JPH01182949A - Magneto-optical recording method for superconducting material - Google Patents

Abstract

PURPOSE:To realize extremely high speed writing without making an irradiating laser beam particularly strong by holding a micro area where is changed to a normal-conductor by irradiating a superconducting membrane with the beam with a magnetic flux. CONSTITUTION:A superconducting membrane 1 is formed on a substrate 5, and a bias magnetic field 6, which is smaller than the critical magnetic field of the superconductor film 1 and uniform, is impressed from a vertical direction to the face of the superconducting membrane 1. A laser beam 2 irradiates the superconducting membrane 1 in the condition with a micro spot converged with a convergent lens 4. When an insulating membrane which consists of a micro crystal grain and whose grain boundary is particularly thin, and a ceramic to constitute a Josephson junction, in which an inter-grain becomes the weak bonding of a point shape, are used for the superconducting membrane 1 to be used, the superconducting condition of the superconducting membrane 1 is broken by a comparatively weak light, and it can be made to be a normal- conducting condition. Thus, a particularly high speed writing can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to magneto-optical recording that uses a ceramic superconductor film and has an extremely high operating speed.

<Prior Art> Conventional magneto-optical recording uses a thin film of magnetic material as a recording medium.

There are various methods of magneto-optical recording using magnetic recording media, but the following method was used for boat fishing. A thin film of magnetic material is irradiated with laser light focused to a diameter of about 1 μm, and the irradiation energy raises the temperature of the magnetic material in that area, lowers the coercive force (Hc), and reverses the magnetization, thereby creating information bits. was written. For reading, linearly polarized laser light, which is weaker than writing, is focused and erodes the thin film of magnetic material, and the written information is transferred to the region where the magnetization has been reversed by magneto-optic effects such as the Faraday effect or the magnetic Kerr effect. It was detected by changing the rotation of the polarization plane of the linearly polarized light.

FIG. 6 shows an example of writing in the conventional magneto-optical recording as described above.

The magnetic film 14 produced on the substrate is completely magnetized perpendicularly.

A bias magnetic field 15 having a magnetic field opposite to the direction of magnetization of the magnetic film 14 is applied by a magnetic field generator 16, and a laser beam 2 is irradiated to a spot 3, which is a minute region of the magnetic film 16, to remove the spot. When the temperature of 3 becomes above a certain level, the magnetization is reversed and an information bit is written.

<Problems to be Solved by the Invention> Conventional magneto-optical recording using a magnetic thin film writes information bits that reverse the magnetization by the thermal effect of light, so a laser beam that reduces the thickness of the magnetic film is required. Even if improvements such as increasing the strength of the recording speed are made, the recording speed remains at around 106 to 102 bits/second.

The present invention provides a magneto-optical recording method that has an extremely high writing operation speed that exceeds the writing speed limit of conventional magneto-optical recording methods.

Means for Solving the Problems> The magneto-optical recording of the present invention does not reverse magnetization due to the thermal effect of light, but instead uses magnetic flux to hold a micro region made into a normal conductor by irradiating a superconductor film with light. This is magneto-optical recording.

If the superconductor film used is an insulating film made of minute monocrystalline grains with extremely thin grain boundaries, or a ceramic that forms a Joseph 4-junction with hosoint-like weak bonds between the grains, it is possible to The superconducting state of a superconductor film can be broken down to a normal conducting state using weakly focused light. Moreover, this change in state is due to the extremely high operating speed of the Josephusian element, which is unique to superconductors.

<Function> The recording medium used in the magneto-optical recording of the present invention is a thin film of superconductor, and when irradiated with a light beam for writing, the superconducting state is broken and changes to normal conductivity. This makes it possible to write at a speed of about 1012 bits/second, which is much faster than with conventional magneto-optical recording methods.

Furthermore, the use of ceramic superconductors has made it possible to write with light of low energy.

<Example> Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows writing of information bits into a superconductor film 1 according to an embodiment of the present invention.

A superconductor film 1 is produced on a substrate 5, and this superconductor film 1
A uniform bias magnetic field 6 smaller than the critical magnetic field Hc is applied from a direction perpendicular to the surface of the film 1. The superconductor film 1 in this state is irradiated with laser light in a minute spot converged by a converging lens.

The part of the superconductor film 1 that is irradiated with the focused laser beam 2
The superconducting state is broken and becomes a normal conductor, and the perfect diamagnetism, which is a characteristic of superconductors, disappears.

FIG. 2 shows the change in the bias magnetic field 6 due to the irradiation of the laser beam 2. When the superconductor film 1 is in a superconducting state, the magnetic field 6 cannot penetrate into the film 1 due to its complete diamagnetic property. However, when the spot 8 is irradiated by the laser beam 2 and that part becomes a normal conductor, the bias magnetic field is concentrated on the spot 8, and the spot 8 becomes a normal conductor.
Increase the magnetic flux density of the part.

