JPH0746444B2 - Magneto-optical memory medium and recording method using the medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a medium for a magneto-optical memory and a method for recording information using this medium.

[Conventional technology]

Since the magneto-optical memory is a kind of magnetic recording, it has the advantage that the recorded information can be rewritten, but on the other hand, even information that should not be erased disappears due to an erroneous operation or due to an unexpected external magnetic field application. There is a drawback that ends up. On the other hand, a draw (DRAW) type optical memory is stable with respect to an external magnetic field, and although the information disappears as described above, the recorded information cannot be rewritten.

[Problems to be solved by the invention]

The object of the present invention is to solve the above-mentioned conventional problems, and the information once written can be rewritten, and on the other hand, the written information is stable against an external magnetic field and does not disappear due to an unexpected situation that may normally occur. It is an object of the present invention to provide a medium for a magneto-optical recording memory and a recording method using this medium.

[Means for solving problems]

The above object can be achieved by the present invention described below. That is, the present invention is directed to an antiferromagnetic layer made of a transparent antiferromagnetic material arranged on the light incident side, and a low coercive force ferromagnetic material having a Curie temperature higher than the Neel temperature of the antiferromagnetic material. A medium for a magneto-optical memory having a multilayer film of two or more layers including at least a ferromagnetic layer consisting of: a magnetic moment of the antiferromagnetic layer and a magnetic moment of the ferromagnetic layer; The magneto-optical memory medium is characterized in that it is parallel or anti-parallel at the interface of layers by the exchange interaction and the thickness of the antiferromagnetic material is adjusted to a thickness that enhances the Kerr effect. Another aspect of the present invention is an antiferromagnetic layer made of a transparent antiferromagnetic material arranged on the light incident side, and a low coercive force ferromagnetic material having a Curie temperature higher than the Neel temperature of the antiferromagnetic material. A multilayered film having two or more layers including at least a ferromagnetic layer made of a body, and the magnetic moment of the antiferromagnetic layer and the magnetic moment of the ferromagnetic layer are exchange-coupled at the interface between the two layers. The antiferromagnetic material is parallel or antiparallel and the thickness of the antiferromagnetic material is adjusted to a thickness that enhances the Kerr effect. Recording is performed by locally irradiating from the body side to heat the antiferromagnetic layer to a temperature T equal to or higher than the Neel temperature and at the same time apply an external magnetic field larger than the coercive force of the ferromagnetic layer itself at the temperature T. This is a magneto-optical recording method.

The present invention is described in detail below. As shown in FIG. 1A, the medium for magneto-optical memory of the present invention has a basic structure of an exchange-coupling bilayer film including a ferromagnetic layer 1 and an antiferromagnetic layer 2.
It should be noted that the substrate supporting the bilayer film, such as glass or plastic, is omitted.

The ferromagnetic layer 1 is made of a ferromagnetic material (including a ferrimagnetic material in the present invention), the ferromagnetic material has a low coercive force, and the antiferromagnetic Neel temperature constituting the antiferromagnetic layer 2 Also has a high Curie temperature (preferably higher than 50 ° C.).
Here, "low coercive force" means magnetization reversal in a magnetic field generated by an ordinary coil or magnet (1 to 2 kOe at most, generally several hundred Oe) under conditions above the Neel temperature of the antiferromagnetic material. It means the coercive force to the extent that it does.

As shown in FIG. 1A, the magnetic moments of the antiferromagnetic material forming the antiferromagnetic layer 2 are arranged antiparallel to each other, and macroscopic net magnetization does not exist. In the two-layer film, the magnetic moment of the ferromagnetic layer 1 and the magnetic moment of the antiferromagnetic layer 2 are parallel or antiparallel at the interface due to quantum exchange interaction (parallel in the figure). . Whether it is parallel or antiparallel depends on the type of atom or the interatomic distance.

The principle of the recording system of the present invention using the above-described medium for magneto-optical memory is as follows. First of all,
As shown in FIG. 1B, a magnetic field H in the direction of the arrow is applied to the medium, and then laser light is focused from the antiferromagnetic layer side by the lens 3 and applied to the film to reinforce the temperature of a part of the medium. The temperature is raised to a temperature T higher than the Neel temperature of the magnetic material. Although the temperature T does not have an upper limit, it does not have to be unnecessarily high and may be equal to or lower than the Curie temperature of the ferromagnetic material.

