Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-09-24
2003-03-18
Rickman, Holly C. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S690000, C428S900000
Reexamination Certificate
active
06534204
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 Prior Art
As recording information, which is dealt with in an information processing apparatus, is increased, it is needed to provide a magnetic storage, which is used as an external storage unit of the information processing apparatus, with a compactness and the more large capacity. For this reason, the magnetic storage needs a magnetic storage medium capable of recording at high recording density.
Generally, a magnetic storage medium has a magnetic recording layer on which magnetic information is recorded. A 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 magnetic recording layer. The respective magnetizations of the plurality of ferromagnetic crystal particles 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 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 different direction are mixed on a zigzag basis. This area is referred to as a magnetization transitional region. In order to satisfactorily reproduce magnetic information which is recorded on a magnetic recording layer of a magnetic storage medium at high recording density, there is a need to prepare a small width of the magnetization transitional region.
It is known that the width of the magnetization transitional region is narrower as the thickness of the magnetic recording layer of the magnetic storage medium is decreased. Hence, hitherto, there is made an attempt that the thickness of the magnetic recording layer is decreased, and there is proposed a magnetic storage medium having a multiple zone of magnetic recording layer in which the above-mentioned magnetic recording layer is divided with a non-magnetic layer.
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 regenerative signal is lowered (the medium noise N
m
is increased with respect to the output S of the regenerative signal).
One of the causes of occurrence of the medium noise resides in 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 N
m
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.
In this manner, with the thinner magnetic recording layer and the smaller particle size of the ferromagnetic crystal particles in the magnetic recording layer, a signal representative of magnetic information may be regenerated with higher S/N
m
. For example, when the magnetic recording layer is given 10 nm or so in thickness and the particle size is given 8 nm to 10 nm or so in an in-plane direction of the magnetic recording layer, it is considered that even a signal representative of magnetic information recorded in high recording density on the order of 10 G bit/inch
2
may be regenerated with high S/N
m
.
However, As the thickness of the magnetic recording layer as well as the particle size of the ferromagnetic crystal particles are decreased, energy K
u
·V (anisotropy energy×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. The behavior of the thermal fluctuation phenomenon is determined by ratio of the energy K
u
·V to thermal energy K
B
·T (Boltzmann constant×absolute temperature). Assuming that the thickness of the magnetic recording layer of the conventional magnetic storage medium and the particle size are given by the above-mentioned values, the ratio becomes a small value of the order of 40 to 100 or so at the room temperature (T=300 K). In a case where the ratio is a small value, there occurs the thermal fluctuation phenomenon in magnetization of each of the ferromagnetic crystal particles. Thus, a magnitude of the recording magnetization on one bit cell consisting of the total sum of pieces of magnetization is attenuated. This is associated with a problem that it is difficult to stably maintain for long time magnetic information represented by the recording magnetization.
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 plurality of magnetic recording layers of ferromagnetism; and
(3) a dividing layer of antiferromagnetism for dividing said plurality of magnetic recording layers from one another through intervening between the magnetic recording layer-to-layer.
According to the magnetic storage medium of the present invention as mentioned above, the plurality of magnetic recording layers of ferromagnetism of the item (2) are divided by the dividing layer of the item (3). Thus, each of the divided individual layers of the magnetic recording layers is thinner as compared with a non-divided magnetic recording layer. Generally, in a magnetic storage medium, a width of a magnetization transitional region of a magnetic recording layer is narrowed with thinner magnetic recording layer. This enhances the resolution which is an index indicative of the limit of the recording density of magnetic information recorded on the magnetic recording layer with respect to a fine regeneration. Consequently, the magnetic storage medium of the present invention as mentioned above is suitable for a medium for recording information at high recording density.
According to the magnetic storage medium of the present invention as mentioned above, the plurality of magnetic recording layers of ferromagnetism of the item (2) are in contact with the dividing layer of antiferromagnetism of the item (3). On the interface of the contact, the exchange interaction acts on between magnetization of the respective magnetic recording layers and magnetization of the dividing layer. The existence of the exchange interaction serves to apparently increase magnetic anisotropy energy K
u
of ferromagnetic crystal particles constituting the magnetic recording layer. Thus, the ferromagnetic crystal particles is stabilized in magnetization with respect to thermal fluctuation. Accordingly, magnetic information stored in the magnetic storage medium of the present invention may be stored therein stably for a long time.
In the magnetic storage medium of the present invention as mentioned above, it is preferable that said dividing layer consists of a material having a body-centered cubic structu
Akimoto Hideyuki
Okamoto Iwao
Sato Kenji
Yoshida Yuki
Fujitsu Limited
Greer Burns & Crain Ltd.
Rickman Holly C.
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