KR100304873B1 - magneto-optical recording medium and method for reading of the same - Google Patents

Abstract

PURPOSE: A magneto-optical recording medium is provided to transfer information recorded on a recording layer to a reproduction layer by irradiating a laser beam on a region of the reproduction layer, and to expand the transferred information by applying a magnetic field to the reproduction layer, then to turn off the laser beam and the magnetic field, so as to improve a data transfer speed by repeating the whole procedure to reproduce the information. CONSTITUTION: The first dielectric layer(12) is formed on a substrate(11). A reproduction layer(13) formed on the first dielectric layer(12) expands transferred information to magnify a playback signal, and has a horizontal magnetic anisotropy at a room temperature, then has a vertical magnetic anisotropy at a specific temperature. The second dielectric layer(14) is formed on the reproduction layer. A heat absorption layer(15) is formed on the second dielectric layer(14). A recording layer(16) formed on the heat absorption layer(15) transfers information recorded at the specific temperature to the reproduction layer(13). A protective layer(17) is formed on the recording layer(16).

Description

Magneto-optical recording medium and method for reading of the same

The present invention relates to a magneto-optical recording medium and a reproduction method thereof.

In general, the magneto-optical disk uses a phenomenon in which the angle of the polarization plane rotates when the polarized light reflects the magnetic thin film plane, and in the case of the magnetic thin film having magnetic anisotropy in a direction perpendicular to the film plane.

This magneto-optical effect is called a Kerr effect, and the angle of the rotating polarization plane is called a rotation angle.

The signal-to-noise ratio (SNR) of a magneto-optical disk is

Where η is the quantum efficiency of the photodiode, P is the read power, R is the medium reflectivity, θ _K is the rotation angle, e is the electron charge, and B is Band width.

In the above equation, the figure of merit is only proportional to Rθ _K ² considering only R and θ _{K, which} are parameters of the medium.

Therefore, it is more efficient to increase θ _K than R.

Usually, the rotation angle of the magnetic thin film used for magneto-optical recording has a small value of about 0.3 degrees.

Therefore, in order to increase this value, a multilayer is used using a dielectric and a reflective layer.

That is, as shown in FIG. 1, a structure made of a substrate / antireflective layer / recording layer / phase layer / reflective layer / uv coating layer is generally used.

Magneto-optical disks of this structure are used as first-generation magneto-optical disks.

As a recording method, there are typically two methods, mark position recording and mark edge recording.

Mark position recording is applied by applying an external magnetic field while applying a laser beam to the recording medium. The magnetic field is generated in the same direction as that of the external magnetic field while cooling, thereby forming a recording mark.

At this time, "on" and "off" or "0" and "1" are displayed according to the magnetic domain direction.

Mark edge recording is a method of increasing the recording density compared to mark position recording. The mark edge is changed from amorphous to crystalline or crystalline to amorphous during the progress of an internal clock having a certain length of time. The case of forming the edge of " 1 "

In this case, the position of the mark edge becomes important because it is necessary to distinguish between "1" and "0" in the unit time.

After such a first generation optical disc, the greatest interest began to focus on increasing the recording density.

Therefore, the structure of the disk is gradually multilayered, and the shape of the recording laser beam and the external magnetic field is gradually complicated.

With the development of magneto-optical disks, a method called laser-pumped magnetic field modulation, which efficiently records information on a disk, has emerged.

This method is able to form a small and stable magnetic domain by simultaneously applying an external magnetic field while applying a laser pulse.

In order to increase the density of the magneto-optical disk, it is necessary to read a small recorded mark as well as a high density recording. The above-described laser-pump magnetic field modulation method was able to record a size smaller than the laser beam size during recording. Special methods were required when reading the recorded signal.

In the first method, a method of using a mechanism of replicating a signal of the recording layer by opening a window only in the center of the reproduction layer having a high temperature of the laser beam is read.

