JPH08241544A - Magneto-optical medium - Google Patents

Abstract

PURPOSE: To obtain a magneto-optical medium capable of reproducing high density recorded information without applying a magnetic field for initializing or a magnetic field for reproduction. CONSTITUTION: An underlayer 3 of A/N is formed on a glass substrate 2 in 90nm thickness and a reproducing layer 4 of GdFeCo, a nonmagnetic middle layer 5 of SiN, a recording layer 6 of TbFeCo and a protective layer 7 of SiN are successively formed on the underlayer 3 in 40nm, 5nm, 40nm and 45nm thickness, respectively. At the time of reproducing a recorded mark of 0.38-0.4μm size, an intrasurface magnetization mask is formed in a low-temp. region in a beam spot, a perpendicular magnetization mask is formed in a high-temp. region and the recorded mark of the recording layer is transferred to a medium- temp. region.

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 capable of high density recording.

[0002]

2. Description of the Related Art A magneto-optical medium capable of rewriting information signals has been required to have a larger capacity as the amount of information has increased due to the rapid development of multimedia in recent years. To record information on a magneto-optical disk, which is one of the magneto-optical media, the magneto-optical recording film is irradiated with a laser beam and heated, and the direction of magnetization (recording mark) at that portion is changed to an external magnetic field according to the recorded information. Do by aligning. On the other hand, at the time of reproduction, the track of the recording mark is irradiated with a laser beam, and the Kerr effect in which the polarization plane of the reflected light rotates depending on the direction of magnetization is used for reproduction. The recording and reproducing linear density of the magneto-optical disk depends on the beam spot diameter of the laser beam on the disk.
This is limited by the wavelength of the light source and the numerical aperture of the objective lens.

For example, when recording is performed at a high density by narrowing the mark intervals of the recording marks, a plurality of recording marks exist in the beam spot during reproduction. In the case of a magneto-optical disk, by controlling the power of the laser beam at the time of recording, the area above the Curie temperature can be made smaller than the beam spot diameter, so it is not so difficult to form recording marks at high density. However, when reproducing the recording marks formed with high density, the presence or absence of the recording marks cannot be identified because the reproduction output does not change even if the beam spot moves on the disk.

There has been proposed a method of reproducing a recording mark having a beam spot diameter smaller than this (for example, JP-A-3-93058 and JP-A-4-271039). In all of these, while reproducing one recording mark in the beam spot, other recording marks are masked to enhance the reproduction resolution.
duced super resolution reproduction, hereinafter referred to as MSR reproduction) is used. The magnetic super-resolution medium (hereinafter referred to as MSR medium) used in this method is a medium in which a plurality of magnetic films having different magnetic characteristics depending on temperature are stacked, and has a recording layer for recording marks and reproducing in a beam spot. The recording layer includes a mask layer or a reproduction layer for transferring a desired recording mark and masking a mark other than the recording mark.

Japanese Unexamined Patent Publication No. 3-93058 proposes a method of reproducing information from a magneto-optical recording medium in which a non-magnetic intermediate layer is interposed between a reproducing layer and a recording layer both of which are perpendicularly magnetized films. . An initialization magnetic field of several kilo Oersted (kOe) is applied to the magneto-optical recording medium on which information is recorded to align the magnetization direction of the reproducing layer to initialize it (hereinafter, such a magnetization state of the reproducing layer is initialized. State). Due to the temperature distribution when the laser beam is emitted during reproduction, the recording mark is masked in the initialized state in the front direction of the beam spot movement, and the recording mark is transferred to the reproduction layer in the rear direction. As a result, the recording mark is reproduced in the unmasked area in the beam spot, and the recording mark having the beam spot diameter or less can be reproduced. However, this method has a problem that as the reproduction beam power is increased, the unmasked recording mark transfer area is enlarged, and the reproduction output is reduced.

