Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-06-30
2003-05-27
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S692100, C428S900000
Reexamination Certificate
active
06569545
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention:
This invention concerns a magnetic storage device, concretely the magnetic storage device having the recording density over 5 gigabits per square inch and the magnetic recording medium to realize the magnetic storage device having the high output, low noise and high stability caused by suppressing the attenuation of output by moderating the thermo-magnetization.
2. Description of the Related Art:
Recently, because the recording density has been improved in the magnetic storage device for the computer, more and more noise reduction and high coercivity have been required. The minimizing the crystal grain size in the magnetic layer and the reduction of the magnetic combination of interparticles are effective for the media noise reduction. As a method for minimizing the magnetic crystal grain, forming the new layer (for example, called the seed layer) is being tried. For example of the new layer, it is shown in Japanese Open Patent Application H4-153910, that seed layer of amorphous or very small grain which consists from a kind of Y,Ti,Zr,Hf,V,Nb,Ta,Cr,Mo,W is formed. It is shown in Japanese Open Patent Application H7-73441 that magnetic crystal grain is minimized and media noise is reduced by forming seed layer of amorphous which consists from Cr or V.
A small magnetism crystal grain receives the effect of the heat disturbance. So, the phenomenon that the recorded magnetization disappears with the passage of the time becomes remarkable.
Therefore, extremely small magnetism crystal grains are not desirable because the reliability is down when the recorded data is preserved in the long term. Also, when magnetism crystal grains are minimized and the magnetic combination of the interparticle is strong, many magnetism crystal grains are inverted their magnetic direction at the same time. So the effect of reducing noise can not be obtained. So, it is necessary to reduce the exchange interaction between magnetic particles. For this purpose, it is effective to increase Cr concentration in the magnetic layer and to increase the nonmagnetic segregation region of the interface of the magnetic particles. But, magnetization reduces when the Cr concentration increases. So, the record and reproduction output reduces so much that good record and reproduction characteristic can not be obtained.
In the meantime, S. H. Liou proposed a medium that the crystal grain Fe dispersing in the amorphous SiO2 takes the Granular structure. (S. H. Liou and C. L.Chien: Appl. Phys. Lett. 52(6), Feb. 8, 1988) The Granular medium (i.e. the medium which magnetic layer takes Granular structure) has characteristics that the magnetic interaction between the magnetic particles is weak because the magnetic crystal grains are separated by the nonmagnetic phase and media noise is low because the magnetic crystal grains are very small.
As another prior art, it is shown in Japanese Open Patent Application H7-311929 that the Granular medium has a magnetic layer with magnetic crystal grains of Co alloy and nonmagnetic phase of Al2O3, TiO2, ZrO2, Y2O3. But there is a problem in Japanese Open Patent Application H7-311929 that the high coercive force is not obtained because magnetic crystal grains are too small.
It is shown in Japanese Open Patent Application H7-98835 and Japanese Open Patent Application H8-45073 that the high coercivity is realized by applying the alternating current bias during forming a film or it is heat-treated in the vacuum after forming a film.
SUMMARY OF THE INVENTION
But in the Granular medium, magnetic crystal grains are small and C axis which is easy magnetic orientation axis of magnetic crystal grains has randomly been orientated. So, as it is above-mentioned, coercive force improves to some extent by applying the alternating current bias or heat-treating. But the coercive force obtained from this Granular medium is not sufficient for the high density recording over square inch 5 gigabits. So, good record and reproduction characteristic can not be obtained because of reproduction output is low in recording at high recording density but noise is low. Furthermore, magnetic crystal grains: are so small that the phenomenon that the thermomagnetization redueases is very remarkable and the sufficient reliability in the high recording density region can not be obtained.
As is mentioned above, the Granular medium of prior art is a low noise medium but sufficient stability for the heat disturbance is necessary for the Granular medium to realize the high recording density.
A purpose of this invention is to get high coercivity and high coercivity squareness in the low noise medium which magnetic layer takes Granular structure by giving the magnetic anisotropy to circumferential direction of magnetic crystal grain in the magnetic layer. By this, it is possible to get the magnetic recording medium which has high reproducing output in high recording density and the sufficient stability for the reduction of thermomagnetization.
Furthermore, if this medium is combined with the supersensitive magnetic head and the condition of the magnetic storage apparatus is optimized, it is possible to get the magnetic storage with the high reliability and the recording density over 5 gigabits per 1 inch.
Above mentioned purpose can be obtained by the magnetic storage apparatus which comprising a magnetic recording medium having a magnetic layer with Granular structure and a magnetic crystal grain in the magnetic layer with circumferentially magnetic anisotropy, means for moving said magnetic recording medium in the recording direction, the magnetic head having recording part and reproduction part, means for moving said magnetic head relatively to said magnetic recording medium and means for processing the recording and reproduction signal which inputs the signal to said magnetic head and reproducing the signal output from said magnetic recording medium wherein said reproduction part of the magnetic head is magnetoresistive magnetic head.
The Granular structure is that magnetic crystal grains are separated by nonmagnetic phase in a magnetic layer.
The typical crystal grain image of an embodiment of the magnetic recording medium is shown in
FIG. 1
that is showing the grain boundary drawn the line along based on TEM image of the surface of magnetic layer observed by the transmission electron microscopy(TEM).
Adjoining magnetism crystal grain has been over 1 nm to each other and it is observed clearly that the nonmagnetic phase exists between crystal grain.
The shape of the magnetic crystal grain is approximately a sphere or an ellipsoid. The thickness of magnetic crystal grain (the length of the direction which is perpendicular on the surface of a film) is smaller than the thickness of the magnetic film.
However, some crystal grains with the hemisphere or the semi-ellipsoid shape in growing process near the surface of the magnetic layer may exist. Some magnetic crystal grains with the conic, hemisphere or the semi-ellipsoid shape in initial growing process may exist that grow on the crystal grain of under layer epitaxially. To get these magnetic crystal grains, hcp (hexagonal closed packed) structure which comprised of Co as a main component is used. Especially, to get higher coercive force, it is desirable that the magnetic layer includes Pt to over 20 at %. Furthermore, it is desirable that the magnetic layer are comprised of the alloy including rare earth like Nd,Sm,Pr, etc to get higher coercive force. As the alloy including rare earth, the alloy comprising of rare earth metal and transition metal which shows the high crystal magnetic anisotropy like SmCo, FeSmN, NdFeB, PrFeN is desirable and either amorphous or crystal grains can be used as the alloy.
As the nonmagnetic layer, it is possible to use oxides such as Al2O3, SiO2, Ta2O5, TiO2 and ZrO2 or non- solution elements to Co such as C and Ag, etc. The good contact start stop characteristics (the CSS characteristics) is obtained by the oxides such as Al2O3, SiO2, Ta2O5, TiO2 and ZrO2 . The corrosion resistance is more
Hosoe Yuzuru
Kanbe Tetsuya
Matsunuma Satoshi
Shiroishi Yoshihiro
Takahashi Yoshio
Mattingly Stanger & Malur, P.C.
Rickman Holly
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