Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2003-04-11
2004-11-09
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S336000, C428S611000, C428S900000, C427S130000, C427S131000, C204S192200
Reexamination Certificate
active
06815098
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic recording medium, a method for producing the same, and a magnetic storage apparatus. In particular, the present invention relates to a magnetic recording medium of the type in which a head makes contact therewith temporarily or steadily, such as in the case of a hard disk or a floppy disk. The present invention also relates to a method for producing the magnetic recording medium, and a magnetic storage apparatus.
2. Related Art
In response to the development of the advanced information society in recent years, there is a steady increase in need for the realization of high capacity and high density of the information-recording apparatus. A magnetic storage apparatus is known as one of information-recording apparatuses to respond to the need as described above. The magnetic storage apparatus is used as a large capacity storage unit, for example, for large servers, parallel-connected type computers, personal computers, network servers, movie servers, and mobile PC's. The magnetic storage apparatus comprises a magnetic recording medium on which information is recorded, and a magnetic head which is used to record and reproduce information on the magnetic recording medium. The magnetic recording medium includes a ferromagnetic thin film composed of cobalt alloy or the like which is formed as a recording layer on a disk-shaped substrate, for example, by means of the sputtering method. A protective film and a lubricant film are formed on the recording layer in order to enhance the resistance to sliding movement and the corrosion resistance.
In association with the realization of the high capacity of the magnetic storage apparatus, the improvement in recording density of the magnetic recording medium is advanced on the basis of the recording of fine and minute recording magnetic domains in the recording layer of the magnetic recording medium. The perpendicular magnetic recording system attracts attention as a method for finely recording the recording magnetic domains. In the perpendicular magnetic recording system, the magnetic recording is performed by forming magnetic domains having perpendicular magnetization in the recording layer by using the magnetic recording medium having the recording layer which exhibits perpendicular magnetization. In the perpendicular magnetic recording system as described above, the minute magnetic domains can be formed in the recording layer. Therefore, it is possible to increase the recording density of the magnetic recording medium.
A polycrystal film based on the Co—Cr system has been hitherto used as a material for the recording layer of the magnetic recording medium in accordance with the perpendicular magnetic recording system as described above. The polycrystal film has a structure in which a Co-rich area having ferromagnetism and a non-magnetic Cr-rich area are separated from each other. The magnetic interaction, which may be exerted between the adjacent ferromagnetic areas, is blocked by the non-magnetic area. Accordingly, the high density and the low noise are realized.
In order to efficiently apply the magnetic field from the magnetic head to the recording layer in the perpendicular magnetic recording system, a magnetic recording medium provided with two layers of magnetic films has been suggested, in which a soft magnetic layer composed of a soft magnetic material and a recording layer composed of a hard magnetic material for recording information are combined.
In order to further improve the areal recording density of the magnetic recording medium, it is necessary to reduce the medium noise. It has been revealed that the development of fine unit of inversion of magnetization (or recorded bits) and the development of high sensitivity of the reading head are effective for this purpose. Especially, it has been revealed that the size of the magnetic crystal grain may be made fine in order to realize the fine unit of inversion of magnetization. However, if the magnetic crystal grain is made too fine, the so-called thermal fluctuation is caused, in which the magnetization state of the magnetic crystal grain is thermally unstable. In order to avoid such an inconvenience, for example, Japanese Laid-Open Patent Publication No. 8-30951 discloses a magnetic recording medium comprising a soft magnetic layer, a first intermediate layer composed of carbon, a second intermediate layer, and a recording film having an artificial lattice structure which are stacked in this order on a non-magnetic substrate.
A magnetic layer, which has magnetic anisotropy higher than that of the polycrystal film based on the Co—Cr system as described above and which is excellent in resistance to the thermal fluctuation, has been progressively studied as a recording layer for the magnetic recording medium. Those known as such a magnetic layer include, for example, an artificial lattice multilayered film (also referred to as “alternately stacked multilayered film”) in which Co and Pd or Co and Pt are alternately stacked, and a ordered alloy film which is obtained by thermally treating an alloy film of, for example, Fe and Pt or Co and Pt at a high temperature. The artificial lattice multilayered film and the ordered alloy film are expected to have high resistance to the thermal fluctuation, because such films have high magnetic anisotropy.
However, such a film has the following drawback unlike the polycrystal film based on the Co—Cr system, because the magnetic interaction is strong in the in-plane direction (direction parallel to the surface of the substrate). That is, it is impossible to form small magnetic domains, and the transition medium noise is large. In the case of the magnetic recording medium disclosed in Japanese Laid-Open Patent Publication No. 8-30951 described above, the second intermediate layer composed of Pt or Pd is provided on the first intermediate layer composed of carbon formed on the soft magnetic layer, and the artificial lattice film of Co/Pt or Co/Pd is formed thereon. Accordingly, the crystal orientation of the artificial lattice film is improved, the perpendicular magnetic anisotropy is enhanced, and thus the coercivity is improved. However, in the case of such a magnetic recording medium, the magnetic exchange coupling force in the in-plane direction of the recording layer is strengthened, and the transition noise, which appears as the jitter when the linear recording density is increased, is increased. As a result, it has been difficult to perform recording and reproduction at a high recording density. Further, the following problem also arises. That is, the writing magnetic field supplied from the magnetic head does not arrive at the soft magnetic layer effectively, and the saturation recording characteristics are inferior, because the two intermediate layers, i.e., the first intermediate layer and the second intermediate layer are used.
Japanese Patent No. 2727582 discloses a perpendicularly magnetizable film comprising an artificial lattice film of Co—Pt stacked on an underlying base film composed of composite oxide based on any oxide of Fe, Co, and Ni or an arbitrary combination thereof, as a perpendicular magnetic recording film which is excellent in practical characteristics such as corrosion resistance and durability and which is excellent in perpendicular magnetization characteristics and magneto-optical characteristics.
The present invention has been made in order to solve the problems involved in the conventional technique as described above, an object of which is to provide a magnetic recording medium and a method for producing the same, in which the magnetic exchange coupling force in the in-plane direction of a magnetic layer is low, the transition noise is reduced, and information can be reproduced at high SIN.
Another object of the present invention is to provide a magnetic recording apparatus provided with excellent thermal fluctuation resistance characteristics in which information can be reproduced at high S/N even when the infor
Hieida Harumi
Matsunuma Satoshi
Onuma Tsuyoshi
Takayama Takanobu
Wakabayashi Kouichirou
Hitachi Maxell Ltd.
Oliff & Berridg,e PLC
Rickman Holly
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