JPH04263149A - Magneto-optical recording system - Google Patents

Abstract

PURPOSE:To perform optical modulation overwrite in magneto-optical recording by a method wherein three layers of magnetic films between which exchange couplings are provided are employed. CONSTITUTION:A recording medium has a recording layer 1, a bias layer 3 which gives a bias magnetic field to the layer 1 and a layer 2 which controls the rate of exchange couplings between the layers 1 and 3. By utilizing the fact that difference in temperature gradient in the film thickness direction in accordance with the inbtensity of a luminous power, (a) when the power of the applied light is low, the recording layer is magnetized in the direction following bias layer auxiliary lattice magnetization and, (2) when the power of the applied light is high, the recording layer is magnetized along the direction of an external magnetic field. Magneto-optical recording which facilitates overwrite with a simple record/reproduction apparatus is realized.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to magneto-optical recording in which information is recorded, reproduced and erased using an energy beam such as a laser beam, and relates to a magneto-optical recording system that allows high speed rewriting and overwriting.

0002

2. Description of the Related Art There are two methods for overwriting in magneto-optical recording: a magnetic field modulation method and an optical modulation method.

[0003] In the magnetic field modulation method, a magneto-optical recording film is continuously irradiated with light, the recording area is heated by the energy of the irradiated light, and at the same time, a magnetic field modulated based on the information to be recorded is applied. By reversing the magnetization of the magneto-optical recording film,
Perform overwriting (for example, Japanese Patent Application Laid-Open No. 60-2515
39, JP 60-261051, JP 61-224
52 etc.).

On the other hand, as a method for overwriting by optical modulation, a method using two layers of magnetic films magnetically exchange-coupled with each other has been reported (Japanese Patent Laid-Open No. 175948/1983). This method uses a recording medium consisting of two exchange-coupled magnetic films, a recording layer and an auxiliary layer, and each time recording, the auxiliary layer magnetic film is initialized by applying a magnetic field by an initializing magnet. Additionally, a method of overwriting without an initialization magnet using the same exchange-coupled two-layer film has been reported.
Page 191, lecture number 23aC-3). This utilizes the fact that the temperature difference between the recording layer and the auxiliary layer changes due to modulation of laser light intensity to modulate the magnitude of exchange coupling, thereby performing overwriting.

[0005]

[Problem to be solved by the invention] Among the above conventional techniques,
The magnetic field modulation overwrite method requires a magnetic field generating electromagnet that can switch a magnetic field with an intensity of several hundred Oe at high speed. For this reason, there is a drawback that the magnetic field application mechanism in the recording/reproducing apparatus becomes complicated. on the other hand,
The optical modulation overwrite method using an exchange-coupled two-layer recording film and an initialization magnet requires an initialization magnet that generates a large magnetic field of about 4 kOe to be incorporated into the recording/reproducing device.
Therefore, there are problems in that the device configuration becomes large and complicated, and magnetic shielding is also difficult.

[0006] The above-mentioned problems can be solved in a system that uses an exchange-coupled two-layer recording film and performs overwriting without an initializing magnet. However, the margins regarding the applied magnetic field and laser output during recording are small, and the magnetic properties of the recording layer and auxiliary layer as well as the magnitude of exchange coupling between the two layers must be controlled within a narrow range when manufacturing the medium. There is. Another drawback is that there is a lot of noise during recording.

An object of the present invention is to realize a magneto-optical recording system that can perform optical modulation overwriting without the need for initialization by applying a magnetic field each time recording, while eliminating the problems of the prior art described above. It is to be.

[0008]

[Means for Solving the Problems] The above object is to provide a recording layer that records information depending on the direction of magnetization, a bias layer that applies an effective bias magnetic field to the recording layer through magnetic exchange coupling, and a structure in which the recording layer and the bias layer are connected to each other. Using a magneto-optical recording medium that has three layers of magnetic films, a control layer that exists between This is achieved by employing a magneto-optical recording method that takes advantage of this change and performs overwriting through optical modulation.

