Magnetic recording medium

Details Magnetic recording medium Magnetic recording medium

2001-09-13

2003-07-29

Rickman, Holly (Department: 1773)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S690000, C428S690000, C428S900000

Reexamination Certificate

active

06599646

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-311019, filed Oct. 11, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an information recording technique and particularly relates to a high density magnetic recording medium consisting of a novel information recording layer having a very small magnetic domain structure and realizing high recording resolution.
In recent years, the research and development of means for recording an enormous quantity of information have been actively underway. Among these means, the a real recording density of a magnetic recording medium employed for a computer hard disk apparatus has become higher with great strides.
At present, a recording system, which is referred to as “longitudinal magnetic recording”, for recording signals with a magnetization vector oriented toward the in-plane direction of a recording film has been employed as a magnetic recording medium technique for a recording medium of this type. Further, attention is being paid to “Perpendicular Magnetic Recording” (S. Iwasaki and Y. Nakamura; IEEE Trans. Magn., vol. MAG-13, pp. 1272-1277, 1977) for recording signals with a magnetization vector oriented toward the perpendicular direction of a recording film, as a method for realizing higher density recording.
Meanwhile, Co—Cr-based alloys have been mainly used as magnetic recording materials for recording layers according to any recording systems. The crystal orientation of a Co—Cr-based alloy provided right on an underlayer can be controlled according to the material, crystal orientation or lattice constant of the underlayer. It is, therefore, possible to control the direction of an easy axis of magnetization determining the direction of a magnetization vector. Currently, the research and development of longitudinal recording media and perpendicular recording media each using a Co—Cr-base alloy thin film made by the above method as an information recording layer is actively underway.
By contrast to the information recording medium using the Co—Cr-based alloy thin film stated above, Japanese Patent No. 3010156 teaches the structure of a perpendicular magnetic recording medium using a thin film of ordered alloy with L
1
0
crystal structure having excellent thermal stability and high magnetocrystalline anisotropy, as shown in
FIG. 12A
, as well as a manufacturing method therefor. The perpendicular magnetic recording medium manufactured according to this manufacturing method is an information recording medium wherein an underlayer
40
mainly consisting of an element selected from Cr, Pt, Pd, Au, Fe, Ni, MgO and NiO and a compound thereof is employed and a thin film of ordered alloy with L
1
0
crystal structure is used as an information recording layer
12
(the medium having the structure shown in
FIG. 12A
will be referred to as “single-layer perpendicular magnetic recording medium” hereinafter).
Further, the perpendicular magnetic recording medium is an information recording medium wherein a layer
30
(
FIG. 12B
) consisting of a soft-magnetic material such as Fe, FeSi alloy or Permalloy is provided and a thin film of ordered alloy with L
1
0
crystal structure is used as the information recording layer
12
(the medium having the structure shown in
FIG. 12B
will be referred to as “double-layered perpendicular magnetic recording medium” hereinafter).
Also, Japanese Patent Application No. 11-276414 proposes the structure of a perpendicular magnetic recording medium employing a thin film of ordered alloy with L
1
0
crystal structure realizing high signal output and high recording resolution and having high magnetocrystalline anisotropy as shown in
FIG. 12C and a
manufacturing method therefor.
In case of the perpendicular magnetic recording medium using a thin film of ordered alloy with L
1
0
crystal structure as stated above, however, it is not easy to control the magnetic characteristics of the thin film of ordered alloy with L
1
0
crystal structure or, to be specific, the coercivity, saturation magnetization and magnetic domain size of the thin film. To improve the recording resolution of the recording medium and reduce medium noise for improving a signal to noise ratio, in particular, a technique for controlling the microstructure of the thin film of ordered alloy with L
1
0
crystal structure and for reducing magnetic domain size is required.
Meanwhile, K. R. Coffer, M. A. Parker and J. K. Howard (IEEE Trans. Mag., vol. 31, pp. 2737-2739 (1995)) proposes a method for manufacturing a thin film of a composite obtained by adding ZrO
X
to a thin film of ordered alloy with L
1
0
crystal structure and for controlling the microstructure of the thin film of ordered alloy with L
1
0
crystal structure. With the technique proposed therein, the crystal orientation of an ordered phase with L
1
0
crystal structure is not controlled, with the result that an obtained perpendicular magnetic component is small, making it difficult to use the perpendicular magnetic component for the perpendicular magnetic recording system suited for high density recording. Further, since annealing is performed after forming the composite thin film so as to form an ordered phase with L
1
0
crystal structure exhibiting high magnetocrystalline anisotropy, this method requires a complicated medium manufacturing step.
As additives used for a composite thin film consisting of ordered alloy with L
1
0
crystal structure, TaN (e.g., T. Shimatsu, E. G. Keim, T. Bolhuis, and J. C. Lodder; J. Magn. Soc. Jpn., S2-21, pp. 313-316 (1997)), Ag (e.g., S. Stavroyiannis, I. Panagiotopoulous, D. Niarchos, J. A. Christodoulides, Y. Zhang, and G. C. Hadjipanayis; Appl. Phys. Lett., 73, pp. 3453-3455 (1988)), C (e.g., M. Yu, Y. Liu, A. Moser, D. Weller, and D. J. Sellmyer; Appl. Phys. Lett., 75, pp. 3992-3994 (1999)), B (e.g., N. Li, and B. M. Lairson; IEEE Tran. Magn. vol. 35, pp. 1077-1081 (1999)), SiO
2
(e.g., C. Chen, O. Kitakami, S. Okamoto, Y. Shimada, K. Shibata, and M. Tanaka; IEEE Trans. Magn., vol. 35, pp. 3466-3468 (1999)), Al
2
O
3
(e.g., M. Watanabe, T. Masumoto, D. H. Ping, and K. Hono; Appl. Phys. Lett., 76, pp. 3971-3973 (2000)) and the like have been reported.
However, in case of a composite thin film consisting of ordered alloy with L
1
0
crystal structure to which any one of the above additives is added, the crystal orientation of an ordered phase with L
1
0
crystal structure is not controlled. Due to this, an obtained perpendicular magnetization component is small or an in-plane magnetization component is large, making it difficult to use such a composite thin film for the perpendicular magnetic recording system suited for high density recording.
That is, as for the thin film of ordered alloy with L
1
0
crystal structure, an additive select guideline appropriate for a perpendicular magnetic recording medium, i.e., appropriate for controlling the crystal orientation of an ordered phase with L
1
0
crystal structure and forming the ordered phase with L
1
0
crystal structure has not been clarified so far.
Under these circumstances, demand for proposing a new composite thin film of ordered alloy with L
1
0
crystal structure for a perpendicular magnetic recording medium is rising.
It is, therefore, an object of the present invention to provide a magnetic recording medium which is a perpendicular magnetic recording medium using a new composite thin film of ordered alloy with L
1
0
crystal structure having high magnetocrystalline anisotropy, which can control the magnetic characteristic of an information recording layer or particularly reduce a magnetic domain size and which can ensure high density recording.
BRIEF SUMMARY OF THE INVENTION
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advanta

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