Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2001-11-29
2004-04-13
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013460, C428S690000
Reexamination Certificate
active
06721238
ABSTRACT:
RELATED APPLICATION DATA
The present application claims priority to Japanese Application(s). P2000-363554 filed Nov. 29, 2000, which application(s) is/are incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magneto-optical recording medium such as a magneto-optical disc, a magneto-optical card, or magneto-optical tape, which is used for a magneto-optical recording and reproducing apparatus.
2. Description of the Related Art
For magneto-optical recording media, many new technologies called magnetically induced super resolution (MSR), which overcome optical limitations caused by the numerical aperture NA of an objective lens and the laser beam wavelength &lgr;, have been proposed.
In these technologies, the resolution is increased by using the following techniques: providing at least a magnetic recording layer (hereinafter referred to as a recording layer) and a magnetic reproducing layer (hereinafter referred to as a reproducing layer) on a magneto-optical recording medium; generating a temperature distribution in the medium by laser beam irradiation for reproduction, wherein the laser beam is focused on the medium to form a beam spot; transferring, by using the temperature distribution, the magnetization of the recording layer only to a region of the reproducing layer having a specific temperature, wherein the region having the specific temperature is called an aperture; and forming a magnetic mask in another region having a temperature other than the specific temperature. The MSR technologies are excellent in increasing resolution without changing a main parameter, such as optical pickup characteristics, of the magneto-optical recording and reproducing apparatus.
In the MSR technologies, an example of this technology called Center Aperture Detection (CAD), which decreases both the linear density and the recording track width and reduces distortion generated in waveforms of reproduced signals (hereinafter referred to as carriers), is disclosed in the Japanese Unexamined Patent Application Publication No. 9-320134.
Referring to
FIG. 9
, the reproduction principle of the magneto-optical recording medium disclosed the Japanese Unexamined Patent Application Publication No. 9-320124 will be now described.
The magneto-optical recording medium
10
has the following layers: a reproducing layer
11
of which the magnetic anisotropy changes from a in-plane direction to a perpendicular direction at a predetermined temperature Tc
1
; an auxiliary reproducing layer
12
which has a Curie temperature Tc
2
higher than the predetermined temperature Tc
1
and has a in-plane magnetic anisotropy up to the Curie temperature Tc
2
; a non-magnetic layer
14
composed of an Al alloy, a dielectric material such as SiN or AlN, or the like; and a recording layer
13
having a perpendicular magnetic anisotropy up to the Curie temperature.
In the recording layer
13
, magnetic domains having different directions of magnetization are formed according to information. By being irradiated with a reproducing laser beam LB focused with an objective lens or the like into a spot, the temperature distribution generated on the magneto-optical recording medium
10
has a peak at the center of a curve
15
in FIG.
9
.
As described above, because the reproducing layer
11
has in-plane magnetic anisotropy in a low temperature range, the magnetic domains of the recording layer
13
are not transferred to a region of the reproducing layer
11
having a low temperature, that is, the region functions as a mask.
In the above temperature range, the exchange coupling force of the auxiliary reproducing layer
12
maintains a strong in-plane magnetic anisotropy to increase mask performance.
On the other hand, a part of the reproducing layer
11
which is in a region of the auxiliary reproducing layer
12
having a higher temperature than the Curie temperature Tc
2
is released from the magnetic constraint force of the auxiliary reproducing layer
12
to be formed into the aperture. The magnetic domains of the recording layer
13
are transferred to the resulting aperture by the magnetostatic coupling force of the magnetic field leaking from the recording layer
13
.
According to the above reproduction principle, the MSR technology based on CAD increases the resolutions of both the linear density and the recording track width. The technology reduces distortion generated in waveforms of the reproduced carriers because the aperture is located in the vicinity of the center of the laser beam spot.
As described above, CAD is an excellent technology but has the following problems: sensitiveness to disturbances; instability in size of an aperture; and large noise. The problems are caused by using only the aperture having the highest temperature in the temperature distribution generated by laser beam irradiation because the magnetic coupling force is used for transferring the magnetic recording information, namely, magnetic domains, in the recording layer
13
.
The strength of the leaked magnetic field varies according to the size of the magnetic domain of the recording layer
13
, that is, a leaked magnetic field generated from a long recorded magnetic domain is stronger than another leaked magnetic field generated from a short recorded magnetic domain.
The strength of the leaked magnetic field significantly affects carrier reproduction characteristics of the magnetic domains according to the recorded state thereof. Thus, in particular, when magnetic domains are defective in recording, the long recorded magnetic domain is not perfectly transferred to a reproducing layer. Consequently, the following phenomenon frequently arises: the ratio of the bit error rate to the magnetic recording field is large even if the ratio of the carrier-noise intensity rate to the magnetic recording field or the rate of jitter to the magnetic recording field is small.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a magneto-optical recording medium which solves the problems described above.
The magneto-optical recording medium for recording and reproducing carriers by laser beam irradiation, according to the present invention, includes a first magnetic layer which is magnetized in the in-plane direction at room temperature and is perpendicularly magnetized at a predetermined temperature T
1
or more; a second magnetic layer which is in contact with the first magnetic layer, has a Curie temperature Tc
2
higher than the predetermined temperature T
1
, and has in-plane magnetic anisotropy up to the Curie temperature Tc
2
; a third magnetic layer which has a Curie temperature Tc
3
higher than the predetermined temperature T
1
and has perpendicular magnetic anisotropy at least in a predetermined range of a temperature distribution of the magneto-optical recording medium during laser beam irradiation when reproducing; and a rare earth metal layer formed between the third magnetic layer and the second magnetic layer.
The magneto-optical recording medium preferably includes a transparent substrate on which the first magnetic layer, the second magnetic layer, the rare earth metal layer, and the third magnetic layer are deposited in that order.
The rare earth metal layer of the magneto-optical recording medium is preferably composed of Gd.
The rare earth metal layer preferably has a thickness of 1 to 20 nm.
The magneto-optical recording medium preferably includes a fourth magnetic layer in contact with a face of the third magnetic layer away from the rare earth metal layer, wherein the fourth magnetic layer comprises a rare earth-transition metal alloy.
The magneto-optical recording medium of the present invention reproduces carriers with a reduced power, that is, a wide range of power is usable for the magneto-optical disc when reproducing carriers, and thus that is advantageous for designing the driving device for the magneto-optical recording medium such as a magneto-optical disc.
In the magneto-optical recordin
Muto Yoshihiro
Tanaka Yasuhito
Sonnenschein Nath & Rosenthal LLP
Sony Corporation
LandOfFree
Magneto-optical recording medium having multiple magnetic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magneto-optical recording medium having multiple magnetic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magneto-optical recording medium having multiple magnetic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3259694