JPH046642A - Magneto-optical disk - Google Patents

Abstract

PURPOSE:To decrease the noises included in information reproducing light and to improve the information recording sensitivity of the magneto-optical disk by specifying the film thickness of the inorg. dielectric thin film of a 1st layer and the film thicknesses of the thin film of the magneto-optical recording medi um of a 2nd layer and the inorg. dielectric thin film of a 3rd layer. CONSTITUTION:The inorg. dielectric thin film 12 of the 1st layer on a transparent substrate 11 satisfies the conditions of the film thickness d1 within the range of d1=[lambda/(4 n1)]+ or -10% when the refractive index thereof is designated as n1, the film thickness as d1 and the wavelength of the semiconductor laser beam used for recording and reproducing of the magneto-optical disk as lambda. The magneto-optical recording medium thin film 13d2 of the 2nd layer is formed to 50 to 200Angstrom . The refractive index of the inorg. dielectric thin film 14 of the 3rd layer, designated as n3 and the film thickness thereof as d3 are so determined that the film thickness d3 satisfies the conditions within the range of d3=[3.lambda/(8.n3)+ or -10%]. The magnetic Kerr rotating angle is increased in this way and the noises included in the information reproducing light from the magneto-optical disk are decreased while the reflectivity of this light is increased. The C/N of the information reproducing is thus greatly improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical disk in which information is recorded, reproduced and erased on a perpendicularly magnetized film using a laser beam.

[Prior Art] Many attempts have been made to increase the magnetic Kerr rotation angle of magneto-optical recording media. In particular, magneto-optical disks using rare earth element-transition metal amorphous alloy films, which have excellent information recording properties, have a small magnetic Kerr rotation angle and poor information reproduction sensitivity. Efforts have been made to improve information reproduction sensitivity by forming a transparent inorganic dielectric thin film and increasing the apparent rotation angle of the magnetic force by about twice through the enhancement effect of this transparent inorganic dielectric thin film layer. This is a well-known fact.

However, the increase in the magnetic Kerr rotation angle due to the conventional enhancement effect is accompanied by a decrease in the reflectance from the magneto-optical medium.
Despite the increase in the magnetic Kerr rotation angle, little improvement in recording sensitivity was obtained as a result.

Therefore, as a method for improving this low or low reflectance, studies have been conducted on magneto-optical disks having a multilayer film structure in which a reflective film is formed on the back surface of the magneto-optical recording medium film. However, although magneto-optical disks with a multilayer structure using this reflective film can improve information reproducing sensitivity to some extent by increasing the Kerr rotation angle and improving reflectance, on the other hand, there is It has the disadvantage that the information reproducing light that comes in has a large amount of noise.

[Problems to be Solved by the Invention] The present invention is based on the optical principles of reflection and transmission of light rays at the interfaces of each layer in the magneto-optical recording film of a magneto-optical disk, absorption of light rays within a thin film, and multiple interference. By making full use of the magneto-optical effect, we aim to increase the Kerr rotation angle, increase the reflectance, and reduce the noise contained in the information reproducing light from the magneto-optical recording film, and at the same time improve the information recording sensitivity of the magneto-optical disk. The purpose is to improve.

[Means for Solving the Problems] The present invention provides a first layer made of an inorganic dielectric thin film on a transparent substrate, a second layer made of a magneto-optical recording medium thin film, and a third layer made of an inorganic dielectric heat-insulating and protective thin film. In a magneto-optical disk having at least

ia) The first layer of inorganic dielectric thin film has a refractive index of n +
) film thickness d1. When considering the wavelength of the semiconductor laser beam used for recording and reproducing on magneto-optical disks, the film thickness d,
is d, = [E/(4-n,)] within the range of ±lO% fb) The second layer magneto-optical recording medium thin film d2 is 50 Å ~
200 people (cl) The third layer of inorganic dielectric thin film has a refractive index of n a
, when the film thickness is d3, the film thickness d3 is.

