JP3359102B2 - Magneto-optical recording method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a laser beam and an external magnetic field to record information by forming bits of a reversed magnetic domain, and uses a magneto-optical effect by irradiating a polarized laser beam. And a magneto-optical recording system for reading information. More specifically, the present invention relates to a technology for realizing an improvement in data transfer speed by confirming information recording at the same time.

[0002]

2. Description of the Related Art Conventionally, as a rewritable high-density recording method, information is recorded by writing magnetic domains in a magnetic thin film using the heat energy of a semiconductor laser and an external magnetic field, and the information is read out using a magneto-optical effect. Magneto-optical recording media are receiving attention.

[0003] This magneto-optical recording method has a feature that information can be rewritten and the recording medium can be exchanged because a disk-shaped magnetic material is used for the recording medium.

The most basic method of rewriting information in a magneto-optical recording method involves performing the following three-stage process on a rotating disk-shaped recording medium.

[0005] A DC external magnetic field is applied in the erasing direction, and a place where recording is desired is irradiated with continuous laser light to erase previous information.

Next, a DC external magnetic field is applied in the recording direction, and a laser beam modulated in accordance with the recording information is applied to a position where recording is desired to record information.

[0007] Finally, the recording information is read out by irradiating a weak continuous light laser beam to the place where recording is desired, and it is confirmed whether the recording has been performed correctly.

In the case of a magneto-optical recording medium, it is conceivable that the recording cannot be performed correctly due to defects, deterioration, corrosion, dust, failure of the magneto-optical recording device, etc. of the recording medium. There is a need.

As is clear from the above description, it takes time for three revolutions of the disc to rewrite the information. If this can be performed by two revolutions of the disc and one revolution of the disc, the rewriting of the information is required. The processing speed becomes very fast.

For this purpose, various methods have been proposed.

(That is, the disk 1
A method of irradiating continuous laser light under an external magnetic field modulated according to recorded information,
Alternatively, a method has been proposed in which a special medium is used to irradiate a laser beam that is modulated intensely or weakly according to recorded information under a direct-current external magnetic field.

In order to perform the above operations simultaneously, a method has been proposed in which two laser beams are incorporated in one optical system, recording is performed by a preceding beam, and recording is confirmed by a rear beam. By using all of the above methods, the above process can be performed in one rotation of the disk.

[0013]

However, in checking the recording by incorporating two laser beams into one optical system, the optical system becomes complicated and the optical system has high mechanical accuracy. The required optical system is disadvantageous in that the optical system is large and complicated, and the cost is high.

[0014]

[Means and Actions for Solving the Problems] An object of the present invention is to solve the above problems and to use a single laser beam,
It is an object of the present invention to provide a method for confirming recording by using the reflected light while recording.

An object of the present invention is to provide a first magnetic layer which is an in-plane magnetic film at room temperature and has a compensation temperature between room temperature and Curie temperature, and a first magnetic layer which is a perpendicular magnetic film at room temperature. Using a magneto-optical recording medium having a second magnetic layer having a lower Curie temperature than that of This is achieved by recording information by applying a magnetic field in a predetermined direction while performing exchange coupling with the magnetic layer, and confirming the recording using the reflected light of the laser light.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIGS. 1 and 2 show examples of the temperature dependence of the saturation magnetization Ms and the coercive force Hc of the first magnetic layer and the second magnetic layer, respectively. Tcomp and Tc mean a compensation temperature and a Curie temperature, respectively.

<When the compensation temperature of the first magnetic layer is lower than the Curie temperature of the second magnetic layer> In the case of the magnetic characteristics shown in FIGS. PA-Type and AP-Type
e (the definition will be described later) can be considered (FIGS. 3 and 4).

