JPH087349A - Magneto-optical recording medium and recording method thereof and magneto-optical recording apparatus - Google Patents

Abstract

PURPOSE:To realize overwrite recording of multi-level information with a simplified optical system by providing n magnetic layershaving different coercive forces within the period where temperature rises from the room temperature with irradiation of optical pulse and returns again to the room temperature. CONSTITUTION:A substrate is loaded into a sputter apparatus having a plurality of targets. The apparatus is evacuated up to the higher vacuum condition. Thereafter inactive gas is introduced up to the predetermined pressure. Under this condition, after the SiN layer is formed on the substrate to prevent oxidation and obtain the interference effect, TbFeCo is formed as a first magnetic layer 3 in the composition to provide the Curie temperature of Tc1 and TbFeCo is also formed as a nonmagnetic layer 4 and a second magnetic layer 5 which cuts off the exchange coupling to provide the Curie temperature of Tc2. Using this medium, a couple of magnetic heads are allocated matching with the track direction within the predetermined interval and any one is irradiated with a laser beam from the opposite side of the medium. After the disk is rotated in the predetermined number of rotations while it is irradiated with laser pulse, a magnetic pattern is independently applied to the magnetic layers 3 and 5 with magnetic heads for the recording purpose.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical medium which records and reproduces information with a laser by utilizing a magneto-optical effect, and more particularly, to enable overwrite recording of independent information on a plurality of magnetic layers. The present invention relates to a magneto-optical recording medium capable of high-density and high-speed recording, a recording method therefor, and a magneto-optical recording device.

[0002]

2. Description of the Related Art As a rewritable high density recording system,
Attention has been focused on a magneto-optical recording medium in which magnetic domains are written in a magnetic thin film to record information by using thermal energy of a semiconductor laser beam and this information is read out by using a magneto-optical effect.

In recent years, there has been an increasing demand for increasing the recording density of this magneto-optical recording medium to make it a large-capacity recording medium and recording and reproducing data at high speed.

Of these requirements, the increase in capacity can be achieved by improving the recording density in the plane of the medium or in the film thickness direction, or by simultaneously performing them.

Among them, in order to improve the areal density, there is a method of using a short wavelength laser to reduce the spot system of light.
The search for materials that exhibit the magneto-optical effect at short wavelengths is being enthusiastically carried out.

Further, there is known a proposal for enabling multi-value recording by using two magnetic films in order to improve the recording density. (For example, the Digest of Interm Conference.
ag Conference 1986, FC05))). This is to record and erase desired information on two different magnetic layers by using two lasers having different wavelengths.

Further, Japanese Patent Laid-Open No. 64-7322 has been proposed as a device capable of multi-valued recording using a laser.

[0008]

However, in a magneto-optical recording medium, it is usually necessary to sandwich the magnetic layer between a dielectric and a substrate made of plastic, glass or the like in order to protect the magnetic layer responsible for recording and reproduction. Since a dielectric substance such as glass or polycarbonate resin has a plasma absorption edge at 300 to 400 nm, light having a wavelength shorter than this wavelength cannot be transmitted.

Therefore, there is a limit in reducing the spot system to improve the recording density. Also, due to masking of adjacent bits, etc., the signal output will decrease even when reading bits smaller than the spot diameter of the light.
There is a limit.

The former proposal that enables multi-value recording also has a problem that the optical system becomes complicated and it is difficult to control the optical constant of the film thickness of the medium.

According to the proposal of Japanese Patent Laid-Open No. 64-7322, multi-valued recording can be performed by using one laser, but when new information is recorded, overwriting cannot be performed, and a two-step process of erasing and recording. Therefore, high-speed data transfer is impossible.

