Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2001-02-13
2003-09-02
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013470
Reexamination Certificate
active
06614731
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an information recording method, recording apparatus, reproducing method and reproducing apparatus which scans with heating means recording tracks configured by perpendicular magnetic anisotropy substance and stores information signals by applying a magnetic field to a heated region of the recording tracks.
2. Related Background Art
Various method for reproducing information signals recorded in magnetic recording media are conventionally known. In particular, the present applicant discloses a domain wall displacement type reproducing method in Japanese Patent Application Laid-Open No. 6-290496. This method is characterized by recording on tracks of a magneto-optical medium information signals that are formed by a magnetic domain wall, applying a driving power to this magnetic domain wall so as to rapidly move (displace) the magnetic domain wall, and detecting that movement so as to reproduce the information signals. This method enables recording/reproducing of the information signals with extremely high storing density and high resolution capability.
A method of recording information signals into a magneto-optical medium and a reproducing method for reproducing the information signals by a magnetic wall displacement method will be described below as follows.
FIGS. 10A and 10B
are partially enlarged views showing a configuration of a magneto-optical medium
1
, where
FIG. 10A
is a longitudinal section view and
FIG. 10B
is a plan view. Here, the magneto-optical medium
1
includes a substrate
2
which is configured by a transparent resin material, such as polycarbonate, etc., and is shaped as a belt so that a groove G and a land L are alternately formed in parallel, a magnetic layer
3
formed on the substrate
2
and configured by a perpendicular magnetic anisotropy substance, and a protection coat
4
configured by ultraviolet hardened resin. The magnetic layer
3
formed on the land L forms a belt-shape recording track RT on which information signals are recorded. The magnetic layer
3
is configured by laminating three layers made of a perpendicular magnetic anisotropy substance, a rare earth material such as, for example, Tb, Gd and Dy, and a transition metal such as Fe and Co, etc.; that is, a displacement layer
3
a
, a switching layer
3
b
, and a memory layer
3
c
. Here, the displacement layer
3
a
is a perpendicular magnetic anisotropy film having magnetic domain wall coercively which is smaller than memory layer
3
c
and a large magnetic wall movement, the switching layer
3
b
is a perpendicular magnetic anisotropy substance film having a curie temperature lower than the domain wall displacement layer
3
a
and the memory layer
3
c
, and the memory layer
3
c
is a perpendicular magnetic anisotropy film.
In addition, with a method such as radiating highly powered laser beams locally for heating, etc., a magnetic feature of the magnetic layer
3
on a bottom surface and a side surface of a groove G has been reduced (for example, deterioration of the perpendicular magnetic anisotropy). This weakens magnetic coupling between the recording track RT and a region in which the magnetic feature on its side surfaces has been reduced.
Next, a method to implement thermal magnetic recording information signals to the above-described magnetic recording media
1
with a storing apparatus will be described. The recording apparatus comprises driving means for an optical head, a magnetic head and magneto-optical medium
1
.
FIGS. 8A and 8B
are partially enlarged views of the magneto-optical medium
1
, showing a recording method of information signals, where
FIG. 8A
is a cross-sectional view, and
FIG. 8B
is a plan view as viewed from the direction of a lower surface. At the time when information signals are recorded, the optical head implements radiation by concentrating a highly powered recording light beam
7
which constitutes heating means for heating a recording track RT through a substrate
2
. At the same time, the driving means drives the magneto-optical medium
1
, whereby the recording light beam
7
scans the recording track RT in the direction indicated by an arrow A. A temperature of a magnetic layer
3
increases with radiation of the recording light beam
7
, and in the periphery of the radiation region of the recording light beam
7
a thermal distribution, shown by isothermal lines in
FIG. 8B
is formed. Here, a reference numeral
8
denotes an isothermal line of a temperature Tc approximately equal to the curie temperature of the magnetic storing layer
3
c.
Radiation of the light beam
7
by way of an optical head occurs concurrently with the application of a perpendicular magnetic field by the magnetic head, where the direction of the magnetic field is varied upward and downward relative to the radiation region of the recording light beam
7
in accordance with information signals. The memory layer
3
c
loses magnetization when it passes the front portion of the isothermal line B as a result of its temperature being not less than the curie temperature To, which permits magnetization thereof in the same direction as the magnetic field applied at the time when it passes the back portion of the isothermal line
8
as a result of its temperature being not more than Tv. Moreover, as it moves in a direction more remote from the back portion of the isothermal line
8
, the temperature drops while coercively increases, so that the above-described applied magnetization is fixed. Thus, magnetization regions having alternating magnetization in the upward direction and in the downward direction, corresponding with the alternating direction of the applied magnetic livid, are formed in the storing back RT, as shown by arrows in the upward and downward directions in
FIG. 8A
; in the boundary portion between each magnetization region and the preceding and following magnetization regions, magnetic domain walls W
1
, W
2
, W
3
, W
4
, W
5
and W
6
are formed. These magnetic domain walls, which are fanned along the back portion of the isothermal line
5
, have an arc shape which bends convexly in the direction opposite from the scanning direction (arrow A) of the light beam
7
. In addition, the displacement layer
3
a,
the switching layer
3
b,
and the memory layer
3
c
are mutually brought into exchange coupling so that magnetization and the magnetic domain walls W
1
, W
2
, W
3
, W
4
, W
5
and W
6
are transfer-formed onto the displacement layer
3
a
and the switching layer
3
b
as well.
The thermal magnetic storing method as described above is referred to as a magnetic field modulation storing method, and can form magnetic walls at an interval shorter than the concentration diameter of the light beam, and therefore is suitable to store information signals at high density.
Next, a method for reproducing information signals from the above-described magneto-optical medium
1
with a reproducing apparatus will be described. The reproducing apparatus comprises driving means for an optical head and magneto-optical medium
1
.
FIGS. 9A and 9B
are partially enlarged views of the magneto-optical medium
1
showing a reproducing method of information signals by way of a displacement layer system, where
FIG. 9A
is a cross-section view, and
FIG. 9B
is a plan view as viewed from the direction of a lower surface. At the time when information signals are reproduced, the optical bead implements radiation by concentrating a low power reproducing light beam
9
to a recording back WE through a substrate
2
. At the same time, the driving means drives the magneto-optical medium
1
, whereby the reproducing light beam
9
scans the recording track RT in the direction indicated by an arrow A. A temperature of a magnetic layer
3
increases with radiation of the light reproducing light beam
9
, and in the periphery of the radiation region of the reproducing light beam
9
a thermal distribution, shown by isothermal lines in
FIG. 9B
, is formed. Here, a reference numeral
30
deno
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