JPS63311645A - Magneto-optical recording system - Google Patents

Abstract

PURPOSE:To eliminate a bias magnetic field by applying a processing magnetizing the entire medium in a direction in advance. CONSTITUTION:A magnetic thin film of two-layer structure composed of a recording layer 3 and an auxiliary layer 2 is used as a magneto-optical recording medium. The Curie temperature of each layer is lower in the order of the auxiliary layer 2 and the recording layer 3, the auxiliary layer and the recording layer are made of perpendicular magnetization film and the perpendicular magnetic anisotropy is smaller in the order of the recording layer 3 and the auxiliary layer 2. The medium is magnetized uniformly in perpendicular direction to the film face in advance (the processing is called as the initial magnetization and the magnetized direction is referred to as positive direction as the convenience of explanation). Then when a light beam 5 irradiates a recording area to heat the corresponding part and to record the information, the light beam intensity is changed into two levels of strong/weak levels in response to the information signal. Thus, no bias magnetic field is required, the device is simplified, and the miniaturization of the device and the reduction of the weight are attained.

Description

[Detailed Description of the Invention] <Industrial Application> The present invention is a magneto-optical device with a so-called overwrite function that allows new information to be sequentially rewritten on an already recorded area by changing the intensity of a light beam. This concerns the recording method.

<Conventional technology> Conventionally, recording (writing information) on a magneto-optical disk was done by
A uniformly magnetized optical recording medium (perpendicularly magnetized thin film such as Th-Fer4 film) is irradiated with a laser beam while applying a bias magnetic field below the anisotropy field in the opposite direction to the magnetization, and the temperature of the irradiated area is brought to the Curie temperature. After the above temperature is increased, the magnetization is reversed in the direction of the bias magnetic field Hb during the cooling process of the medium, and information is recorded as a sequence of magnetization reversals by turning the laser beam on and off. In this method, when new information is to be recorded again in an area that has been previously recorded, a continuous laser beam is irradiated in an opposite bias magnetic field to heat the medium and align all the magnetization in one direction (
This is called an elimination process). In other words, it is necessary to erase and then record again, and just like writing information in normal magnetic recording, recording new information over the previously recorded area automatically erases the previous information. There is no so-called overwriting function, which has been an obstacle to increasing access speed and compatibility with conventional magnetic recording devices.

Recently, a magneto-optical disk using a 2NJ thin film and capable of overwriting has been proposed. Below, I will explain its operating mechanism.

FIG. 2 shows an outline of a magneto-optical disk. 1 is a magneto-optical disk substrate, 2 is an auxiliary layer (low anisotropic magnetic field, high Curie temperature), 3 is a recording layer (high anisotropic magnetic field, low Curie temperature),
4 is an optical head, and 5 is a laser beam (light beam).

When the disk 1 is rotating in the direction of the arrow, first a strong perpendicular magnetic field Hini is applied to the disk surface by the permanent magnet 6 to completely magnetize only the auxiliary layer 2 in the direction of the magnetic field (this is called initialization). ). Next, this medium is moved under the optical head 4 and heated by a light beam 5 having two levels of optical power: strong and weak. Here, a weak bias magnetic field Hb is applied in the opposite direction to the initializing magnetic field Hini.

When the power of the light beam 5 is small, the aXa of the irradiated area
The temperature is higher than the Curie temperature of recording layer 3, but it is auxiliary 1'! t
The temperature is set to be below the Curie temperature of 2. In this case, only the recording layer 3 becomes nonmagnetic, and the magnetization of the auxiliary layer 2 remains without being lost. When the medium moves and the temperature of the area irradiated with the laser beam 5 decreases, the recording Nj3
The magnetization of is aligned in the same direction as the magnetization of the auxiliary layer 2 due to spin interaction. On the other hand, when the laser power is large, the temperature of the medium is auxiliary F! ! Set it so that it is higher than the Curie temperature of 2. In this cooling process, the magnetization of the auxiliary layer 2 is first aligned in the direction of the external bias magnetic field Hb, and following this magnetization, the magnetization of the recording layer 3 is also aligned in the direction of the bias magnetic field Hb, thereby completing recording. Since the above recording process does not depend on the magnetization state of the recording layer 3, this shows that recording can be performed at any time depending on the strength of the power of the light beam 5, that is, overwriting can be performed. Information written in the recording 1'5i3 can be read out as a difference in the slope of the polarization plane of the reflected light of the laser beam. The laser power during reproduction must be set so that the medium temperature is sufficiently lower than the Curie temperature of the Tb-Fe1 film.

<Problems to be solved by the invention> However, as the auxiliary layer 2, T b -F e -C
.

In an example where a Tb-Fe thin film is used as the recording Fi3, the initializing magnetic field Hi is 6000 Gauss.
A high magnetic field of s is required (National Conference of Japan Society of Applied Physics,
Lecture presented on March 28, 1986; Masatoshi Sato, Shun Saito,
Hiroyuki Matsumoto, Hideki Akasaka "Single beam overwriting method using multilayer magneto-optical recording media" Lecture number 28 p-z
l-3).