In this method, the magnetization direction of the regeneration layer is horizontal at room temperature.

The second method is to enlarge the playback signal by enlarging the recorded mark in the recording layer in the reproduction layer in order to solve the problem that the size of the signal to be read is small when the recording mark is made smaller to increase the recording density.

This method is called MAMMOS (Magnetic AMplifying Magneto-Optical System) technology. The magneto-expanded regeneration technology called mammos requires at least two layers of magnetic layers.

As shown in FIG. 2, the structure of the mammoth disc includes a substrate, a first dielectric layer, a regeneration layer, a second dielectric layer, a heat absorption layer, a recording layer, a protective layer, and a UV coating layer.

When reproducing a diamond disk having such a structure, an AC magnetic field as shown in FIG. 3 is applied.

That is, when magnetic domains smaller than the spot diameter of light are recorded in the recording layer, when light is irradiated to the reproduction layer to reproduce the magnetic domains, the small magnetic domains recorded in the recording layer are locally opened only at the spot center portion of the light. Is received and copied to the playback layer.

When the AC external magnetic field as shown in FIG. 3 is applied, the magnetic domain copied to the reproduction layer is enlarged and reproduced.

At this time, the amplitude of the reproduction signal reaches more than several times or the saturation amplitude of the conventional medium.

The saturation amplitude refers to a state in which the magnified radiative domain exceeds the diameter of the light spot.

When the amplitude of the reproduced signal reaches this state, the state of the next magnetic domain cannot be discriminated. Therefore, the reproduced magnetic domain is contracted or extinct by reversing the polarity of the external magnetic field, whether or not reproduced and reproduced.

Then, the next magnetic domain of the recording layer is copied to the enlarged reproduction layer and again an AC external magnetic field is applied to obtain a large reproduction signal.

In this case, however, the external magnetic field is a decisive factor in the data rate.

This is because the impedance of the magnetic coil increases in proportion to the frequency of the external magnetic field.

Therefore, as the frequency of the external magnetic field increases, the impedance of the magnetic coil increases, which limits the data transmission speed.

[0004] The following problems have arisen in the conventional magneto-optical recording medium and its reproduction method.

The application of the AC external magnetic field used for reproducing the magneto-optical recording medium increases the impedance of the magnetic coil in proportion to the frequency increase, thereby limiting the data transmission rate and making the production of a device for generating the magnetic field complicated.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object thereof is to provide a magneto-optical recording medium and a reproduction method thereof capable of increasing the data transmission speed by a simple reproduction method.

1 and 2 show typical magneto-optical disks

3 is a view showing a waveform of a magnetic field applied to the magneto-optical disk of FIG.

4 shows a magneto-optical disk according to the present invention.

5A, 5B and 6 show waveforms of magnetic fields applied to the magneto-optical disk of FIG.

Explanation of symbols for main parts of the drawings

11 substrate 12 first dielectric layer

13 reproduction layer 14 second dielectric layer

15: heat absorption layer 16: recording layer

17: protective layer 18: UV coating layer

The characteristics of the magneto-optical recording medium according to the present invention are that the first dielectric layer formed on the substrate and the information transferred and formed on the first dielectric layer are enlarged to increase the reproduction signal, horizontal magnetic anisotropy at room temperature, and vertical magnetic anisotropy at a specific temperature. And a second dielectric layer formed on the reproduction layer, a heat absorption layer formed on the second dielectric layer, a recording layer formed on the heat absorption layer and transferring information recorded at a specific temperature to the reproduction layer, and on the recording layer. It consists of the protective layer formed.

