Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2001-03-19
2003-01-21
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S664000, C428S666000, C428S667000, C428S680000, C428S065100, C428S065100, C428S065100, C428S141000, C428S156000, C428S336000, C428S409000, C428S690000, C428S690000, C428S690000, C428S163000, C204S192200, C360S135000
Reexamination Certificate
active
06509108
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a magnetic recording medium. More particularly, the present invention relates to a magnetic recording medium which is particularly used in a magnetic disc apparatus equipped with a flying type magnetic head, which is excellent in a characteristic of friction sliding with a magnetic head, which can improve a reproducing output and a signal-to-noise (S/N) ratio by keeping the low noise of the magnetic recording medium without any change, and which hardly produces bit errors. The present invention also relates to a magnetic disc apparatus in which such a magnetic recording medium is used and which records and reproduces information.
BACKGROUND ART
High-density assembly of a magnetic disc apparatus used as a computer external memory has come to be highly required with the development of information processing technologies. In order to meet the requirements, as is well known, a CSS (contact-stop-and-start) system wherein a magnetic head is contacted with a magnetic recording medium when the magnetic recording medium stops, the magnetic head slides on the medium in the initial stage of starting, the magnetic head then departs from the medium and floats, and the head then flies while maintaining a constant flying distance, has widely been adopted in currently used magnetic disc apparatuses.
Magnetic disc apparatuses based on the CSS system have been variously improved. Specifically, in a reproducing head part of a magnetic disc apparatus, a magnetoresistance effect type head in which a magnetoresistance element changing its resistance in accordance with the intensity of the magnetic field is used, namely, an MR head has been used, in place of a conventional winding type inductive thin film magnetic head. The MR head uses the magnetoresistance effect, that is a change in the resistance of the magnetic material caused by application of an external magnetic field, in the reproduction of signals on a recording medium, and is characterized by the following advantages: a reproducing output amplitude several times as much as that of a conventional inductive thin film magnetic head can be obtained; the inductance is small; and a large S/N ratio can be expected. Moreover, in addition to the MR head, users have begun to use an AMR head utilizing an anisotropic magnetoresistance effect, a GMR head utilizing a giant magnetoresistance effect and a spin bubble type GMR head that is a practical type of GMR head. Note that these magnetoresistance effect type heads are generically referred to as “MR heads, etc.” in the present specification.
Furthermore, a magnetic recording medium to be used in the magnetic disc apparatus is also required to have improved characteristics corresponding to those of the MR head, etc. That is, a magnetic recording medium is required to have an excellent CSS resistance, have a high coercive force (Hc) and have a low noise.
A conventional magnetic recording medium usually has a layer construction as shown by the cross-sectional view in FIG.
1
. That is, a magnetic recording medium
110
comprises a nonmagnetic substrate
101
of aluminum or its alloy, having applied thereon a magnetic recording layer
105
of an alloy that contains cobalt as its major component. Moreover, a nonmagnetic underlayer
104
of chromium or its alloy is sandwiched between the substrate
101
and the magnetic recording layer
105
. The nonmagnetic underlayer
104
is aimed at making the direction of easy magnetization of the magnetic recording layer locate in a film plane of the magnetic recording layer. Furthermore, when the substrate
101
is composed of aluminum or its alloy, an electroless Ni—P plating layer
103
is applied to improve the adhesion of the Cr-based underlayer
104
to the substrate
101
. A protective layer
106
of carbon or the like is formed on the surface of the magnetic recording layer
105
to protect the medium
110
. A lubricating layer (not shown) is generally applied to the protective layer
106
.
As explained above, an electroless Ni—P plating layer is ordinarily formed on the substrate of aluminum or its alloy in a magnetic recording medium. The Ni—P plating layer is formed to lower the friction coefficient between the magnetic head and the magnetic recording medium in the magnetic disc apparatus in which the CSS system is adopted. Stripe-like grooves composed of protruded portions and recessed portions are formed on the surface of the Ni—P plating layer on the substrate in the circumferential direction. That is, as schematically shown in
FIG. 2
, grooves formed of fine protruded portions
3
a
and fine recessed portions
3
b
having shapes different from each other are formed on the surface of the electroless Ni—P plating layer
103
on the substrate
101
. The treatment for forming the recessed and protruded portions is generally referred to as “texture processing” or “texturing”. Texture processing is conducted by pressing grinding abrasive grains or the like to a surface of the rotating substrate to mechanically produce grooves in the circumferential direction or by similar procedures. Moreover, as is well known, the treatment is also aimed at further directing the direction of easy magnetization in the magnetic recording layer to the circumferential direction so that the treatment contributes to the improvement of a S/N ratio.
As of now, the most commonly employed method as the texturing processing is the mechanical texture processing wherein, as explained above, grinding abrasives or the like are pressed to an aluminum substrate plated with Ni—P or others to form grooves. However, since the aluminum used as a substrate and the Ni—P plating layer formed thereon to improve the CSS resistance are relatively soft materials, deep grooves of about 15 to 20 nm depth may be partially formed when grinding abrasive grains or the like are pressed in the processing method. Since a signal output is decreased in such deep groove portions, bit errors are produced.
Recently, since magnetic disc apparatuses have been used for portable applications, glass or ceramic substrates have been used in place of aluminum substrates or the like in order to increase the impact resistance. However, the conventional mechanical texture processing causes the following problems: when a material having no brittleness and having a high hardness such as glass or ceramics is used, accurate and controlled formation of grooves in the circumferential direction cannot be performed; moreover, the processing deteriorates the anisotropy of the axis of easy magnetization in the circumferential direction to lower the S/N ratio. Methods of forming recesses and protrusions without using the mechanical texture processing include a method of chemically etching the surface of a glass substrate, as disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) Nos. 60-136035, 63-225919, etc. However, even this chemical processing method cannot make the magnetic material have anisotropic properties of the axis of easy magnetization in the circumferential direction, and thus there still remains the problem that the S/N ratio is lowered.
DISCLOSURE OF THE INVENTION
An object of the present invention is to solve the above-described prior art problems, thus providing a magnetic recording medium capable of conducting high density recording, in which various nonmagnetic materials including glass and ceramics which are particularly excellent in impact resistance, can be used as a substrate, on which fine recessed and protruded grooves having a high friction sliding characteristic can be formed while the anisotropy of an axis of easy magnetization in the circumferential direction, leading to a low noise and a high S/N ratio, is maintained, and on which formation of deep grooves reaching the substrate surface can be prevented during the formation of the grooves, thereby enabling removal of bit errors.
Another object of the present invention is to provide a magnetic recording medium which can be particularly advantageously used in a magnetic disc apparatus equ
Kitamoto Yoshita
Okuyama Chiaki
Sato Kenji
Yamaguchi Kiyoshi
Yoshida Yuki
Bernatz Kevin M.
Fujitsu Limited
Greer Burns & Crain Ltd.
Thibodeau Paul
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