[0012]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and achieves high-speed and high-speed overwriting recording of multi-valued information (overwriting that does not require an erasing process) without complicating the optical system. The present invention relates to a high-density magneto-optical recording medium, and the gist thereof is that n magnetic layers exhibiting coercive forces different from each other within a time period in which the temperature rises from room temperature by irradiation of a light pulse and then falls to room temperature again, Using at least the magneto-optical recording medium and the above-mentioned magneto-optical recording medium, laser light is pulse-irradiated to transiently lower the temperature of the first, second ... N magnetic layers to the ambient temperature. In the meantime, n (n is an integer of 2 or more) modulated magnetic fields are sequentially applied to each layer to form magnetic domains having an orientation corresponding to an input signal in each layer, thereby obtaining 2n-valued information. Overlaid Recording method and one laser of the magneto-optical recording medium, characterized by can record and n (n
Is an integer greater than or equal to 2). The magneto-optical recording device according to claim 2 is applied to the magneto-optical recording medium according to claim 1 by a magnetic head capable of applying independent magnetic fields in the recording direction. It is in.

The present invention will be described in more detail below.

FIG. 1 is a schematic diagram showing the basic structure of the present invention.

FIGS. 2A and 2B are schematic views showing an example of the configuration of the embodiment of the magneto-optical recording medium of the present invention.

In the figure, reference numeral 1 denotes an optically transparent substrate made of glass or plastic. A dielectric layer 2 made of an inorganic dielectric material such as SiNx is provided on the substrate 1 to obtain an interference effect and a corrosion prevention effect. Further, a first magnetic layer and a second magnetic layer are provided on the dielectric layer 2.

In FIG. 2, an intermediate dielectric layer is provided between the magnetic layers to enhance the breaking of exchange coupling. Furthermore, in order to prevent corrosion of the magnetic layer and to produce an interference effect, SiNx
And a dielectric layer 6 and a metallic reflection layer 7 are provided.

The dielectric layers 2 and 6 and the reflective layer 7 do not depart from the scope of this patent even if they are absent.

The magnetic layer may be composed of three or more layers. It is desirable that these films be continuously formed without breaking the vacuum.

As a material of the magnetic layers 1 and 2, for example, TbF
e, DyFe, GdFe, TbFeCo, DyFeC
o, rare earth iron group alloys such as GdFeCo, or Pt / C
o, garnet, etc. may be used. Further, in order to improve the corrosion resistance, elements such as Cr, Ti and Ta may be added.

As the dielectric, SiN, AlNx, AlO
x, TaOx, SiOx and the like. The reflective layer may be made of Al, AlTa, AlTi, AlCr, Cu or the like.

Next, as an example, FIG.
A case will be described in which 4-level recording / reproducing is performed on the magneto-optical recording film having the two magnetic layers having the configuration of (a).

1) Recording Method When the medium is irradiated with pulses of laser light, the temperature of the magnetic layer rises and the temperature is transiently lowered to room temperature. The time course of the temperature at this time is shown in FIG. 3 (1) and FIG. 4 (1), and the time course of the coercive force is shown in FIG. 3 (2) and FIG. 4 (2).

Explanation of symbols Temperature of magnetic layer 1; T1 temperature of magnetic layer 2; T2 Curie temperature of magnetic layer 1; Tc1 Curie temperature of magnetic layer 2; Tc2 coercive force of magnetic layer 1; Hc1 coercive force of magnetic layer 2 Hc2 external magnetic field; time when Hb T1 becomes Tc1; time when T1 T2 becomes Tc2; T2 1-1) In case of temperature of each magnetic layer and Curie temperature (1) When Tc1 ≠ Tc2, T1 = T2 ( FIG. 4) When an external magnetic field H _ex ^a is applied in the time region of a, the magnetic layer 1
The temperature becomes lower than the Curie temperature at the time of t ₁ , magnetization is generated, and its coercive force is smaller than the external magnetic field H _ex ^a , so that the magnetization direction is aligned with the direction of the external magnetic field H _ex ^a . At this time, the temperature of the magnetic layer 2 becomes higher than the Curie temperature,
Not affected by external magnetic field.

When an external magnetic field H _ex ^b is applied in the time range of ^b , the temperature of the magnetic layer 2 becomes below the Curie temperature at the time of t ₂ , magnetization is generated, and its coercive force is small, The direction of magnetization is aligned with the direction of the external magnetic field H _ex ^b . At this time, the temperature of the magnetic layer 1 is sufficiently lowered and the coercive force Hc1 is larger than the external magnetic field H _ex, so that it is not affected.

