JP2000119100A - Nonmagnetic garnet single crystal and magnetic garnet single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a nonmagnetic garnet single crystal having a large lattice constant and excellent crystallinity, transparent in the wavelength region used by an optical communication, and suitable as the substrate for growing a magnetooptic crystal by an LPE method, and further to obtain a magnetic garnet LPE single crystal film by using the nonmagnetic garnet single crystal, capable of enlarging a Faraday rotational capacity by substituting a large amount of Bi. SOLUTION: This nonmagnetic garnet single crystal is composed of oxides comprising the all cations of Gd, Eu, Sc and Ga. Typically, the composition formula is represented by Gd3-sEusSCtGa5-tO12 (with the proviso that s and t satisfy the equations 0<s<3 and 1.8<t<2.2), and the lattice constant can be freely adjusted by changing the composition within the range of 1.256-1.262 nm. The magnetic garnet single crystal for a magnetooptic element is obtained by using the nonmagnetic garnet single crystal as a substrate, and carrying out LPE (liquid phase epitaxial)-growing thereof, and represented by the composition formula Gd3-x-yLaxBiyFe5O12 (with the proviso that x and y satisfy the relations 0.1<=x<=0.5 and 1.5<=y<=1.8).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to Gd (gadolinium), Eu (europium), Sc (scandium),
The present invention relates to a nonmagnetic garnet single crystal containing Ga (gallium) and a Bi (bismuth) heavily substituted rare earth iron garnet single crystal grown by a liquid phase epitaxy (LPE) method using the same as a substrate. This nonmagnetic garnet single crystal has a large lattice constant, good crystallinity, and is transparent in a wavelength range used for optical communication, and is therefore particularly useful for manufacturing a magneto-optical element by the LPE method.

[0002]

2. Description of the Related Art Various magneto-optical devices, such as optical isolators, optical circulators, optical switches, and optical attenuators, use a Faraday rotator for rotating the plane of polarization of incident light, and incorporate a magneto-optical element as a component thereof. ing. In recent years, as this magneto-optical element, Bi
A (bismuth) substituted rare earth iron garnet single crystal is used. This is because by replacing a part of the rare earth element with Bi, the Faraday rotation coefficient can be increased, and the thickness of the single crystal for obtaining a required Faraday rotation angle is several hundred μm.
This is because it can be made as thin as possible.

At present, the LPE method is widely used as a method for producing this kind of magnetic garnet single crystal. This is achieved by, for example, using PbO—Bi ₂ O ₃ —B ₂ O ₃ as a flux, (RBi) ₃ (FeM) ₅ O ₁₂ (where R is a rare earth element containing Y, M is Ti, Si, Mn, Al, Ga
After melting the raw material of the Bi-substituted rare earth iron garnet shown in (1), it is cooled to about 800 ° C. to create a supersaturated state of the garnet, and the non-magnetic garnet substrate is brought into contact with the melt to form a liquid phase on the substrate. This is a method of performing epitaxial growth. This LPE method is superior in mass productivity to other single crystal growing methods, and has the advantage that a high quality single crystal film can be manufactured at low cost.

As a substrate, a nonmagnetic garnet single crystal having a lattice constant equivalent to that of the LPE film to be grown and having good crystallinity is used. For example, when the lattice constant of S is about 1.249 nm,
GGG (cation-substituted gadolinium gallium garnet), GSGG (gadolinium scandium gallium garnet) with a lattice constant of 1.256 nm, GGG (gadolinium gallium garnet) with a lattice constant of 1.238 nm
Garnet) is generally used.

By the way, the Faraday rotation ability, which is one of the characteristic indices of a Bi-substituted rare earth iron garnet LPE film for a magneto-optical element, generally increases in proportion to the bismuth content in the film. However, since the lattice constant of the film crystal also increases in proportion to the bismuth content, a nonmagnetic garnet single crystal having a lattice constant larger than that of the above-described substrate material is required, and its development is actively performed. I have. Examples thereof include GLSGG (gadolinium / lutetium / scandium / gallium / garnet: JP-A-4-202096) having a lattice constant of about 1.265 nm, or NGSGG (neodymium / gadolinium / scandium) having a lattice constant of about 1.262 nm. Gallium garnet: JP-A-8-21981).