The magneto-optical disk is characterized in that it satisfies a condition within the range of d,=[3,e/(8·rr,) ±10%.

The transparent substrate may be mainly made of known materials such as glass and polycarbonate.

The film thickness d1 of the first layer is the refractive index of the inorganic dielectric thin film n l
) If the wavelength of the semiconductor laser beam used for recording and reproducing on magneto-optical disks is round, then d, = [λ/ (4・n
+ )] The film thickness should be within the range of ±1O%. When the first layer satisfies this condition, it causes an antireflection effect due to multiple reflection interference of the optical thin film, suppresses the reflectance of the laser beam that occurs at the interface between the first layer and the second layer, and also suppresses the reflectance of the laser beam that occurs at the interface between the first layer and the second layer. It is possible to increase the intensity of the laser beam that enters the layer, and it is possible to reduce noise due to reflected light generated at the interface between the first layer and the second layer.

Although not limited to the inorganic dielectric material of the first layer,
Well-known SiNx, 5iAI2ON.

SiA, 9N, TjO, CrO, etc. can be used.

The second layer is made of a rare earth element such as Sm, Eu, Gd, Tb, DyHo, Er, etc. and a transition metal-amorphous alloy such as Fe, Co, Ni, or MnB1. In a magneto-optical recording medium thin film made of Cu or the like, the medium itself has a light absorption coefficient.

Therefore, in order to increase the reflected light of the laser beam from the interface between the second layer and the third layer, it is necessary to reduce the thickness of the magneto-optical recording medium thin film.

However, in order to improve the magnetic Kerr rotation angle of the magneto-optical disk of the present invention, unlike the conventional method of improving the apparent magnetic Kerr rotation angle by the enhancement effect of the magneto-optical recording film structure, the optical The laser beam is transmitted through the magnetic recording medium thin film to the interface between the second layer and the third layer, and the reflected light at the interface between the second layer and the third layer is transmitted again through the second layer magneto-optical recording medium thin film. This is improved by increasing the distance through which the light passes through the magneto-optical recording medium (Faraday effect of reflected light).

Therefore, the film thickness d of the magneto-optical recording medium thin film is required to a certain extent.

Figures 4 and 5 show changes in the light transmittance of the magneto-optical recording film and the magnetic Kerr rotation angle depending on the thickness of the magneto-optical recording medium thin film of the magneto-optical disk having the film structure shown in Figure 3. It is something.

From FIG. 4 and FIG. 5, it can be seen that when the thickness d2 of the magneto-optical recording medium thin film is 50 Å to 200 nm, the intensity of the light beam transmitted through the magneto-optical recording medium thin film is large and the magnetic Kerr rotation angle is also large. The film thickness d of the third layer, which has been confirmed and found to be a suitable film thickness for a magneto-optical recording medium, is the film thickness d of the third layer, which is the thickness of the laser beam transmitted through the second layer at the interface between the second layer and the third layer. Set to improve the reflection of light that occurs.

As this condition, the refractive index of the inorganic dielectric film rib of the third layer is n
8. Let λ be the wavelength of a semiconductor laser used for recording, reproducing, and erasing information, then the film thickness is d, = [3, e/(8-
n, )] When ±10% is satisfied, the reflectance is improved.

The present invention aims to reduce the noise contained in the information reproducing light generated from the recording film structure of a magneto-optical disk as much as possible, improve the magnetic Kerr rotation angle, and improve the signal strength of the information reproducing light. This solved the above-mentioned problem of magneto-optical disks, such as low recording sensitivity.

The inorganic dielectric material of the third layer only needs to have heat insulating properties and protective properties, and the same material as that of the first layer or a different material can be used as long as the above conditions are satisfied.

[Function] In a normal magneto-optical disk, the C/N is increased by increasing the Kerr rotation angle θk of the magneto-optical phenomenon using multiple interference in the first layer of inorganic dielectric film.

However, in the present invention, (1) absorption is small in the second layer magneto-optical recording medium, but absorption in the first layer is low;
Only the increase in laser light passing through the layer and penetrating into the magnetic layer is utilized.

