JPS63304448A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To eliminate the need for a permanent magnet for generating a perpendicular magnetic field and to reduce the size and weight of a device by increasing the Curie temp. of an auxiliary layer to the temp. higher than the temp. of a recording layer and forming the auxiliary layer of a magnetic film which exhibits a specific minor hysteresis loop. CONSTITUTION:The Curie temp. of the auxiliary layer 13 of the recording medium is set higher than the Curie temp. of the recording layer 12. The auxiliary layer 13 is formed of such magnetic film imparted with the multi-layered film structure or concn. gradient exhibiting such minor hysteresis loop as to attain always the same magnetization state when there are no external magnetic fields and to attain plural stable magnetization states when there is the external magnetic field. The magnetic moments are aligned upward at the time of a laser beam 6 of weak light intensity to this recording film and are aligned downward when the light intensity is strong and, therefore, the over-writing is enabled merely by varying the intensity of the light. The need for the conventional large permanent magnet for a perpendicular magnetic field is, therefore, eliminated and the size and weight of the device are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a magneto-optical recording medium having an overwriting function.

<Prior art> Conventionally, recording (writing information) on a magneto-optical recording medium (magneto-optical disk) is performed using a uniformly magnetized optical recording medium (Tb-
A bias magnetic field below the anisotropy field is applied to the perpendicularly magnetized thin film (such as a Fe thin film) in the opposite direction to the magnetization, and a laser beam is irradiated to raise the temperature of the irradiated area above the Curie temperature, and then the optical recording medium is It takes advantage of the fact that the magnetization reverses in the direction of the bias magnetic field during the cooling process. In this way, information is recorded as a sequence of magnetization reversals by turning the laser beam on and off, and when new information is to be recorded in an area that has been previously recorded, a continuous laser beam is used in a bias magnetic field in the opposite direction. It was necessary to irradiate a beam to heat the optical recording medium and align all the magnetizations in a uniform direction (this is called the erasing process). In other words, since it is necessary to record again after erasing, just like writing information in normal magnetic recording, by recording another information on top of the previously recorded area, the previous information will be automatically replaced. It never disappeared, and it was an obstacle to increasing access speeds.

Therefore, in recent years, a magneto-optical recording medium (magneto-optical disk) using a two-layer thin film and capable of overwriting has been proposed. Third
The figure consists of a conventional two-layer thin film structure. FIG. 2 is an explanatory diagram showing a magneto-optical recording medium. In the figure, reference numeral 1 denotes a magneto-optical recording medium, which includes a substrate 2 made of a glass plate or the like, and an auxiliary layer (for example, T
b-Fe-Co thin film) 3 and a recording layer 4 having a high anisotropy magnetic field and a low temperature (for example, a Tb-Fe thin film) 4. 5 is a magneto-optical recording medium 1 and a laser beam 6
7 is a magnet such as a permanent magnet or an electromagnet placed below the auxiliary layer 3 on the upstream side of the optical head 5;
is a bias magnetic field provided below the auxiliary layer 3 facing the optical head 5.

Recording (writing information) on the magneto-optical recording medium 1 is assisted by first applying a strong perpendicular magnetic field (Hini) to the medium surface with the magnet 7 while the magneto-optical recording medium 1 is rotating in the direction of the arrow. The layer 3 is completely magnetized in the direction of the magnetic field (downward in the figure) (initial magnetization process).Next, when the magneto-optical recording medium 1 moves below the optical head 5, it is irradiated by the optical head 5. It is heated by a laser beam 6 with two levels of light intensity: strong and weak.At this time, a weak bias magnetic field 8 is applied in the opposite direction (upward in the figure) to the magnetic field for initial magnetization.

When the light intensity of the laser beam 6 is weak, the maximum temperature of the irradiated part is set to be higher than the Curie temperature of record 1'14,
In addition, the temperature is set to be equal to or lower than the Curie temperature of the auxiliary layer 3. In this case, only the recording layer 4 becomes non-magnetic and the auxiliary layer 3
The magnetization of the recording layer 4 remains unchanged, and when the magneto-optical recording medium 1 moves and the temperature of the area irradiated with the laser beam 6 decreases, the magnetization of the recording layer 4 changes to that of the auxiliary layer 3 due to spin interaction. Aligns in the same direction as magnetization. On the other hand, when the light intensity of the laser beam 6 is strong, the maximum temperature of the irradiated portion is set to be equal to or higher than the Curie temperature of the auxiliary layer 3. In the cooling process in this case, the magnetization of the auxiliary layer 3 is first aligned in the direction of the bias magnetic field 8, and following this magnetization, the magnetization of the recording layer 4 is also aligned in the direction of the bias magnetic field 8, thereby completing recording.

In this way, since the above-described recording process does not depend on the magnetization state of the recording layer 4, recording according to the light intensity of the laser beam 6 is always possible, and thereby overwriting is possible.

The written information can then be read out as a difference in the slope of the polarization plane of the reflected light of the laser beam 6. still,
The light intensity of the laser beam 6 during reproduction must be set so that the irradiation temperature is sufficiently lower than the Curie temperature of the recording layer 5.