The reproducing method of the magneto-optical recording medium according to the present invention includes a reproducing layer having horizontal magnetic anisotropy at room temperature and vertical magnetic anisotropy at a specific temperature, and a recording layer transferring information recorded at a temperature of 70 ° C. or higher to the reproducing layer. A reproduction method of a magneto-optical recording medium, comprising: a first step of transferring a laser beam to a corresponding area of a reproduction layer to transfer information recorded in the recording layer to the reproduction layer, and applying a pulse magnetic field or a DC magnetic field to the reproduction layer; A second step of enlarging and reading the information transferred to the reproduction layer, and a third step of turning off the laser beam and irradiating the laser beam to the next area of the reproduction layer to repeat the first step and the second step. To lose.

Referring to the accompanying drawings, a magneto-optical recording medium and a reproduction method thereof according to the present invention having the above characteristics are as follows.

First, the technical idea of the present invention is to form a regeneration layer having horizontal magnetic anisotropy at room temperature and vertical magnetic anisotropy at a specific temperature of 70 ° C. or higher, and during regeneration, a magnetic field applied to the regeneration layer is positively pulsed in conventional AC. (positive pulse), negative pulse (negative pulse), or DC to change the device to simplify the application of the magnetic field and increase the data transfer speed.

That is, in the present invention, the application method of the external magnetic field for enlarging and erasing the reproduced information is simplified in the present invention, so that the reproduced information can be continuously and fast only by enlarging the reproduced information.

FIG. 4 is a view showing a magneto-optical disk according to the present invention. As shown in FIG. 4, the information recorded in the first dielectric layer 12 and the recording layer on the substrate 11 is enlarged and reproduced, and at room temperature, the horizontal magnetism is shown. Anisotropy, the reproduction layer 13 having the perpendicular magnetic anisotropy at a specific temperature, the second dielectric layer 14, the heat absorption layer 15, and the recording layer 16 transferring the information recorded at the specific temperature to the reproduction layer 13. The protective layer 17 and the UV coating layer 18 are sequentially formed.

Here, looking at the material of each layer, the first dielectric layer 12, the second dielectric layer 14 and the protective layer 17 is made of Si ₃ N ₄ or AlN, the regeneration layer 13 is Gd _x (FeCo) _y (where x is 26-30, y is 70-74) or a cobalt-based multilayer thin film, the heat absorption layer 15 is made of AlTi, and the recording layer 16 is made of TbFeCo. Or a cobalt-based multilayer thin film.

The regeneration method of the present invention having such a structure is as follows.

Prior to describing the reproducing method, the most important feature of the reproducing method of the present invention is that a magnetic field for enlarging information transferred to the reproducing layer is applied in the form of pulse or DC, and the laser beam is irradiated in the form of pulse.

First, the regeneration method in the case of using a pulsed magnetic field is as follows.

As an example, suppose that the magnetic domain whose magnetic direction is upwards (hereinafter referred to as 1) and the magnetic domain whose magnetic direction is downwards (hereinafter referred to as 0) are recorded in the recording layer.

When the laser beam is irradiated to the reproduction layer above the recording layer on which "1" is recorded to reproduce the "1" recorded on the recording layer, the reproduction layer of the area to which the laser beam is irradiated is recorded on the recording layer as the temperature increases. "1" is transferred to the reproduction layer.

At this time, since "1" is a signal recorded small in the recording layer, the signal reproduced in the reproduction layer is also weak.

Therefore, when a magnetic field having the same magnetic direction as "1" is applied to the reproduction layer on which "1" has been reproduced, the reproduction signal becomes large.

In other words, the magnetic domain recorded smaller than the diameter of the laser beam is reproduced in the reproduction layer with the same size, but when the magnetic field is applied in the same direction as the magnetic direction of the magnetic domain, the magnetic domain spreads around and appears as a large signal.

Then, after reading the enlarged reproduction signal, when the laser beam and the magnetic field are turned off, the reproduction layer has horizontal magnetic anisotropy as in the beginning, so that the next region can be reproduced.

That is, in the present invention, the data of the immediately next area can be reproduced without erasing the reproduced data as in the prior art.

Here, the magnetic field used is a magnetic field in the form of a positive pulse or a negative pulse as shown in FIGS. 5A and 5B.