When the temperature of the medium for magneto-optical memory reaches the temperature T, the antiferromagnetic material loses its magnetic alignment, and the ferromagnetic layer 1 has a small original coercive force. Occurs. The magnitude of the magnetic field H at this time needs to be equal to or higher than the magnetic field for reversing the magnetization of the ferromagnetic substance at the temperature T, that is, equal to or higher than the coercive force of the ferromagnetic substance itself at the temperature T.

Next, when the temperature is lowered to the Neel temperature of the antiferromagnetic material or lower, the antiferromagnetic material is magnetically aligned again, but at this time,
Exchange interaction acts on the spins of the ferromagnetic layer 1 and the antiferromagnetic layer 2 (parallel in the figure). By this interaction,
As shown in FIG. 1C, an array 5 of magnetic moments corresponding to recorded information is formed in the antiferromagnetic layer 2, and a magnetic field of σw / 2Ms h is actually generated in the ferromagnetic layer 1 by the exchange force. It is applied from the ferromagnetic layer 2. Due to this magnetic field, the ferromagnetic layer 1 which originally has small coercive force (ignoring the original coercive force of the ferromagnetic layer 1) apparently has coercive force increased to σw / 2Msh, and the recorded information can be stably retained. it can. Here, σw is the energy density of a kind of domain wall formed at the interface between the two layers, Ms is the saturation magnetization of the ferromagnetic layer, and h is the film thickness of the ferromagnetic layer.

Not only is the apparent coercive force of the ferromagnetic layer 1 improved, but since the antiferromagnetic layer 2 is originally responsible for recording, the recorded information is very stable against an external magnetic field. That is, as shown in FIG. 2A, even if the recorded information of the ferromagnetic layer 1 is damaged by the external magnetic field H, the arrangement of the magnetic moments of the antiferromagnetic layer 2 is still maintained, so that the magnetic field is removed. , The recorded information almost reversibly returns to the original state (FIG. 2 (b)). In order to erase the array once recorded in the antiferromagnetic layer 2 below its Neel temperature, a magnetic field as large as a molecular magnetic field is required, which is much larger than the magnetic field normally obtained.

A semiconductor laser, a He-Ne laser, or the like is used as the recording means. On the other hand, to read information,
The ferromagnetic layer has a function as a read layer, and the same laser is used to reduce the power to irradiate the recording medium, and the Kerr effect is used to read from the ferromagnetic layer. Alternatively, a conventional magnetic head may be used.

In the present invention, the antiferromagnetic material is transparent, the antiferromagnetic layer is disposed on the light incident side, and reading is performed by using the Kerr effect. Since the film thickness is adjusted to enhance the effect, the read characteristic can be improved.

As another embodiment of the magneto-optical memory medium of the present invention which can be used in the above recording method, there is a structure in which a ferromagnetic layer is sandwiched by an antiferromagnetic layer. In this structure, the effective magnetic field applied to the ferromagnetic layer by the exchange force is twice as large as σw / 2Ms h to σw / Ms h, so that the magnetic characteristics are further improved.

When the value of σw is small and the value of Ms is large and the value of σw / 2Ms h is not too large, a very thin ferromagnetic material and a very thin antiferromagnetic material are stacked in layers. The magnetic properties can be improved by increasing the thickness of the entire ferromagnetic layer.

Perpendicular magnetic recording can be performed if the magnetic moment of both the ferromagnetic layer and the antiferromagnetic layer is oriented perpendicular to the film surface. In addition, even if the magnetic moment of the antiferromagnetic layer is perpendicular to the film surface and the ferromagnetic layer is an in-plane magnetized film, the value of σw / 2Ms h is the effective anisotropy of the ferromagnetic layer. The magnetization of the ferromagnetic layer can be oriented in the direction perpendicular to the film surface even if the external magnetic field is zero, by adjusting the magnetic field to be larger than the magnetic field.

Ferromagnetic materials that can be used in the magneto-optical memory medium of the present invention include, for example, the well-known Fe, Co, Ni, and alloys thereof. These Curie temperatures are 10 each
They are 40K, 1390K and 630K. Further, as an antiferromagnetic material that can be used in the magneto-optical memory medium of the present invention, for example, Cr ₂ O ₃ , Mn
There are O, FeS, CoO, and NiO. Each of these nails is 307K,
122K, 593K, 293K, 520K, of which NiO is the most suitable.

