showing a change in coercive force when the Ta content is changed while keeping the Co content in the alloy constant, and the coercive force is lower as the Ta concentration is lower. CoCrNb
Similar relationships apply for alloys.

Regarding the thickness of the magnetic layer, the magnetic layers 5, 7, 9 are
The total layer thickness of each layer is 600-800Å, and the layer thickness of each layer is 100Å
The above is preferable. The reason why the total layer thickness is 600 to 800 Å is that a magnetic recording medium having a Br δ of 450 to 600 G · μ is required to secure a reproduction output and reduce noise. It is 100Å that each layer thickness is 100Å or more
This is because if it is less than this, not the continuous film but the alloy portions are scattered like islands, superparamagnetism appears, and the coercive force sharply decreases. 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 alloy of the magnetic layer and for weakening the magnetic interaction between the magnetic layers,
The layer thickness may be about 50 to 250 Å. When it is less than 50 Å, the magnetic interaction between the magnetic layers sandwiching the Cr layer is too strong, so that the reduction of the medium noise due to the multi-layer formation is difficult to appear. On the other hand, 25
This is because when it exceeds 0 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 is added on the non-magnetic protective layer 20.
You may apply about 50Å. The protective layer 11 and the lubricant coating layer may be formed as needed. In addition, Cr on the substrate
As a means for forming the underlayer, the magnetic layer, the Cr layer, and the carbon-based protective layer, sputtering is generally performed, but other physical vapor deposition methods can also be used.

As an industrial film forming method of the Cr underlayer, the magnetic layer, the Cr layer and the non-magnetic protective layer, a sputtering apparatus equipped with a target material for forming a desired layer is installed in parallel and a substrate is formed. May be sequentially moved to each sputtering apparatus to form a laminated film. 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 Cr underlayer 4 of 1200 liters on the Ni-P plated layer as shown in FIG.
On top of that, magnetic layers 5, 7, 9 (each layer thickness 250 Å) having the composition shown in Table 1 are added.
Three layers were laminated through 100Å Cr layers 6 and 8. Further, a carbon layer of 250 Å was formed on top of that.

A DC 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 50 ° C.

[0017]

[Table 1]

(2) The coercive force, medium noise (SNm) and overwrite characteristics 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.

[0019]

[Equation 1]

[0020]

[Table 2]

(3) From Table 2, it can be seen from Example 2 that the Co content is equal to that of the comparative example, although the coercive force is improved as compared with the comparative example, but the O / W value is significantly reduced. Therefore, a remarkable improvement in overwrite characteristics is recognized. It can be seen that the other examples also have high coercive force and excellent overwrite characteristics. The medium noise was almost the same as that of the comparative example.

[0022]

As described above, the magnetic recording medium of the present invention has a recording density because a plurality of magnetic layers made of CoCrTa alloy or CoCrNb alloy having uniaxial crystal magnetic anisotropy are laminated via Cr layers. Also, the reproduction output can be improved. Moreover, since the lower magnetic layer in the magnetic recording layer has a smaller Ta or Nb content and weaker coercive force, even if the magnetomotive force from the magnetic head decreases, a new pattern can be easily formed in the lower magnetic layer. Can be written, and the overwrite characteristic can be improved.

[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 Ta concentration and the coercive force of CoCrTa alloys according to examples.

[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 Yoshinobu Okumura 5-10 Okuhata, Itami City, Hyogo Prefecture Kubota Amagasaki Plant, Itamibu Plant (72) Inventor Yoshiki Takemura 5-10 Okuhata, Itami City, Hyogo Prefecture Co., Ltd. Kubota Amagasaki Plant Itamibu Plant

Claims (1)

[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 ferromagnetic Co alloy is Co: 80 to 93 at%, Ta or N.
b: CoCrTa alloy or Co containing 1 to 6 at%
When CrNb alloy is used and the direction of the surface facing the magnetic head from the substrate is upward, Ta or N of the lower magnetic layer is used.
A magnetic recording medium characterized in that the b concentration is lower than the same component concentration of the upper magnetic layer.