JPH0438735A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To decrease phase differences and to suppress the fluctuation in the magnitude of carrier signals by a difference in substrates and recording and reproducing devices by forming 1st and 2nd dielectric layers essentially consisting of silicon nitride on a transparent substrate and forming a magnetic layer of a rare earth-iron family amorphous alloy as its essential component. CONSTITUTION:The dielectric layers 2, 4 which consist of the silicon nitride or consist essentially of the silicon nitride and have 2.1 to 2.4 refractive index are provided on the transparent substrate having 1.4 to 1.6 refractive index. The magnetic layer 3 is formed of the thin film of the rare earth-iron family amorphous alloy and the thickness thereof is specified of a 600 to 1200Angstrom range. A metallic layer 5 is preferably formed of Al, Cu, etc., and elements, such as Cr, Ti and Nb, which improve corrosion resistance are added at several atm.% thereto. The fluctuation in the carrier signals by the differences in the substrates and the recording and reproducing device is suppressed in this way and the magneto-optical recording medium which allows stable information reading out is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention records information by forming bits of reversed magnetic domains using a laser beam and an external magnetic field, and uses a polarized laser beam to record information. , relates to a magneto-optical recording medium from which information is read using the magneto-optic effect.

[Conventional technology]

2. Description of the Related Art In magneto-optical recording media, a technique has long been known in which a dielectric layer is sandwiched between a transparent substrate onto which light is incident and a magnetic layer, and the reflectance is lowered by utilizing the interference effect of light. As the reflectance decreases, the amount of light absorbed increases accordingly, so the amount of light needed to heat the material to the required temperature is reduced, and the recording sensitivity increases. In addition, when the reflectance decreases, the CN of the read signal
It is also known that the (carrier to noise) ratio is improved.

In a magneto-optical recording medium using a rare earth-iron group amorphous alloy thin film as a magnetic layer, a silicon nitride film produced by reactive sputtering using a mixed gas of an inert gas and nitrogen gas is preferably used as the dielectric layer. Its use is proposed in Japanese Patent Laid-Open No. 12194.5/1982. This document states that a silicon nitride film having a stable refractive index of 1.9 can be formed by reactive sputtering using a silicon target with a mixed gas of 90% argon gas and 0% nitrogen gas.

Further, in a magneto-optical recording medium having at least a transparent substrate, a dielectric layer, and a magnetic layer in this order, the dielectric layer may include 2.
The inventor has proposed a magneto-optical recording medium which is a dielectric material mainly composed of silicon nitride having a refractive index of 1 to 2.4.

On the other hand, it is also possible to increase the magneto-optical Kerr rotation angle by providing a metal layer on the surface opposite to the light incident surface for a rare earth-iron amorphous alloy thin film having a film thickness of 100 to 400 nm. well known.

[Problems to be Solved by the Invention] However, in the conventional example described above, it has been found that even if the recording sensitivity and CN ratio are the same, the magnitude of the carrier signal varies considerably depending on the substrate and the recording/reproducing device.

SUMMARY OF THE INVENTION An object of the present invention is to provide a magneto-optical recording medium that solves the problems of the prior art described above, suppresses carrier signal fluctuations due to differences in substrates and recording/reproducing devices, and allows stable information reading.

[Failure to solve the problem]

The above object of the present invention is to provide a first dielectric layer on a transparent substrate;
In a magneto-optical recording medium comprising a magnetic layer, a second dielectric layer, and a metal layer formed in this order, the first and second dielectric layers are made of silicon nitride having a refractive index of 2.1 to 2.4. The magnetic layer is formed from a dielectric material whose main component is
This is achieved by forming the magnetic material mainly from a rare earth-iron amorphous alloy having a film thickness of 1,200 μm.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing an embodiment of the magneto-optical recording medium of the present invention. In the figure, 1 is a transparent substrate into which light is incident, 2
is the first dielectric layer, 3 is the magnetic layer, 4 is the second dielectric layer,
5 indicates a metal layer. Here, the refractive index of the transparent substrate 1 is usually about 1.4 to 1.6. Further, the first and second dielectric layers 2.4 are formed so that the refractive index is in the range of 2.1 to 2.4.

