JPS607634A - Photothermomagnetic recording medium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magneto-optical recording medium that is used in magneto-optical memories, magnetic recording/display elements, etc. and can be read using magneto-optic effects such as the magneto-8 Kerr effect and the Alladay effect. In particular, the present invention relates to a magnetic thin film recording medium capable of recording and reproducing information from both sides.

Conventionally, as photothermal magnetic recording media, MnBi, MnCu
Polycrystalline thin film such as B1 - Single crystalline thin film such as 1GdIG,
GdCo, GdFe, TbFe, GdTbFe
, TbFeC! Amorphous thin films such as CdTbFeCo and CdTbFeCo are known.

In the recording method of these photothermal magnetic recording media, first, the recording medium is
The area to be recorded is magnetized in one direction in a magnetic field sufficient to saturate the magnetic film, and the area to be recorded is irradiated and heated with a laser beam, etc. to eliminate or reduce the magnetization of that area, and when cooled, an externally applied magnetic field is applied. Alternatively, this can be done by reversing the direction of magnetization in that part using a leakage magnetic field from the surrounding medium.

In the reproduction method 1, the recording section (perpendicular magnetic film) is irradiated with polarized light r- at a power smaller than the irradiation power used for recording, such as a laser beam. At this time, the polarization plane of the reflected light (or transmitted light) rotates to the right or left depending on the direction of magnetization, so by passing it through an analyzer, it is possible to rotate the polarization plane depending on the direction of magnetization. This is done by converting this amount of light into an electrical signal using a photodetector.

FIG. 11 shows the configuration of a recording/reproducing apparatus for a photothermal magnetic recording medium. The recording medium 1 is rotationally driven by a motor 2, and the beam C emitted from the semi-moving body laser 3 is turned into a parallel light beam by the collimator lens 4. A beam splitter 5 separates incident light and reflected light.

Reference numeral 6 denotes a wavelength plate, and the incident light beam is turned into a minute spot by a condensing lens 7 and is recorded on a recording medium. On the other hand, the reflected light from the recording medium is taken out by a beam splitter and used by a focus controller 18 for focus servo to focus the incident light beam on the surface of the recording medium. 16
is a magnet, and its magnetic field is applied to the recording medium in such a way that it is smaller than the coercive force of the recording medium and is opposite to the magnetization direction of the magnetic film of the recording medium.The size of the magnetic field changes the apparent appearance of the recording medium. Sensitivity is improved. Reproduction is performed using semiconductor laser 6
The light emitted from ' is converted into a parallel light beam by a collimator lens 4 ′, and the light beam is directly polarized by a polarizer 6 ′, and is made incident on the recording medium 1 . 5' is a beam splitter that separates incident light and reflected light from the recording medium. The incident light flux hits the recording medium 1 as a minute spot on the condensing lens 7', and the plane of polarization is changed by the Kerr effect to θk (Kerr rotation angle) or
It is rotated to -θ and reflected. This reflected light is taken out by a beam splitter 5' and split into two directions by a No. 1-7 mirror 8. The divided light beams pass through an analyzer 9.10 and a condenser lens 11.12, respectively, and are guided to a photodetector 16.14, where they are extracted as electrical signals. The difference between these two electrical signals is taken by a differential amplifier 15, and the difference is taken out as an information reproduction signal. Reference numeral 17 denotes an extinction magnet, and the magnitude of its magnetic field is smaller than the coercive force of the medium, and the direction of the magnetic field is the same as the direction in which the medium is uniformly magnetized. Erasing is carried out by bringing the erasing magnet 1.7 close to the substrate, irradiating the recorded area (magnetization reversal area) with a laser beam, and using the magnetic field of the erasing magnet during cooling.
This is achieved by aligning the magnetization in the original direction.

In such a recording medium, if the magnetic films on both sides are of the same type, both sides will be magnetized in the same direction as shown in FIG. Therefore, when applying an external magnetic field during recording, the direction of the applied magnetic field must be reversed for each side. Also, during erasing, the direction of the magnetic field applied to each side must be reversed. Also, during playback, the output of the recording dots is reversed for each side (1), so in reality, it is necessary to detect which side the output is and then process the electrical signal. .