(If the first magnetic layer and the second magnetic layer both have the TM sublattice magnetization dominance, or conversely the RE sublattice magnetization dominance, the P-Type is used. A-Type is when the second magnetic layer is dominant in RE (rare earth atom) sub-lattice magnetization due to lattice magnetization dominance, or vice versa, and PA-Type when room temperature is P-TYPE and A-Type is high at high temperature. A-Type at room temperature, P-Type at high temperature, AP-Type at room temperature, P-TYPE at room temperature, PP at high temperature
-Type, A-TYPE at room temperature, A-Type at high temperature
The case of e is defined as AA-Type. )

FIGS. 3 and 4 show that the first magnetic layer and the second magnetic layer show the magnetic characteristics shown in FIGS. 1 and 2, respectively, PA-Type and AP-type.
FIG. 9 is a diagram schematically illustrating the state of sublattice magnetization of RE and TM when the temperature returns from room temperature (RT) to reproduction temperature after reproduction (Tr) and recording (Tw) from room temperature (RT) in the case of −Type. .

In the recording medium used in the magneto-optical recording method of the present invention, when the temperature of the medium is increased to near Tr during reproduction, the second magnetic layer has a sufficiently large Ms and a large coercive force Hc. Although the recording bit is sometimes preserved, the first magnetic layer approaches the compensation temperature, so that Ms becomes small and the first magnetic layer becomes a perpendicular magnetization film. Then, by forming a perpendicular magnetization film, an exchange coupling force acts on the second magnetic layer, and the magnetization of the first magnetic layer is oriented in a stable magnetization direction with respect to the second magnetic layer.

That is, at the time of reproduction, the magnetization information recorded on the second magnetic layer is transferred to the first magnetic layer, and the recorded information can be read from the first magnetic layer.

When the temperature of the medium is raised to around Tw at the time of recording, the magnetization of the first magnetic layer is lower than the compensation temperature and lower than the Curie temperature. It becomes a perpendicular magnetization film and becomes the same direction as the external magnetic field Hex by the external magnetic field Hex. The second magnetic layer,
The temperature is near or above the Curie temperature, the coercive force is sufficiently small, and the magnetization generated at the time of temperature decrease is exchange-coupled with the second magnetic layer or aligned with the direction of the external magnetic field.

(PA-type) (FIG. 3) At the time of recording, there is a possibility that an interface domain wall is generated between the first magnetic layer and the second magnetic layer in PA-type. Therefore, PA-
Type may take several different states at high temperatures (FIGS. 3 (a)-(f)). However, by adjusting the magnitude relationship between the interface domain wall energy, the Zeeman energy, and the coercive force energy, the desired state can always be achieved.

More specifically, the interface domain wall energy is σ _w , the thicknesses of the first magnetic layer and the second magnetic layer are h 1 and h 2, and the saturation magnetizations of the first magnetic layer and the second magnetic layer are respectively Assuming that Ms1 and Ms2, the effective bias magnetic fields Hw1 and Hw2 due to the exchange interaction coupling applied to the first magnetic layer and the second magnetic layer, respectively,

[0026]

[Outside 1] Further, assuming that the magnetization reversal magnetic fields of the first magnetic layer and the second magnetic layer are Hc1 and Hc2 and the external magnetic field Hex, for example, the path of (b) is as follows: (b) 1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → 11 → 12, and the branch point with other processes in the middle is at 5, 8; therefore, 5 → 6 Hc2> Hex−Hw2 (3) 5 to 6 always occur,

[0027]

[Outside 2] In this case, since 8 to 9 always occur, if these conditions are satisfied with the temperature at each stage, the route (b) will always be achieved.

Similarly, the other steps are as follows.

(A) 1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → 9 → 10

[0030]

[Outside 3] (D) 1 → 2 → 3 → 4 → 5 → 13 → 18 → 19 → 20
→ 21 (e) 1 → 2 → 3 → 4 → 5 → 13 → 18 → 23 → 24
→ 25 (f) 1 → 2 → 3 → 4 → 5 → 13 → 22 → 23 → 26
→ 27 The branch point condition is represented by the following equations (5) to (13). If the condition according to the course in each process is satisfied at the branch point, each path is always achieved.

