Stock material or miscellaneous articles – All metal or with adjacent metals – Having magnetic properties – or preformed fiber orientation...
Reexamination Certificate
1999-12-03
2003-05-13
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having magnetic properties, or preformed fiber orientation...
C428S667000, C428S690000, C428S690000, C428S900000
Reexamination Certificate
active
06562481
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic storage medium suitable for a magnetic disk unit for performing recording and regeneration of information.
2. Description of the Related Art
As recording information, which is dealt with in an information processing apparatus, is increased, it is needed to provide magnetic storage, which is used as an external storage unit of the information processing apparatus, with a compactness and the larger capacity. For this reason, the magnetic storage needs a magnetic storage medium capable of recording at high recording density. However, according to the conventional magnetic storage medium, it is known that as magnetic information is recorded at higher recording density, S/N
m
of the recorded magnetic information to the reproductive signal is lowered (the medium noise N
m
is increased with respect to the output S of the reproductive signal).
Generally, a magnetic storage medium has a recording layer on which magnetic information is recorded. One bit of magnetic information is represented by a direction of a total magnetization consisting of an assembly of the respective magnetizations of a plurality of ferromagnetic crystal particles existing in a one bit cell of the recording layer. It may be considered that the magnetizations in the one bit cell are substantially unified in direction in the state that magnetic information is recorded. However, in the event that the magnetization of the adjacent one bit cell is unified in a direction opposite to that of the noticed one bit cell, the direction of the magnetization is reversed through a certain width near a boundary between the adjacent one bit cell-to-one bit cell, but not rapidly changed on the boundary. In an area having such a width, magnetizations oriented in mutually opposite directions are mixed on a zigzag basis. This area is referred to as a magnetization transitional region. One of the causes of the occurrence of the medium noise mentioned above resides in the unevenness of the magnetization.
It is known that the unevenness of the magnetization is caused by a magnetic interaction between crystal particles offering the ferromagnetism. The inventors of the present application proposed a granular magnetic storage medium as a medium in which the magnetic interaction as mentioned above is weakened (Japanese Patent Application Hei. 07-160437). The proposed granular magnetic storage medium has a recording layer in which a plurality of ferromagnetic crystal particles, which consist of an Fe or Fe system-alloy or a Co or Co system-alloy, are dispersed in a non-magnetic material which is of a non-solid solution to those alloys, and are mutually isolated. Thus, the mutual isolation between the plurality of ferromagnetic crystal particles may substantially completely divide the magnetic interaction between the ferromagnetic crystal particles into parts, and thereby reduce the medium noise due to an unevenness of the magnetization in the magnetization transitional region.
The medium noise occurs also owing to an unevenness of a particle size of the ferromagnetic crystal particles. It is considered that the regenerative output is in proportion to the sum total of the volume of ferromagnetic crystal particles. Hence, as the average particle size of one bit cell becomes large, unevenness of a particle size becomes also large. As a result, unevenness of the regenerative output becomes large and thus the medium noise is increased. Therefore, it is considered that the medium noise Nm of the magnetic storage medium is decreased in such a manner that the particle size of the ferromagnetic crystal particles is controlled in the magnetic recording layer of the magnetic storage medium, so that S/N
m
is improved.
However, with respect to the magnetization recorded on the ferromagnetic crystal particles in which the magnetic interaction is divided into parts and magnetically isolated, as the particle size of the ferromagnetic crystal particles is decreased, the energy K
u
·V (anisotropy energy x volume of particle) representative of a degree of easy orientation of magnetization of the particle into a predetermined direction is reduced. When the energy K
u
·V is reduced, a thermal fluctuation phenomenon wherein a direction of magnetization fluctuates owing to the heat will occur. Consequently, in a case where the particle size of the ferromagnetic crystal particles is less than a predetermined size, there occurs, even in the room temperature, the thermal fluctuation phenomenon in magnetization of each of the ferromagnetic crystal particles. This is associated with a problem that the recording magnetization on a one bit cell consisting of the total sum of pieces of magnetization of the ferromagnetic crystal particles disappears.
In order to maintain the energy K
u
·V with a large value while the volume of ferromagnetic crystal particles is reduced, it is considered that one having the large anisotropy energy K
u
is adopted as the material of the ferromagnetic crystal particles. However, with a conventional recording head now generally used, it is difficult to generate such a strong magnetic field that the magnetization of the crystal particles having such a large anisotropy energy K
u
is reversed. This is associated with a problem that an overwrite characteristic (O/W) of a magnetic storage medium, which is represented by a ratio of magnitudes of a reproductive output of magnetic information remained at the time of re-recording of magnetic information and a regenerative output of magnetic information newly recorded, is deteriorated.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide a magnetic storage medium capable of recording information at high recording density and also to regenerating the information with a high quality of signal (high S/N
m
), and in addition contributing to the elongation of a life span of the recorded information.
To achieve the above-mentioned objects, the present invention provides a magnetic storage medium comprising:
(1) a non-magnetic substrate;
(2) a recording layer in which a plurality of crystal grains consisting of a ferromagnetic material are dispersed in a non-magnetic material and axes of easy magnetization of the plurality of crystal grains are oriented in parallel to the layer,
wherein each of the plurality of crystal grains dispersed in the recording layer is a columnar shaped grain which penetrates a surface of said recording layer and has height of 30 nm or less, and a mean value of grains diameter of said recording layer is 15 nm or less.
Furthermore, (K
u
·V)/(k
B
·T) is preferably not less than 60 where (K
u
·V)/(k
B
·T) denotes a ratio of a product of a mean value K
u
(unit: erg/cm
3
) of anisotropy energies of the plurality of crystal grains and a mean value V (unit: cm
3
) of volumes of the plurality of crystal grains to a product of Boltzmann constant k
B
(unit: erg/K) and temperature T (unit: K), and a mean value H
K
of anisotropic magnetic fields of the plurality of crystal grains is 20 kOe or less.
As a magnetic storage medium of the next generation, a magnetic storage medium having a high recording density exceeding 10G bit/inch
2
is desired. A size of one bit cell of the magnetic storage medium having a recording density exceeding 10G bit/inch
2
is 100 nm×600 nm or so.
In the event that such a large size of one bit cell is provided, a magnetic storage medium of the present invention has characteristics set forth below.
First, according to the magnetic storage medium of the present invention, a mean value of grain sizes of the plurality of crystal grains in an internal direction of the recording layer is kept below 15 nm. This feature makes' it possible that the magnetic storage medium offers a high S/N
m
not less than 25 dB in which magnetic information to be stored is reproduced with great accuracy. Further, in the event that the plurality of crystal grains have such a grain size, the thickness of the recording layer is kept b
Kaitsu Isatake
Okamoto Iwao
Sato Hisateru
Fujitsu Limited
Greer Burns & Crain Ltd.
Rickman Holly
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