KR100253556B1 - Over-writable magneto-optical recording medium - Google Patents

Abstract

PURPOSE: An optical magnetic recording medium is provided to overwrite by using exchange-coupling after producing a triple magnetic layer. CONSTITUTION: A first protect film(2) is formed by sputtering SiN on a polycarbonate substrate(1). A reference layer(3) and a storing layer(5) is formed on the first protect film by using a material of RE-TM group. An intermediate layer(4) is formed between the reference layer and the storing layer by using FeSiAl material. Thus, interface wall energy is performed. A second protect film(6) is formed on the storing layer by using SiN composite, and a reflect film(7) is formed on the second protect film by coating AlTi composite. Thus, an optical magnetic recording medium is completed.

Description

Overwriteable magneto-optical recording media

1 is a cross-sectional view of a conventional magneto-optical recording medium.

2 is a cross-sectional view of an overwriteable magneto-optical recording medium of the present invention.

3 is a cross-sectional view showing the thickness of each magnetic film of FIG.

Figure 4 shows the direction of the magnetic field according to the electric field strength of the present invention, 4a is the direction of the magnetic field when the electric field strength is 0, 4b is the magnetic direction when the field strength is greater than zero.

* Explanation of symbols for main parts of the drawings

2: first protective film 3: reference layer

4: middle layer 5: memory layer

The present invention relates to an overwritable magneto-optical recording medium, and more particularly, to an overwritable magneto-optical recording medium in which a magnetic layer is made of three layers and then overwritten using exchange coupling.

In general, magneto-optical recording technology records information by laser light in a magnetic thin film having vertical magnetic anisotropy having a large magneto-optical effect.

This magneto-optical recording technology has been studied since the late 1950's and now has a storage capacity of 400-600 Mbytes on a 5.25 "disk, 30-200ms of access time and 1,2 data transfer rate. -8 Mbits / s.

Currently, a conventional method of recording digital data on a magneto-optical disk uses a laser modulation method in which a laser output is modulated under a constant external bias magnetic field.

Unlike magnetic recording, this laser modulation method records the data after erasing the already recorded data by continuously scanning the laser in the sector or track to be recorded when new data is recorded on the already recorded data. There is a hassle that has to be done, which results in a slow data transfer rate.

Therefore, the direct overwriting function, which can directly overwrite the recorded part, must be solved to improve the magneto-optical recording technology.

In the direct rewrite function, three methods have been proposed and studied in order to directly rewrite a magneto-optical recording medium, a single layer laser modulation method, an exchange-coupled multilayer film laser modulation method, and a magnetic field modulation method.

Here, the three methods for direct rewriting will be described in more detail as follows.

i) Single layer laser modulation method.

This method is a method of directly rewriting by modulating the laser output or pulse time on a monolayer film having a compensation temperature higher than room temperature.

ii) Exchange coupled multilayer film laser modulation method.

This method directly rewrites using an exchange-coupled bilayer disk composed of two layers of TbFe / TbFeCo or TbFe / GdFeCo.

Here, as shown in FIG. 1, the recording medium includes a memory layer 300 having a high coercive force (Hcm) and a low curie temperature (Tcm), a low coercive force (Hcr) and a high curie temperature (Tcr) at room temperature. It consists of a reference layer (reference layer) of (100).

For example, in order to record the binary information "1", when the memory layer is heated to a high output or higher than the Curie temperature (Tcm), it is cooled, and an upward magnetic domain is first formed in the reference layer by a bias magnet, and then stored by exchange coupling. Upward magnetic domain radiation is also generated in the layers.

On the other hand, in order to record information "0", the memory layer is heated at a low output higher than the Curie temperature Tcm and the reference layer is lower than the Curie temperature Tcr.

In this case, cooling is performed and the magnetic domain direction of the storage layer becomes downward, which is the magnetic domain direction of the reference layer by exchange coupling, so that information " 1 " is erased and " 0 "

iii) Magnetic field modulation method

This method rewrites data by scanning the laser at a constant intensity and modulating the direction of the bias external magnetic field according to newly input data.

However, this conventional rewrite method is the easiest of the three methods in terms of media production or optical head design in the case of the single-layer laser modulation method. However, gray bits remain and the signal noise ratio (CNR) remains because gray bits remain. There was a problem that 20dB lower than other methods.

In addition, the ring-bonded multilayer film laser modulation method has no problem in terms of direct rewriting function, but since the direct rewriting function is dependent on the magnetic properties, uniform physical properties of the entire disk area are required. This problem has emerged.

Lastly, the magnetic field modulation method has no problem in terms of function, but the data transfer rate of 1-2 Mbits / s for the double-sided disk is the upper limit of the current technology due to the increase in power loss due to the increase in the variable frequency.

Accordingly, an object of the present invention is to provide a magneto-optical recording medium that can be overwritten so that the magnetic layer is formed into three layers in an exchange coupled multilayer film laser modulation method, and thus can be overwritten using exchange coupling.

2 is a cross-sectional view of an overwriteable magneto-optical recording medium of the present invention, in which a first protective film 2 is formed by sputtering SiN on a polycoverate substrate 1.

Subsequently, a reference layer 3 and a memory layer 5 are fabricated on the first passivation layer 2 using a RE-TM-based material, and smooth energy transfer between the reference layer 3 and the memory layer 5 is performed. The intermediate layer 4 is made of FeSiAl material to enable overwriting.

Thereafter, a second protective film 6 is formed of a SiN compound on the memory layer 5 and an AlTi compound is coated thereon to form a reflective film 7 to produce a magneto-optical recording medium.

In this case, a bias magnetic field is required for overwriting, and the size of the field is smaller in terms of the stability of the magnetic domain of the memory layer 5 and the drive fabrication.

If the saturation magnetization force of the reference layer 3 is Mr, the thickness of the reference layer 3 is Tr, the saturation magnetization force of the memory layer 5 is Mm, and the thickness of the memory layer 5 is tm, the initial magnetic field Hint is

The conditions of

In Equation 1, σw: domain wall energy density, and Hcm (memory layer): high coercive force.

The smaller the Hcr, the higher the recording noise of the medium. Therefore, the magnetic domain becomes stable when the size of? W / 2Mrtr is reduced.

Since Mr is related to Hcr, it is not easy to control, so it is necessary to increase tr, which is not preferable to cause cost or process problems.

The method of weakening the exchange interaction without increasing the recording noise of the medium, that is, without reducing the Hcr, is a three-layered film structure. The FeSiAl, which is the middle layer 4, has a very small Hc and a very sharp MH loop slope. Because it has a sharp property, it is a material with excellent field sensitivity, so when inserted between RE-TM systems, it sufficiently plays the role of a magnet inside the film, thereby improving the magnetic field strength during recording erasing.

Here, two magnets are required to exchange-coupled multi-layer laser modulation in the three-layer film structure according to the present invention. It is a magnet for initialization of about 5 KOe that makes the direction of the magnetic domain of the reference layer (3) clear without affecting the magnetic domain of the backplane.

In the magnetic layer of the three-layer structure

The conditions of Hwm = sigma / 2Mmtm and Hwr = sigma / 2Mrtr must be satisfied and at the transfer temperature, Hcm + Hrec < … … … … … The condition of (Eq. 5) must be satisfied.

Equation 2 above is an initial stability condition including an interface magnetic wall.

The external magnetic field is determined by Equation 3 and Hcr + Hwr should be as small as possible to reduce the initial magnetic field.

In addition, for _total writing sensitivity, t _total ?

Therefore, in the present invention, the reference layer 3 is 300 mW, the intermediate layer 4 is 300 mW, and the storage layer 5 is 900 mW, for the recording sensitivity.

FIG. 4 shows the direction of magnetism according to the electric field strength when the present invention is applied. FIG. A shows the magnetic domain directions of the reference layer (3), the intermediate layer (4), and the memory layer (5) when the electric field strength (H) is zero. B is the magnetic field direction when the electric field strength (H) is greater than zero.

As described in detail above, in the present invention, the FeSiAl of the intermediate layer has a very sharp inclination in the MH loop, and thus maintains a stable horizontal magnetism in the Weak field, thereby greatly reducing the domain wall energy between the reference layer and the memory layer. Even if caught, there is an effect that can be overwritten.

In addition, since the recording noise is much smaller, the rewriting characteristics are improved and the domain wall energy is reduced, thereby improving the field sensitivity.

Claims (2)

A first process of forming a first protective film 2 by sputtering SiN on the polycoverate substrate 1, and laminating the reference layer 3 with a RE-TM material on the first protective film 2; A second step of forming an intermediate layer (4) with FeSiAl material on the reference layer (3) so as to be overwritten, and a memory layer (5) formed with a polycyclic compound thereon; and a second with SiN compound on the memory layer (5) An overwriteable magneto-optical recording medium, characterized in that it comprises a third step of forming a protective film (6) and coating an AlTi compound thereon to form a reflective film (7). The overwritable magneto-optical recording medium according to claim 1, wherein the reference layer (3), the intermediate layer (4), and the storage layer (5) have a thickness of 300 mW, 300 mW, and 900 mW in order.