In order to obtain a dielectric film having a desired refractive index, it is preferable to use silicon nitride or a dielectric material mainly composed of silicon nitride from the viewpoint of controlling the refractive index and protecting the magnetic film. To make a silicon nitride film,
Reactive sputtering may be performed using a silicon or silicon nitride target in a mixed gas atmosphere of argon and nitrogen. At that time, a desired refractive index can be obtained by adjusting the ratio of argon and nitrogen. When silicon is used as the target, a certain amount of impurity (for example, boron or phosphorus) may be added to increase the conductivity, and a DC sputtering method may be used. Furthermore, when silicon nitride is used as the target, it may contain some sintering material (eg, alumina, ittria). Furthermore, instead of using silicon nitride as a target, sialon or sesion, which mainly contains silicon nitride, may be used.

The magnetic layer 3 is formed from a rare earth-iron group amorphous alloy thin film. As such a thin film, for example, Tb-Fe-C
o, Dy-Fe-Co, Tb-Dy-Fe-C.

or Gd-Fe-Co and T
An exchange-coupled bilayer film of b-Fe-Co is preferably used. Furthermore, these thin films contain Cr, AI, Ti,...
Several atm or % of an element that improves corrosion resistance such as Nb may be added. Moreover, the film thickness of the magnetic layer 3 is 600 to 12
Formed in the range of 00 people.

The material of the metal layer 5 is preferably A1, Cu, etc.
Several atm or % of elements that improve corrosion resistance such as C5Ti and Nb may be added to these.

Information is read from a magneto-optical recording medium using the magneto-optic effect of a magnetic material. When a magnetic material is irradiated with linearly polarized light, the reflected or transmitted light becomes elliptically polarized light due to the magneto-optic effect, and the direction of its principal axis rotates. Since the direction of rotation of the main shaft is opposite depending on the direction of magnetization, the direction of magnetization can be detected by detecting the direction of rotation of the main shaft. The magneto-optic effect in the case of reflected light is called the Kerr effect, and the magneto-optic effect in the case of transmitted light is called the Faraday effect. When a rare earth-iron group amorphous alloy is used as the magnetic material, since it is a metal, reading is normally performed using reflected light, that is, the Kerr effect.

If the Kerr rotation angle is θ, the Kerr ellipticity is 72, and the light intensity reflectance is R, then tan2θ = jan2 a cosφk
(]) sin27 k= 5in2 a
sinφK (2) R= l r−
12+ l ryl
(3) tanα 1ryl/lr, l
(4) One φ in φ, -φ8
(5) rx = l rx l exp
(+φj−(r”+r→/2r, = 1ryl exp
It is given by (iφy)-i(r”-r→/2. Here, r8 and ry are the complex amplitude reflectances in the X direction and the X direction, respectively (assuming the incident polarization direction is the X direction). r゛ and r- are complex amplitude reflectances for right and left circularly polarized light, respectively. α is called the Kerr amplitude ratio, and φ□ is called the Kerr phase difference.

In general, since θ and γ are α(l), it is approximated as follows.

Optical heads that read information from magneto-optical recording media are usually
It is configured to divide the reflected light from the medium into two, and to receive the divided luminous fluxes by two sensors, respectively, via an analyzer. Here, the two analyzers placed in front of each sensor have their transmission axes at angles of +45° and 45°, respectively, with respect to the polarization direction of the light incident on the medium. Also,
Information is obtained by differentiating the outputs of the two sensors.

First, there is no phase difference between the substrate and the optical head.
Consider the carrier signal in the ideal case where the differential sensing sensor is perfectly balanced. In this case, each sensor output is proportional to rll 1r212. Here, r, == rx s in 45°
+rycos45° (11) r2= rx
cos45°-r, 5in45° (12)
It is. From this, using the functions of equations (3) and (5),
r112-V2R+1r! 11ryICO8φk
(13). By the way, from equation (4), 1'xl lryl = V2 (effect!l -1ry1
2) Since tan2α(14), by using equation (1).