(2) By making the magneto-optical recording medium layer ultra-thin, the distance of the laser light passing through this film is short, making it possible to utilize the light reflected from the back surface.

(2) Since the film thickness of the magneto-optical recording medium is thin, light penetrates to the second dielectric layer, and multiple reflections here are used to amplify the signal light at the interface of the magneto-optical recording medium layers.

Therefore, the principle is different from that of conventional magneto-optical disks.

That is, by making the second magneto-optical recording medium layer ultra-thin, it has become possible to utilize the light reflected from the back surface. These performances can be obtained by satisfying the conditions of each of the three layers mentioned above.

1 Example] A magneto-optical disk according to the present invention will be explained using the drawings.

FIG. 1 is a block diagram of the optical system of a conventionally known magneto-optical disk device, in which 1 is a semiconductor laser generator, 2 is a collimator lens, 3 is a prism, and 4 is a half mirror 15.
is a focus lens, 6 is a magneto-optical recording medium film, 7 is a spot lens, 8 is an analyzer, 9 is a photodiode, 10
is a magnetic field generating coil for information recording and erasing.

First, when recording or erasing information, the laser beam emitted from the semiconductor laser 1 passes through a collimator lens 2, a prism 3, a half mirror 4, and a focus lens 5.
The light is focused onto the magneto-optical recording medium film 6 with a diameter of approximately IL1m, raising the temperature of the light-concentrating portion of the magneto-optical recording medium film 6 to above the Curie temperature, and at the same time increasing the magnetization direction opposite to the direction of magnetization of the light-concentrating portion. A magnetic field is applied by the information recording/erasing magnetic field generating coil 1o to record or erase information.

In addition, when reproducing information, the laser beam emitted from the semiconductor laser 1, which has a lower power than that used during information recording or erasing, is transmitted through the collimator lens 2, prism 3, and half mirror 4, and then is optically magnetized by the focus lens 5. After the light is focused on the recording medium film 6 to a diameter of about 1 um, the plane of polarization is rotated by the magnetic Kerr rotation due to the magnetic Kerr effect, and then reflected.

The light is reflected by the half mirror 4 again, transmitted through the spot lens 7 and the analyzer 8, and detected by the photodiode 9.

FIG. 2 is a configuration diagram of an embodiment of the magneto-optical disk according to the present invention, where IJ is a polycarbonate substrate, 12 is a film thickness of 9
00 people, 5i AION film with refractive index n=23, 13 is film thickness ioo people (7) TbFeCo11i, 14 is film thickness 135
It is a S i Al ON film with 5 people and a refractive index n=23.

After the laser light incident from the focus lens 5 of the magneto-optical disk device shown in FIG. 1 passes through the polycarbonate substrate 11 as indicated by the arrow in FIG. and returns to the focus lens 5 of the magneto-optical disk device shown in FIG. Most of the remaining part passes through the TbFeCo film 12 and is reflected at the interface with the 5iAIONIli 14.
Directly return to the focus lens 5 of the magneto-optical disk loading shown in FIG.

The magnetic Kerr rotation angle of the magneto-optical disk constructed in this way was measured using a semiconductor laser (wavelength λ = 830 nm) and was found to be 0.84 degrees.
The magnetic Kerr rotation angle was approximately 2.8 times larger than the magnetic Kerr rotation angle of 0.30 in the case of a single layer.

Further, the reflectance of the information reproducing light from the magneto-optical disk by the recording film is R=45% or more, which is approximately 1.5 times the reflectance R=30% in the case of a single layer TbFeCo film. Furthermore, noise contained in the information reproduction light is reduced.

