Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-08-03
2002-07-30
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S212000, C428S335000, C428S900000
Reexamination Certificate
active
06426157
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a perpendicular magnetic recording medium used as a magnetic disc.
2. Description of the Related Art
Recently, with progress of personal computers and work stations, the hard disc has been required to have a large capacity and small size, i.e., a high density. However, in order to realize a high recording density in the conventional longitudinal direction recording method, there are various problems. For example, if the recording bit is made smaller, there arises a problem of thermal fluctuation of recording magnetization and a problem of high coercive force which may exceed the recording capability of the recording head. To cope with this, a perpendicular magnetic recording method has been studied as means to significantly increase the recording density.
FIG. 156
is a cross sectional view of such a conventional magnetic recording medium. In this perpendicular magnetic recording medium
50
, a perpendicular magnetization film
54
having a perpendicular magnetic anisotropy is formed on a substrate
56
. For example, CoCr alloys are used for the perpendicular magnetization film (Journal of Magn. Soc. Japan, Vol. 8, No. 1, 1984, pp.17-22).
However, in such a conventional perpendicular magnetic recording medium, there has been a problem that medium noise characteristic is very bad in a low recording density region. This is because the perpendicular magnetization film
54
is magnetized perpendicularly, and a demagnetizing field caused by the magnetic poles generated on the medium surface generates a reversed-magnetic domain. The lower is the recording density, the more the reversed-magnetic domains are generated. This has been the main cause to deteriorate the medium noise characteristic in the low recording density region. This medium noise increase in the low recording density region becomes a big trouble when forming a high-density information recording apparatus.
In order to reduce the effect of the demagnetizing field generated by the magnetic pole generated on the medium surface, there has been suggested to provide a soft magnetic layer under the perpendicular magnetization film so as to reduce the magnetic poles generated at the boundary between the perpendicular magnetization film and the soft magnetic layer (Japanese Patent Publication (examined) B58-91). This is generally known as a perpendicular two-layered magnetic recording medium.
However, in this two-layered perpendicular magnetic recording medium, if a perpendicular magnetization film is provided on a soft magnetic layer such as NiFe (Permalloy), there arises a problem that the soft magnetic layer generates a spike-shaped noise, disabling to obtain a preferable medium S/N ratio.
To cope with this, Japanese Patent Publication (unexamined) A59-127235, Japanese Patent Publication (unexamined) A59-191130, Japanese Patent Publication (unexamined) A60-239916, Japanese Patent Publication (unexamined) A61-8719, and Japanese Patent Publication (unexamined) A1-173312 suggest use of a perpendicular magnetization film on a backing layer made from Co or a Co alloy which is more advantageous than use of the permalloy soft magnetic layer.
However, the inventor of the present invention has found that when these soft magnetic films are used, these films easily absorb an external magnetic field generated by a magnetic disc rotation spindle motor. This results in concentration of the magnetic flux in a magnetic head and losing of recording signals. That is, the perpendicular magnetic recording medium of the two-layered film configuration can reduce the effect of the demagnetizing field caused by the magnetic poles generated on the medium surface, but this cannot be a solution for medium noise reduction.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a perpendicular magnetic recording medium having a reduced effect of the demagnetizing field caused by a magnetic poles generated on a perpendicular magnetization film surface and having a preferable medium noise characteristic in a low recording density region.
The perpendicular magnetic recording medium according to the present invention has a perpendicular magnetization film formed on a substrate, wherein a high perpendicular orientation film having higher perpendicular orientation than the perpendicular magnetization film is formed over or/and under the perpendicular magnetization film.
A backing soft magnetic film may be formed under the high perpendicular orientation film, or under the perpendicular magnetic film if there is no high perpendicular orientation film under the perpendicular magnetization film.
It is preferable-that the high perpendicular orientation film have a perpendicular magnetic anisotropic energy Ku [erg/cc] and a saturation magnetization Ms [emu/cc] which are in the relationship R defined as 2Ku/4
&pgr;
Ms
2
equal to or greater than (≧) 1.4.
Moreover, it is preferable that the high perpendicular orientation film have a greater perpendicular magnetic anisotropic energy than that of the perpendicular magnetization film. The perpendicular magnetic anisotropic energy of the high perpendicular orientation film is preferably equal to or greater than 1×10
6
[erg/cc], and more preferably equal to or greater than 2×10
7
[erg/cc]. The high perpendicular orientation film preferably has a thickness equal to or greater than 50 [nm]
The high perpendicular orientation film is preferably made from: a CoCrM alloy (wherein M represent three elements selected from a group consisting of Pt, Ta, La, Lu, Pr, and Sr); an alloy containing RCo
5
(R=Y, Ce, Sm, La, Pr) as a main content; an alloy containing R
2
Co
17
(R=Y, Ce, Sm, La, Pr) as a main content; Ba ferrite (BaFe
12
O
19
BaFe
18
O
27
and the like); Sr ferrite (SrFe
12
O
19
, SrFe
18
O
27
and the like), PtCo, and the like.
The backing soft magnetic film is preferably made from FeSiAl, FesiAl alloy, FeTaN, FeTaN alloy, and the like.
In the perpendicular magnetic recording medium according to the present invention, the perpendicular magnetization film on its upper surface or lower surface a high perpendicular orientation film having a higher perpendicular orientation than that of the perpendicular magnetization film. Accordingly, it is possible to significantly suppress generation of a reversed magnetic domain in the vicinity of the surface of the perpendicular magnetization film.
When the high perpendicular orientation film is made from a CoCr alloy, it is preferable that the perpendicular magnetic anisotropic energy Ku [erg/cc] and the saturation magnetization Ms [emu/cc] be in the relationship as R=2Ku/4
&pgr;
Ms
2
wherein R≧1.4.
On the other hand, when the high perpendicular orientation film is made from a SmCo alloy (i.e., a material other than the CoCr alloy), it is preferable that the high perpendicular orientation film have a perpendicular magnetic anisotropic energy Ku greater than that of the perpendicular magnetization film. This enables to reduce generation of reversed magnetic domain in the vicinity of the surface of the perpendicular magnetization film.
REFERENCES:
patent: 5851643 (1998-12-01), Honda et al.
patent: 6033536 (2000-03-01), Ichihara et al.
patent: 6037052 (2000-03-01), Chen et al.
patent: 6080476 (2000-06-01), Kanbe et al.
patent: 6146776 (2000-11-01), Fukuzawa et al.
patent: 5891 (1983-01-01), None
patent: 59127235 (1984-07-01), None
patent: 59191130 (1984-10-01), None
patent: 60239916 (1985-11-01), None
patent: 618719 (1986-01-01), None
patent: 1173312 (1989-07-01), None
patent: 10-334440 (1998-12-01), None
patent: 11-102510 (1999-04-01), None
“Recording Performances and Preparation of Double Layer Medium for Perpendicular Magnetic Recording” Ouchi et al Journal of Magn. Soc. Japan; vol. 8, No. 1; 1984; pp. 17-22.
Hokkyo Hirotaka
Tagami Katsumichi
Tsuboi Shinzo
Hayes & Soloway P.C.
NEC Corporation
Rickman Holly
Thibodeau Paul
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