Metal treatment – Stock – Magnetic
Reexamination Certificate
2001-01-08
2003-08-19
Rickman, Holly (Department: 1773)
Metal treatment
Stock
Magnetic
C148S302000, C148S313000, C148S315000, C420S436000, C428S611000, C428S668000, C428S900000, C428S690000
Reexamination Certificate
active
06607612
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a magnetic alloy, a magnetic recording medium and a method of producing the same, a target, and a magnetic recording device and, more particularly, to a magnetic alloy which has a high normalized coercive force, suppresses thermal agitation and also has thermally stable magnetic characteristics, a magnetic recording medium and a method of producing the same, a target for forming a magnetic film, and a magnetic recording device comprising the magnetic recording medium. The magnetic alloy and magnetic recording medium of the present invention are suited for use as hard disks, floppy disks, and magnetic tapes.
BACKGROUND ART
Although magnetic recording media have widely been employed as recording media having high density and large capacity in hard disk devices, recently, an improvement of recording/reproduction characteristics has been required to increase the recording density.
FIG.
19
and
FIG. 20
are schematic views showing a hard disk as an example of a magnetic recording medium.
FIG. 19
is a perspective view showing the whole body of a disk type magnetic recording medium, while
FIG. 20
is a cross-sectional view taken along lines A-A′ of the magnetic recording medium shown in FIG.
19
.
The magnetic recording medium
50
shown in
FIG. 19
is composed of a substrate
51
made of a disk type non-magnetic substance, and an underlayer
54
, a recording layer
55
and a protective layer
56
, which are formed on the substrate
51
.
In the magnetic recording medium
50
of this example, for example, a substrate comprising a base
52
made of an Al alloy, and a non-magnetic layer
53
made of Ni—P provided on the surface of the base
52
is used as the substrate
51
made of the non-magnetic substance. As the substrate
51
, a base made of glass is sometimes used. On the substrate
51
, an underlayer
54
made of Cr, a recording layer
55
made of a magnetic film of CoCrTa or CoCrTaPt, and a protective layer
56
made of C (carbon) are laminated in order. The protective film
56
is sometimes coated with a lubricating film made of a fluororesin such as perfluoropolyether. In the cross-sectional structure shown in
FIG. 20
, a lubricating film is omitted.
With respect to the magnetic film, which constitutes the recording layer
55
in this kind of magnetic recording medium
50
, a magnetic film made of a CoNiCr alloy (having Hc of about 1200 Oe) has been used in first generation magnetic recording media and a magnetic film made of a CoCrTa alloy with a composition which is close to Co
84-86
Cr
10-12
Ta
4
has been used in second generation magnetic recording media and, furthermore, a magnetic film (having an Hc of about 1800 Oe) made of a CoCrTa alloy with a composition close to Co
78-80
Cr
15-17
Ta
5
has been used in third generation magnetic recording media and a magnetic film made of a CoCrTaPt alloy with a composition close to Co
54-77
Cr
16-22
Ta
2-4
Pt
5-10
has been used in fourth generation magnetic recording media.
These changes in generations were caused by the requirements for more excellent magnetic characteristics for the magnetic film to be used in keeping with improvements in the recording density of magnetic recording media, resulted in the development of various materials.
By the way, the present inventors had already learned that, even if a magnetic film made of an alloy having the above magnetic characteristics is formed on a substrate, only a coercive force which is drastically smaller than the coercive force that the film should ideally exhibit, is obtained in the magnetic film. For example, it can be surmised that the coercive force of about 3000 Oe of an isotropic medium can; be exhibited by a CoNiCr alloy and a coercive force of about 2500 Oe can be exhibited by a CoCrTa alloy. However, it is considered that a magnetic films having a coercive force which is far smaller than the above values are sometimes obtained in magnetic films made of these alloy materials obtained by a general film forming process and only a magnetic film having a half or less of the ideal coercive force are obtained in some cases.
Therefore, the present inventors have intensively studied intensively methods of producing magnetic films made of CoCrTa and CoCrTaPt alloys, which are exclusively used at present, in order to cope with the increase of the recording density of magnetic recording media and found a method capable of significantly improving the magnetic characteristics of these magnetic films. They termed this method an ultra clean process and various patent applications were filed (see U.S. Pat. No. 5,853,847 and National Application PCT/JP94/01184). According to the technology of the above patent, it is made possible to obtain a CoNiCr magnetic film or a CoCrTa magnetic film having a high coercive force within a range from 2700 to 3000 Oe by purifying the film forming atmosphere and control the ultimate vacuum degree to 3×10
−9
Torr (400×10
−9
Pa) or less and by dry-eyching using an Ar gas containing about 1 ppb of impurities such as H
2
O, the surface of the substrate, on which an underlayer of Cr is formed, to remove impurities such as oxides from the surface of the substrate. This kind of a magnetic film obtained by general film forming processes usually exhibits a coercive force within a range from about 1500 to 2000 Oe.
However, considerable progress has been made in magnetic recording media and it is required to develop a more excellent magnetic film in place of the CoCrTa alloy magnetic film or CoCrTaPt alloy magnetic film. It is also required to develop a magnetic film which exhibits excellent magnetic characteristics under general film forming conditions without using the above ultra clean process.
An object of the present invention is to provide a magnetic alloy which has a high normalized coercive force, suppresses thermal agitation and also has thermally stable magnetic characteristics, or a magnetic recording medium comprising a magnetic film made of the alloy.
Another object of the present invention is to provide a method of producing a magnetic recording medium having the above characteristics.
Still another object of the present invention is to provide a target suited for use in the production of a magnetic recording media having the above characteristics.
Yet another object of the present invention is to provide a magnetic recording device comprising a magnetic recording medium having the above excellent characteristics.
DISCLOSURE OF THE INVENTION
The magnetic alloy of the present invention is a magnetic alloy consisting essentially of cobalt (Co), chromium (Cr) and germanium (Ge), the composition of said magnetic alloy being represented by the general formula:
Co
x
Cr
y
Ge
z
where x, y and z, which represent the composition ratio, satisfy the relationships: 78≦x≦87, 2.5≦y≦25, 2≦z≦15, and x+y+z=100 (provided that x, y, and z represent the composition ratio in terms of atomic %).
According to the magnetic alloy with the above composition, it is possible to obtain a magnetic alloy which has magnetic characteristics capable of accommodating increases in recording density, i.e. both a high normalized coercive force and magnetocrystalline anisotropy, and also has a more excellent magnetic anisotropy field.
In the present invention, the composition ratio can preferably satisfy the relationships: 82≦x≦87, 2.5≦y≦13, and 2.5≦z≦14.
With a composition within the above range, the relationship 4&pgr;Ms/H
k
grain
≦1.0, which is the condition required to obtain a high normalized coercive fore(Hc/H
k
grain
) of 0.35 or more, is secured to obtain a magnetocrystalline anisotropy (K
u
grain
) of 1.5×10
6
erg/cm
3
or more, thus making it possible to form a magnetic alloy which also has thermally stable magnetic characteristics.
The magnetic alloy of the present invention is a magnetic alloy consisting essentially of cobalt (Co), chromium (Cr), germanium (Ge), and an element T (T represents one or more of the elements of Ta, Si,
Rickman Holly
Takahashi Migaku
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