JP-A-4-271039 discloses a method of reproducing information from a magneto-optical recording medium in which a magnetic intermediate layer is interposed between a reproducing layer and a recording layer. An initialization magnetic field is applied to the magneto-optical recording medium on which information is recorded, and the magnetization direction of the reproducing layer is aligned to initialize. Then, a reproducing magnetic field of about 200 Oersted (Oe) is applied together with the irradiation of the laser beam. The directions of magnetization of the reproducing layer and the magnetic intermediate layer are aligned so as to mask the recording mark in front of and in the rear of the beam spot moving direction, depending on the temperature distribution when the laser beam is irradiated during reproduction. In such a type of magneto-optical recording medium, since two mask regions are formed in the beam spot in the high temperature region and the low temperature region of the medium, the reproduction output does not decrease even if the beam power is increased during reproduction.

[0007]

By the above method, a recording mark having a beam spot diameter or less can be reproduced, but an initializing magnetic field of several kilo-oersted (kOe) and a reproducing magnetic field of about 200 oersted (Oe). Need. The normally used magneto-optical disk device does not apply a magnetic field at the time of reproduction, so that there is a problem that the ordinary magneto-optical disk device cannot reproduce the information recorded on the magneto-optical medium as described above.

The present invention has been made in view of such circumstances, and the non-magnetic layers sandwiching the reproducing layer of the MSR medium are formed of different kinds of dielectric materials, so that the initializing magnetic field and reproducing at the time of reproducing in MSR reproducing are performed. It is an object of the present invention to provide a magneto-optical medium capable of reproducing recorded high-density information without applying a magnetic field and achieving improvement in reproduction resolution.

[0009]

A magneto-optical medium according to the first invention comprises a non-magnetic underlayer, a magnetic reproducing layer, a non-magnetic intermediate layer,
A magnetic recording layer and a non-magnetic protective layer are laminated in this order, and the magnetization direction recorded in the magnetic recording layer within a predetermined temperature range within the spot is transferred to the magnetic reproducing layer by irradiation of a reproducing light beam. The magneto-optical medium is characterized in that the underlayer and the intermediate layer are made of different dielectric materials.

The magneto-optical medium according to the second aspect of the present invention comprises a non-magnetic underlayer, a magnetic reproducing layer, a magnetic intermediate layer, a magnetic recording layer and a non-magnetic protective layer, which are laminated in this order. A magneto-optical medium in which a magnetization direction recorded in the magnetic recording layer within a predetermined temperature range within the spot is transferred to the magnetic reproducing layer, and the underlayer and the protective layer are formed of different dielectric materials. It is characterized by being

[0011]

In general, the minimum radius R of the recording mark for stable existence of the recording mark is R = σ / (MsHc) ^1/2 (1) σ = 4 (KuA) ^1/2 (2 ) Where σ: Bloch domain wall energy density Hc: coercive force of reproducing layer Ms: saturation magnetization Ku: perpendicular magnetic anisotropy constant A: exchange stiffness constant.

From equations (1) and (2), it can be seen that the minimum radius R of the recording mark increases when the perpendicular magnetic anisotropy energy is increased. As the minimum radius R increases, the smaller recording mark becomes unstable. That is, by increasing the perpendicular magnetic anisotropy energy of the reproducing layer,
The mark transferred to the reproducing layer in the beam spot is, when the magnetostatic coupling force or exchange coupling force from the recording layer weakens,
It is possible to enter the initialized state without applying the reproducing magnetic field and the initializing magnetic field.

Further, the present inventor measured the reproduction signal level of the MSR medium provided with the reproduction layer, the magnetic intermediate layer and the recording layer by changing the reproduction magnetic field, and obtained the following findings. FIG. 6 is a graph showing the signal level when the information recorded on the MSR medium is reproduced by changing the reproduction magnetic field. The vertical axis represents the carrier level (dBm), and the horizontal axis represents the magnitude of the reproducing magnetic field (Oe). A recording mark of 0.4 μm is formed on the MSR medium. In the graph, “○” is the measurement result for the MSR medium in which the non-magnetic layer sandwiching the magnetic layer is made of different dielectrics, and “×” is the non-magnetic layer sandwiching the magnetic layer made of the same kind of dielectric. It is a measurement result about the prepared MSR medium. As can be seen from the figure, when the same kind of dielectric material is used, the carrier level becomes higher as the reproducing magnetic field is increased. That is, it indicates that a reproducing magnetic field is necessary to obtain a high reproducing signal level. On the other hand, when different kinds of dielectrics are used, a high carrier level is shown regardless of the reproducing magnetic field. That is, it is shown that a high reproduction signal level can be obtained without applying a reproduction magnetic field, and the reproduction magnetic field is unnecessary for forming the mask.

