Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-06-19
2004-05-11
Ometz, David (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C428S690000, C428S900000
Reexamination Certificate
active
06735057
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of magnetic recording/reproducing. More particularly, the present invention relates to a method of magnetic recording/reproducing which attains a high S/N ratio in a system in which signals recorded in a coated-type magnetic recording medium (i.e., a magnetic recording particulate medium) for high-density recording are reproduced with an MR head.
BACKGROUND OF THE INVENTION
In the field of magnetic disks, 2-MB MF-2HD floppy disks employing a cobalt-modified iron oxide have come to be mounted as a standard external storage medium in personal computers. However, as a result of the recent rapid increase of the quantity of data to be dealt with, the capacity of the floppy disks has become insufficient. There has hence been a desire for a capacity increase in floppy disks.
In the field of magnetic tapes also, investigations are recently being made enthusiastically on magnetic tapes as external storages for recording computer data (the so-called backup tapes), with the spread of minicomputers, personal computers, and office computers such as work stations. For practically using magnetic tapes in such applications, there is an especially strong desire for an improvement in recording capacity for attaining an increased recording capacity and a reduced recording-medium size, besides the desire for a size reduction and an increase in information-processing ability in computers.
Magnetic recording media heretofore in wide use comprise a nonmagnetic support and, formed thereover by coating, a magnetic layer comprising a binder and dispersed therein iron oxide, cobalt-modified iron oxide, CrO
2
, ferromagnetic metal particles, or hexagonal-ferrite particles. Of these magnetic materials, fine particles of hexagonal ferrites are known to have excellent high-density recording characteristics. However, in recording/reproducing with an inductive head which has hitherto been mainly used in the systems employing flexible media, the fine particles of a hexagonal ferrite have a low saturation magnetization and a sufficient output has not been obtained therewith.
In the removable recording employing such flexible media, however, the magnetoresistive heads (MR heads) in use with hard disks have come to be used. Since MR heads have high sensitivity, a sufficient reproduction output is obtained even with use of fine particles of a hexagonal ferrite. It is known that due to the noise reduction characteristic of hexagonal ferrites, a high C/N ratio is obtained. For example, Japanese Patent Application (Laid-Open) No. 302243/1998 discloses a technique which employs fine particles of barium ferrite (BaFe) and uses an MR head for reproduction.
The design of the MR heads heretofore in use is based on a thin magnetic film or acicular ferromagnetic alloy particles, and there is a desire for an MR head design optimized for barium ferrite particles.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of magnetic recording/reproducing which is for a coated-type magnetic recording medium (i.e., a magnetic recording particulate medium) with excellent productivity for use in a system of recording/reproducing with an MR head and which attains satisfactory electromagnetic characteristics and a greatly improved S/N ratio especially in a high-density recording region.
The present invention provides a method of magnetic recording/reproducing which comprises reproducing with a magnetoresistive head (MR head) signals recorded in a magnetic recording medium comprising a support having thereon a magnetic layer comprising mainly ferromagnetic particles and a binder, wherein the MR head has an element thickness of 50 nm or smaller and the ferromagnetic particles are hexagonal-ferrite magnetic particles having an average tabular diameter of from 10 to 40 nm and an average tabular thickness smaller than the element thickness of the MR head used for reproduction.
In a preferred embodiment of the present invention, the method of magnetic recording/reproducing is applied to a magnetic recording medium in which the magnetic layer has a machine direction coercive force H
c
of from 158 to 350 kA/m and an average thickness of from 30 to 300 nm.
According to the method of magnetic recording/reproducing of the present invention, signals can be recorded at a high density due to the use of fine hexagonal-ferrite magnetic particles having an average tabular diameter as small as from 10 to 40 nm, and the signals recorded m can be reproduced with an MR head while diminishing the noise in the reproduced signals because the magnetic particles have an average tabular thickness smaller than the element thickness (50 nm or smaller) of the MR head. Furthermore, by regulating the magnetic layer so as to have a coercive force H
c
of from 158 to 350 kA/m and an average thickness of from 30 to 300 nm, the method of magnetic recording/reproducing can be made to attain an increased linear recording density, freedom from MR head saturation, and excellent suitability for overwriting.
In case where the hexagonal-ferrite magnetic particles in the recording medium for use in the present invention have an average tabular diameter of smaller than 10 nm, it is difficult to obtain stable magnetic recording by the cause of thermal fluctuations. On the other hand, average tabular diameters of the magnetic particles exceeding 40 nm result in a decrease in S/N, impaired suitability for overwriting, and reduced resolution.
In case where the MR head to be used in the present invention has an element thickness exceeding 50 nm, resolution is impaired.
The thickness of the magnetic layer is desirably small from the standpoint of improving resolution in overwriting and short-wavelength recording. A specific technique for attaining a reduction in magnetic-layer thickness is to form a substantially nonmagnetic lower layer between a magnetic layer and a support, as has been known. This technique is more preferred in that it attains reduced surface roughness and improved productivity.
As stated above, the noise in reproduced signals can be diminished by regulating the hexagonal-ferrite magnetic particles so as to have an average tabular thickness smaller than the element thickness of the MR head. The reason for this is that due to such a small average tabular thickness, a larger number of magnetic particles are present in the unit length for magnetic flux revolution which are detectable by the element.
The term “element thickness of the MR head” means the thickness as measured along the head travel direction.
Examples of MR heads usable in the present invention include anisotropic MR heads and shield type MR heads.
Although the MR head to be used in the method of magnetic recording/reproducing of the present invention is not particularly limited, a thin-film magnetic head of the electromagnetic induction type such as, e.g., an MIG head is advantageously used.
DETAILED DESCRIPTION OF THE INVENTION
The magnetic recording medium to be used in the present invention will be explained below in detail.
Magnetic Layer
The magnetic recording medium may have a magnetic layer either on one side only or on each side of the support. When a magnetic layer is to be formed on a lower layer, a coating solution for forming the magnetic layer (also called “upper layer” or “upper magnetic layer”) may be applied either by the wet-on-wet (W/W) method in which it is applied while a coating solution for lower-layer formation which has been applied is still in a wet state or by the wet-on-dry (W/D) method in which the coating solution for magnetic-layer formation is applied after the coating solution for lower-layer formation applied has been dried. From the standpoint of production efficiency, simultaneous or successive wet-on-wet coating is preferred. In the case of disks, however, the wet-on-dry coating method also is sufficient. The use of simultaneous or successive wet-on-wet (W/W) coating in forming a multilayer constitution is advantageous in that surface-treating steps including a calendering ste
Ometz David
Sughrue & Mion, PLLC
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