An object of the present invention is to provide a photothermal magnetic recording medium capable of recording and reproducing from both sides, which is capable of reversing the direction of an externally applied magnetic field during recording and erasing on each side, and reversing electrical signal processing during reproduction. An object of the present invention is to provide a novel photothermal magnetic recording medium having a perpendicular magnetic film that does not shift.

In the present invention, magnetic films having easy magnetization axes perpendicular to the surfaces are formed on both sides of the substrate, and the compositions of both magnetic films are exactly related to the composition on both sides of the magnetic compensation composition at room temperature. This is a photothermal magnetic recording medium characterized by the following.

In the present invention, the relationship between the compositions of both magnetic films on both sides of the magnetic compensation composition at room temperature means, for example, rare earth elements such as Ga, Tb, Dy, or alloys thereof, and rare earth elements such as Fe, Co, etc. Alternatively, in the case of using an amorphous magnetic film with a transition metal that is an alloy of these, one surface of the planar recording medium has a composition that magnetically has a rare earth lynchium with respect to the compensation composition of the rare earth-transition metal perpendicular magnetic film. On the other hand, the other surfaces only need to have a composition that is magnetically rich in transition metals.

The compositions of both magnetic films in the present invention may be just the relationship between the compositions on both sides of the magnetic compensation composition at room temperature as described above, but in practical terms, it is desirable that the coercive force is 10 KOe or less. On the other hand, the magnitude of the magnetization must be such that a magnetic film having an axis of easy magnetization perpendicular to the film surface is formed.

In the photothermal magnetic recording medium of the present invention, the compositions of the magnetic films on both sides of the substrate are in the same relationship as the compositions on both sides of the magnetic compensation composition at room temperature. When placed between the magnetic poles and applying a strong magnetic field, a fourth
As shown in the figure, the directions of magnetization on both sides are opposite to each other. Therefore, if this recording medium is used for recording and reproduction in an apparatus such as that shown in FIG. After detecting which side the recording section is on, no electrical signal processing is performed to prevent the output of the recording dots from being reversed, and the erasing magnet 1 is also used during erasing.
Since it can be carried out without changing the direction of the magnetic field in step 7, the troublesomeness during use is completely eliminated.

The present invention will be further explained below based on Examples.

Example 1 In a high frequency sputtering device, a white plate glass of 100 wn ψ and a thickness of 1°2 wn was used as a substrate, a Tt)2 o F es o alloy of 4 inch ψ was used as the first target, and Tb25Fe75 of 4 inch ψ was used as the second target. The film was formed using an alloy. 1.5X inside the chamber
After evacuation to 10P& or less, Ar gas was evacuated to 4
By introducing up to ×10" 2P2L and operating the main valve of the vacuum exhaust system, the Ar pressure was set to 3 Pa. First, the first target was sputtered with a power of 250
Assuming that W was constant, 10,001 Tb2°Fe8° films were formed. Next, apply a second layer to the back side of the glass substrate in the same manner.
Using Keratra Te'rb,, 5pe7s membrane 100
OA film-formed 9, No. 6: Figure (a) shows the Tb2°Fe@o film, and Figure 6 (b) shows the Tb25Fe75 film as much as possible.
Showing magnetic hysteresis due to effect - $2. Since the compensation composition of the TbFe film is that Tb is 22at□rr+%, the Tb2oFe8o film is magnetically Fe ric
h composition film, Tt)2s Fa7s film is magnetically T
b rich film tear, coercive force IKOe for both films
It was a perpendicular magnetic film. Furthermore, Fig. 6 (a) and (b)
In the figure, the horizontal axis represents the magnitude of coercive force, and the vertical axis represents the magnitude of the output of the photodetector due to the maximum effect of the magnetic film, and the magnitude of IKOe is shown in each figure.

For actual recording and reproduction, 70O of SiO is applied as a protective film and anti-reflection layer on the magnetic films on both sides of this air recording medium.
A film was formed, and then N 4rdj three poles were placed in the gap between a pair of opposing magnets and magnetized by applying a magnetic field of 5 KOe.

The direction of magnetization at this time is shown in FIG.

Recording is performed without changing the direction of the magnetic field of the magnet 16, and after detecting which side is used for reproduction, special electrical signal processing is performed to prevent the output of recording dots from being reversed on each side. The data could be erased without any problems, and erasing was also possible without changing the direction of the magnetic field of the erasing magnet 17.