5 → 13 Hc2 <Hex-Hw2 (5) 13 → 14 Hc1 <Hw1-Hex (6) 13 → 18 Hc2> Hex-Hw2 (7) and Hc1> Hw1- Hex (8) 13 → 22 Hc2 <Hw2-Hex (9) 19 → 16 Hc1 <Hw1 + Hex (10) 19 → 20 Hc1> Hw1 + Hex (11)

[0032]

[Outside 4]

(AP-type) (FIG. 4) In the AP-type, there are processes (a) to (d), and the following steps are respectively performed.

(A) 1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 → 9 (b) 1 → 2 → 3 → 4 → 5 → 6 → 10 → 11 → 12 (c) 1 → 2 → 3 → 4 → 5 → 6 → 10 → 13 → 14 (d) 1 → 2 → 3 → 4 → 5 → 6 → 10 → 15 → 16 The branch point condition is expressed by the following equations (14) to (19). And
If the conditions according to the course in each process are satisfied at the fork,
Each route will always be achieved.

6 → 10 Hc1 <Hex−Hw1 (14) 10 → 11 Hc2 <Hw2-Hex (15) 10 → 13 Hc1 <Hw1-Hex (16) 10 → 15 Hc2 < Hw2-Hex (17) and Hc1 <Hw1-Hex (18) 6 → 7 Hc1> Hex-Hw1 (19) <The compensation temperature of the first magnetic layer is the Curie of the second magnetic layer. When the temperature is higher than the temperature> When the compensation temperature of the first magnetic layer is higher than the Curie temperature of the second magnetic layer (the magnetic characteristics of each magnetic layer in this case are not shown), AA-Type In each case of PP-Type (FIGS. 5 and 6), AA-
As described above, in TYPE, there is a possibility that an interface domain wall is formed. However, if a medium characteristic is set as described below, it is possible to always follow a desired path.

(AA-type) (FIG. 5) In the AP-type, there are steps (a) to (d), and the following steps are performed respectively.

(A) 1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 (b) 1 → 2 → 3 → 4 → 5 → 9 → 10 → 11 (c) 1 → 2 → 3 → 4 → 5 → 9 → 12 → 13 (d) 1 → 2 → 3 → 4 → 5 → 9 → 14 → 15 The branch point condition is expressed by the following equations (20) to (25).
If the conditions according to the course in each process are satisfied at the fork,
Each route will always be achieved.

5 → 9 Hc2 <Hex−Hw2 (20) 9 → 10 Hc1 <Hw2-Hex (21) 9 → 12 Hc2 <Hw2-Hex (22) 9 → 14 Hc1> Hw1-Hex and (23) Hc2> Hw2-Hex (24) 5 → 6 Hc2> Hex-Hw2 (25)

In PP-type, a fixed route is always followed regardless of conditions (FIG. 6).

As described above, the external magnetic field, the magnetization reversal magnetic field,
It is easy to control the value of the exchange energy by adjusting the composition of the membrane or the like. Therefore, if the magnetization reversal of the first magnetic layer is confirmed during recording, the recording can be confirmed.

However, PA-type, AP-type, A
In each type of A-type, the process of generating an interface domain wall (processes (c) to (f) of PA-type, AP-type)
Steps (b) to (d) of pe, (b) of AA-type
To (d)) have many unstable elements with many branch points. On the other hand, the process (PA-ty) in which no interface domain wall occurs
The steps (a) and (c) of pe, the step (a) of AP-type, and the step (a) of AA-type) are transfer by exchange coupling between the first magnetic layer and the second magnetic layer. Is performed, and it is desirable that the number of branch points is small and the recording can be confirmed more reliably.

In PA-type, when a coercive force at room temperature is used for the second magnetic layer to stably store recorded information, the coercive force of the second magnetic layer becomes larger than the external magnetic field. Since the magnetization of the first magnetic layer and the second magnetic layer does not reverse, the process (a) does not occur. Therefore PAtyp
In e, the process (b) is a more desirable process.