<Problems to be Solved by the Invention> In the prior art described above, Tb-Fe-C is used in the auxiliary layer 3.
o When a Tb-Fc thin film is used as the recording layer 4, the perpendicular magnetic field (Hini) generated by the magnet 7 is 6
A magnetic field as high as 000 Gauss is required (Lecture rA presented at the Japan Society of Applied Physics National Conference, March 28, 1986: Masatoshi Sato, Shun Saito, Fussho Matsumoto, Hideki Akasaka, “One Beam Opalight System” Lecture number 28p
-zl-3).

Since the magneto-optical recording medium 1 is generally housed in a cassette (not shown), and considering that the distance between the medium surface and the magnet 7 is larger than the quantity, the perpendicular magnetic field (Hini) is 6000 Gauss. In order to obtain a high magnetic field, the size of the magnet 7 for initial magnetization becomes considerably large, making it impossible to reduce the size and weight of the magneto-optical recording and reproducing apparatus.

The present invention was made for the purpose of solving the above-mentioned problems, and aims to provide a magneto-optical recording medium that does not require a perpendicular magnetic field (H-th) for initial magnetization in a magneto-optical recording medium that can overlap. It is.

Means for Solving the Problems> To solve the above problems, the present invention provides a magneto-optical recording medium consisting of a magnetic thin film of 21tNlt3m as a recording layer and an auxiliary layer, in which the Curie temperature of the auxiliary layer is lower than the Curie temperature of the recording layer. is also set high, and the auxiliary layer has a multilayer film structure exhibiting minor and steric loops such that it always has the same magnetization state in the absence of an external magnetic field, and has a plurality of stable magnetization states in the presence of an external magnetic field, or Rare earth/transition alloy magnetism with concentration gradient! It is characterized by being a membrane.

Practical example Hereinafter, the present invention will be explained in detail with reference to illustrated embodiments.

FIG. 1 is an explanatory diagram showing the structure of a magneto-optical arrangement 1i1f3& body according to the present invention. As shown in this figure, high coercive force and low temperature are recorded (for example, a 21% Tb-79% Fe731 film) by sputtering or vacuum evaporation on a transparent substrate 11 formed into a disk shape such as glass. etc.) 12
is formed, and an auxiliary layer having a Curie temperature higher than that of the recording layer 12 (for example, 23%Tb-65%Fe-1
2% Co thin film, etc.) 13 is formed.

This auxiliary layer 13 has a compensating composition (a composition in which the magnetic moment due to the rare earth element and the magnetic moment due to the transition metal are equal to each other) in which transition metals such as Co and Fe are present in the initial stage of thin film deposition during fabrication. ). In the later stages of deposition, a concentration gradient is given such that rare earth elements such as Tb are present in a higher amount than in the compensation composition, or a thin film with a two-layer structure consisting of a thin film with more transition metals and a thin film with less transition metals than in the compensation composition is formed. Note that 5 is an optical head, 6 is a laser beam, and 8 is a bias magnetic field, which are the same as in the conventional case.

The magnetization (M)-magnetic field (H) curve of the auxiliary WB 13 forms a stepped hysteresis loop as shown in FIG. 2, and also shows the state of magnetization at each stage of this hysteresis loop. In this hysteresis loop, what is not particularly noteworthy is the minor loop indicated by ABCDEF in the figure. In state ABC, the magnetic moments of the high transition metal layer 13m are aligned antiparallel to the magnetic moments of the high rare earth M layer 13b, while in state DEF: the moments of both layers are aligned parallel to each other.

That is, only the magnetic moment of the t&transition metal layer 13a is reversed in this minor loop, and if no magnetic field is applied (point 0 in the figure), the magnetization state is the same as ABC from any state of ABCDEF. return. In addition, a magnetic field (Hl o w # H
h i) both decrease as the temperature increases.

The above-mentioned different magnetization reversal behavior between the upper and lower layers has been reported in Gd-Co alloy thin films with a concentration gradient, and is a known phenomenon (S, Esho; Ancmalous M
agneto-optical hysteresis
Loops of 5 puttered Gd-Co
Films-Jpn.

J people pp1. Phys, vol IIFL PP9
3-9 & 1976).