In the above embodiments, TbFe is used as the magneto-optical recording medium.
Co film and inorganic dielectric film are 5iAION with refractive index n=23.
Although information has been given regarding the case where the magneto-optical disk according to the present invention is made using a film, the magneto-optical disk according to the present invention has Tb
Similar results apply when magneto-optical recording media other than FeCo film, such as GdTbFe film, MnB1Cu film, TbDyFe film, DyCo film, etc. are used, and when inorganic dielectric films other than 5iAION film, such as SiO film, SiN film, TiO film, etc. are used. It was found that it has the following effect.

[Effects of the Invention] As described above, the magneto-optical disk according to the present invention consists of a first layer made of an inorganic dielectric thin film on a transparent substrate, a second layer made of a magneto-optical recording medium, and an inorganic dielectric heat-insulating and protective thin film. Third
The refractive index of the first layer of inorganic dielectric thin film is n +
When the film thickness is d r and the wavelength of the semiconductor laser beam used for recording and reproducing on magneto-optical disks is, the film thickness d is
The thickness of the inorganic dielectric thin film was controlled so that d1 = [λ/(4-n,)] ±10%, and the thickness of the second layer magneto-optical recording medium thin film d2 was 50 Å to 200 Å. The refractive index of the third layer of inorganic dielectric thin film is n! ) film thickness d s
, when the wavelength of the semiconductor laser beam used for recording, reproducing, and erasing information is λ, the film thickness d is within the range of da=[3, er/[8・n−) ±lO%]. By controlling the thickness of the dielectric thin film, the magnetic Kerr rotation angle can be increased compared to conventional magneto-optical disks, and the noise contained therein can be suppressed while increasing the reflectance of information reproducing light from the magneto-optical disk. As a result, the C/N of information reproduction is lower than that of conventional magneto-optical disks.
It has the effect of greatly improving the

[Brief explanation of drawings]

FIG. 1 is a block diagram of an optical system in a conventionally known magneto-optical disk device, and FIG. 2 is a block diagram of an embodiment of a magneto-optical disk according to the present invention. FIG. 3 shows a film structure prepared to measure the change in light transmittance depending on the film thickness of a magneto-optical recording medium film. Figure 4 shows the wavelength of the light beam according to the recording film configuration shown in Figure 3 = 83
It shows the light transmittance depending on the film thickness of the magneto-optical recording medium at 0 nm. FIG. 5 is a graph showing the change in the Kerr rotation angle depending on the film thickness of the magneto-optical recording medium in the recording film structure of the magneto-optical disk of the present invention. FIG. 6 shows the first film structure of the magneto-optical disk of the present invention.
The layer is a 5iAION film with a thickness of 900, and the second layer is a 5iAION film with a thickness of 10.
3 is a graph showing changes in the reflectance of information reproducing light depending on the film thickness of the third layer of 5iAION, using a TbFeCo film of 0. l...Semiconductor laser 2...Collimator lens 3...-Prism 4...Half mirror 5...-Focus lens 6...-Magneto-optical recording medium film 7...Spot lens 8...-Detection Photon 9--Photodiode 10--Magnetic field generating coil for information 2 erasing 11--Polycarbonate substrate 12--Film thickness 900 people 5iAION3iii13.
・-TbFeCo11i14 with a thickness of 100 people...5iA1ON film 15 with a thickness of 1355 people...Glass substrate 16...5iA1ON film 17 with a thickness of 900 people...-'rbpeCo film with a thickness of 50 people-1000 people

Claims (1)

[Claims] (1) In a magneto-optical disk having at least a first layer made of an inorganic dielectric thin film, a second layer made of a magneto-optical recording medium thin film, and a third layer made of an inorganic dielectric heat-insulating and protective thin film on a transparent substrate, (a ) The first layer of inorganic dielectric thin film has a film thickness d_1 of d_1 = [λ/(4・n_1)] within the range of ±10% (b) The second layer magneto-optical recording medium thin film d_2 is 50 Å to 2
00 Å (c) The third layer of inorganic dielectric thin film has a refractive index of n_3 and a film thickness of d_3, and the film thickness d_3 is as follows: d_3=[3. A magneto-optical disk characterized in that it satisfies a condition within the range of λ/(8・n_3)]±10%.