FIG. 7 is a schematic view showing an example of an apparatus for performing the magneto-optical recording method of the present invention. In FIG. 7, 1 is a coil for applying an external magnetic field, 2 is a recording medium, 21 is a first magnetic layer, 22 is a second magnetic layer, 3 is a semiconductor laser,
4 is a half prism, 5 is a polarizing beam splitter,
Reference numerals 6 and 7 are photodiodes, and 8 is a differential amplifier.

FIG. 3 shows an example in which the present invention is applied to a method of irradiating continuous laser light under an external magnetic field modulated in accordance with recording information 9.

Next, the operation principle of the present invention will be described.

When the recording medium 2 is irradiated with a laser beam, the temperature of the medium rises and the magnetization of the second magnetic layer 22 disappears.
However, the first magnetic layer 21 has a high Curie temperature so that the magnetization remains, but the magnetization decreases to become a perpendicular magnetization film, and the magnetization of the first magnetic layer is reversed by the external magnetic field generated by the coil 1. The magnetization of the second magnetic layer is always in the stable magnetization state following the same path, such as being exchange-coupled with the magnetization of the first magnetic layer after generation, so if the magnetization reversal of the first magnetic layer can be confirmed, the recording Confirmation is possible.

The magnetization reversal of the first magnetic layer is performed by using the photodiodes 6 and 7 as the change in the magneto-optical effect of the reflected light of the irradiation laser light during recording because the magnetization remains even during recording. It is detected and taken out as a reproduced signal by the differential amplifier 8. If recording cannot be performed correctly due to a defect, deterioration, corrosion, dust, failure of the magneto-optical recording device, or the like of the recording medium, the reproduced signal becomes abnormal, so that recording can be confirmed at the same time as recording.

In the present invention, the reason for using a magneto-optical recording medium having at least a first magnetic layer composed of a magnetic film that is an in-plane magnetic film and a second magnetic layer composed of a perpendicular magnetic film at room temperature. Will be described below. FIG. 8 shows a case where a normal magnetic substance having a high coercive force and a low Curie temperature is used as a single-layer recording medium. When the recording medium is irradiated with laser light, the temperature of the medium rises and the magnetization of the magnetic layer disappears. When the magnetization disappears, the magneto-optical effect disappears, and the reproduced signal hardly changes (it changes only slightly due to the reflected light from the tail of the laser beam). Therefore, when a normal magnetic material is used as a single-layer recording medium, it is not possible to confirm the recording.

<Structure of Recording Medium> The recording medium has a compensation temperature between room temperature and the Curie temperature, is an in-plane magnetic film at room temperature, and changes to a perpendicular magnetic film when the temperature rises. It is only necessary to have a layer and a second magnetic layer having a lower Curie temperature than the first magnetic layer, which is a perpendicular magnetization film both at room temperature and at elevated temperature. By stacking layers to enhance the interference effect and increase the playback signal,
The recording sensitivity may be improved or the magnetic layer may be protected.

<Composition of Magnetic Layer> As the first magnetic layer, a rare earth-iron group amorphous alloy, for example, GdCo, GdFeCo, TbFeCo, D
yFeCo, GdTbFeCo, GdDyFeCo, TbDyFeCo, NdFeCo, NdGdFeCo, N
dTbFeCo, NdDyFeCo, or a platinum group-iron group periodic structure film, for example, Pt / Co, Pd / Co platinum group-iron group alloy, for example, Pt
Co, PdCo, etc. are desirable.

As the second magnetic layer, a rare earth-iron group amorphous alloy, for example, TbFeCo, DyFeCo, TbDyFeCo or the like is desirable.

The first magnetic layer and the second magnetic layer include Cr, Al, Ti, P
Elements such as t and Nb for improving corrosion resistance may be added.

