Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2000-11-22
2004-02-03
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S690000, C428S336000, C428S900000
Reexamination Certificate
active
06686070
ABSTRACT:
BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to a perpendicular magnetic recording medium which is suitable for high-density magnetic recording and a magnetic recording apparatus using the same.
(ii) Description of the Related Art
A magnetic disk storage device that has been actually used at present utilizes longitudinal magnetic recording. It is the technical problem to form longitudinal magnetic domains at high densities on a longitudinal magnetic recording medium which is easily magnetized in a direction parallel to a disc substrate, parallel to the surface of the disk substrate. To increase an areal recording density, particularly a linear recording density, in this recording mode, it is required to reduce the thickness of a magnetic film for recording while improving the coercivity of the longitudinal magnetic recording medium. When the coercivity is greater than 4 kOe, it becomes difficult to conduct recording by a magnetic head. Meanwhile, when the thickness of the magnetic film made of, for example, a Co alloy is equal to or smaller than 15 nm, intensity of recorded magnetization decreases with time due to thermal fluctuation. The longitudinal magnetic recording essentially has the problem that a magnetization transition region having wide boundaries is formed due to opposing magnetizations of adjacent recording bits. Therefore, mainly due to the above reasons, a technical difficulty is expected in order to achieve an areal recording density of 40 Gb/in
2
or higher.
The perpendicular magnetic recording, in which magnetization occurs in a direction perpendicular to the surface of a thin-film medium, differs from the conventional longitudinal magnetic recording in its recording principle and mechanism for causing a medium noise. Since adjacent magnetizations are antiparallel in the perpendicular magnetic recording, it has drawn attention as a recording mode that is essentially suitable for high-density magnetic recording, and a medium structure suitable for the perpendicular magnetic recording has been proposed. The perpendicular magnetic recording is classified into two types, one of which uses a single-layer perpendicular magnetization film and the other of which uses a perpendicular magnetization film having a magnetic back film formed thereon. The technique using a dual-layer perpendicular magnetic recording medium using the magnetic back film is described in, for example, IEEE Transaction on Magnetics, Vol.MAG-20, No.5, September 1984, pp.657-662, “Perpendicular Magnetic Recording—Evolution and Future”. As the perpendicular magnetic recording medium for this recording mode, there has been considered a medium having a perpendicular magnetization film made of a Co—Cr alloy formed on a soft magnetic back film made of a Permalloy.
To commercialize a magnetic recording apparatus capable of high-density magnetic recording of 40 Gb/in
2
or higher by the perpendicular magnetic recording using the dual-layer perpendicular magnetic recording medium, it is essential to reduce the medium noise, secure a magnetic signal strength from recorded magnetization and improve the recording efficiency of a recording head.
The medium noise is manufactured from both the perpendicular magnetization film and the magnetic back film, and the spike noise manufactured from the magnetic back film has been particularly problematic. An example of such a noise is described in, for example, IEEE Transaction on Magnetics, Vol.MAG-20, No.5, September 1984, pp.663-668, “Crucial Points in Perpendicular Recording”. To deal with such a problem, a method of forming a longitudinal magnetization film underneath the magnetic back film has been proposed in, for example, The Magnetics Society of Japan Journal, Vol.21, Supplement No.S1, pp.104-108, “Improvement in S/N of three-layer perpendicular medium and stability of recording signal”. Such proposals have not been always satisfactory for commercializing a magnetic recording apparatus capable of high-density magnetic recording of 40 Gb/in
2
or higher.
As for securing the magnetic signal strength from recorded magnetization, although the dual-layer perpendicular magnetic recording medium can secure almost twice as much signal strength as the single-layer perpendicular magnetic recording medium having no soft magnetic back layer, it has had a problem with the spike noise which is inherent in the soft magnetic back layer as described above. In a magnetic recording system comprising the dual-layer perpendicular recording medium and a single pole-type recording head, it is necessary for improving the recording efficiency of the recording head to urge the quick regression of a magnetic flux, which has emerged from the recording pole, to the head after passing through the perpendicular magnetization film. For this reason, the soft magnetic back film must be at least several times thicker than the perpendicular magnetization film for recording.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a perpendicular magnetic recording medium for achieving a high-speed and high-density recording density of 40 Gb/in
2
or higher and to facilitate the attainment of a high-density recording and reproducing apparatus, by securing (1) a high-density magnetic recording property, (2) the signal strength from recorded magnetization, and (3) the efficiency of the recording head, which are the characteristics of the magnetic recording system comprising the dual-layer perpendicular magnetic recording medium and the single pole-type recording head, and providing a method for preventing the. production of the noise inherent in the magnetic back layer, which has been a big problem heretofore.
To attain a perpendicular magnetic recording medium having a low-noise property, high recording efficiency of a recording head and a high signal output property from a recording bit, the present invention is constituted by a perpendicular magnetic recording medium having a perpendicular magnetization film formed on a non-magnetic substrate via a magnetic back film, in which the magnetic back film comprises two or more soft magnetic films which are separated at least by a non-magnetic layer, the soft magnetic film closer to the perpendicular magnetization film serves as a soft magnetic keeper layer for keeping perpendicular magnetization, and the magnetization of the soft magnetic film(s) closer to the substrate has magnetization orientation(s) different from the above soft magnetic keeper layer.
The magnetic back film in the dual-layer perpendicular magnetic recording medium serves to (1) increase the intensity of magnetization leaked from the surface of the medium while stabilizing the magnetization recorded on the perpendicular magnetization film and (2) increase the recording efficiency of the recording head. The present inventor has found according to experiments and studies that the conventional problems can be solved with the above features intact by multiplying the soft magnetic back layer in a certain multilayer structure.
A description will be given to the structure and effect of the perpendicular magnetic recording medium according to the present invention with reference to
FIGS. 1 and 2
.
FIG. 1
is a cross-sectional schematic diagram of the perpendicular magnetic recording medium according to the present invention, and
FIG. 2
exemplarily shows the magnetization orientations in the soft magnetic film at the A—A cross-section and the B—B cross-section. In the present invention, as the fundamental structure of the soft magnetic back film, a structure is employed that comprises a soft magnetic film
17
, which serves to increase the intensity of magnetization leaked from the surface of the medium while stabilizing the magnetization recorded on the perpendicular magnetization film, soft magnetic films
13
and
15
supplied for particularly improving the recording efficiency of the recording head, and a non-magnetic layer
16
which is interposed between the film
17
and the films
13
and
15
.
FIG. 1
shows the struc
Futamoto Masaaki
Hirayama Yoshiyuki
Honda Yukio
Kikugawa Atsushi
Yoshida Kazuetsu
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