(2) When Tc1 = Tc2, T1 ≠ T2 (FIG. 3) In this case as well, similar to (1), there is a difference in the timing of generation of the coercive force between the magnetic layer 1 and the magnetic layer 2. This difference in the magnitude of the coercive force can be recorded in multiple values even if the Curie temperatures of the magnetic layers are not necessarily different as long as the difference in thermal response as shown in FIG.

(3) When Tc1 ≠ Tc2 and T1 ≠ T2 (1), as in (2), multi-value recording is possible if there is a difference in the timing of generation of coercive force.

1-2) Number of magnetic heads (1) One magnetic head First, a magnetic field for recording on the first magnetic layer is applied from one magnetic head, and then a magnetic field for recording on the second magnetic layer is applied. By applying the voltage, signals independent from each other can be written in different layers in the same plane. (See FIGS. 5 (a) and 5 (b)) (2) Multiple magnetic heads Further, since the disk is rotating at the time of a and b, two disks are arranged at an interval equal to the distance the bit moves during this time. A magnetic head may be installed as shown in FIG. 6, and magnetic fields of H _ex ^a and H _ex ^b may be generated from the magnetic head and the magnetic head to write different signals in different layers.

In this case, it is necessary to bring the magnetic head closer to the medium in order to eliminate the mutual interference of magnetic fields, but the distance between adjacent bits can be made smaller.

That is, by continuously operating the above operation, overwriting of multi-valued recording can be realized with only one laser.

The coercive force shown in FIGS. 1 (a) and 2 (b) does not necessarily have to be the coercive force, and may be a reversal nucleus generating magnetic field, a magnetization reversal magnetic field or the like depending on the case.

Further, the magnetic layer is not limited to two layers, but a multi-layer n layer (n
Is an integer of 2 or more), each layer may be recorded by magnetic field modulation of a number corresponding to the total number.

2) Reproducing Method When performing binary recording on each of the two magnetic layers and reproducing, there are four kinds of magnetization states as shown in FIG.

Of these two layers, for example, the magnetic field θ of the magnetic layer 1
_K can be made larger than that of the magnetic layer 2 by controlling the film thickness, composition and the like.

When the linearly polarized light transmitted through the polarizer hits the medium and is reflected, it corresponds to each magnetization state of FIG.
The car rotation angle changes like. Here, if the reflected light is transmitted through an analyzer placed at the position shown in the figure and detected by a detector, a signal corresponding to each magnetization state can be obtained.

As a result, it becomes possible to read out signals having a total of four values recorded in each of the two magnetic layers.

The same applies to the case of a multilayer n layer (n is an integer of 2 or more) without being limited to two layers.

[0038]

【Example】

EXAMPLE 1 A sputtering apparatus having six targets of SiN, Tb, Gd, Fe, Co and Al was charged with a polycarbonate substrate having a pre-groove of 130 mm in diameter and 5 × 10 ⁻⁵ Pa.
After evacuating with a cryopump to a high vacuum of the following pressure, Ar gas was introduced so as to have a pressure of 0.2 Pa.

In this state, a SiN layer having a thickness of 1000 angstroms is formed on the substrate in order to obtain an antioxidation effect and an interference effect, and then TbFeCo having a film thickness of 200 angstroms as the magnetic layer 1 has a Curie temperature of about 250.degree. A SiN layer having a thickness of 200 Å is formed as a non-magnetic layer for blocking exchange coupling, and a magnetic layer 2 is made of TbFeCo having a thickness of 200 Å so as to have a Curie temperature of about 170 ° C. Then, SiN of 300 angstroms and an Al layer of 450 angstroms as a reflective layer were successively formed without breaking the vacuum in order to prevent oxidation and enhance the interference effect, and the magneto-optical recording medium of the present invention was prepared.

Using this medium, two magnetic heads were arranged so that their distance was 0.1 mm or less and aligned with the track direction, and one of them was irradiated with laser light from the opposite side of the medium. .

This disk was rotated at 3600 rpm, a 60 m pulse of 6 mW laser having a radius of 50 mm was irradiated for 60 ns, and then a random magnetic field pattern was independently applied to each of the magnetic layers 1 and 2 by a magnetic head for recording.

The flying height of the magnetic head from the medium is about 10 μm.
m.

