KR100203828B1 - Direct over-write optical magnetic media - Google Patents

Abstract

The present invention relates to a direct overwrite magneto-optical recording medium, and more particularly to a magneto-optical recording medium in which a protective film, a memory layer, a recording layer, a protective film and a reflective film are sequentially stacked on a substrate. A direct recording magneto-optical recording medium comprising a [Pr _x {Fe _0.08 Co _0.02 } _1-x ] _y Cr _1-00-y intermediate layer formed between a memory layer and a recording layer of a film formation.

Description

Magneto-optical recording media

1 is a cross-sectional view schematically showing the layer structure of a direct recording magneto-optical recording medium having two layers of magnetic films according to the prior art.

2 is a cross-sectional view schematically showing the layer structure of a direct recording magneto-optical recording medium having three layers of magnetic films according to the present invention.

3 is a graph showing the basic conditions of the coercive force according to the curie temperature of the memory layer and the recording layer of the magneto-optical recording medium of the present invention.

4 is a graph comparing recording and reproduction characteristics of a bias magnetic field of a direct recording medium according to the prior art and the present invention.

5 is a graph comparing recording reproduction characteristics (CNR) with respect to the recording frequency of a direct recording medium according to the prior art and the present invention.

6 is a graph showing changes in recording reproduction characteristic values with respect to the repeated recording frequency of the recording medium of the related art and the present invention.

FIG. 7 is a graph showing the change of the Kerr rotational angle with respect to the laser wavelength for the direct recording medium of the prior art and the present invention.

8 is a schematic diagram showing the basic concept and recording process structure of the optical modulation direct recording system according to the present invention.

9 is a schematic diagram showing a magnetization state of a recording layer and a memory layer during an overwrite process according to the present invention.

* Explanation of symbols for main parts of the drawings

1: substrate 2, 11: protective film

3: memory layer 4: recording layer

5: intermediate layer 6: laser

7: lens 8: reflecting film

13, 14: magnet 43: memory layer

44: intermediate layer 45: recording layer

The present invention relates to a rare earth-transition metal film direct overwrit magneto-optical disk recording medium. More specifically, two magnetic films having different magnetic properties are adjacent to each other so that vertical magnetization is performed by exchange coupling. Contrary to the conventional first-generation magneto-optical disk, the present invention relates to a magneto-optical recording medium capable of directly recording in an optical modulation method without the need for a series of erasing steps in the state where some information is already recorded.

Recently, a magneto-optical recording medium has been attracting attention as a recording medium capable of erasing and rewriting information such as a magnetic recording medium. (Japanese Patent Laid-Open No. 55-52535, Japanese Patent Laid-Open No. 56-163546).

In a magneto-optical recording medium, the recording film is a vertical magnetization recording film, and information is recorded by changing a direction of magnetization of 1 and 0 of information to form a small magnetic domain. In the recording process of the magneto-optical recording medium, when a laser beam focused on the recording film is irradiated, a part of the recording medium locally rises above the curie temperature and an electromagnet placed on the opposite side when the part is demagnetized. By applying an external magnetic field by means of a magnet coil, only the portion irradiated by the laser is magnetized in a desired direction to form an inverted magnetic domain so that information corresponding to 1 bit of the information signal can be recorded.

In addition, the recorded information can be read out by reflecting linearly polarized light on the recording medium and using the rotational effect of the linearly polarized light.

However, the conventional magneto-optical disk technology has a drawback in that the recording time is long because it is possible only after a series of erasing procedures to record new arbitrary information on the recorded information.

Due to the above-described problems, a direct writing method has been proposed that does not require a series of erasing steps. As shown in FIG. 1, a rare earth-transition metal magnetic film of a direct recording magneto-optical recording medium using an optical modulation method generally exhibits different characteristics according to temperature as shown in FIG. 3, and at an initial temperature, a recording layer The coercivity of the memory layer should be less than that of the memory layer, and as the temperature increases, the recording layer and the memory layer should have a higher curie temperature of the recording layer as shown in FIG. In the case of the optical modulation method, when the direction of magnetization is reversed, one state and zero state are recorded by laser light modulation of high power and low power, and magnetization is performed at low power on the information already recorded at high power. When inverted, the residual information caused by the domain size recorded at high output is larger than that recorded at low output, causing noise, leading to deterioration of recording and reproduction characteristics, and error in information reading. Could be generated. As another problem, as shown in FIG. 1, since the two rare earth-transition metal films are adjacent to each other, inter-diffusion occurs at the interface, and when used repeatedly for a long time, the error rate (byte error rate) increases and the lifetime is shortened. Tended to lose. In addition, the conventional direct recording magneto-optical disk has a problem in that the recording / reproducing characteristic (CNR) is reduced because the rotation angle is small because the laser wavelength is short, that is, in the short wavelength region.