Focusing on the above findings, in the magneto-optical medium of the present invention, when different kinds of dielectric materials are used for the magnetic layer of the MSR medium, especially for the non-magnetic layers sandwiching the reproducing layer, the same kind of dielectric material is used. By increasing the magnitude of the perpendicular magnetic anisotropy energy of the reproducing layer and shifting the transferred mark to the initializing state as the temperature rises, the reproducing magnetic field and the initializing magnetic field are not required to form a mask, Get the playback signal level.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 1 is a diagram showing a configuration and a reproducing principle of an MSR medium of a first embodiment according to the present invention. MSR
The medium 1 is a magneto-optical disk, which comprises an underlayer 3, a reproducing layer 4, a non-magnetic intermediate layer 5, a recording layer 6 and a protective layer 7 in this order from the glass substrate 2 side, and the recording layer 6 has a recording mark of 0.38 μm. Are formed.

Such an MSR medium is manufactured by laminating each layer on the glass substrate 2 by a sputtering method at an ultimate vacuum of 5 × 10 ^-5 Pa or less in a vacuum container. First, an AlN underlayer 3 having a thickness of 90 nm is formed on the glass substrate 2. Next, a GdFeCo reproducing layer 4 of 40 nm, a SiN non-magnetic intermediate layer 5 of 5 nm, and a TbFeCo recording layer 6 of 40 nm were formed on the underlayer 3.
A protective layer 7 of SiN is formed to a thickness of 45 nm. As for the sputtering conditions, when the underlayer 3, the non-magnetic intermediate layer 5 and the protective layer 7 are formed, the gas pressure is 0.2 Pa and the input power is 0.8 kW.
When forming the magnetic layers of the reproducing layer 4 and the recording layer 6, the gas pressure is set to 0.5 Pa and the input power is set to 1.0 kW. The reproducing layer 4 was formed with both RE-rich composition (rare earth metal magnetization dominant composition) and TM-rich composition (transition metal magnetization dominant composition) (not shown).

The Curie temperature of the reproducing layer 4 of GdFeCo is 320 in both RE-rich and TM-rich.
The compensation temperature is 150 ° C for RE-rich type and room temperature for TM-rich type. The Curie temperature of the TbFeCo recording layer 6 is 300 ° C., and the compensation temperature is room temperature.

[0018]

[Table 1]

Table 1 shows the measurement results of the perpendicular magnetic anisotropy constant Ku of the reproducing layer 4 in the MSR medium having such a structure. It is shown together with the perpendicular magnetic anisotropy constant Ku of the MSR medium in which the reproducing layer is sandwiched by dielectric layers (underlayer and non-magnetic intermediate layer) of the same kind. From the table, the reproducing layer sandwiched between the underlayer of AlN and the intermediate layer of SiN, which are different types of dielectric layers, has a perpendicular magnetic anisotropy constant Ku that is about twice that of the one sandwiched between the dielectric layers of the same type. You know that you have.

The MSR medium formed as described above has a density of 0.38
A recording mark of μm is formed. The recording conditions are linear velocity 9m / s, recording power 12.8mW, recording frequency 11.8MHz.
Is. A glass substrate 2 of an MSR medium for reproducing a light beam
The operation of reproducing the recording mark by irradiating from the side will be described below. At room temperature, the magnetization direction of the reproducing layer 4 is RE
In the case of rich, the in-plane magnetization direction forms an in-plane magnetization mask (see FIG. 1, low temperature region), and in the case of TM rich, the perpendicular magnetization direction is always the same regardless of the orientation of the recording layer 6. Form a perpendicular magnetization mask (not shown). However,
In the range (intermediate temperature region) within the beam spot where the temperature rises due to the irradiation of the reproducing light beam and the magnetostatic coupling force becomes larger than the coercive force of the reproducing layer, the recording mark of the recording layer 6 is generated by the magnetostatic coupling force. Is transferred to the reproducing layer 4, and the transferred recording mark is reproduced.

