Stock material or miscellaneous articles – Structurally defined web or sheet – Honeycomb-like
Reexamination Certificate
2002-08-29
2004-06-08
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Honeycomb-like
C428S212000, C428S323000, C428S409000, C428S690000, C428S697000, C428S701000, C428S702000
Reexamination Certificate
active
06746749
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an information recording medium for reading and writing a large volume of information at high speed and with high precision, and more specifically to a magnetic recording medium for a magnetic disk, a substrate for the magnetic recording medium, and a magnetic storage apparatus, all having high performance and high reliability.
DESCRIPTION OF THE RELATED ART
Recent years have seen a remarkable advance of sophisticated information society and multimedia combining a variety of forms of information have found a widespread use. One of information recording apparatus that support these developments is a magnetic recording disk drive. At present, efforts are being made to reduce the size of the magnetic recording disk drive while at the same time improving its recording density. The magnetic recording disk drive is also experiencing a rapid cost reduction. To realize high recording density of the magnetic recording disk, the following essential requirements must be met: (1) the distance between the magnetic recording disk and the magnetic head should be reduced; (2) coercivity of the medium should be increased; and (3) a signal processing method should be improved.
The magnetic recording medium among others requires an increased coercivity to realize a high density recording. In addition, to realize a recording density in excess of 10 Gb/in
2
requires a reduction in a unit area in which magnetization reversal occurs. For that purpose, magnetic crystal grains must be reduced in size to a microfine level. Further, in addition to the grain size reduction of magnetic crystal grains, it is important in terms of thermal fluctuation to reduce the extent of grain size distribution. To meet these requirements, it has been proposed to provide a shield thin layer under a magnetic layer. One such example is U.S. Pat. No. 4,652,499.
SUMMARY OF THE IVNENTION
In the related technology described above, there is a limitation to the control on the distribution of crystal grain size of the information recording magnetic layer and there are cases where fine grains and coarse grains coexist. The coexistence of fine and coarse grains poses problems when magnetization is reversed to record information. Small grains are influenced by leakage fields from surrounding magnetic crystal grains, while large grains interact with the surrounding magnetic crystal grains, so that ultra-high density magnetic recording in excess of 10 GB/inch
2
may not be performed in stable condition.
To overcome these problems, an object of the present invention is to provide a substrate or platelike body suited for manufacturing a high performance magnetic recording medium. Another object of the present invention is to provide a high performance magnetic recording medium with little noise by refining the crystal grain size in a magnetic layer. Still another object of the present invention is to provide a magnetic recording medium with low noise, low thermal fluctuation and low thermal demagnetization by suppressing the dispersion of the crystal grain size distribution. A further object of the present invention is to provide a magnetic recording medium suited for high density recording by controlling the crystallographic orientation of the magnetic layer. A further object of the present invention is to provide a high density magnetic recording medium by reducing the magnetic interaction among magnetic grains to reduce the magnetization reversal unit for recording and erasure. A further object of the present invention is to provide a magnetic storage apparatus suited for high density magnetic recording.
The above objectives can be achieved by: forming an inorganic compound layer over the substrate, the inorganic compound layer including crystal grains having as main elements at least one of cobalt oxide, chromium oxide, iron oxide and nickel oxide and at least one kind of oxide lying as a non-crystalline phase in boundaries between the crystal grains and selected from among silicon oxide, aluminum oxide, titanium oxide, tantalum oxide and zinc oxide; and forming a magnetic layer over the inorganic compound layer, the magnetic layer having a structure in which magnetic crystal grains are epitaxially grown from the surface of the crystal grains of the inorganic compound layer and a non-magnetic element or compound exists in grain boundaries between the magnetic crystal grains. Alternatively, it is possible to form the substrate from the inorganic compound and epitaxially grow the magnetic crystal grains of the magnetic layer over the substrate.
The crystal grains in the inorganic compound layer have a columnar structure with the crystallographic orientation, in which the columns extend in the layer thickness direction. It is preferred that the crystal grains have a uniform size when viewed in the in-plane direction of the inorganic compound layer, that the grain size distribution be a normal distribution, and that the standard deviation of the grain size distribution be 10% or less of the average grain size. The inorganic compound layer typically has a honeycomb structure in which hexagonal crystal grains are regularly arrayed two-dimensionally in the in-plane direction. When one crystal grain is considered, it is preferred that the number of crystal grains neighboring that one crystal grain in the in-plane direction be almost constant and the number of crystal grains surrounding (or adjoining) it two-dimensionally be between 5.7 and 6.3. Such a structure of the inorganic compound layer can be controlled by changing a ratio between a material forming a crystalline phase and a material forming a noncrystalline phase and a composition of the material forming the non-crystalline phase when the inorganic compound layer is formed.
The crystal grains in the substrate formed of the inorganic compound have at least near the surface of the substrate a columnar structure with a crystallographic orientation in which the columns extend in the direction of thickness of the substrate. The columnar structure is surrounded by a noncrystalline phase. It is preferred that in a plane near and parallel to the surface of the substrate the crystal grains be almost uniform in size, that their grain size distribution be a normal distribution and that the standard deviation of the grain size distribution be 10% or less of the average grain size. At least on the substrate surface, the substrate typically has a honeycomb structure in which hexagonal crystal grains are regularly arrayed two-dimensionally in a plane parallel to the substrate surface. When one crystal grain on the substrate surface is considered, it is preferred that the number of crystal grains neighboring that one crystal grain be almost constant and the number of crystal grains surrounding (or adjoining) it two-dimensionally be between 5.7 and 6.3. Such a structure of the substrate can be controlled by changing a ratio between a material forming a crystalline phase and a material forming a noncrystalline phase and a composition of the material forming the non-crystalline phase when the substrate is formed of an inorganic compound.
Over the substrate of inorganic compound or the inorganic compound layer having the characteristics described above, a magnetic layer is formed. In this case, it is advantageous that the magnetic crystal grains of the magnetic layer are epitaxially grown from the crystal grains of the inorganic compound substrate or inorganic compound layer. Surrounding the crystal grains of the crystal grains of the substrate or inorganic compound layer is a non-crystalline phase. The magnetic layer grows epitaxially over the underlying crystal grains and its epitaxial growth is suppressed over the non-crystalline phase. Because the growth mechanism of the magnetic layer over the crystal grains differs from that over the grain boundaries when the magnetic layer is grown, the orientation and structure of the magnetic layer change in the in-plane direction. This change leads to a change in magnetic characteristics, which is
Hosaka Sumio
Inaba Nobuyuki
Kirino Fumiyoshi
Koyama Eiji
Kuramoto Hiroki
Bernatz Kevin M.
Hitachi , Ltd.
Kenyon & Kenyon
Thibodeau Paul
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