Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-10-11
2004-01-06
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S690000, C428S336000, C428S900000, C427S128000, C427S130000, C427S131000
Reexamination Certificate
active
06673475
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic recording medium and a method for manufacturing the same. More particularly, the present invention relates to a magnetic recording medium used in magnetic recording devices, for example in computers.
2. Description of the Related Art
High quality magnetic recording mediums require both high recording density and low noise. In an effort to achieve these goals, various compositions and structures for magnetic layers and non-magnetic under-layers have been proposed. Recently, a magnetic layer called a granular magnetic layer has been proposed having a structure, in which a ferromagnetic grain is surrounded by a non-magnetic and non-metallic substance, such as an oxide or a nitride.
Technology related to the granular magnetic layer is shown in Japanese Unexamined Patent Application Publication No. H8-255342 and U.S. Pat. No. 5,679,473.
In Japanese No. H8-255342, a method for manufacturing a magnetic recording medium comprises multiple steps. These steps include, sequentially depositing, on a non-magnetic substrate, a non-magnetic film, a ferromagnetic film and a non-magnetic film, and heat-treating the resulting lamination. This process forms a recording layer in which ferromagnetic grains are dispersed in the non-magnetic film.
The technology of this disclosure proposes to attain low noise by means of forming a granular recording layer in which ferromagnetic grains are dispersed in a non-magnetic film structure. Silicon oxide and nitride are used for the non-magnetic film in this technology.
U.S. Pat. No. 5,679,473 discloses the formation of a low noise granular recording film by means of RF sputtering using a CoNiPt target containing an oxide additive, such as SiO
2
. In this granular recording film, each magnetic grain is surrounded and separated from others by a non-magnetic oxide.
Reduced recording noise is obtained since each of the magnetic grains in the above granular magnetic film is physically separated along a grain boundary by a non-magnetic and non-metallic phase thus reducing magnetic interaction between the magnetic grains, and suppressing the formation of magnetic domain walls having a zigzag shape at the transition region of a recording bit.
In conventional Co—Cr metallic magnetic film, to reduce magnetic interaction between the individual magnetic grains, chromium is segregated from a cobalt alloy magnetic grain toward a grain boundary. In the conventional Co—Cr metallic magnetic layer, when laminating the layer, heating the substrate to 200° C. is essential for sufficient segregation of chromium.
In the conventional granular magnetic layer, the grain boundary phase is a non-magnetic and a non-metallic substance, which segregates more easily than the conventional, thereby enhancing isolation of the magnetic grains.
The granular magnetic layer has the advantage that the non-magnetic and non-metallic substance segregates evenly in lamination without heating.
Unfortunately, high density, together with low noise of magnetic recording mediums require both reduction of magnetic interaction between the grains due to enhancement of the segregation structure in the magnetic layer, and control of crystal orientation of Co—Cr ferromagnetic grain.
More specifically, the c-axis of the ferromagnetic grains requires a hexagonal closed-packed grain structure to align the grains in the plane of the film surface. The control of the crystal orientation of the magnetic layer in conventional magnetic recording mediums having metallic magnetic layers is accomplished by controlling structure and crystal orientation of the non-magnetic under-layer.
In conventional magnetic recording mediums having a granular magnetic film, the effect of an under-layer is small since the ferromagnetic grains are separated from the under-layer by the segregation substance comprising the grain boundary, namely an oxide.
A publication entitled “Effect of Cr—Mo under-layer in CoPt—SiO
2
” in “Nihon Oyojiki Gakkaishi” ((Journal of the Japanese Society for Applied Magnetics) Vol. 23, No. 4-2, pp. 1017-1020 (1999)) discloses that using an under-layer of a special composition of a Cr-Mo alloy (having a preferential orientation in the (110) plane) causes preferential orientation of the (100) plane and the (101) plane in ferromagnetic grains in a granular magnetic layer. Use of such an under-layer results in an improvement of magnetic property and electromagnetic conversion characteristics.
Unfortunately, when a ferromagnetic grain has a preferential orientation of it's the (101) plane, the c-axis does not align parallel to the film surface. Instead, the c-axis rises up from the film surface at an angle. As a result, the magnetic anisotropy of the crystal grain contains a component perpendicular to the film surface. This perpendicular component creates a corresponding perpendicular component of magnetization, resulting in increased media noise.
The preferential orientation of the (101) plane in the ferromagnetic grain is caused by the preferential orientation of (110) plane in the CrMo alloy under-layer. As a result, the orientation control of a magnetic layer, disclosed in the reference, must be regarded as insufficient. In sum, more precise control of crystal orientation is needed for obtaining a low noise medium.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a magnetic recording medium that overcomes the concerns raised above.
It is another object of the present invention to provide a magnetic recording medium and method for manufacture that allows more precise control of crystal orientation without thermal processing.
It is another object of the present invention to provide a magnetic recording medium having a low recording noise.
It is another object of the present invention to provide a method for manufacturing a magnetic recording medium that has low noise.
It is another object of the present invention to provide a medium and manufacturing method therefore which achieves the above objects and overcomes the above-noted concerns.
Briefly stated, the present invention provides a magnetic recording medium achieves excellent noise reduction by controlling the crystal orientation of a magnetic layer without thermal processing. The magnetic recording medium includes multiple layers laminated to a substrate. These layers include at least the magnetic layer and a non-magnetic under layer. The magnetic layer has a granular structure consisting of ferromagnetic grains with a hexagonal close-packed structure and non-magnetic grain boundaries composed mainly oxide or a nitride. The non-magnetic under-layer is a material having a body centered cubic crystal structure with a preferential orientation along a (200) plane parallel to a film surface of the under-layer. The present invention also provides a manufacturing process for the above-noted product.
According to an embodiment of the invention there is provided a magnetic recording medium, comprising: a non-magnetic substrate, at least a non-magnetic under-layer on the non-magnetic substrate, at least a magnetic layer on the non-magnetic under-layer, at least a protective layer on the magnetic layer, the magnetic layer having a substantially granular structure, the substantially granular structure including at least a plurality of ferromagnetic grains having a non-magnetic grain boundary phase surrounding the plurality of ferromagnetic grain, the plurality of ferromagnetic grains each having a hexagonal close-packed lattice structure, the non-magnetic grain boundary phase including at least one of a metal oxide and a metal nitride, and the non-magnetic under-layer having a body-centered cubic crystal lattice structure and a preferential crystal orientation of (200) plane parallel to a film surface of the non-magnetic under-layer, whereby a c-axis of each the ferromagnetic grain preferentially aligns parallel to the film surface and minimizes a perpendicular component of magnetization in the magnetic layer thus reducing noise.
Oikawa Tadaaki
Shimizu Takahiro
Takizawa Naoki
Uwazumi Hiroyuki
Darby & Darby
Fuji Electric & Co., Ltd.
Rickman Holly
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