Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2000-03-10
2003-04-08
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S332000, C428S336000, C428S611000, C428S665000, C428S667000, C428S670000, C428S690000
Reexamination Certificate
active
06544667
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is related to a magnetic recording medium on which large capacity information can be recorded, a producing method of the medium, and a magnetic recording system. Especially, the present invention is related to a magnetic recording medium which is suitable for high density magnetic recording, and producing method of the medium, and a large capacity magnetic recording system using this magnetic recording medium.
Today, it is strongly required to increase storage capacity of a magnetic recording system. To reproduce signals from fine recorded bits, in relation to a magnetic head, a composite type head is being employed rapidly in which a magnetoresistive head (MR) having higher efficiency than a conventional inductive head is used as a reproducing element. Further, to obtain higher efficiency, a head which utilizes very large magnetoresistive effect (giant magnetoresistive effect or spin valve effect) produced in a multi-layered magnetic layer in which plural magnetic layers are piled up with insertion of a non-magnetic layer between the magnetic layers, is being used actually. On the other hand, to obtain a magnetic recording medium on which high density magnetic recording is possible, it is required that out put voltage at high linear recording density region is increased and that medium noise is decreased simultaneously. Especially, being accompanied by employing of a high efficiency magnetic head, it is strongly required for a magnetic recording medium to decrease its medium noise.
As a magnetic recording medium, a in-plane magnetic recording medium is used which comprises a Co-based alloy magnetic layer as follows: CoNiCr, CoCrTa, CoCrPt, CoCrPtTa, CoCrPtB, CoCrPtTaB, etc. Especially, a Co-based alloy magnetic layer containing Pt has high coercivity and high output voltage at high linear recording density region, therefore, it is suitable for high density magnetic recording. These Co-based alloy have hexagonal closed packed structure (h c p structure) of which c axis is easy magnetization axis, and, to use as a in-plane magnetic recording medium, it is desired that the c axis is oriented to in-plane direction. Therefore, it is a generally used method that an underlayer having body-centered cubic structure (b c c structure) is formed on a substrate first, then a Co-based alloy magnetic layer is grown with epitaxial growth mode on the underlayer, and the c axis is oriented to in-plane direction as a result.
As the underlayer, Cr is used generally, but, when a magnetic layer contains large atoms such as Pt, etc., methods to orient c axis of a magnetic layer along parallel direction to the film surface, are disclosed, in which lattice matching between a magnetic layer and an underlayer is improved by using Cr alloy underlayer of which lattice space is increased with addition of Ti to Cr (disclosed in Japanese patent publication number 63-197018) or with addition of V to Cr (disclosed in U.S. Pat. No. 4,652,499).
About materials of the underlayer besides the above mentioned materials, it is disclosed in Japanese patent publication number 63-187416 that extensive materials including Mo, W, Hf, etc. can be used. Especially, a Cr-based alloy to which Ti is added, as described in Journal of Applied Physics (J. Appl. Phys.), vol. 79, pp5351-5353, has fine crystal grains and accordingly has low medium noise, therefore it is a suitable underlayer material for high density magnetic recording. Further, it is disclosed in Japanese patent publication number 63-187416 that signal to noise ratio and reproduced signal modulation can be improved by forming an underlayer consisting of double layers. An example of the underlayer having double layers structure is disclosed in Japanese patent publication number 7-73427 and 8-30954, in which 2
nd
underlayer consisting of a Cr-based alloy with additive elements Mo, Zr, Ta, V, Nb, Ti, is formed on 1
st
underlayer comprising Cr. Further, as disclosed in Japanese patent publication number 10-74314, medium noise is decreased by providing a Co-based non-magnetic alloy layer under the above-mentioned underlayer. As disclosed in Japanese patent publication number 10-143865, medium noise is decreased even more and in a stable manner because Cr or Zr having high oxidation tendency is contained in this Co-based non-magnetic alloy layer and its surface is oxidized a little by exposing the surface in oxygen atmosphere. A magnetic recording medium in which a Cr-based underlayer having b c c structure is formed on Cr-based composite film (seed layer) containing Zr, Ti, etc., is disclosed in Japanese patent publication number 9-265619 and 10-214412.
According to the above mentioned conventional technologies, as a magnetic recording medium to be suitable for high density magnetic recording, a magnetic recording medium which comprises a Co-based alloy magnetic layer containing Pt to obtain high coercivity easily in combination with a CrTi alloy underlayer to be able to have small crystal grains, is considered. But, the magnetic recording medium having such structure has technological problems that in-plane orientation of c axis in the magnetic layer is loose and that squareness of magnetization curve or coercivity squareness is easy to decrease. If coercivity squareness s* becomes excessively small, output voltage at high linear recording density is decreased. Especially, this tendency is remarkable in the case of magnetic layers comprising CoCrPtTa alloy, CoCrPtB alloy, or CoCrPtTaB alloy to which a lot of Pt and Ta, or Pt and B are added to obtain high crystal magnetic anisotropy field required to have high coercivity.
SUMMARY OF THE INVENTION
It is 1st object of the present invention to solve the above mentioned problems and to provide a magnetic recording medium having high signal to noise ratio at high recording density region.
It is 2nd object of the present invention to provide a producing method which produces with high repeatability a magnetic recording medium having high signal to noise ratio at high recording density region.
It is 3rd object of the present invention to provide a small size large capacity magnetic recording system having high recording density over 5 Gbits per square inch (5 Gbits/in
2
).
To solve the above mentioned problems, the inventors of the present invention examined a lot of magnetic recording media with various structures and it was found that, by forming 2nd Cr-based alloy underlayer containing at least one element selected from a group comprising Mo and W between a magnetic layer and a Cr-based alloy underlayer containing Ti, the c axes of the magnetic layer were oriented along parallel direction to the film surface and the crystal grain diameters were decreased, namely superior results were obtained.
As a results of analyzing by X-ray diffraction a crystalline structure of a magnetic layer with addition of Pt and Ta, or Pt and B which was formed directly on a CrTi underlayer, it was confirmed that the underlayer had b c c structure and its {001}surface was oriented along parallel direction to the film surface. And, it was also confirmed that the magnetic layer formed on the underlayer had h c p structure and c axes of the magnetic layer was oriented along vertical direction to the film surface. Generally, It is well known that a magnetic layer having h c p structure with (11.0) orientation grows generally in epitaxial mode on a underlayer having b c c structure with (001) orientation as above mentioned. The above mentioned orientation is differ from this, and it is considered that the epitaxial growth is prevented by some reasons. In the case of using CrMo or CrW underlayer instead of the CrTi underlayer, it was confirmed that a magnetic layer having h c p structure with (11.0) orientation grew in epitaxial mode on a underlayer with (001) orientation, therefore, it is supposed that adding Ti caused chemical or structural variation on the surface of the underlayer, and this affected the epitaxial growth.
In the case of using CrMo or CrW underlayer, the crystal grain d
Hosoe Yuzuru
Kato Akira
Matsuda Yoshibumi
Sakamoto Koji
Suzuki Hiroyuki
Bernatz Kevin M.
Mattingly Stanger & Malur, P.C.
Thibodeau Paul
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