For this reason, considering that magneto-optical disks are generally housed in cassettes and the distance between the medium and the magnet is several inches, in order to obtain such a high magnetic field Hini, the size of the permanent magnet or electromagnet must be quite large. Therefore, it can be said that there are inherent problems such as difficulty in reducing the size and weight of the device.

Furthermore, it is necessary to generate magnetic fields Hini and Hb in two directions, positive and negative, which complicates the device configuration.

An object of the present invention is to provide an overwriting method that does not require a bias magnetic field in a magneto-optical recording system.

This differs from the conventional overwriting method in that, in addition to not requiring a bias magnetic field, the entire medium is previously magnetized in one direction, that is, initial magnetization is performed.

Principle of the Present Invention> FIG. 1 shows a detailed explanatory diagram of the present invention. Recorded as a magneto-optical recording medium NJ3, auxiliary W! Use a J2 2ps structure magnetic thin film. The Curie temperature of each layer is lower in the order of auxiliary NJ2 and recording layer 3, and the auxiliary layer and recording layer are perpendicularly magnetized films, and the perpendicular magnetic anisotropy thereof is lower in the order of recording layer 3 and auxiliary PJ2.

The medium is uniformly magnetized in advance in a direction perpendicular to the film surface (this process is called initial mization, and the direction of magnetization is conveniently referred to as the positive direction).

Next, when the light beam 5 is irradiated onto the recording area to heat the corresponding area and record information, the light beam intensity is changed in two levels depending on the information signal.

When the light beam intensity is at a high level, recording is performed to near the Curie temperature of the auxiliary layer 2. Since W3 and the auxiliary layer 2 are heated together, their magnetization changes to the recording I on both sides of the recording track when cooled.
The magnetic field generated from I3 and the magnetization of the auxiliary layer 2 aligns the initial magnetization direction in the opposite direction (minus direction). At this time, there are several possibilities for the contribution of the magnetic fields generated from the previous and subsequent bits on the same track depending on the information written there. The state in which writing is most difficult is when the magnetization of the front and rear bits is in the negative direction, and in this case, a demagnetizing field is applied to the light beam irradiated area from the front and rear bits in the positive direction. However, the magnetic field generated from the front and rear bits is relatively small compared to the magnetic field generated from both sides of the track because the magnetization of the recording layer 3 and the auxiliary II 2 are opposed, as will be described later, and its influence can be ignored. .

On the other hand, at a low level where the light beam intensity is weak, the recording layer 3 is heated to around its Curie temperature to provide additional support! 52 is maintained at a temperature sufficiently lower than its Curie temperature, the magnetization of the recording layer 3 is reduced to auxiliary I! during the cooling process. ! Due to the spin interaction with the auxiliary layer 2, the magnetization is aligned in the same direction as the auxiliary layer 2 (ie, in the positive direction). Therefore, by changing the light beam intensity,
Either positive or negative magnetization can be written in the recording N3 depending on the information.

The next conversion is performed before new information is recorded again in the previously recorded portion. After the medium moves away from the light beam 5 and cools down to room temperature, the intensity is more than necessary for externally reversing the magnetization of the auxiliary R2, and at the same time the recording F! Auxiliary I adds a magnetic field of insufficient strength in the positive direction to reverse the magnetization of 53.
! ! Align only 2 in the positive direction and initialize the medium. That is, since the perpendicular magnetic anisotropy of the recording layer 3 is larger than that of the auxiliary IW2, regardless of the magnetization state of the recording layer 3, only the direction of magnetization of the auxiliary layer 2 can be made to coincide with the positive direction after initialization. Apply strength 2 again to the medium in this state.
By irradiating with the light beam 5 of the same level, the above-mentioned magnetization reversal behavior is repeated, and new information can be re-recorded one after another. If a bit with magnetization in the negative direction is written in the recording layer 3, the demagnetizing field exerted on the light beam irradiation area is canceled out because the magnetization of the recording NJ3 and the auxiliary layer 2 are opposite after initialization. . As a result, when writing bits in the negative direction by increasing the light beam intensity, the influence of the magnetic field generated from the preceding and succeeding bits described above is reduced.

When detecting recorded signals using the magneto-optic effect, the light beam intensity is set sufficiently lower than the Curie temperature of the recording layer.
Make sure that the magnetization state of the medium does not change.

EXAMPLE A medium having the same configuration as that shown in FIG. 1 was prepared to verify the effects of the present invention. Substrate 1 is a glass disk. A recording layer of 21% Tb-79 was formed on this substrate 1 by sputtering.
After forming the 500% Fe thin film 3, 2 was added as an auxiliary layer.
3%Tb-65%Fe-12%co thin film 2so.

The people were thick. This medium is manufactured using a so-called initial magnetization process in which the magnetization of the recording layer 3 and the auxiliary layer 2 are aligned in one direction (for convenience, in the positive direction) by applying an external magnetic field of 20 KO@ perpendicularly to the thin film surface. Apply. Since the coercive forces of the recording layer 3 and the auxiliary layer 2 are 15 KOe and 5 KOa, respectively, a magnetic field of 20 KOe is strong enough for initial magnetization.

