Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2002-12-27
2004-10-26
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S900000
Reexamination Certificate
active
06808830
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic recording medium used in, for example, peripheral devices of calculators, or magnetic disk apparatuses used for recording of image and sound data, a process and apparatus for producing the magnetic recording medium, and a magnetic recording and reproducing apparatus incorporating the magnetic recording medium.
2. Description of the Related Art
As recording density of magnetic recording media is increased, reduction in noise and enhancement of resolution by means of miniaturization or magnetic isolation of magnetic grains in a magnetic layer, and or reduction of the thickness of the magnetic layer, for example, has been proposed.
However, when the magnetic grains are miniturized or magnetically isolated, or when thickness of the magnetic layer is reduced, the size of the magnetic grains is reduced, and therefore, there is a problem wherein thermal stability is decreased. The term “thermal decay” refers to a phenomenon in which recording bits become unstable and recorded data are lost. In a magnetic recording and reproducing apparatus, this is manifested in the form of reduction in reproduction output of recorded data over the passage of time.
Hitherto, as substrates used for magnetic recording media, non-magnetic metallic substrates comprising aluminum alloys and the like have been frequently used. Usually, a hard film comprising NiP or the like is provided on such a non-magnetic metallic substrate in order to harden its surface, then the surface of the substrate is subjected to texturing, and the substrate is used for producing a magnetic recording medium.
Texturing is a process for forming irregularities on the surface of a substrate along a predetermined direction (usually in a circumferential direction). By carrying out texturing, the crystal orientation of an undercoat layer and a magnetic layer, which are formed on the substrate, is enhanced, the magnetic anisotropy of the magnetic layer is enhanced, and magnetic characteristics, such as thermal stability, can be enhanced.
In recent years, instead of a metallic substrate comprising aluminum or the like, a non-metallic substrate comprising glass, ceramic, or the like has been widely used as a substrate for a magnetic recording medium. In the non-metallic substrate, head slap does not easily occur due to the high hardness, and furthermore, there is an advantage in the point of glide height characteristics because it has high surface smoothness.
In order to solve such problems, formation of a hard film which can be easily textured on a non-metallic substrate comprising glass, ceramics, or the like has been proposed.
For example, Japanese Unexamined Patent Application, First Publication No. Hei 5-197941 discloses a magnetic recording medium including a non-metallic substrate formed by sputtering with an NiP film which is a hard film that can be easily textured.
A magnetic recording medium including a hard film formed on a non-metallic substrate is produced through the following process: the hard film is formed on the substrate in a film formation apparatus such as a sputtering apparatus; thereafter, the substrate is temporarily removed from the film formation apparatus and subjected to texturing by use of a texturing apparatus; the resultant substrate is again placed in the film formation apparatus, and then an undercoat layer and a magnetic layer are formed.
However, in the case of the aforementioned conventional magnetic recording medium which uses a non-magnetic metallic substrate such as an aluminum substrate or a non-metallic substrate such as a glass substrate, when a hard film formed from NiP, which is formed on the surface, is subjected to texturing, the magnetic anisotropy of a magnetic layer can be enhanced but the surface smoothness of the medium tends to be lowered because of surface irregularities of the hard film. Consequently, glide height characteristics are deteriorated, and attainment of high recording density becomes difficult. In addition, the production process for the magnetic recording medium includes complicated production steps, resulting in high production costs.
The present invention was made in view of the foregoing conditions, and an object of the present invention is to provide: a magnetic recording medium which exhibits excellent magnetic characteristics such as thermal stability and excellent glide height characteristics and which is easily produced; a process and apparatus for producing the magnetic recording medium easily; and a magnetic recording and reproducing apparatus which uses the magnetic recording medium exhibiting excellent magnetic characteristics such as thermal stability.
SUMMARY OF THE INVENTION
The magnetic recording medium of the present invention has as a basic structure of a non-magnetic substrate, a non-magnetic undercoat layer, a magnetic layer, and a protective layer, the layers being formed on the substrate, wherein the non-magnetic undercoat layer has a bee structure; an orientation-adjustment layer for causing the non-magnetic undercoat layer to have a predominant plane of (200) is formed between the non-magnetic substrate and the non-magnetic undercoat layer; the magnetic layer has a crystal structure in which columnar fine crystal grains are inclined in the circumferential direction; the ratio of the coercive force in the circumferential direction of the magnetic layer Hcc to the coercive force in the radial direction of the magnetic layer Hcr, i.e., Hcc/Hcr, is more than 1.
The non-magnetic undercoat layer is preferably constituted to have a crystal structure in which columnar fine crystal grains are inclined in the radial direction.
The magnetic layer includes a plurality of magnetic films having an hcp structure and a predominant orientation plane of (110), and a structure in which it is possible to form antiferromagnetic coupling between the magnetic films is preferable.
The orientation-adjustment layer is preferably constituted to have a crystal structure in which columnar fine crystal grains are inclined in the radial direction.
Due to the above constitution, the magnetic anisotropy of the magnetic layer in the circumferential direction can be enhanced and crystal magnetic anisotropy constant (Ku) can be improved. Therefore, it is possible to improve magnetic characteristics such as the coercive force, the S/N ratio of the recording and reproduction signal, and thermal stability.
In addition, in the present invention, due to antiferromagnetic bonding between magnetic films, regarding the magnetization of the magnetic films other than the primary magnetic film which has the highest coercive force, it is possible to achieve a state wherein there is no apparent magnetization, or a state wherein the magnetization of the primary magnetic film is apparently reduced by an amount of magnetization corresponding to the magnetization of the magnetic films other than that of the primary magnetic film.
Therefore, the volume of the magnetic grains can be increased sufficiently without adversely affecting noise and resolution, thermal stabilization can be attained, and thermal stability can be improved.
The magnetic layer may have a laminated ferrimagnetic structure in which the directions of the magnetic moments of adjacent magnetic films are opposite to each other.
The magnetic layer may have a structure including a plurality of magnetic films and an intermediate film provided therebetween.
The magnetic layer may have two or more laminated structures, each including a magnetic film and an intermediate film adjacent thereto.
Preferably, the antiferromagnetic bonding magnetic field of a magnetic film adjacent to the primary magnetic film having the largest coercive force among the plurality of magnetic films is set to be larger than the coercive force of the magnetic film adjacent to the primary magnetic film.
Preferably, the intermediate film is formed from a material predominantly comprising at least one element selected from among Ru, Cr, Ir, Rh, Mo, Cu, Co, Re, and V.
The or
Sakai Hiroshi
Sakawaki Akira
Rickman Holly
Showa Denko K.K.
Sughrue & Mion, PLLC
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