[0009]

[Operation] FIG. 1 shows the structure of a magneto-optical recording medium used in the present invention. The recording medium has three magnetic layers: a recording layer 1, a bias layer 2, and a control layer 3. The recording layer holds recorded information, and this information is read out using laser light 6 during reproduction. After the bias layer is formed, a magnetic field is applied to initially magnetize the entire surface of the medium in one direction. Since the bias layer has a high Curie temperature, the magnetization does not reverse during recording and reproduction and maintains the initial magnetization direction semi-permanently. An exchange coupling force acts from the bias layer to the recording layer via the control layer to align the transition metal sublattice magnetizations 5 in the same direction. This exchange coupling force acts on the magnetization of the recording layer as if a bias magnetic field was applied in the direction perpendicular to the film surface. Therefore, hereinafter, the effect of this exchange coupling force added to the magnetic field actually applied from the outside will be referred to as the effective bias magnetic field applied to the recording layer. The control layer is located between the recording layer and the bias layer, and has a function of controlling the exchange coupling force exerted on the recording layer from the bias layer.

It is assumed that the writing laser beam 6 is always irradiated onto these three magnetic layers from the recording layer 1 side. The laser light is irradiated in pulses or as continuous light onto a medium moving at high speed, and in either case, the magnetic film is cooled rapidly after irradiation with the laser light.

FIG. 2 shows the recording layer, control layer, and
An example of the temperature dependence of the coercive force Hc of the bias layer is shown. Let the Curie temperatures of the recording layer, control layer, and bias layer be T1, T2, and T3, respectively. In order to realize the overwriting of the present invention, a recording medium in which these temperatures satisfy the relationship T2<T1<T3 is suitable.

FIG. 3 shows the recording principle of optical modulation overwriting according to the present invention. The left side shows a conceptual diagram of the recording medium, and the right side shows the distribution of the recording film temperature T in the film thickness direction z. Since the recording film temperature is always kept sufficiently lower than the Curie temperature T3 of the bias layer, the orientation of the sublattice magnetization of the bias layer is maintained semi-permanently. The direction of this sublattice magnetization is tentatively shown upward in FIG. This recording medium is irradiated with a laser beam from the recording layer 1 side under a fixed externally applied magnetic field 8 (Hex).

During low power irradiation, the temperature of the recording layer reaches the Curie temperature T1, and the direction of magnetization of the recording layer is fixed immediately after the temperature reaches its peak. At that point, the temperature distribution in the recording film thickness direction is such that the recording layer on the light incident side is at a high temperature, and as shown in FIG. 3(a), there is a large temperature difference between the recording layer and the control layer. At this time, since the temperature of the control layer is sufficiently lower than its Curie temperature T2, a large exchange coupling force acts from the bias layer to the recording layer via the control layer. In the present invention, the effective magnetic field due to this exchange coupling force is set to be opposite to and sufficiently larger than the externally applied magnetic field Hex. Then, the sublattice magnetization of the recording layer follows the exchange coupling force and is oriented in the same direction as the sublattice magnetization of the bias layer.

On the other hand, during high power irradiation, the medium temperature is
After being heated to a temperature sufficiently higher than the Curie temperature T1 of the recording layer, it is slowly cooled. Therefore, when the recording layer temperature drops to its Curie temperature T1 and the direction of magnetization of the recording layer is fixed, the temperature distribution in the recording film thickness direction becomes more uniform, as shown in Figure 3(b). As shown,
The temperature difference between the recording layer and the control layer is smaller than in the case of low power irradiation. In this case, the recording layer has its Curie temperature T1
Even when the temperature of the control layer is reached, the temperature of the control layer is still above or just below its Curie temperature T2, and exchange coupling in the control layer does not exist or is very weak. therefore,
The exchange coupling force exerted from the bias layer to the recording layer via the control layer is small, and the effective bias magnetic field that magnetizes the recording layer is dominated by the externally applied magnetic field Hex. Therefore, the recording layer magnetization is oriented in the direction of the externally applied magnetic field,
Fixed. Even in this case, if the temperature further decreases and the control layer becomes sufficiently lower than its Curie temperature T2, the exchange coupling force from the bias layer will reach the recording layer. However, at that point, the temperature of the recording layer is already sufficiently lower than its Curie temperature T1 and the coercive force is large, so the recording layer is affected by exchange coupling from the bias layer. The magnetization will not be reversed again. As a result, during high power irradiation, the direction of magnetization of the recording layer is fixed in the opposite direction to that during low power irradiation.

[0015] The temperature of the recording layer is once set to the Curie temperature T1 in both cases of high power irradiation and low power irradiation.
The magnetic domain pattern previously recorded in the recording layer is erased during the temperature rise process. In other words, direct overwriting is possible regardless of the previously recorded information.

Based on the above recording principle, it is possible to record information by controlling the direction of magnetization of the recording layer by modulating the intensity of the laser beam between two levels: strong and weak. After recording, when the recording film temperature drops to room temperature (RT), recording magnetic domains 9 are formed only at low power irradiation positions, as shown in FIG. 3(c).