Here, it is suitable that positive pulse or DC is 100-300 Oe, and negative pulse is -100-300 Oe.

This pulse magnetic field may be used in synchronization with the pulse of the laser beam.

On the other hand, when the laser beam is irradiated for reproducing "0", the regeneration layer of the area irradiated with the laser beam is transferred with the temperature "0" recorded in the recording layer as the regeneration layer.

When the magnetic field having the same magnetic direction as "1" is applied to the reproduced layer on which "0" is reproduced, the magnetic signal of "0" reproduced on the reproduced layer is different from the magnetic direction of the magnetic field. "0" has a vertical magnetic anisotropy pointing downward, and signals adjacent to "0" have horizontal magnetic anisotropy, so they can be easily distinguished.

Subsequently, after reading the reproduction signal, the laser beam and the magnetic field are turned off, so that the reproduction layer has horizontal magnetic anisotropy as in the beginning, so that the next region can be reproduced.

As described above, since the regeneration layer has horizontal magnetic anisotropy at room temperature and vertical magnetic anisotropy at a specific temperature, for example, 70 ° C. or higher, if only a magnetic field having a pulse in one direction is applied, the next layer is not erased. Data can be played back.

Conventionally, the data of the recording layer is reproduced and then erased, and then the data of the next area is reproduced and erased again. In the present invention, continuous data reproduction is possible without erasing data, and by simplifying the method of applying an external magnetic field, The magnetic field applying device is also simplified and the data transfer speed is increased.

The external magnetic field used in the present invention can obtain the same effect by using the DC shown in FIG. 6 in addition to the positive pulse or the negative pulse.

The regeneration method using the DC magnetic field is as follows.

First, in order to reproduce the data recorded in the recording layer, the laser beam is irradiated to the reproduction layer above the recording layer on which the data is recorded, so that the temperature of the reproduction layer in the area where the laser beam is irradiated increases the data recorded in the recording layer. Transferred to the reproduction layer.

Then, a DC magnetic field is applied to enlarge the data reproduced small.

Subsequently, after reading the enlarged reproduction data, the laser beam is turned off, so that the reproduction layer has horizontal magnetic anisotropy as in the beginning, so that the next region can be reproduced.

If only the laser beam is turned on or off in this manner, the data in the next region can be reproduced without erasing the reproduced data.

As such, the use of a DC magnetic field requires only the laser beam to be turned on and off, resulting in a faster data transfer rate than the pulsed magnetic field.

On the other hand, in order to improve jitter of a reproduction signal, a pulse shape is most advantageous for both an external magnetic field and a reproduction laser.

The magneto-optical recording medium and its reproduction method according to the present invention have the following effects.

The present invention can simplify the magnetic field application device and improve the data transmission speed by changing the external magnetic field application from the conventional AC form to the pulse or DC form during reproduction.

Claims (5)

In a reproducing method of a magneto-optical recording medium comprising a reproducing layer having horizontal magnetic anisotropy at room temperature and vertical magnetic anisotropy at 70 ° C. or higher and a recording layer for recording information, A first step of irradiating a laser beam to a corresponding region of the reproduction layer to transfer the information recorded in the recording layer to the reproduction layer; A second step of applying a pulse magnetic field or a DC magnetic field to the reproduction layer to enlarge and read the information transferred to the reproduction layer; And a third step of turning off the laser beam and irradiating the laser beam to a next region of the reproduction layer to repeat the first step and the second step. The method of claim 1, wherein the laser beam is irradiated in a pulse form. 2. A method of reproducing a magneto-optical recording medium according to claim 1, wherein the pulse magnetic field is a positive pulse or a negative pulse. 4. The method of claim 3, wherein the positive pulse or DC is 100 to 300 Oe, and the negative pulse is -100 to 300 0e. The method of claim 1, wherein the pulse magnetic field is synchronized with the pulse of the laser beam.