(Experimental Example) Hereinafter, the present invention will be described in more detail using experimental examples.
The present invention is not limited to the following experimental examples unless it exceeds the gist.

EXPERIMENTAL EXAMPLE 1 On a polycarbonate substrate having a groove of 130 mm in diameter, an SiN layer was formed at 900.degree. In order to obtain an antioxidant effect and an interference effect using a magnetron sputtering apparatus, and then a GdTbCo layer was formed at 400.degree. Then, a TbFeCo layer was formed as a second magnetic layer at a thickness of 400 °. Thereafter, in order to prevent oxidation and enhance the interference effect, a SiN layer was continuously formed at 300 ° without breaking the vacuum to produce a magneto-optical recording medium of the present invention.

The refractive index n of the SiN layer is about 2.
1. The composition of the TbFeCo layer was such that the proportions of Tb, Fe, and Co were 21, 72, and 7 at%, respectively.

The GdTbCo layer was set so that the compensation temperature was 240 ° C. and the Curie temperature was 350 ° C. or higher.

The magneto-optical recording medium has a laser power of 9 m.
A 3 MHz signal was recorded at W. Thereafter, the reflected light was detected and observed while recording a 1 MHz signal, and a signal as shown in FIG. 9 was obtained. It can be seen that the signal of 1 MHz is reproduced clearly despite the fact that 3 MHz is mixed. Next, after recording a 1 MHz signal, 3
When the reflected light was detected while recording the signal of MHz, it was found that the signal as shown in FIG. 10 was obtained, and the signal of 3 MHz was reproduced finely although it was modulated at 1 MHz.

[0058]

According to the magneto-optical recording method of the present invention, at the time of recording, the reflected light of the recording light is used to confirm the data at the same time as the recording, so that the conventional optical system can be used. Confirmation of records can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of temperature dependence of a saturation magnetization Ms and a coercive force Hc of a first magnetic layer.

FIG. 2 is a diagram showing an example of temperature dependence of a saturation magnetization Ms and a coercive force Hc of a second magnetic layer.

FIG. 3 is a diagram schematically illustrating a sublattice magnetization state and a net magnetization state at room temperature (RT), at the time of reproduction and at the time of recording when the magnetic layer configuration is PA-type.

FIG. 4 is a diagram schematically illustrating a sublattice magnetization state and a net magnetization state at room temperature (RT), at the time of reproduction and at the time of recording, when the magnetic layer configuration is AP-type.

FIG. 5 is a diagram schematically illustrating the states of sublattice magnetization and net magnetization at room temperature (RT), at the time of reproduction and at the time of recording, when the configuration of the magnetic layer is AA-type.

FIG. 6 is a diagram schematically illustrating the state of sub-lattice magnetization and net magnetization at room temperature (RT), at the time of reproduction and at the time of recording, when the magnetic layer configuration is PP-type.

FIG. 7 is a schematic view showing an example of an apparatus for performing the magneto-optical recording method of the present invention.

FIG. 8 is a diagram showing a case where a normal magnetic substance having a high coercive force and a low Curie temperature is used as a single-layer recording medium.

FIG. 9 shows a magneto-optical recording method according to the present invention,
FIG. 3 is a diagram illustrating a detection waveform of reflected light of a recording light beam.

FIG. 10 is a diagram showing a detection waveform of reflected light of a recording light beam during recording in the magneto-optical recording method of the present invention.

Claims (1)

(57) [Claims] 1. An in-plane magnetized film and a room at room temperature.
Magneto-optical system comprising a first magnetic layer having a compensation temperature between the temperature and the Curie temperature, and a second magnetic layer which is a perpendicular magnetization film at room temperature and has a lower Curie temperature than the first magnetic layer. Using a recording medium, at the time of recording, the first magnetic layer is heated by a laser beam to form a perpendicular magnetization film to exchange-couple with the second magnetic layer and to apply a magnetic field in a predetermined direction to record information. And confirming the recording by using the reflected light of the laser light at the same time.