In the range where the temperature is further increased by the irradiation of the light beam (high temperature area), the magnetostatic coupling force from the recording layer 6 is weakened, and the perpendicular magnetic anisotropy energy is larger than in the conventional case, and the recording mark becomes unstable. Reproduction layer 4
The magnetization direction of the above is in the initialized state as described above, and the reproducing layer 4 in the low temperature region and the high temperature region serves as a mask for covering the recording mark. As a result, the transfer recording marks on the recording layer 6 can be reproduced from the reproducing layer 4 in the intermediate temperature region without applying the initializing magnetic field and the reproducing magnetic field. After that, the recording mark of the recording layer 6 is transferred as the magnetization direction of the reproducing layer 4 is lowered. When the temperature is further lowered, the one using the RE-rich composition reproducing layer 6 is in the direction of in-plane magnetization,
When the reproducing layer 6 having the TM-rich composition is used, the direction of perpendicular magnetization is obtained.

FIG. 2 is a graph showing the results of measuring the carrier reproducing power dependency without applying a reproducing magnetic field using the MSR medium as described above. The vertical axis represents the carrier level (dBm), and the horizontal axis represents the reproduction power (mW). The sharp increase in carriers seen in the graph indicates that when a light beam with a reproducing power of about 1.7 mW was irradiated, a mask was formed in the beam spot and the resolution increased. As a conventional example, the same measurement was performed on an MSR medium having a structure in which a reproducing layer having the same composition as that of the above-described present example was sandwiched by dielectric layers of the same kind, and the result is shown in a graph.
As is apparent from the graph, it is understood that the carrier rising of the MSR medium of the first embodiment shifts to the reproducing power side lower than that of the conventional example. This result shows that
It was the same regardless of the RE-rich composition and the TM-rich composition. From this, it can be said that the MSR medium of the first embodiment can obtain high reproduction resolution even when the reproduction power of the light beam is low.

In the case of the MSR medium of the first embodiment, which is provided with a different kind of dielectric, the compressive stress due to the SiN layer and the tensile stress due to the AlN layer act on the reproducing layer 4, so that the same kind of dielectric is used. The stress dielectric magnetic anisotropy energy is larger than that of the MSR medium. As the anisotropy energy increases, the recording mark with a small radius tends to become unstable as the temperature rises as described above, and the recording mark tends to be in the initialized state. , The recording mark of the optical density can be reproduced by MSR.

FIG. 3 is a graph showing the reproducing magnetic field dependence of C / N of the MSR medium shown in the first embodiment, with the vertical axis representing C.
/ N (dB), and the horizontal axis represents the reproducing magnetic field (Oe). The reproducing power of the light beam is 2.5 mW. In the graph, '○' indicates the result of the reproducing layer of TM rich composition, and '×' indicates the result.
The result of the reproducing layer of RE rich composition is shown. As is clear from the graph, in both of the TM-rich composition reproducing layer and the RE-rich composition reproducing layer, even when the reproducing magnetic field is not applied, it is almost the same as when the reproducing magnetic field of about 400 (Oe) is applied. It can be seen that a C / N of

FIG. 4 shows the MSR of the second embodiment according to the present invention.
It is a figure which shows the structure and reproducing principle of a medium. The MSR medium 11 is a magneto-optical disk, which comprises an underlayer 3, a reproducing layer 4, a magnetic intermediate layer 15, a recording layer 6 and a protective layer 7 in this order from the glass substrate 2 side, and a recording mark of 0.40 μm is formed on the recording layer 6. Are formed.

Such an MSR medium is manufactured by laminating each layer on the glass substrate 2 by a sputtering method at an ultimate vacuum of 5 × 10 ^-5 Pa in a vacuum container. First, an AlN underlayer 3 having a thickness of 90 nm is formed on the glass substrate 2. Next, the reproducing layer 4 of GdFeCo is 40 nm, the magnetic intermediate layer 5 of TbFe is 10 nm, the recording layer 6 of TbFeCo is 40 nm, and Si on the underlayer 3.
A protective layer 7 of N is formed to a thickness of 45 nm. As for the sputtering conditions, when forming the underlayer 3 and the protective layer 7, the gas pressure was set to 0.2 Pa and the input power was set to 0.8 kW.
When forming the magnetic layers of the magnetic intermediate layer 15 and the recording layer 6, the gas pressure is set to 0.5 Pa and the input power is set to 1.0 kW.