Next, the recording (writing) process on the magneto-optical recording medium of the present invention will be explained with reference to FIG. The state of the magnetic moment of the auxiliary layer 13 is set in advance to a state indicated by the 0 point, and a bias magnetic field 8 of an intensity indicated by Hb is applied at the position where the recording laser beam 6 is irradiated. The directions of the bias magnetic field 8 and the magnetic moment of the high transition metal FJ 13 a of the auxiliary W 113 are antiparallel. Then, as the auxiliary layer 13 is heated, the magnetic field Hhi decreases. When the auxiliary layer 13 is heated above the temperature 7th at which the magnetic field Hhi is equal to the bias magnetic field 8, the high transition gold 111 layer 13 of the auxiliary layer 13
The magnetic moment of a is transferred to the DEF state i1. Therefore, by changing the light intensity of the laser beam 6 into two levels of strength and weakness, it is possible to select one of the two stable states ABC and DEF for the magnetization state of the auxiliary layer 13. In other words, when the light intensity of the laser beam 6 is low and the auxiliary layer 13 is at a temperature below Tth, the state is ABC, and when the light intensity of the laser beam 6 is high and the auxiliary layer 13 is heated to a temperature above Tth, the state is DEF. It is. Further, the Curie temperature of the recording PJ 12 is set to a temperature of 7th or lower, and is set so that the recording layer 12 can be heated to a temperature higher than the Curie temperature even when the light intensity of the laser beam 6 is weak. In this way, during the recording process on a magneto-optical recording medium, the recording layer 12 is always cooled from a temperature above the Curie temperature, and the direction of its magnetic moment is determined by the spin interaction of the contact surface with the auxiliary layer 13. It is determined to point in the same direction as the magnetic moment of the 7: & transition metal 13a in the auxiliary layer 13. In FIG. 2, the magnetic moments of the recording NJ 12 align upward when the light intensity of the laser beam 6 is weak, and downward when the light intensity is strong.

In addition, in the cooling process of the magneto-optical recording medium, the bias magnetic field 8
ABC and DEF of the minor loop as long as is applied
Since the state is stable, the magnetization state transferred to the recording layer 12 is also stably maintained up to room temperature. Next, when the magneto-optical recording medium moves further and the bias magnetic field 8 is no longer applied, the magnetic moment of the auxiliary layer 13 returns to the 0 point, which is the same as when the bias magnetic field 8 was applied. It remains constant regardless of the state. If the recording layer 12 is magnetized downward, the magnetic moment of the recording layer 12 and the magnetic moment of the high transition metal oil 13a in the auxiliary layer 13 will be antiparallel after cooling, but the coercive force of the recording layer 12 will be Since it is large at room temperature, the magnetization state of the recording layer 12 is maintained stably.

Then, other information is recorded on the magneto-optical recording medium (
When writing), overwriting can be performed by repeating the above-mentioned recording process again. Note that during reproduction, the light intensity of the laser beam 6 is set to be low enough to not affect the magnetization state of the recording layer 12.

In order to demonstrate that overwriting is possible in the magneto-optical recording medium of the present invention shown in FIG. 1, the following experiment was conducted.

Recording layer 12 of the magneto-optical recording medium configured as described above
and the auxiliary layer 13 are formed to have a thickness of 0.05 μm and 1 μm, respectively. Furthermore, the magnetic field Hhi at which the magnetization reversal of the high transition metal layer 13a of the auxiliary FJ 13 occurs at room temperature and 150°C is as follows:
They were 7 KOe and 2.5 KOe, respectively. The Curie temperature of each of the recording layer 12 and the auxiliary layer 13 is 12
0°C and 200°C. The magneto-optical recording medium was previously magnetized in the negative direction with a magnetic field of 20 KOe, and then heated while applying a bias magnetic field 8 of 2.5 KOe in the positive direction. At this time, remove the magneto-optical recording medium. i It was confirmed that when the samples were heated to 120° C. and 160° C. and then cooled to chamber 1, the magnetic moments of the records P412 were aligned in the same direction. It was also confirmed that the direction of magnetization of the recording layer 12 depends only on whether the maximum temperature during heating is 120° C. or 160° C., and does not depend on the previous history. Therefore,
It is clear that overwriting recording can be realized in magneto-optical recording by replacing the heating method with laser beam irradiation.

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the present invention, the initial magnetization process that was necessary in the conventional overwriting method using light intensity modulation of a laser beam can be omitted, so Since a permanent magnet or an electromagnet for generating a magnetic field (Hini) is not required, the magneto-optical recording and reproducing apparatus can be made smaller and lighter.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the structure of the magneto-optical recording medium according to the present invention, FIG. 2 is an explanatory diagram showing the hysterin loop of the auxiliary layer and the direction of the magnetic moment at each stage, and FIG. FIG. 1 is an explanatory diagram showing the configuration of a conventional magneto-optical recording medium. In the drawing, 5 is an optical head, 6 is a laser beam, 8 is a bias magnetic field, 11 is a substrate, 12 is a recording layer, 13 is an auxiliary layer, 13a1. 13b is a true transition metal layer, and 13b is a high rare earth metal layer. Patent applicant: Agent of Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] In a magneto-optical recording medium consisting of a magnetic thin film with a two-layer structure of a recording layer and an auxiliary layer, the Curie temperature of the auxiliary layer is set higher than that of the recording layer, and the auxiliary layer is not exposed to an external magnetic field. It must be a multilayer film structure or a rare earth/transition alloy magnetic film with a concentration gradient that exhibits a minor hysteresis loop such that it always remains in the same magnetization state when there is no external magnetic field and becomes multiple stable magnetization states when an external magnetic field is present. A magneto-optical recording medium characterized by: