JPH0697515B2 - Overwritable magneto-optical recording medium - Google Patents

Description

The present invention relates to a magneto-optical recording medium, in particular, enables overwriting which is indispensable for high-speed access, and further eliminates the need to install an external magnetic field applying means. Thus, the present invention relates to an overwritable magneto-optical recording medium that contributes to miniaturization of an optical pickup.

[Conventional technology]

Optical discs are capable of high-density recording and are attracting attention as large-capacity memories. Currently, read-only optical discs for video and digital audio have been put to practical use, and write-once type and rewritable erasable optical discs that can be recorded only once are being put to practical use.

Among them, a magneto-optical disk is attracting attention as an erasable optical disk. An optical disk uses a perpendicularly magnetized film as a recording film and heats a laser spot while applying a magnetic field H to the recording film to raise the laser irradiation portion to a Curie temperature so that the coercive force H _C of the recording film is equal to or lower than the magnetic field H. By reversing, information is recorded as pits in which only the laser spot irradiating portion is magnetized reversal.

The reproduction is performed by irradiating a weak laser beam, and the rotation of the polarization plane changes depending on the direction of magnetization, and the pit is reproduced by changing the amount of reflected light by interposing an analyzer in the detection optical path. .

Further, when erasing and rewriting data, the magnetic field H is reversed to perform the recording operation to erase the data, and then the direction of the magnetic field H is returned to perform the rewriting.

However, since the magnetic field H cannot be changed at a high frequency corresponding to the data recording speed, rewriting is erased once and new data is recorded after the disk has made one revolution. Therefore, it takes a lot of time to rewrite.

This is because it is necessary to apply a strong magnetic field of several hundred Oe from a distance of 1 to 2 mm in order to achieve the non-contact characteristic of the optical disk, and a large magnet or coil is used as the magnetic field applying means. is there.

That is, in the method using the magnet, the magnetic field reversal must be performed mechanically, and the magnetic field reversal speed becomes slow. on the other hand,
This is because the method using a coil has an extremely large inductance, making it impossible to drive at a high frequency.

[Problems to be solved by the invention]

As described above, when attempting to rewrite data using the conventional device, it takes two steps of erasing and recording, and sufficient consideration is given to the high-speed access performance that is essential as a large capacity memory for data. There was a problem that not.

Further, in order to obtain the external magnetic field, the magnetic field applying means must be incorporated in the optical pickup, which makes the optical pickup large and heavy. Therefore, the movement of the optical pickup between the tracks becomes slow, and there is a problem in that high speed access is not taken into consideration in this respect as well.

Note that techniques close to the present invention include those disclosed in JP-A-56-153546 and JP-A-55-52535. These publications extend the technology to make the magnetic film, which is a recording film, multi-layer, but these increase the magneto-optical effect and improve the S / N at the time of reproduction, enabling high-speed access. No consideration has been given to this.

An object of the present invention is to eliminate the above-mentioned problems of the conventional device,
The magneto-optical recording medium can be overwritten, and a magneto-optical recording medium that does not require an external magnetic field for recording can be provided to enable high-speed access. Another object is to provide a compact and lightweight magneto-optical recording medium.

[Means for solving problems]

The above object is achieved by providing a recording magnetic field generating magnetic film magnetically coupled to the recording film as a magnetic field applying means of the recording film. More specifically, the magnetic film for generating the recording magnetic field is a ferrimagnetic film having a compensation point temperature close to the Curie temperature of the recording film and its ferrimagnetic material so that the laser irradiation power profile can be overwritten. It is composed of a magnetic field reversal magnetic film that is magnetically reversed by the magnetic field generated by the magnetization of the film, and the combined magnetization M _{T of} the ferrimagnetic film and the magnetic field reversal magnetic film almost eliminates the Curie temperature of the recording film during the temperature rising / cooling process. and to have a hysteresis characteristic as the center, magnetization M temperature T ₁ of the two points in the hysteresis loop magnetization reversal with respect to the temperature _T, then one of _{T 2, H CR> 4πM T} ( here below the temperature T ₁ of the low-temperature side Where H _{CR is} the coercive force of the recording film, M _{T is} the combined magnetization of the ferrimagnetic film and the magnetic film for magnetic field reversal, and 4πM _R <H _CF (where M _{R is} the magnetization of the recording film, H _CF; ferrimagnetic It is accomplished by the coercive force) of the membrane.

[Action]

From the relationship of 4πM _R <H _CF at room temperature, the direction of the recording magnetic field, that is, the direction of the magnetic field generated from the combined magnetization of the ferrimagnetic film and the magnetic field reversal magnetic film is determined by the magnetization written in the recording film. The direction of initial magnetization is always retained without reversal.

When the laser is irradiated from room temperature to heat to the Curie temperature and then the temperature is lowered, the direction of the recording magnetic field does not reverse but remains at the room temperature, while the coercive force H _CR 0 of the memory film at the Curie temperature is maintained. Therefore, the recording film is magnetized in the direction of the recording magnetic field at room temperature regardless of the magnetization direction before the recording film.

This magnetization direction is referred to as "0" information recording, and the opposite direction magnetization is referred to as "1" information recording.
It is clear that it is possible to overwrite the "0" information.

Next, it will be explained that it is possible to overwrite the information of "1".

When the laser irradiation from the room temperature is performed with a stronger power and the temperature is raised to a temperature higher than the Curie temperature by a predetermined value, the recording magnetic field is inverted by the magnetization reversal of the ferrimagnetic material and the magnetic reversal of the magnetic film for magnetic field reversal. Therefore, regardless of the previous state, the recording film is once magnetized in the direction of “0” when passing the Curie temperature, but when heated to a predetermined value, the magnetization is reversed in the direction of “1”. After that, when the temperature is lowered, the recording magnetic field retains the direction of "1" even if the temperature is lowered to the Curie temperature because the recording magnetic field has the hysteresis characteristic, and the recording film has "0". Never flip to.

When the temperature is further lowered, the recording magnetic field reverses to the direction of “0”, that is, the room temperature state. At this time, the coercive force H _CR is not zero because the recording film is lower than the Curie temperature.
By setting the recording magnetic field strength H _F 4πM _T <H _CR at this point, the recording film can maintain the recording state of “1” even if the recording magnetic field is reversed to “0”.

As described above, regardless of the state before the recording film, by changing the laser irradiation power and changing the heating profile, it is possible to overwrite the information of "0" and "1" without once erasing, and to newly write from outside. It is not necessary to apply a recording magnetic field.

〔Example〕

 An embodiment of the present invention will be described below with reference to FIG.

In the figure, 1 is a polycarbonate injection molded plate having a tracking guide groove 7. Reference numeral 2 is an enhancement film having a Kerr rotation angle formed by sputtering on the substrate 1 using Si ₃ N ₄ as a base material, and the film thickness is about 850Å. The Henhans film has a Kerr rotation angle of about 0.3 without the enhancer film.
Amplify the point that is ゜ to about 0.5 ゜.

Reference numeral 3 is a recording film, which is an amorphous perpendicular magnetization film of Tb ₃₀ Fe ₆₂ Co ₈ (atomic%), and was formed by rotating the substrate by the ternary simultaneous sputtering method of Tb, Fe, and Co. The film thickness is about 500Å. Its Curie temperature T _C is about 200 ° C, and coercive force H _CR at room temperature
Is about 5 KOe and the magnetization M _R is about 80 emu / cc.

4 is a magnetic film for magnetic field reversal, which is formed of an amorphous perpendicular magnetization film of Co ₈₀ Cr ₂₀ . Its film thickness is about 500Å, Curie temperature T _C is about 600 ℃, coercive force is 0.5KOe, and magnetization is 100emu / c.
c. Reference numeral 5 is a ferrimagnetic film, which is formed of an amorphous perpendicular magnetization film of Tb ₂₂ Fe ₆₃ Co ₁₅ . Compensation point temperature is 19
At 0 ℃, coercive force is 5KOe and magnetization is 200emu / cc.

Reference numeral 6 is a protective film, and the same Si ₃ N ₄ film as the enhance film 2 was formed by sputtering to a thickness of about 1000Å.

In the present embodiment, the following relationship is satisfied when the magnetization of the recording film 3 at room temperature is M _R and the coercive force of the ferrimagnetic film 5 is H _CF.

4πM _R <H _CF Therefore, the direction of the storage magnetic field, which will be described later, that is, the direction of the magnetic field generated from the combined magnetization of the ferrimagnetic film 5 and the magnetic field reversal magnetic film 4 should be reversed by the magnetization written in the recording film 3. Instead, the initial magnetization direction is always maintained.

Next, before describing the recording operation of this embodiment, a method of generating a recording magnetic field will be described. The recording, that is, the control of the magnetization reversal of the recording film is performed by adjusting the laser power at the time of heating the laser spot and using the binary temperatures T ₁ and T ₂ to change the recording film 3, the magnetic field reversing magnetic film 4 and the ferrimagnetic film 5. It is performed by heating.

FIG. 2 shows composition of recording magnetic fields. The vertical axis represents the magnetization strength and the horizontal axis represents the temperature.

A curve 5a shows the temperature change of the magnetization of the ferrimagnetic film 5. The Curie temperature of the recording film 3 becomes zero at the compensation point temperature (about 200 ° C.) set in the vicinity, and when the temperature is further raised, the magnetization is generated again, and the direction thereof is reversed. Further, when the Curie temperature of this film is raised, the magnetization becomes zero.

The alternate long and short dash line 4a shows the magnetization of the magnetic film 4 for magnetic field reversal.
The Curie temperature of the magnetic film 4 for magnetic field reversal is as high as 600 ° C., and there is almost no characteristic change due to temperature near the Curie temperature of the recording film of 200 ° C. However, the magnetization of the ferrimagnetic film 5 is 4πM _F
As a result, the magnetization is inverted at temperatures T ₁ and T ₂ at which the coercive force H _CS = | 4πM _F | of the film 4 is obtained.

A broken line 10 indicates the combined magnetization (that is, 4a + 5a) of the ferrimagnetic film 5 and the magnetic field reversal magnetic film 4. It has positive and negative two-valued magnetization around 200 ° C with respect to temperature, and also operates as a hysteresis.

Heating from room temperature to the Curie temperature of the recording film 3, 200 ° C,
Then, when the temperature is lowered, the synthetic magnetization 10 changes only in A, H, B, H, A and the negative region. Curie temperature (20
(0 ℃) to point E, and then lowering the temperature, A,
H, B, C, D (film 4 has positive magnetization reversal, temperature T ₂ ), E, D, F, G, H
(The film 4 has a negative magnetization reversal, temperature T ₁ ), and operates in the path of A,
The positive magnetization can be maintained near the Curie temperature of 200 ° C. of the recording film 3 when the temperature is lowered.

In this embodiment, the synthetic magnetization 10 is used as a source of the recording magnetic field of the recording film 3.

Next, the recording operation of this embodiment will be described with reference to FIG. FIG. 3 shows the coercive force H _CR of the recording film 3 and the temperature of the magnetic field (broken line 10) 4πM _T (where M _T is the combined magnetization of the ferrimagnetic film 5 and the magnetic film 4 for magnetic field reversal) due to the above-mentioned combined magnetization. It is the figure which showed change. Change the coercive force on the positive side of recording film 3 with temperature
1. The coercive force on the negative side is shown at 11 'with temperature change.

Near room temperature, the holding force H on the positive and negative sides of the recording film 3
_CR has a larger absolute value than that of the broken line 10 as shown by solid lines 11 and 11 '(ie, H _CR > 4
πM _T ) and the magnetization of the recording film 3 cannot be reversed. Therefore, the data written on the recording film 3 is stable.

When heated or cooled down to around 200 ° C., the coercive force 11 ′ on the negative side of the recording film 3 changes from negative to zero. At this time, the recording magnetic field follows the profile of A, H, B, H, A, and the magnitude of the coercive force H _CR 11 ′ of the recording film 3 at B becomes smaller than that of the recording magnetic field. Therefore, the recording film 3 does not depend on the previous state,
It is magnetized in the negative direction, which is the direction of the recording magnetic field, and the positive recording magnetic field is not applied when the temperature is lowered to B, H, A. It is possible to record the information of.

When the laser power is further increased and the temperature is increased to around 250 ° C., the recording magnetic field 10 changes from negative to positive at D (temperature T ₂ ) via A, H, B and C. When the temperature is lowered, the recording magnetic field 10 has a hysteresis characteristic, and therefore passes through the paths of D, F, G, H, and A. When passing the Curie temperature of the recording film between D and G, the coercive force 11 on the positive side of the recording film is zero and smaller than the recording magnetic field 10, so the recording film 3 is magnetized positively. temperature
The recording magnetic field is inverted from positive to negative between T _1, that is, between G and H. However, at this time, the coercive force 11 is already larger than the recording magnetic field 10, the recording film is not negatively magnetized, and the positive magnetization is preserved when the temperature returns to room temperature. Can be done.

In the above description, the initial holding force 11 'of the recording film 3 is negative, but the same operation as above is performed even when the initial holding force 11 of the recording film 3 is positive. Overwriting can be performed regardless of the initial magnetization state of the recording film 3.

The recording method described above is shown in FIG. 4 by the correspondence between the intensity of laser irradiation power and "0" or "1". Recording is started at the time t = 0 from the small power reproduction mode, and when the irradiation power is high at every clock τ, that is, when T ₂ ℃ or more, "1"
When the irradiation power is medium, that is, when the temperature is lower than T ₂ ℃ and close to this, “0” is recorded.