Therefore, even if information is written in the spot 3 with the laser beam 2 and the laser beam irradiation is stopped as shown in FIG. 2, the critical magnetic field H
If the bias magnetic field 6 is designed to satisfy the above requirements, the written information will be retained without being lost.

Through the above steps, writing to the superconductor film 1 is performed, but
Instead of the conventional method of reversing magnetization using the thermal effect of laser light, the present invention uses a phenomenon in which the superconducting state is changed using laser light 2, so writing can be performed very quickly, in about 10-12 seconds.

The reading of information written with the laser beam 2 is weaker than the laser beam 2 used for writing, as in the conventional case, and
The laser beam 2 that is irradiated with a linearly polarized laser beam is rotated by a magnetic field due to the Faraday effect or the magnetic Kerr effect, so it is sufficient to detect the rotation.

In the embodiment, laser light was used for writing and reading using optical energy because laser light has little aberration such as chromatic aberration when converged and can create an extremely small light spot.

Next, the ceramic superconductor used in this example will be explained.

It is desirable that the state of superconductors used in magneto-optical recording can be controlled with low energy.

In superconductivity, which changes the superconducting state with small energy,
There is a ceramic superconductor shown in FIG. 3 and used in a magnetoresistance element. A constant current is passed through the magnetoresistive element from an unillustrated power source through the electrode 8 and lead wires 9 and 10. This ceramic superconductor magnetoresistive element exhibits a superconducting state when there is no magnetic field, and the voltage of element 1 is not detected. The voltage of element 1 is detected.

As this magnetic field increases, the resistance of the element increases rapidly.

The characteristics of the superconductor of the magnetoresistive element described above are as shown in FIG. This is due to ceramic superconductors assembled through bonding. FIG. 5 shows an equivalent circuit of this ceramic superconductor.

Ceramic superconductors with Josephson junctions at grain boundaries are
Application of a relatively weak magnetic field or current, or irradiation with light affects the tunnel current in the Josephson junction, causing the superconducting state to break.

As explained above, a ceramic superconductor having a Josephson junction at the grain boundary can break the superconducting state from the junction and become a normal conductive state even by short-term irradiation with light. Therefore, if a thin film of such a ceramic superconductor is used in the above-mentioned superconducting magneto-optical recording, it is possible to create a device that can write with a small amount of external energy using a ceramic superconductor, which is currently the superconductor with the highest critical temperature. .

Note that since the critical magnetic field Hc of the ceramic superconductor is low, the bias magnetic field that holds the entire writing section can be made small.

Furthermore, the ceramic superconductor thin film with the above characteristics is
Film production technology using sputtering method, CVD method, etc.
It can be manufactured by heat treatment with controlled atmosphere and temperature conditions. Further, as the substrate of this superconductor film 1, a ceramic substrate such as alumina or zirconia, or a heat-resistant glass substrate can be used when a transparent substrate is required.

<Effects of the Invention> In magneto-optical recording using a ceramic superconductor film made of crystal grains according to the present invention, the superconducting state is destroyed by irradiation with a small amount of energy due to the characteristics of the grain boundaries, so the irradiated laser light does not need to be particularly strong. It is also possible to perform extremely high-speed writing. Furthermore, since the critical magnetic field Hc is also small, the bias magnetic field can also be made small.

Further, since this readout can also be performed optically at high speed, extremely high speed superconductor magneto-optical recording can be realized with low energy consumption.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
A partially enlarged view of the figure, FIG. 3 is an explanatory diagram of the superconductor of the present invention,
FIG. 4 is a partially enlarged view of a superconductor, FIG. 5 is an equivalent circuit diagram of FIG. 4, and FIG. 6 is a configuration diagram of a conventional example. 1 is a superconductor film, 2 is a laser beam, 3 is a spot, 8 is an electrode, 9 and 10 are lead wires, 11 is a superconductor particle, 12 is a grain boundary, 13 is a Josephson junction, 14 is a magnetic film, 15
is a bias magnetic field, and 16 is a magnetic field generator. Agent: Patent attorney Takeshi Sugiyama (and 1 other person) 6 by “r”
S λ-1, ]L 1st ■ Figure 2! Figure 3 Figure A

Claims (1)

[Claims] 1. A uniform bias magnetic field smaller than the critical magnetic field of the superconductor thin film is applied perpendicular to the film surface of the ceramic superconductor thin film consisting of crystal grains, and the superconductor film is locally irradiated with light. The input of the light irradiation is recorded by partially converting into a normal conductor, converging the magnetic flux of a bias magnetic field on the normal conductor part, and keeping it above the critical magnetic field of the superconductor thin film. Superconductor magneto-optical recording method.