Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2001-12-31
2004-09-21
Neyzari, Ali (Department: 2655)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013470, C369S013520
Reexamination Certificate
active
06795379
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magneto-optical medium for reproduction of information by utilizing domain wall displacement, and a method of reproduction of information.
2. Related Background Art
In recent years, the magneto-optical mediums are attracting attention as a rewritable high-density recording medium: the magneto-optical medium which records information in magnetic domains of a magnetic thin film utilizing thermal energy of a semiconductor laser and reads out the recorded information by utilizing a magneto-optical effect. The treatment data are becoming diversified into sounds, pictures, animations, and so forth, and the data size thereof is increasing. Therefore, higher recording density and higher recording capacity are required for the magneto-optical mediums.
Generally, the line recording density of the magneto-optical medium depends largely on the laser wavelength of the reproducing optical system and the numerical aperture of the lens NA. Since the beam waist diameter depends on the laser wavelength &lgr; of the reproducing optical system and the numerical aperture NA of the lens, the spatial frequency of the signal-reproducing recording pits is limited to about 2NA/&lgr;. Therefore, for realizing the high density of a conventional optical disk, the laser wavelength of the reproducing optical system should be shortened, or the numerical aperture of the objective lens should be increased. However, the shortening of the laser wavelength is difficult because of the efficiency and heat generation of the element. The increase of the numerical aperture of the objective lens causes the problem that the lens and the disk are brought extremely close, causing collision or a like mechanical problem.
To solve such problems, super-resolution techniques are being developed in which the recording density is increased by improvement of the constitution of the recording medium or by improvement of the reproduction process without changing the laser wavelength or the numerical aperture of the objective lens. For example, Japanese Patent Application Laid-Open No. 7-334887 discloses a super-resolution system in which a lamination structure is formed from a memory layer for memorizing recorded information, a reproducing layer for masking a part of a reproducing light spot area, and an intermediate layer for controlling the exchange coupling between the above layers: the recorded information is transferred to the reproducing layer by utilizing only a part of the reproducing light spot by the temperature distribution caused by irradiation of the reproducing light spot in the recording medium to reproduce the fine magnetic domain.
In the above system, a portion of the reproducing light spot is masked and the temperature gradient is utilized. In other words, the resolution power is raised by restricting the aperture for reading the recorded pitches to a smaller region substantially. Therefore, the masked portion of the light is ineffective, decreasing the amplitude of the reproduction signals. Since the light projected to the masked portion does not contribute for producing the information signals, the smaller aperture for higher resolution will decrease the effective light to lower the signal level disadvantageously.
For utilizing effectively the reproducing light without causing the above problems, Japanese Patent Application Laid-Open No. 6-290496 discloses a reproducing method in which a domain wall displacement layer having a lower domain wall coercivity is provided on the reproduction light-introducing side and the domain in the domain wall displacement layer is displaced toward a high temperature side by utilizing the temperature gradient in the reproducing light spot to enlarge and reproduce the domain within the spot. According to this reproduction method, even if the recorded mark (magnetic domain) is small, the signal is reproduced with enlargement of the domain to utilize effectively the reproducing light to raise the resolution power without decreasing the reproducing signal amplitude.
The reproduction process disclosed in the above Japanese Patent Application Laid-Open No. 6-290496 is explained in detail by reference to drawings.
FIGS. 6A
to
6
C are drawings for explanation of construction of the magneto-optical recording medium and the principle of information reproduction disclosed in the above Patent Laid-Open publication.
FIG. 6A
is a schematic cross-sectional view illustrating the constitution of the magneto-optical recording medium and the magnetization state of the portion irradiated by a reproducing light.
FIG. 6B
is a graph showing a temperature distribution in the magneto-optical recording medium on irradiation of the reproducing light beam.
FIG. 6C
is a graph showing the distribution of the domain wall energy density &sgr; of the domain wall displacement layer corresponding to the temperature distribution shown in FIG.
6
B.
As shown in
FIG. 6A
, this magneto-optical recording medium has a recording layer constituted of magnetic layer
111
as a domain wall displacement layer, magnetic layer
112
as a switching layer, and a magnetic layer
113
as a recording layer, laminated successively. In this recording medium, magnetic layer
111
is formed on the side of introduction of the reproducing light beam. Arrows
114
indicate orientation of atomic spins in the layers. Magnetic walls
115
are formed at the interface of the regions where the orientation of the atomic spins are reversed. The signal waveform in the lower part of
FIG. 6A
shows the recorded signals corresponding to the magnetization state of this recording layer.
Arrow
118
indicates the direction of movement of the recording medium. With the movement of the recording layer in the direction of arrow
118
, light beam spot
116
is moved relatively along the information track of the recording layer. At the portion irradiated with this light beam spot
116
, the temperature distribution is caused such that the temperature rises from before the front of the light spot and the temperature peak is formed behind the light spot. In this example, the medium temperature T reaches the temperature Ts near the Curie temperature of magnetic layer
112
at the position Xs.
In magnetic layer
111
, the domain wall energy density &sgr; distributes as shown in
FIG. 6C
in such a manner that the energy density is minimum near the point of temperature peak behind the light beam spot
116
and is higher before the light beam spot. The gradient of the domain wall energy density &sgr; along the position X direction causes exertion of the force F, shown by the equation below, to the domain walls at the position X in each of the layers.
F=∂&sgr;/∂X
(1)
This force F acts on the domain walls to move toward the lower domain wall energy side. Since magnetic layer
111
has a lower domain-wall coercivity and a higher domain-wall mobility, domain walls
115
are driven readily by this force F in this layer. However, in the region before position Xs in the front of the light spot, the medium temperature is lower than Ts, which prevents movement of domain wall
115
and fixes it at the position corresponding to the domain wall in magnetic layer
113
having a higher coercivity.
With tyis magneto-optical medium, with movement of domain walls
115
in the movement direction
118
, the temperature of the portion of domain wall
115
of the medium rises to reach the temperature Ts near the Curie temperature of magnetic layer
112
at the position Xs. Thereby the exchange coupling between magnetic layer
111
and magnetic layer
113
is canceled. Consequently, domain wall
115
of magnetic layer
111
is driven instantaneously to the region of a higher temperature and a lower domain wall energy density. In
FIG. 6A
, this movement direction is shown by dotted arrow
117
. After passage of domain walls
115
through under light beam spot
116
, the atomic spins of magnetic layer
111
within the light spot are oriented in one and the s
LandOfFree
Magneto-optical medium utilizing domain wall displacement... 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 medium utilizing domain wall displacement..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magneto-optical medium utilizing domain wall displacement... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3257740