+, 12=V2R+! , 4(b,l −1r12)t
an2αCO8φk or r+12=V2R+V2(l rx l −l
ry l") tan2θk. Here, 1rx
Approximating as l −l r, 12~R, tan2 a~2α, r, 12=HR+Rα cosφk (1
7). Similarly, r212='4R-Ra cosφ, (
18), and the carrier signal is the difference between these, r+l-1rz12=2RαCO3φk (19
) is proportional to

Next, consider the carrier signal when a phase difference occurs between the substrate and the optical head and there is imbalance in the differential detection sensor. However, it is assumed that the fast axis (or slow axis) of the birefringence of the substrate matches the direction of the incident polarization.

The phase difference due to birefringence of the substrate is φ5 (single pass value)
, the phase difference by the optical head is φ7, and the photoelectric conversion and amplifier gain of each differential detection sensor is 01.
, G2 (G,≠G2).

If the fast axis (or slow axis) of birefringence matches the direction of incident polarization, the incident linearly polarized light will pass through the substrate as it is without being affected by the birefringence of the substrate, and will pass through the magnetic layer. reach. Since the reflected light that has undergone the magneto-optic effect in the magnetic layer has an X component as well as an X component, when the reflected light passes through the substrate again, a phase difference corresponding to a single pass is added. Furthermore, when passing through the optical head, a phase difference due to the optical head is added.

Therefore, the first sensor output RF of differential detection.

is RF, = G, r, '
It is given by (20). Here, r,′ is (11
) multiply ry of the formula exp(lφh) eXp (iφ5), r1'-r, 5in45°+exp (iφ
h) exp (+φ,) r, cos45°(2]).

From this, RF+=Cy+[! , 4R+Ra cos(φ□+φ,
1φh) ] (22). Compared to equation (17), COSφ has been changed to COS (φ□+φ, +φh). Similarly, the second sensor output RF2 is RF 2 = G 2 ['A RRαcos(φ to 1φ, 1φh) ] (23), and the carrier signal is the difference between these, RFI RF2 = (GI G2) V2R+
(Gl+G2)Rαcos(φ5+φh) (
24). The first term in this equation represents the DC component, and the second term represents the AC component (carrier signal).

Now, looking at equation (24), if φ5=φh−〇, even if Rα is large and CO3−, is small, or Rα
Even if Rα cosφ3 is small and cosφ3 is large, Rα cosφ,
If the values of are the same, the carrier signals are the same. However, in the case of φ,≠0 and φ,≠0, when φ8 and φ change, the carrier signal changes.

Therefore, even if the recording sensitivity and CN ratio are the same, the magnitude of the carrier signal varies considerably depending on the substrate and recording/reproducing device, due to the difference in φ5 and φ.

Therefore, in order to prevent the carrier signal from changing much even if φ5 and φ change, Rα should be large and φ
It is desirable that □ be small. This is because the carrier signal is proportional to COS (φ2+φ, +φh), so φ5
This is because even if and φゎ change by the same value, if φ is small, the drop in the carrier signal can be suppressed to a small level. Alternatively, if φ or φ has a certain value but does not change, φo may be set so that φ□+φ5+φ5 is as small as possible.

n of 1, = n
2) Figures 2 (a) and (b) are glass substrate/first dielectric layer (refractive index n, = 2.1)/magnetic layer of rare earth-iron group amorphous alloy (film thickness hM In the configuration of the AI metal layer, the first dielectric It shows changes in Rα, R (indicated by broken lines), and φ□ with respect to the thickness h1 of the body layer. hl is about 97
With 5 people, φ3 becomes almost 0, and R at that time is about 0.3
It is 1.