Next, a light beam was focused on the medium from the glass substrate side to heat the recording layer 3 and the auxiliary layer 2.

The moving speed of the medium is 8 m/min, and the optical beam diameter is 1.
It is μm. When the light beam intensity is 11 mW, the magnetization of the recording layer 3 and the auxiliary layer 2 are reversed and aligned in the negative direction, which is a sign of light damage II! It was confirmed by observation. Below 5 mW, no reversal of magnetization occurs. Next, a magnetic field of 6 KOe is applied from the outside in the positive direction, and the auxiliary F! After only the magnetization of No. 12 was reversed to the positive direction, the entire medium was gradually heated.

The previously recorded magnetization reversal region in the negative direction stably exists until the medium temperature reaches 120° C., but disappears when the temperature reaches 120° C. or higher.

The above experiment can be interpreted as follows. When the light beam intensity is 11 mW or more, the Curie temperature of the auxiliary layer 2 (2
Since both the recording layer 3 and the auxiliary layer 2 are heated to around 00° C., in the subsequent cooling process, the light beam heated region is magnetized in the negative direction due to the demagnetizing field generated from its surroundings. Next, the process of applying an external magnetic field of 6 KOs from the outside is an initialization process. The fact that only the magnetization of the auxiliary @2 in the light beam irradiation area was reversed in the positive direction by initialization means that when the whole is heated next, the magnetization reversal region of the recording layer 3 disappears when it is heated to the Curie temperature of the recording layer 3. You can prove it by putting it away. That is, the magnetization of the recording layer 3 is directed in the positive direction due to the spin interaction with the auxiliary layer 2.

In this example, the entire sample was heated in a furnace, but if this heating was also done by light beam irradiation, the light beam intensity could be modulated into two levels of strength and weakness, allowing the irradiation area to be heated. It is clear that this is equivalent to being able to direct the direction of magnetization of the recording FJ3 in any positive or negative direction. In addition, the magnetization state of the recording layer 3 was observed using an optical microscope, but if the inclination due to the magneto-optic effect of the polarization plane of the same light beam as that used for heating is detected, the overwriting process of magneto-optical recording can be achieved. Then, the regeneration process is completed.

<Effects of the Invention> As described above, by using the method of the present invention, the bias magnetic field required in the conventional overwrite recording method is no longer required, and the device configuration can be made simpler, smaller, and lighter. The feature is that it is possible to

[Brief explanation of drawings]

Fig. 1 shows the principle of the present invention, Fig. 2 shows the conventional technology,
The same figure (al is an explanatory diagram of initialization, the same figure [b] is an explanatory diagram of the recording state when the optical power is low, and the same figure (C) is an explanatory diagram of the recording state when the optical power is high. In the drawing, 1 is a substrate, 2 is an auxiliary layer, 3 is a recording layer, 4 is an optical head, 5 is a light beam, 6 is a permanent magnet, Hini is an initializing magnetic field, and Hb is a bias magnetic field. No./111\\Hini Figure 2

Claims (2)

[Claims] (1) A magnetic thin film with a two-layer structure of a recording layer and an auxiliary layer is used as a magneto-optical recording medium, and initial magnetization is performed in advance to uniformly magnetize the recording layer and the auxiliary layer in the direction perpendicular to the thin film surface. Later, when recording information by irradiating the recording area with a light beam and heating the corresponding area, two levels of light beam intensity, strong and weak, are used, and when the light beam intensity is at a high level, the magnetization of the auxiliary layer and recording layer is The magnetic field generated by the magnetization of the recording layer and the auxiliary layer on both sides of the recording track is set to heat the recording layer to a temperature higher than that aligned in the direction opposite to the initial magnetization direction.On the other hand, when the light beam intensity is at a low level, the recording layer The magnetization of the auxiliary layer is aligned with the initial magnetization direction in the same direction as that of the auxiliary layer due to the spin interaction with the auxiliary layer, but the magnetization of the auxiliary layer is heated to a temperature that does not change. Correspondingly, the magnetization in either direction is written to the recording layer, and the intensity is greater than that required for externally reversing the magnetization of the auxiliary layer before recording new information on the medium; At the same time, a magnetic field with insufficient strength to reverse the magnetization of the recording layer is applied to the initial magnetization direction, and initialization is performed to align only the auxiliary layer with the initial magnetization direction, and the direction of the magnetization of the recording layer is controlled by the magneto-optic effect. 1. A magneto-optical recording method, characterized in that the light beam intensity is sufficiently lower than the Curie temperature of the recording layer and does not change the magnetization state of the medium during detection using the magneto-optical recording method. (2) In claim 1, the Curie temperature of the medium is lower in the order of the auxiliary layer and the recording layer, the auxiliary layer and the recording layer are perpendicularly magnetized films, and the perpendicular magnetic anisotropy is lower in the order of the recording layer and the auxiliary layer. A magneto-optical recording method characterized by the use of small media.