Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
1997-02-13
2001-01-09
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S065100, C428S141000, C428S336000, C428S690000, C428S690000, C428S690000, C428S690000, C428S900000, C427S128000, C427S129000, C427S130000, C427S131000
Reexamination Certificate
active
06171676
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to a magnetic recording medium used with a hard disk drive or the like for storing information by changing magnetization states and to its manufacture, and more particularly to a magnetic recording medium of low noises and its manufacture suitable for suppressing noises to be generated when information is read from the medium.
b) Description of the Related Art
For low noise magnetic recording of a magnetic recording medium used with a magnetic disk drive, it is desired that the size of each magnetic grain of the magnetic film is a single magnetic domain size or finer and to make magnetic interaction between magnetic grains substantially negligible. The single magnetic domain size is defined by a maximum size of magnetic material allowing the material to generate only a single magnetic dipole.
Conventionally, non-magnetic material is added to magnetic material of a magnetic film of a polycrystal structure, and precipitated on the crystal grain boundaries after the magnetic film is formed in order to isolate each crystal grain. In order to make a crystal grain finer, an underlying layer is made thin and crystallized finer, and a magnetic film is hetero-epitaxially grown on the underlying layer.
With the conventional method, non-magnetic material is required to be precipitated at crystal grain boundaries. However, precipitation is likely to be hindered and in many cases non-magnetic material remains in crystal grains more than a solubility limit. This non-magnetic material contained in crystal grains more than a solubility limit lowers a coercive force of crystal grains. If the underlying layer is made thin, it becomes difficult to obtain crystal orientation with excellent magnetic characteristics.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a magnetic recording medium and its manufacture, the magnetic recording medium having fine crystal grains of magnetic material on a substrate and providing a high recording density and low noises.
According to one aspect of the present invention, there is provided a magnetic recording medium comprising: a substrate of a disk shape having a non-magnetic surface and a through hole formed at the central area of the substrate; and a plurality of dispersed island regions made of magnetic material and directly formed on the non-magnetic surface.
According to another aspect of the present invention, there is provided the magnetic recording medium, wherein a size of each of the island regions is a single magnetic domain size or finer of the magnetic material.
If the size of each island region is a single magnetic domain size or finer, only one magnetic dipole is generated in one island region. Since a plurality of magnetic dipoles will not cancel one another, low noise and high density magnetic recording is possible.
According to another aspect of the present invention, there is provided the magnetic recording medium, the nonmagnetic surface is irregular.
Crystals of a hexagonal system have a strong tendency of growing with the c-axis being oriented to the direction vertical to the underlying surface. Therefore, the c-axis of crystals growing on the slanted surface of the irregular substrate does not orient vertical to the substrate surface. If the c-axis is an easy-to-magnetize axis, this easy-to-magnetize axis does not intersect with the substrate plane at a right angle, which is suitable for magnetization in the substrate in-plane direction.
According to another aspect of the present invention, there is provided the magnetic recording medium, further comprising at least one laminated structure including a separation layer made of non-magnetic material and covering at least the surfaces of the island regions and other island regions made of magnetic material and dispersed on the surface of the separation layer.
The distribution density of island regions can be raised by forming a plurality of island region layers.
According to another aspect of the present invention, there is provided a method of manufacturing a magnetic recording medium comprising the steps of: preparing a substrate with a non-magnetic surface; and forming dispersed island regions made of magnetic material and formed on the non-magnetic surface of the substrate.
According to another aspect of the present invention, there is provided the method, wherein the island region forming step includes the steps of: forming a magnetic film made of magnetic material on the non-magnetic surface of the substrate; and cohering atoms of the magnetic film by subjecting the substrate to a heat treatment after the magnetic film is formed on the non-magnetic surface.
According to another aspect of the present invention, there is provided the method, further comprising, after the island region forming step, the steps of: forming a separation layer made of non-magnetic material and covering at least the surfaces of the island regions; and forming, after the separation layer forming step, other island layers of magnetic material and dispersed on the uppermost surface of the substrate.
According to the present invention, crystal grains of magnetic material are formed to be dispersed on the substrate surface. If each fine crystal grain has the size of a single magnetic domain size or finer and magnetic interaction between adjacent fine crystal grains is almost negligible, low noise magnetic recording is possible.
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European Patent Office Communication with attached European Search Report for European Patent Application No. 97300834.5 dated Apr. 25, 1997.
Kobayashi Kazuo
Mukai Ryoichi
Yamanaka Kazunori
Armstrong, Westerman Hattori, McLeland & Naughton
Fujitsu Limited
Kiliman Leszek
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