Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1999-11-03
2002-09-24
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S690000, C428S690000, C428S690000, C428S900000, C360S059000, C360S116000, C365S122000, C369S275200, C369S275300
Reexamination Certificate
active
06455174
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic recording medium comprising a magnetic film having perpendicular magnetization, the magnetic film being used for a recording layer. The present invention also relates to a recording and reproducing head and a magnetic recording and reproducing method for such a magnetic recording medium. In particular, the present invention relates to a magnetic recording medium on which any disappearance of data, which would be otherwise caused by the thermomagnetic relaxation phenomenon, is prevented or suppressed, and recording and reproduction can be performed at a surface recording density of not less than 20 Gbits/in
2
. The present invention also relates to a recording and reproducing head and a novel magnetic recording and reproducing method which are preferably used to perform recording and reproduction on such a magnetic recording medium.
2. Description of the Related Art
The hard disk (magnetic recording medium) is widely used as an external storage medium for computers and the like. Usually, the longitudinal magnetic recording is adopted for the hard disk, in which information is recorded in parallel to a recording film surface by using, for example, a ring-shaped magnetic head (hereinafter referred to as “ring head”) carried on a floating type slider.
In recent years, a variety of data including, for example, graphic data, animation data, and document data are processed in various ways in advanced manners, in which a huge amount of information is dealt with. In order to successfully deal with such a huge amount of data, one of the most important technical tasks in the field of hard disk is to increase the surface recording density. At present, the hard disk has achieved a surface recording density of 4 Gbits/in
2
.
A means for achieving the high density process has been suggested, for example, in
IEEE Transactions on Magnetics
, Vol. MAG-15, No. 6, pp. 1456-1458 (1979). This document describes a perpendicular magnetic recording system and a perpendicular magnetic recording medium which are based on the use of a recording film of a Co—Cr film having perpendicular magnetization so that information is recorded in the perpendicular direction with respect to a recording film surface.
In order to further increase the surface recording density of the hard disk, it is known that the magnet (magnetic particle), which is a recording unit for constructing the recording layer, is allowed to have a small size. However, if the magnetic particles are allowed to have a minute size so that the surface recording density is increased to be not less than 10 to 20 Gbits/in
2
, the following problem arises. That is, the magnetic particles become unstable due to the thermomagnetic relaxation phenomenon, and the recorded data disappears.
SUMMARY OF THE INVENTION
The present invention has been made in order to solve the problem involved in the conventional technique as described above, an object of which is to provide a magnetic recording medium in which minute magnetic particles successfully exist in a stable manner, and information subjected to fine recording can be reproduced at a high S/N ratio, even when the surface recording density is increased by using the minute magnetic particles to serve as the recording unit.
Another object of the present invention is to provide a recording and reproducing head which is preferably used to record and reproduce information by using the magnetic recording medium as described above.
Still another object of the present invention is to provided a novel magnetic recording and reproducing method in which information is recorded at a super high density by using the magnetic recording medium and the recording and reproducing head as described above, and the recorded information can be reproduced at a high SIN ratio.
According to a first aspect of the present invention, there is provided a magnetic recording medium comprising:
a substrate;
a recording holding layer composed of a magnetic material; and
a recording layer composed of a ferri-magnetic material having perpendicular magnetization, wherein:
information is recorded by applying a recording magnetic field while heating a predetermined area of the magnetic recording medium so that a recording magnetic domain in the recording layer is inverted, and the information is reproduced by detecting a magnetic field obtained from the recording magnetic domain in the recording layer.
The magnetic recording medium of the present invention includes the recording layer which is formed of the ferri-magnetic material having the perpendicular magnetization, and the recording holding layer which is formed of the magnetic material. The recording holding layer can be composed of, for example, a ferri-magnetic material and an antiferromagnetic material. The recording holding layer is preferably provided between the substrate and the recording layer. Especially, it is preferable that the recording holding layer is provided so that it makes contact with the recording layer with each other. When the recording holding layer is provided as described above, the recording holding layer makes exchange coupling with the recording magnetic domain of the recording layer to hold the recording magnetic domain in a stable state in the perpendicular direction. Those preferably usable as the ferri-magnetic material for the recording holding layer include, for example, rare earth-transition metal alloys such as TbFeCo, GdTbFeCo, TbFeCoCr, TbFe, GdFeCo, GdTbFe, and DyTbFe. Those preferably usable as the antiferromagnetic material for the recording holding layer include, for example, transition metal (Cr, Mn, Fe, Co, Ni) alloys, alloys of noble metal (Au, Pt, Rh, Pd) and transition metal (Cr, Mn, Fe, Co, Ni), and transition metal oxides. For example, it is preferable to use FeMn, NiO, NiMn, PtMn, FeNiMn, AuMn, ZnZr, and FeRh.
Concerning the magnetic recording medium of the present invention, in order to ensure the thermal stability of the recording magnetic domain in the recording layer, it is necessary that the recording layer has a coercive force of not less than 5 kOe within a temperature range from the room temperature (about 10° C.) which is the preservation temperature for the medium, approximately to the temperature in the apparatus (about 100° C.). Therefore, it is preferable that the recording layer has a coercive force of not less than 5 kOe in a temperature range of 10° C. to 150° C. However, there is no limitation thereto when a reproducing layer is used to increase the magnetic field from the recording layer as described later on. Further, when the information recorded in the recording layer is reproduced, the magnetic field, which is generated from the recording magnetic domain of the recording layer, is detected. Accordingly, it is advantageous to use a recording layer having a high Curie temperature. Therefore, in order to obtain a sufficient magnetic field intensity from the recording magnetic domain at a temperature in the vicinity of the reproducing temperature, it is preferable that the recording layer has a Curie temperature of not less than 300° C.
As described above, when the recording layer having the large coercive force within the temperature range of 10° C. to 150° C. is used, even if the minute recording mark is formed in the recording layer, then the disappearance of the recording mark is suppressed, which would be otherwise caused by the thermomagnetic relaxation phenomenon after the recording. During the recording, the coercive force of the recording layer can be decreased by heating the magnetic recording medium to a temperature of not less than 200° C. Therefore, the recording can be performed with ease by using a weak applied magnetic field. When the recorded information is reproduced, the magnetic field from the recording magnetic domain in the recording layer is directly detected by using, for example, a magnetic resistance element to reproduce the information. In other words, the magnetic recording medium of the present
Awano Hiroyuki
Imai Susumu
Shimazaki Katsusuke
Takao Hiroki
Yamazaki Yuji
Hitachi Maxell Ltd.
Kiliman Leszek
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