Example 2 In a high frequency sputtering device, 1[]Qmψ thickness 1.2
A white glass plate was used as a substrate, a first target was a 4 inch ψ Fe''251 angle Gds o T 婉0 12 uniformly arranged pieces, and a second target was 4 in. Gds of 5 angles on Fe of ψ
oT v's.

Film formation was performed using 15 uniformly arranged alloy pieces. A (Gd5o Tb5o)z+' Fe79 film was deposited at 100O on one side of a glass substrate using the same process as in Example 1.
A film was formed and (Gd5o Tb5o)zs F was formed on the other surface.
A 100OA film of eys +d was formed. (Gd5o T field o)zx Fe7g film and (G'ao Tb1o)
The magnetic hysteresis due to the Kerr effect of the 25Fe75 film was similar to that in Figures 6(a) and 6(b), respectively (the compensation composition of the GdTbFe film was (Gd
5o' Tb5o) is around 26 atom%, so the (Gd5o Tb50)21 Feys film is a magnetically For]-Ch composition film (G45o Ttbo)
The 25Fey5 film is magnetically rare earth (GdTb) ri
Both films on both sides were perpendicular magnetic films with coercive force IKOθ. Next, SiO which serves as both a protective film and an anti-reflection film.
((Jr+o Tt)so)z
The tFe7g film was formed by controlling the reflectance to 27%, and (Gd5oTbs o )25Fe
The film 7-5 was formed with a controlled reflectance of 22%. This is (Gd5゜Fl)5 o) 2't
This is because the Fe79 film has a lower Curie temperature and better sensitivity than the (G-derived OT and 0)25Fe75 film, so the sensitivity on both sides was made equal during reflection by the 11-film. Note that there was almost no influence on the reproduced S/N due to the difference in reflectance.

After uniformly magnetizing this double-sided recording medium, recording and reproduction were performed using the above-mentioned apparatus. As a result, recording was performed on both sides of the recording medium without changing the direction of the magnetic field of the magnet 16.
In addition, playback can be performed without special electrical signal processing that detects which side the recording pattern is on and prevents the output of the recorded pattern from being reversed for each side, and erasing can also be performed using the magnetic field of the erasing magnet. This was done without changing direction. In another embodiment of the present invention, a perpendicular magnetic film is formed on only one side of the substrate, and two perpendicular magnetic films are formed on the substrate side or one side. Even in a double-sided recording medium that is bonded together on the film side, a similar effect will appear if the compositions of the two perpendicular magnetic films are on both sides of the compensation composition at room temperature.

As described above, according to the present invention, perpendicular magnetic films having perpendicular easy magnetization axes are formed on each side of a double-sided recording medium, and it is possible to determine whether the compositions of both perpendicular magnetic films are on both sides of the compensation composition at room temperature. By using a photothermal magnetic recording medium, we provide a double-sided recording medium that allows recording and reproduction without the hassle of reversing the direction of an externally applied magnetic field during recording or erasing on each side, or reversing electrical signal processing during reproduction. can.

[Brief explanation of drawings]

The first tooth is a conceptual diagram for explaining a recording/reproducing device using a photothermal magnetic recording medium. FIG. 12 is a schematic diagram showing the magnetization direction when a conventional double-sided recording photothermal magnetic recording medium is magnetized. FIG. 4 is a schematic diagram showing the direction of magnetization when the photothermal magnetic recording medium for double-sided recording according to the present invention is magnetized. FIG. 6 is a steresis curve due to the magnetic Kerr effect at room temperature of the magnetic film of the example of the present invention. 1......Photothermal magnetic recording medium 2...
...Motor 6.6'...Semiconductor laser 4.4\...Collimator lens 5.5'...Beam splitter 6...1/4 wavelength plate 6' ...Polarizer 7.7'...Condensing lens 8...Half mirror 9, 10...Analyzer 11, 12...Condensing lens 13.14 ... Photodetector 15 ... Differential amplifier 16 ... Recording magnet 17 ... Erasing magnet 18 ... Focus controller patent applicant Canon Co., Ltd.

Claims (1)

[Claims] Magnetic films having easy magnetization axes perpendicular to the surfaces are formed on both sides of the substrate, and I4. A photothermal/magnetic recording medium characterized in that the compositions of both magnetic films are in a relationship of compositions on both sides of a magnetic compensation composition at room temperature.