Since the above does not depend on the initial magnetization state of the recording film 3, overwriting is possible, and there is no need to once erase and record later as in the conventional case, and there is an effect that access time is shortened and high speed access is possible. . Furthermore, there is an effect that the magnetic field application from the outside, which is conventionally required, is unnecessary.

Although the magnetic field generated by the magnetization of the recording film 3 is actually related to the timing of the magnetization reversal of the magnetic field reversing magnetic film 4, since the magnetization of the recording film 3 near the Curie temperature is extremely small, it is practically used. Can be ignored.

Also, as described above, the magnetization of the M _R at room temperature of the recording film 3, when the coercivity of the ferrimagnetic material film 5 and H _CF, since the conditions of 4πM _R <H _CF is satisfied, at room temperature The direction of the recording magnetic field is not reversed by the magnetization written in the recording film, and the initial magnetization direction can always be maintained.

FIG. 5 is an explanatory view showing the second embodiment of the present invention. The feature of this embodiment is that the substrate 1 is provided with the tracking pits 12 of the sample servo system instead of the guide grooves. This example illustrates that the present invention is substrate independent.

FIG. 6 shows a third embodiment of the present invention, which is characterized in that the protective film portion is formed of a metal film 13 of Al, stainless steel or the like. According to the present embodiment, heat is propagated in the film stacking direction by using the high thermal conductivity of the metal together with the protection function, the lateral diffusion is prevented, the size of the recording pit is stabilized, and the recording pit has a small diameter. Has the effect of increasing the density.

FIG. 7 shows a fourth embodiment of the present invention. This embodiment is characterized in that a Faraday film 14 having a small holding force is interposed between the enhancement film 2 and the recording film 3. In this embodiment, the rotation angle of polarized light at the time of reproduction is large, and a high S / N is obtained.

FIG. 8 shows a fifth embodiment of the present invention. In the present embodiment, the ferrimagnetic film 5 and the magnetic field reversing magnetic film 4 are replaced with each other. According to this embodiment, there is no great difference in magnetic coupling, and
It has the same effect as the configuration of the figure.

FIG. 9 shows a sixth embodiment of the present invention. In this embodiment, two magneto-optical recording media are laminated with an adhesive layer 15,
It is possible to provide a magneto-optical recording medium that can be used on both sides.

Although a TbFeCo-based film was used as the magnetic film in the above examples, the present invention is not limited to the above magnetic material. It is obvious that other rare earth / transition metal based magnetic films, oxide magnetic films, Mn / Bi based magnetic films, and those containing additional elements for adjusting magnetic properties and corrosion resistance can be used.

〔The invention's effect〕

According to the present invention, since the magnetic film is used as the magnetic field applying unit for the recording film, there is no need to incorporate the magnetic field applying unit in the optical pickup, and the optical pickup can be made small and lightweight. In addition to this, since overwriting is possible, there is a great effect that access time can be significantly shortened and high-speed access becomes possible.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of the first embodiment of the present invention, and FIG.
FIG. 4 is a diagram for explaining the method of generating a recording magnetic field, FIG. 3 is a diagram for explaining the recording operation of this embodiment, FIG. 4 is a diagram for explaining the recording operation by the irradiation power of the laser, and FIGS. The structural sectional views of Embodiments 2 to 6 of the present invention are shown respectively. 1 ... Substrate, 3 ... Recording film, 4 ... Magnetic field reversal magnetic film,
5: Ferrimagnetic film

Claims (4)

[Claims] 1. In a magneto-optical recording medium for recording information by applying a magnetic field and a light spot to a recording film to invert the magnetization to record information, a means for applying a magnetic field to the recording film compensates for the Curie temperature of the recording film. The magnetic film is composed of a ferrimagnetic material having a point temperature and a magnetic material whose magnetization is inverted by the magnetization of the ferrimagnetic material. The magnetic film is magnetically coupled to the recording film and has a coercive force of the recording film. Is H _CR , the magnetization is M _R , the coercive force of the ferrimagnetic film is H _CF , and the synthetic magnetization of the ferrimagnetic film and the magnetic film whose magnetization is inverted by the magnetization of the magnetic film is M _T , 4πM _R < An overwritable magneto-optical recording medium, characterized in that H _CF H _CR > 4πM _T (however, below the Curie temperature and below the temperature at which M _T causes magnetization reversal). 2. An overwritable magneto-optical recording medium according to claim 1, wherein an enhancing film is provided on the light incident side of the magnetic film. 3. A metal protective film is provided on a side of the magnetic film opposite to a light incident side thereof.
2. An overwritable magneto-optical recording medium according to item 2 or 3. 4. The overwritable magneto-optical recording medium according to any one of claims 1 to 3, wherein a Faraday film is provided on the light incident side of the magnetic film.