Accordingly, an object of the present invention is to provide a direct recording magneto-optical recording medium by forming an intermediate layer (PrFeCoCr) between the recording layer and the magnetic layer of the memory layer in order to solve the problem of mutual diffusion of the magnetic film and deterioration of recording and reproduction characteristics at short wavelengths. To provide.

In order to achieve the above object, the magneto-optical recording medium of the present invention is a magneto-optical recording medium in which a protective film, a memory layer, a recording layer, a protective film and a reflective film are sequentially stacked on a substrate, between the memory layer and the recording layer. Pr _x {Fe _0.08 Co _0.02 } _1-x ] _y Cr _100-y .

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

As shown in FIG. 2, the intermediate layer according to the present invention is made of [Pr _x {Fe _0.08 Co _0.02 } _1-x ] _y Cr _100-y and has two magnetic layers above and below the memory layer 3 and The recording layer 4 is formed, covered with dielectric protective films 2 and 11 on the top and bottom thereof, and coated with a reflective film 8 on the protective film 11 to form a disk.

The memory layer 3 and the recording layer 4 used in the present invention are rare earth-transition metal magnetic films, and exchange coupling force is applied to each other. The coercive force of the memory layer should be larger than the coercive force of the recording layer at room temperature, and the switching magnetic field should decrease faster than the recording layer when heated by a laser. The composition of the intermediate layer 5 is 0.1 <x <0.3, 50 <Y <80, and the thickness is 50-60 Hz when the laser wavelength is 830 nm, and 40-50 Hz, 633 nm when 780 nm. In the case of 30-40 mu m, and in the case of 532 nm, 10-20 mu m is preferable. At this time, the Pr component having the composition range of X contributes to improving the rotational angle in the short wavelength region, and when Cr is 10 to 50 atm% in the total content, the corrosion resistance is excellent. In addition, in the case of the thickness range, because the Kerr rotation angle is maximized according to each wavelength, if the outside of the range has the disadvantage that the Kerr rotation angle and CNR characteristics of the reproduction characteristics are reduced.

According to the present invention, since the [Pr _x {Fe _0.08 Co _0.02 } _1-x ] _y Cr _100-y is used as the intermediate layer 5, interdiffusion between the upper and lower magnetic layers is prevented, thereby recording with reduced noise level. Regeneration characteristics were improved. 8 and 9 show the recording principle of the magneto-optical disk having the intermediate layer of the present invention satisfying the above conditions. In this case, reference numeral 6 is a laser, 7 is a lens for integrating light irradiated from the laser, 13 is an initialization magnet, 14 is a bias magnet, 43 is a memory layer, 44 is an intermediate layer, and 45 is a recording layer.

On the other hand, there are three requirements for the direct write optical modulation method. First, the coercivity of the memory layer must be greater than the coercivity of the recording layer at room temperature, and the switching field of the memory layer must be reduced faster than the recording layer when heated. do. Secondly, there must be a laser pick-up device for two recordings and one reproduction, i.e. three output levels. Third, an initial magnetic field capable of generating a magnetic field larger than the coercive force of the recording magnetic film and a bias magnetic field for information recording generating magnetic fields of several hundred Oe are required.

The direct recording process of the two-layer magnetic film that satisfies the above conditions is also shown in FIG. 8, in which the magnetization direction of the initialization magnetic field is downward (↓) and the magnetization direction of the bias magnetization (H _b ) is upward (↑). In this case, the magnetization direction of the recording layer is directed downward (↓) by the initialization magnetic field H _ini , and the memory layer is hardly affected at room temperature because the coercive force is large. At this time, if the laser is modulated to high and low power to correspond to binary information of 1 and 0, the temperature of the medium increases to the Curie temperature in the case of high power, so that both the memory layer and the recording layer lose their magnetic properties. After that, the magnetic film of the recording layer which lost its magnetism is cooled and follows the magnetization direction of the bias magnetic field, and the memory layer is copied as it is along the magnetization direction of the recording magnetic film. That is, if the high output is 1 state, the low output can be recorded as 0 state.

Initialization field (H _ini ) required for initialization of the recording layer is

H _ini H _o2 + σω / 2 M _si T ₂

The condition under which a bit written in the memory layer can exist stably

H _C1 H _ini + σω / 2 M _s1 T ₂

In addition, the condition of transferring magnetization to the memory layer of the recording layer initialized by the

σω / 2M _s1 T ₁ H _c1 + H _b .

Where H _c1 and H _c2 are the coercive _forces of the memory layer and the recording layer, T ₁ and T ₂ are the thicknesses of the memo layer and the recording layer, M _s1 and M _s2 are the saturation magnetization of the memory layer and the recording layer, and H _b is the bias magnetic field. _{, σ · ω / 2 M s1} T 2 is the exchange force received the memory layer from the recording layer.

Although the effects of the present invention will be described in more detail with reference to the following examples and comparative examples, the scope of the present invention is not limited to the following examples.