Figure 3 (a), (b) Figure 4 (a), (b) and Figure 5
Figures (a) and (b) show that the refractive index of the first and second dielectric layers is 2.2.2.
3 and 2.4.

Table 1 summarizes the conditions for φ□-0 from the results shown in FIGS. 2 to 5.

Table 1 When n+ (=12) changes, hl where φ6 becomes almost 0
and R change, but Rα does not change much.

Therefore, it can be seen that in order to make φk 0 under a desired reflectance, the refractive index and film thickness of the first dielectric layer can be controlled and controlled.

2 (n+=12)
FIGS. 6(a) and (b) respectively show glass substrate/first dielectric layer (n+=2.1)/magnetic layer of rare earth-iron group amorphous alloy (film thickness 11+z=800 layers)/ In the configuration of the second dielectric layer (n2=2.1)/Al metal layer, hl
It shows the changes in Rα, R (indicated by broken lines) and φ with respect to h2 when the number of people is 775. When +12 changes, φ□ changes considerably and can be set to 0, but
Rα and R do not change much.

7(a), (b), FIG. 9(a), (b), and FIG. 11(a), (b) show that the first and second The refractive index of the dielectric layer is 2.2.
This is data when the values are 2.3 and 2.4. In FIGS. 7, 9, and 11, the thickness of the first dielectric layer is 675, 525, and 450, respectively.

Similarly, Fig. 8(a), (b), Fig. 10(a), (b)
) and FIGS. 12(a) and 12(b) show that the refractive index of the first and second dielectric layers is 2.2.2.3 and 2.4, respectively, in a medium having the same structure as in FIG. This is the data when 8, 10, and 12, the film thicknesses of the first dielectric layer are 800, 850, and 85, respectively.
There are 0 people.

Therefore, by controlling the refractive index and film thickness of the second dielectric layer, φ3 can be changed, and can even be made zero.

2 of (n+≠nz
) Figure 13 (a), (b) and Figure 14 (a), (1)
) is glass substrate/first dielectric layer (n+ = 2.2
) / magnetic layer of rare earth-iron group amorphous alloy (thickness hM-8
00 people)/second dielectric layer (nz = 2.4)/A
In the configuration of l metal layer, hl is 675 and 80, respectively.
It shows changes in Rα, R (indicated by broken lines) and φ□ with respect to +12 when there is no person. Also in this case, φ□
can be set to 0, and nl and ! ] It can be seen that it does not matter if 2 are different.

Figure 15 (a), (b) and Figure 16 (a), (b)
These are data when the refractive indexes of the first and second dielectric layers are set to 2, 4, and 2.2, respectively, in a medium having the same configuration as in FIG. 13. Thickness of the first dielectric layer.

In the case of Figure 15, there are 450 people, and in the case of Figure 16, there are 85 people.
There are 0 people.

In this way, even if the first dielectric layer and the second dielectric layer have different refractive indexes, φ□ can be changed and can even be made zero.

Magnetic n+=12 Fig. 17 (
a), (b) to FIG. 22 (a), (b) are glass substrate/first dielectric layer (n+ = 2.2)/rare earth -
Magnetic layer of iron group amorphous alloy/second dielectric layer (n22.2
) is a diagram showing changes in Rα, R (indicated by broken lines), and φ□ with respect to the film thickness h2 of the second dielectric layer in the configuration of the /Al metal layer.

The thickness h1 of the first dielectric layer is 675 in the cases of FIGS. 17, 19, and 21, and 800 in the cases of FIGS. 18, 20, and 22. In addition, the film thickness hM of the magnetic layer is 600 people in the case of FIGS. 17 and 18;
In the case of FIGS. 19 and 20, there are 1000 people, and in the cases of FIGS. 21 and 22, there are 1200 people.

In this way, by controlling h2, φ can be changed.

Therefore, when the thickness hM of the magnetic layer is in the range of 600 to 1000, φ1 can be changed by changing h2, and can even be set to 0.