In the above explanation of the recording principle, T1,
Although T2 is the Curie temperature of the recording layer and the control layer, more generally, the same result can be obtained by replacing T1 with the temperature at which the magnetic domain of the recording layer is fixed and T2 with the temperature at which the exchange coupling of the control layer becomes small. The recording principle holds true.

FIG. 4 shows an example of a laser beam modulation method according to the present invention. For the binary recording information (a), the laser light output P is as shown in (b), corresponding to the recording signal 0,
The recording medium is irradiated with a high laser energy level PH corresponding to recording signal 1 and a low laser energy level PL . At this time, a pattern of recording magnetic domains 9 is formed on the recording layer as shown in (c). In this example, at a position on the medium corresponding to information 1, the magnetization of the recording layer is reversed, and at a position corresponding to information 0, the recording layer magnetization is in the initial magnetization direction. The magnetic domain pattern recorded in this manner can be reproduced by a laser beam at the reproduction light level PW and by using the Kerr effect using a reproduction apparatus commonly used in the present technology.

[0019]

EXAMPLES The present invention will be explained in detail below based on examples.

[Example 1] The recording layer was made of TbGd with a Curie temperature of 150°C, a compensation temperature of 40°C, and a film thickness of 40 nm.
FeCo was used as an auxiliary layer, and a TbCo film with a Curie temperature of 400°C or higher, a compensation temperature of 150°C, and a film thickness of 60 nm was used as an auxiliary layer.
As the control layer, a TbGdFeCo film with a Curie temperature of 130° C., a compensation temperature of below room temperature, and a film thickness of 8 nm is used. The above magnetic film was formed by magnetron sputtering on a glass substrate on which grooves were formed by the 2p method. SiNx films were placed above and below the magnetic film as protective layers.

Using this recording medium, the laser beam is modulated with a waveform consisting of two levels of PH and PL (duty ratio 50%) similar to that shown in FIG. , were alternately and repeatedly overwritten on the same track. High power level PH and low power level PL
were set at film surface energies of 15 mW and 12 mW, respectively. The relative linear velocity of the recording medium to the laser spot was 20 m/s. The external magnetic field applied during recording was 200 Oe.

FIG. 5 shows the carrier-to-noise ratio (C/N) of 5 MHz and 3 MHz signals (bandwidth 30 kHz). C/
N is 43 dB for a 3 MHz signal and 41 dB for a 5 MHz signal. Furthermore, the C/N of each frequency signal decreased to 0 dB after overwriting with another frequency signal, confirming that overwriting without any unerased data is possible.

[0023]

[Effects of the Invention] According to the present invention, overwritable magneto-optical recording can be performed by optical modulation without using an initialization magnet, so high-speed recording can be performed using a simple and compact recording/reproducing device. becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a magneto-optical recording medium used in the present invention.

FIG. 2 is a diagram showing an example of temperature changes in coercive force Hc of each of a recording layer, a bias layer, and a control layer used in the present invention.

FIG. 3 is a diagram illustrating the principle of optical modulation overwriting according to the present invention.

FIG. 4 is a diagram showing an example of a laser modulation method according to the present invention.

FIG. 5 is a diagram showing the carrier wave-to-noise ratio when overwriting is repeated with 5 MHz and 3 MHz recording signals in Example 1.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Recording layer, 2... Control layer, 3... Bias layer, 4... Substrate,
5... Sublattice magnetization of transition metal, 6... Laser light, 7... Lens, 8... Externally applied magnetic field, 9... Recording magnetic domain, 10... Groove.

Claims (2)

[Claims] Claim 1: A recording layer that records information based on the direction of magnetization;
a bias layer that provides an effective bias magnetic field to the recording layer by magnetic exchange coupling; and a control layer that is present between the recording layer and the bias layer and controls the strength of exchange coupling between both layers. Recording occurs when the temperature difference between the recording layer and the control layer changes as the intensity of the irradiated laser light changes, and the direction of magnetization of the recording layer is thereby fixed. A magneto-optical recording method that performs overwriting by modulating the intensity of laser light by utilizing changes in the effective bias magnetic field applied to the layer. 2. The Curie temperature T1 of the recording layer, the Curie temperature T2 of the control layer, and the Curie temperature T3 of the bias layer are T2.
2. The magneto-optical recording method according to claim 1, wherein the magneto-optical recording method satisfies the relationship <T1<T3.