EXAMPLES 1-6

Si ₃ N ₄ 900Å / T _b30 Fe ₇₀ 100Å / by conventional sputtering method on a polycarbonate substrate in an In Line Sputtering System composed of 6 sputtering chambers _{[Pr x {Fe 0.08 Co 0.02} } 1-x] y Cr 100-y ZÅ / T b24 Fe 53 Co 23 to a _{400Å / Si 3 N 4 300Å /} AlTi (Ti 3 at%) 400Å of six-layer film disk table Prepared as 1.

[Comparative Example]

In Example 1, except that the intermediate layer [Pr _x {Fe _0.08 Co _0.02 } _1-x ] _y Cr _100-y Z 1 was not deposited, a 5-layered magneto-optical disk was manufactured.

For each of the samples (kerr loop tracer) using a Kerr loop tracer (kerr loop tracer) was measured by the rotation angle according to the wavelength, the results are shown in Table 2 below.

As can be seen in Table 2, it can be seen that there is a composition and thickness in which the Kerr rotation angle is greatest depending on the wavelength of the laser. The rotation angle of the Kerr was measured by a Kerr loop tracer made by the Institute of Advanced Materials Research, MOD (magneto-optic disk) lab. In addition, by using the magneto-optical disk drive system (OM 2000, NAKAMICHI Co, retrofitted with an initialization magnetizer) as shown in FIG. 7, the recording and reproducing characteristics of the fabricated specimens were measured at a frequency of 10 MHz, a linear velocity of 15 m / sec, and a high power. : Ph) is 16mW in frequency and 7mW in low power, and the recording and reproducing characteristic (CNR) are measured after recording by changing the bias magnetic field (H). Comparative Example 1 It can be seen that the improvement is about 3 to 5 dB. At this time, the existing information of the disk was recorded at high power of 16mW, low power of 7mW, and frequency of 5MHz.

In the graph of FIG. 5, information recorded at high power: 16mW, low power: 7mW, bias magnetization: 500 Oe, and frequency of 5MHz is recorded at the same power without erasing, and the recording frequency is measured. One result.

As a result, it can be seen that there is almost no residual information since it is improved by 5 dB over the entire frequency range compared to Comparative Example 1. In addition, in order to find out the change in the noise level of the repeating proxy, the noise level was measured while repeatedly overwriting with high power of 16mW, low power of 6mW, and frequency of 2MHz. In the case of a two-layer magnetic film without a magnetic intermediate layer as shown in the graph, it is 10 In the case of more than one noise level, the noise level rapidly increases, whereas when there is a PrFeCoCr layer between two magnetic films, it is 10 Since there is no change up to more than one time, it can be seen that almost no interdiffusion occurs.

FIG. 7 shows the measurement of the Kerr rotational angle at various wavelengths with respect to the conventional direct recording disk and Example 6 of the present invention. Can be.

A conventional magneto-optical recording medium having a single recording film can be recorded only after a series of erasing processes when recording arbitrary information and then recording new information. According to the direct recording magneto-optical medium of the present invention, such a series of erasing Since the time required for the process is not required, the recording time can be shortened, and the disadvantage of the optical modulation direct recording, i.e., the presence of residual information generated because the high power (P) recording domain is larger than the size of the low output (P) recording domain, It was found that the recording and playback characteristics were reduced due to a read error or an increase in the noise level, and the recording and playback characteristics were improved by about 3 to 5 dB as shown in FIG. Due to the interdiffusion between films, the PrFe could not be used due to an increase in the byte error rate when repeated for a long time. Since the CoCr layer plays a role of preventing interdiffusion, it can be seen that the noise level does not increase at all even after repeated use for a long time as shown in FIG. In particular, when the wavelength of the laser is shortened to increase the capacity of the magneto-optical disk, the thickness of the intermediate layer of the present invention is controlled to reduce the rotational angle and the recording and reproduction characteristics.

Claims (6)

In a magneto-optical recording medium in which a protective film (2), a memory layer (3), a recording layer (4), a protective film (2) and a reflective film (8) are sequentially stacked on a substrate, the memory layer and the recording layer of the magnetic film. [Pr _x {Fe _0.08 Co _0.02 } _1-x ] _y Cr _100-Y interlayer formed between the direct recording magneto-optical recording medium. A direct recording magneto-optical medium according to claim 1, wherein the intermediate layer has a composition of 0.1X0.3 and 50Y90. The direct recording magneto-optical recording medium according to claim 1, wherein the intermediate layer has a thickness of 50 to 60 Hz when the wavelength of the laser is 830 nm. The direct recording magneto-optical recording medium according to claim 1, wherein the intermediate layer has a thickness of 30 to 40 kHz when the wavelength of the laser is 780 nm. The direct recording magneto-optical recording medium according to claim 1, wherein the intermediate layer has a thickness of 30 to 40 Hz when the wavelength of the laser is 633 nm. The direct recording magneto-optical recording medium according to claim 1, wherein the intermediate layer has a thickness of 10 to 20 kHz when the wavelength of the laser is 532 nm.