These magnetic layers are formed by an ordinary FAD (Front
Aperture Detection) is the same as the composition medium.
The Curie temperature of the reproducing layer 4 of GdFeCo is 320 ° C., and the compensation temperature is room temperature or lower. Magnetic intermediate layer of TbFe
The Curie temperature of 15 is 130 ° C and the compensation temperature is below room temperature. The Curie temperature of the recording layer 6 of TbFeCo is 260
C, and the compensation temperature is below room temperature.

[0028]

[Table 2]

Table 2 shows the measurement results of the perpendicular magnetic anisotropy constant Ku of the reproducing layer 4, the intermediate layer 15, and the recording layer 6 which are the magnetic layers in the MSR medium having such a structure. The perpendicular magnetic anisotropy constant Ku of the MSR medium in which the magnetic layer is sandwiched between the same kind of dielectric layers (underlayer and protective layer) is shown. From the table, it can be seen that the magnetic layer sandwiched between the underlayer of AlN and the protective layer of SiN, which are different dielectric layers, has a larger perpendicular magnetic anisotropy constant Ku than that sandwiched between the dielectric layers of the same type. You can see that

The MSR medium formed as described above has a thickness of 0.4 μm.
Recording marks of m are formed. The recording condition is a linear velocity of 9
m / s, recording power 12.8 mW, recording frequency 11.8 MHz. The operation of irradiating the reproducing light beam from the glass substrate 2 side of the MSR medium to reproduce the recording mark will be described below. At room temperature, the magnetization direction of the reproducing layer 4 becomes the same as that of the recording layer 6 due to the exchange coupling force via the magnetic intermediate layer 15 (see FIG. 4), and the Curie temperature of the magnetic intermediate layer 15 is higher than that in the beam spot. In the low region (low temperature region), the recording mark of the recording layer 6 is transferred to the reproducing layer 4 and the magnetic intermediate layer 15.

However, in a range (high temperature region) in which the temperature rises due to the irradiation of the light beam and exceeds the Curie temperature of the intermediate layer 15 in the beam spot, the exchange coupling force from the recording layer 4 is cut off and the perpendicular magnetic anomaly is generated. Due to the destabilization of the recording mark due to the larger anisotropic energy than before, the magnetization direction of the reproducing layer 4 becomes the initialized state as described above, and the mask serves as a mask for covering the recording mark. As a result, the transfer recording mark of the recording layer 6 can be reproduced only from the reproducing layer 4 in the low temperature region without applying the initialization magnetic field and the reproducing magnetic field.

FIG. 5 is a graph showing the reproducing magnetic field dependence of C / N of the MSR medium shown in the second embodiment, with the vertical axis representing C.
/ N (dB), and the horizontal axis represents the reproducing magnetic field (Oe). The reproduction power of the light beam is 2.5mW. As is clear from the graph, even when reproducing without applying the reproducing magnetic field, the C / N is about the same as when the reproducing magnetic field is applied.
It can be seen that

In the first and second embodiments, the underlayer 3
Al nitride is used for the non-magnetic intermediate layer 5 or protective layer 7
Although the case where Si nitride is used has been described above, the present invention is not limited to this. The results of measuring the carrier reproducing power dependence in the case of using different oxide dielectrics are almost the same as those in the graph shown in FIG. 2, and the reproducing magnetic field in the case of using different oxide dielectrics is shown. The result of measurement of the signal characteristic for γ was almost the same as the graph shown in FIG. Thus, the underlayer 3 may be formed of Al oxide, and the nonmagnetic intermediate layer 5 or the protective layer 7 may be formed of Si oxide.

In the first embodiment, the case where AlN is used for the underlayer 3 and SiN is used for the intermediate layer 5 has been described, but the same effect can be obtained even if the materials of the underlayer and the nonmagnetic intermediate layer are reversed. Is obtained. Similarly, the second embodiment describes the case where AlN is used for the underlayer 3 and SiN is used for the protective layer 7, but the same effect can be obtained even if the materials of the underlayer and the protective layer are reversed.