The magneto-optical memory medium of the present invention is manufactured by using an ordinary vapor deposition apparatus or sputtering apparatus. Exchange coupling works through the interface between the two layers, so the two-layer interface requires special attention. In order to prevent unnecessary oxygen, nitrogen, water, etc. from adsorbing to the interface, it is desirable to continuously manufacture the two layers without breaking the vacuum in manufacturing the recording medium.

In order to align the oxidation state of the medium in one direction prior to recording, the medium is scanned over the entire surface with laser light while applying a magnetic field according to the same principle as recording, or the entire medium is heated to the Neel temperature of the antiferromagnetic material. After that, the medium may be cooled while applying a magnetic field.

By applying the present invention, it is possible to manufacture a magnetic tape, a magnetic card or the like which is extremely stable against an external magnetic field.

〔Example〕

Ni as a ferromagnetic material (thickness: about 250Å, Curie point: 630
k), NiO as antiferromagnetic material (thickness: 500Å, Neel temperature: 5
20 k) was sequentially formed on a glass substrate using a sputtering device without breaking the vacuum, to fabricate a magneto-optical memory medium according to the present invention. Before recording, the medium was heated to a temperature higher than the NeO Neel temperature and then cooled while applying a magnetic field to align the magnetization state of the Ni layer in one direction.

Recording was performed by heating with a laser beam (wavelength: 780 nm) from the antiferromagnetic layer side while applying a magnetic field of 500 Oe. It was confirmed by the Kerr effect that the shift amount of the Ni hysteresis loop was different between the recorded part and the unrecorded part, and it was confirmed that the recording was actually performed. As a result, it was confirmed that the reading characteristics were improved. The difference between the magnetization states of both parts of Ni is 20
It was also observed after applying an external magnetic field of kOe and was found to be very stable against the external magnetic field.

〔The invention's effect〕

As described above, in the recording method using the medium for the magneto-optical memory having the basic structure of the exchange-coupling bilayer film composed of the antiferromagnetic recording layer and the ferromagnetic reading layer, the written recording Is very stable against an external magnetic field and practically does not disappear due to an unforeseen event. In addition, a transparent antiferromagnetic layer is placed on the light incident side if necessary to make the Kerr effect. Since the film thickness is adjusted to enhance
The readout characteristic is improved, which is very useful in practice.

[Brief description of drawings]

1A to 1C show a medium for a magneto-optical memory including a ferromagnetic layer and an antiferromagnetic layer and a recording process, and FIGS. 2A and 2B show the medium. 2 shows the stability of the recording magnetic domain with respect to the external magnetic field. 1 is a ferromagnetic layer, 2 is an antiferromagnetic layer, 3 is a condenser lens, 4 is a magnetic domain written in the ferromagnetic layer, and 5 is an array of magnetic moments corresponding to recorded information.

Claims (2)

[Claims] 1. An antiferromagnetic layer made of a transparent antiferromagnetic material arranged on the light incident side, and a low coercive force ferromagnetic material having a Curie temperature higher than the Neel temperature of the antiferromagnetic material. A medium for a magneto-optical memory having two or more multilayer films including at least a ferromagnetic layer formed of the antiferromagnetic layer and the magnetic moment of the antiferromagnetic layer. A medium for a magneto-optical memory, characterized in that it is parallel or antiparallel and the film thickness of the antiferromagnetic material is adjusted to a film thickness which enhances the Kerr effect by exchange interaction at the interface. 2. An antiferromagnetic layer made of a transparent antiferromagnetic material arranged on the light incident side, and a low coercive force ferromagnetic material having a Curie temperature higher than the Neel temperature of the antiferromagnetic material. A ferromagnetic layer, the magnetic moment of the antiferromagnetic layer and the magnetic moment of the ferromagnetic layer are parallel to each other due to exchange interaction at the interface between the two layers. Alternatively, the anti-ferromagnetic material is antiparallel, and the thickness of the antiferromagnetic material is adjusted to a thickness that enhances the Kerr effect. Recording is performed by locally irradiating to heat the antiferromagnetic layer to a temperature T equal to or higher than the Neel temperature and at the same time apply an external magnetic field larger than the coercive force of the ferromagnetic layer itself at the temperature T. Magneto-optical recording method.