The dynamic layer in FIGS. 23(a), (b) and 24(a), (b) shows the glass substrate/first dielectric layer (n+ = 2.2)
/Magnetic layer of rare earth-iron group amorphous alloy (thickness hM=800
person)/second dielectric layer (r+z = 2.2)/C
In the u metal layer configuration, hl is 675 and 80, respectively.
It shows changes in Rα, R (indicated by a broken line) and φ□ with respect to h2 when there is no person. By controlling h2, φ can be changed.

Therefore, even if the metal layer is Cu, by changing h2, φ,
can be varied and can also be set to 0.

[Measurement] J1 Results A magneto-optical recording medium having the above-mentioned structure was prepared using a conventional magnetron sputtering method, and Rα, R and φ,
Measurements were made.

The target used for making silicon nitride was 125 m.
mφ silicon nitride, and input RF power was 500W. When the argon gas pressure was set to about 0.3 Pa and the nitrogen gas partial pressure ratio was changed to 0.0.65%, ■, and 0.1.65%, the refractive index of the fabricated silicon nitride film was 2°5.
It changed to 2.2.35.2.27.2.13.

Magneto-optical recording media are produced by forming a silicon nitride underlayer as a dielectric layer for protection and interference on a glass substrate, then forming Tb (Fe, 92.CO, o□5) as a magnetic layer, and then First, silicon nitride was fabricated as a dielectric layer for protection and interference, and finally, an A1 or Cu metal layer was fabricated. Several types of silicon nitride were manufactured by changing the refractive index and film thickness, and by changing the film thickness of the magnetic layer.

The measurements of Rα, R, and φ were carried out using a measuring instrument having a semiconductor laser light source of parallel light with a wavelength of 830 nm and a differential detection system of a PIN photodiode. The ellipticity was measured by inserting a quarter wavelength plate between the reflected light and the detector, and the angle was calibrated using a Faraday cell. The results are shown in Tables 2 and 3.

Table 2 (Aff metal layer) Table 3 (Cu metal layer) As can be seen from the above results, it is not preferable that the dielectric layer has a refractive effect ratio of 2.52 because Rα becomes small. This is because absorption occurs in the dielectric layer.

〔Effect of the invention〕

As explained above, the present invention provides a magneto-optical recording medium in which a first dielectric layer, a magnetic layer, a second dielectric layer, and a metal layer are sequentially formed on a transparent substrate. The dielectric layer is formed from a dielectric material mainly composed of silicon nitride having a refractive index of 2.1 to 2.4, and the magnetic layer is formed of a dielectric material having a refractive index of 600 to 2.4.
By forming it from a magnetic material whose main component is a rare earth-iron group amorphous alloy with a film thickness of 1,200 μm, the phase difference is reduced and the fluctuation in carrier signal magnitude due to differences in substrates and recording/reproducing devices is suppressed. It has a suppressing effect.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view, not showing an embodiment of the magneto-optical recording medium of the present invention. Figures 2 to 24 are diagrams showing the relationship between the dielectric film thickness and the product of reflectance and Kerr amplitude ratio in the magneto-optical recording medium of the present invention, respectively. FIG. 3 is a diagram showing the relationship between dielectric film thickness and reflectance. Zero ko familiar 匝娑 6' O 3 familiar 3 R J 匝p :l:1. g Zechi ζ13 i:l Koze familiar S :l+-+ 8 R Sin 昂′ S 79匝娑 国′ Ukow6′ :1.13

Claims (1)

[Claims] (1) A magneto-optical recording medium comprising a first dielectric layer, a magnetic layer, a second dielectric layer and a metal layer formed in this order on a transparent substrate, wherein the first and second dielectric layers are , the magnetic layer is made of a dielectric material mainly composed of silicon nitride having a refractive index of 2.1 to 2.4, and the magnetic layer is mainly composed of a rare earth-iron group amorphous alloy having a film thickness of 600 to 1200 Å. A magneto-optical recording medium characterized by being made of a magnetic material.