After that, the Kerr rotation angle of the laser reflected light is detected, the four-valued information recorded according to the level is detected, converted into the respective information of the magnetic layers 1 and 2, and read out. It was confirmed as shown in Table 1 that the information matches the recorded information and that recording and reading are possible.

Example 2 TbFe having a film thickness of 150 Å was used as the magnetic layer 1.
Co was formed into a composition having a Curie temperature of about 220 ° C., a SiN layer having a thickness of 50 Å as a non-magnetic layer, and a Tb having a thickness of 220 Å as a magnetic layer 2.
A magneto-optical recording medium similar to that of Example 1 was prepared except that FeCo was prepared to have a composition with a Curie temperature of about 180 ° C., a random pattern was recorded, and then the same recording / reproducing method as in Example 1 was performed. As a result, as shown in Table 1, the read information and the recorded information coincided with each other, and it was confirmed that 4-value recording and reading were possible. It was also confirmed that overwrite recording is possible.

Example 3 TbFe having a film thickness of 150 Å was used as the magnetic layer 1.
Co is deposited with a composition such that the Curie temperature is about 220 ° C., a SiN layer having a thickness of 50 Å is used as the nonmagnetic layer, and a Tb having a thickness of 220 Å is used as the magnetic layer 2.
A magneto-optical recording medium similar to that of Example 1 was prepared except that FeCo was prepared with a composition having a Curie temperature of about 180 ° C., a random pattern was recorded, and then the same recording / reproducing method as in Example 1 was performed. As a result, as shown in Table 1, the read information and the recorded information coincided with each other, and it was confirmed that 4-value recording and reading were possible. It was also confirmed that overwrite recording is possible.

[0046]

[Table 1]

[0047]

According to the present invention, multi-valued information of four or more values can be recorded by overwriting, and recording / reproduction of a high-speed and high-density magneto-optical recording medium becomes possible.

[Brief description of drawings]

1A and 1B are schematic views showing a basic configuration of a magneto-optical recording medium used in the present invention.

FIGS. 2A and 2B are magneto-optical media of the present invention in the case where multi-value recording of four values is performed on two magnetic layers and when two-value multi-value recording is performed on an magnetic layer n layer, respectively. FIG.

FIGS. 3 (1) and 3 (2) are schematic views showing changes in temperature of a magnetic layer of a medium and changes in coercive force of the medium when irradiated with a laser spot, respectively.

FIGS. 4 (1) and 4 (2) are schematic views showing changes in temperature of a magnetic layer of a medium and changes in coercive force of the medium when irradiated with a laser spot, respectively.

5A and 5B are schematic views showing a recording process when multilevel recording is performed on two layers of magnetic films by one magnetic head according to the method of the present invention.

6A and 6B are schematic views showing a recording process when multilevel recording is performed on a two-layer magnetic film by two magnetic heads according to the method of the present invention.

FIG. 7 is a graph showing one magnetization state which occurs when multivalued recording of a total of four values of two values is performed on two layers of magnetic films by the method of the present invention.
The schematic diagram which shows an example.

8 is a diagram showing a change in Kerr rotation angle corresponding to the magnetization state of FIG. 7 recorded by the method of the present invention.

[Explanation of symbols]

 1 Substrate 2 Dielectric Layer 3 First Magnetic Layer 4 Intermediate Dielectric Layer 5 Second Magnetic Layer 6 Dielectric Layer 7 Reflective Layer

Claims (3)

[Claims] 1. A light having at least n magnetic layers having coercive forces different from each other within a time period in which the temperature rises from room temperature by irradiation with a light pulse and then falls to room temperature again. Magnetic recording medium. 2. The magneto-optical recording medium according to claim 1 is used to pulse-irradiate laser light to transiently lower the temperature of the first, second ... (N is 2
The above-mentioned integer) modulated magnetic fields are sequentially applied to each layer to form magnetic domains having an orientation corresponding to an input signal in each layer, whereby 2n-valued information is overwritten and recorded. Recording method for magneto-optical recording medium. 3. The magneto-optical recording medium according to claim 1, wherein a single laser and a magnetic head capable of applying n (n is an integer of 2 or more) independent magnetic fields in the recording direction are used. A magneto-optical recording apparatus characterized by performing a recording method.