Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Reexamination Certificate
2000-08-31
2002-12-03
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
Reexamination Certificate
active
06488908
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-035119, filed Feb. 14, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a spinel ferrite thin film exhibiting a high-temperature spin glass state and capable of spin control by light and a method of manufacturing the same.
A magneto-optical recording medium (MO) is known to the art as one of the magnetic recording media that have put to a practical use at present. In the conventional magneto-optical recording medium, a structural change is brought about within a recording medium by using a laser as a heat source so as to carry out recording. However, since a structural change is brought about by heat in the conventional medium, shortening in recording speed is limited. Since improvements in recording speed and in processing speed are required with recent increase in data, it is required to develop a magneto-optical recording medium in which data can be recorded directly with light, not with heat.
In a spin glass material, it is expected that magnetic properties, specifically its spin, can be controlled by light irradiation. Therefore, the spin glass material is a prominent candidate for a new magneto-optical recording medium. However, many spin glass materials exhibit the spin glass state only under very low temperatures such as 50 K or lower. This is because spin exchange interaction that determines a temperature at which the spin glass state is exhibited is low. Therefore, elevation of temperature at which the glass phenomenon is exhibited is a serious problem to be solved for putting the spin glass material to a practical use.
As examples of the material that exhibits the spin glass state at a high temperature such as room temperature, bulk Zn
0.5
Co
0.5
Fe
2
O
4
(spin freezing temperature T
f
=320 K) and an amorphous film of CoFe
2
O
4
(T
f
=284 K) have been reported to date. However, in order to use a spin glass material as a memory material, it is required to increase the width of selection of materials that achieve a spin glass state at temperatures around room temperature. In addition, concerning the above two materials, no report has yet been made relating to control of the spin state by light.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a spinel ferrite thin film capable of exhibiting a spin glass state under temperatures around or higher than room temperature and capable of controlling the spin state by light, and a method of manufacturing the same.
According to a first aspect of the present invention, there is provided a spinel ferrite thin film selected from the group consisting of compounds represented by the formula:
AE
1+t
Fe
2−2t
TM
t
O
4
where AE represents an alkaline earth metal or an alkali metal, TM represents a transition metal, and t falls within a range of between 0.2 and 0.6, i.e., 0.2≦t≦0.6, and
compounds represented by the formula:
Zn
1−x
Co
x
Fe
2
O
4
where x falls within a range of between 0.2 and 0.7, i.e., 0.2≦x≦0.7.
In the spinel ferrite thin film of the present invention, the alkaline earth metal or the alkali metal is selected from the group consisting of magnesium and lithium, and the transition metal is selected from the group consisting of cobalt, titanium, zinc, vanadium, manganese, chromium and nickel.
According to a second aspect of the present invention, there is provided a method of manufacturing a spinel ferrite thin film, comprising steps of:
disposing a substrate and a target within a vacuum chamber, followed by setting an oxygen partial pressure within the vacuum chamber to 1×10
−5
Torr or less; and
depositing by a laser beam deposition a spinel ferrite thin film selected from the group consisting of compounds represented by the formula:
AE
1+t
Fe
2−2t
TM
t
O
4
where AE represents an alkaline earth metal or an alkali metal, TM represents a transition metal, and t falls within a range of between 0.2 and 0.6, i.e., 0.2≦t≦0.6, and
compounds represented by the formula:
Zn
1−x
Co
x
Fe
2
O
4
where x falls within a range of between 0.2 and 0.7, i.e., 0.2≦x≦0.7.
In the method of the present invention, it is desirable for the substrate to be selected from the group consisting of a sapphire single crystal and a strontium titanate single crystal.
According to a third aspect of the present invention, there is provided a method of controlling magnetization of a spinel ferrite thin film by light, comprising steps of:
applying at least 30% of a magnetic field relative to coercive force Hc to the spinel ferrite thin film; and
irradiating the spinel ferrite thin film with light, while applying the magnetic field to the thin film, so as to increase the magnetization of the thin film.
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 advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
REFERENCES:
patent: 4624901 (1986-11-01), Glass
patent: 5698131 (1997-12-01), Saitou et al.
patent: 6193904 (2001-02-01), Schoch, Jr. et al.
patent: 389297 (1990-09-01), None
Fuji, et al., “Preparation of Co Ferrite Film . . . Vapor Deposition,” Jpn. J. Appl. Phys., Part 1, 1995, Jan., 34(1), pp. 130-131.*
Suzuki, et al., “Preparation of Zinc-and . . . Faraday Rotation,” Jpn. J. Appl. Phys., Part 1, 1988, Mar., 27(3), pp. 361-365.*
Yamazaki, et al., “Preparation of cobalt zinc ferrite thin films . . . ” IEEE Trans. Magn., 1987, no month, MAG-23(5, Pt.2), pp. 3320-3322.*
Mirebeau, et al., “Neutron study of the spinel . . . interaction”, J. of Magnetism and Mag. Materials, 169, 1997, no month, 279-88.*
Purushotham, et al., “Thermopower and electrical . . . ferrites”, Phys. Status Solidi A, 1993, no month, 140(2), K89-K94.*
Persoons, et al., “Resolution of the A and B-site . . . state”, Hyperfine Interact., 1990, no month, 54(1-4), 661-6.*
“Extended Abstracts (The 60thAutumn Meeting, 1999); The Japan Society of Applied Physics”, No. 1, Nov. 1999, pp. 1, 45, and 122.
Kawai Tomoji
Muraoka Yuji
Tabata Hitoshi
Bos Steven
President of Osaka University
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