Further, in the first and second embodiments, the reproducing layer 4 is made of GdFeCo and the recording layer 6 is made of TbFeCo. The reproducing layer 4 is preferably a magnetic film having a large Kerr rotation angle at the temperature at which a signal is reproduced and a small coercive force so that recording marks can be easily transferred by perpendicular magnetization. GdFeCo, GdTbFeCo, Gd
There are Co and the like. The recording layer 6 is preferably a perpendicular magnetization film having a large coercive force so that the recording mark is stable at the reproducing temperature. In addition to TbFeCo, DyFeCo, NdT
bFe and the like.

Furthermore, in the second embodiment, the magnetic intermediate layer
TbFe with a Curie temperature of 130 ° C. is used for 15. This is because in the case of the FAD medium as in the second embodiment, when the magnetic intermediate layer 15 exceeds 150 ° C., even if the reproducing power is 3 mW, the high temperature region for masking the recording mark cannot be formed in the beam spot and the MSR reproduction is performed. Is not possible. Therefore, it is desirable to use a material having a Curie temperature of 150 ° C. or lower for the magnetic intermediate layer 15.

Furthermore, in the above-described embodiment, the case where the non-magnetic medium is a disk type has been described, but the present invention is not limited to this, and other shapes such as a card type may be used.

[0038]

As described above, in the present invention, in the magnetostatic coupling type magneto-optical medium, the non-magnetic underlayer and the non-magnetic intermediate layer sandwiching the magnetic reproducing layer are formed of different dielectric materials. In the exchange-coupling type magneto-optical medium, a non-magnetic underlayer and a non-magnetic protective layer sandwiching a magnetic layer are formed of different dielectric materials, so that a fine recording transferred from the magnetic recording layer to the magnetic reproducing layer is performed. The mark is likely to become unstable in a high temperature region, and the recording mark of the magnetic recording layer can be masked by shifting to the initializing state without applying the initializing magnetic field and the reproducing magnetic field, and thus the information recorded at high density can be recorded. The present invention has excellent effects such as improvement in reproduction resolution.

[Brief description of drawings]

FIG. 1 shows the configuration of an MSR medium according to a first embodiment of the present invention.
It is a figure which shows the reproduction principle at the time of using a RE rich reproduction layer.

FIG. 2 is a graph showing the reproduction power dependence of carriers of the MSR medium of the first embodiment.

FIG. 3 is a graph showing the reproducing magnetic field dependency of C / N of the MSR medium of the first embodiment.

FIG. 4 is a diagram showing a configuration and a reproducing principle of an MSR medium of a second embodiment according to the present invention.

FIG. 5 is a graph showing the reproducing magnetic field dependence of C / N of the MSR medium of the second embodiment.

FIG. 6 is a graph showing reproduction signal characteristics with respect to a reproduction magnetic field.

[Explanation of symbols]

 1,11 Magneto-optical medium 2 Glass substrate 3 Underlayer 4 Reproducing layer 5 Non-magnetic intermediate layer 6 Recording layer 7 Protective layer 8 Recording track 15 Magnetic intermediate layer

Claims (2)

[Claims] 1. A non-magnetic underlayer, a magnetic reproducing layer, a non-magnetic intermediate layer, a magnetic recording layer and a non-magnetic protective layer are laminated in this order, and a predetermined temperature within the spot is formed by irradiation of a reproducing light beam. In the range, in the magneto-optical medium in which the magnetization direction recorded in the magnetic recording layer is transferred to the magnetic reproducing layer,
A magneto-optical medium, wherein the underlayer and the intermediate layer are made of different dielectric materials. 2. A nonmagnetic underlayer, a magnetic reproducing layer, a magnetic intermediate layer, a magnetic recording layer, and a nonmagnetic protective layer are laminated in this order, and within a predetermined temperature range within the spot upon irradiation with a reproducing light beam. In the magneto-optical medium in which the magnetization direction recorded in the magnetic recording layer is transferred to the magnetic reproducing layer and reproduced, the underlayer and the protective layer are formed of different dielectric materials. Magneto-optical medium.