[0006]

In order to grow an LPE film having a large bismuth substitution amount (a large Faraday rotation capability) as described above, it is desirable to use a substrate crystal having a large lattice constant such as GLSGG or NGSGG. . However, these substrate crystals have the following problems. That is, in the case of GLSGG, the price of lutetium oxide used as a raw material is high. In the case of NGSGG,
There is light absorption peculiar to neodymium ions near the wavelength of 1550 nm used in optical communication. Therefore, when the LPE film grown on the substrate is used as a magneto-optical element, the substrate crystal is removed in advance by grinding or other means. Must be kept.

An object of the present invention is to have a large lattice constant, good crystallinity, and transparency in a wavelength range used in optical communication.
An object of the present invention is to provide a nonmagnetic garnet single crystal suitable as a substrate for growing a magneto-optical crystal by the LPE method. Another object of the present invention is to provide a magnetic garnet LPE single crystal film that can increase the Faraday rotation ability by replacing a large amount of Bi.

[0008]

SUMMARY OF THE INVENTION The present invention is a nonmagnetic garnet single crystal in which at least a cation comprises an oxide containing all of Gd, Eu, Sc, and Ga. Typically, composition formula _{Gd 3-s Eu s Sc t} Ga 5-t O 12 ( where 0 <
It is a nonmagnetic garnet single crystal represented by s <3, 1.8 <t <2.2). Here, a beautiful single crystal can be formed even if the value of s is freely changed between 0 and 3. The value of t is from 1.8 to
If it is out of the range of 2.2, a clean single crystal cannot be formed. The lattice constant of the nonmagnetic garnet single crystal can be freely adjusted in the range of 1.256 nm to 1.262 nm by changing the composition. This nonmagnetic garnet single crystal is particularly useful as a substrate for growing a bismuth heavily substituted rare earth iron garnet LPE film used as a magneto-optical element, but is also useful as a decorative jewelry.

Further, according to the present invention, the lattice constant is 1.256 nm or more.
The at least cation at 1.262 nm is Gd, E
u, Sc, the non-magnetic garnet single crystal of an oxide containing all of Ga and substrate was LPE-grown on the substrate, a composition formula _{Gd 3-xy La x Bi y} Fe 5 O 12 ( where 0 .1 ≦ x ≦ 0.5, 1.5 ≦ y ≦ 1.8) is a magnetic garnet single crystal for a magneto-optical element.

The magnetic garnet single crystal film grown by the LPE method has a large Faraday rotation coefficient by replacing a large amount of Bi (bismuth). By increasing the lattice constant of the crystal, 800 nm
The absorption of iron at 1000 nm can be shifted to shorter wavelengths. By using only an element having no absorption, the absorption is reduced. Thus, magneto-optical characteristics with excellent characteristics are exhibited in a wide range from the 980 nm band to the 1500 nm band.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A non-magnetic garnet single crystal as a substrate material of the present invention can be produced as follows. Oxides of the respective components are mainly weighed at predetermined molar ratios as raw materials, and then wet-mixed using a ball mill or the like. After sufficient mixing, the mixture is dried and pressed by a hydrostatic press. The garnet phase may be formed by previously firing the molded body. Thereafter, a single crystal is grown by a pulling method (Czochralski method). Alternatively, a growing method such as a floating zone method may be used. In the lifting method, an iridium crucible is used. The growth is performed in a low-oxygen atmosphere of about 1% by volume in order to suppress oxidation of iridium, precipitation of iridium, and the like.

In this composition system, the melting point varies depending on the composition of the crystal, but it is about 1850 ° C. or less. After melting the raw material using high-frequency heating, a single crystal is grown by bringing the seed crystal into contact with the melt and pulling it up. The crystal pulling speed is about 0.1 to 20 mm / h, and the crystal rotation speed is about 1 to 60 rpm. When a predetermined amount of crystals has been pulled up, the crystals are separated from the melt and slowly cooled. By such a method, a high-quality single crystal having very few macro defects such as crystal twists and cracks and micro defects such as crystal dislocations can be grown. In this composition system, a small amount of another element may be added for fine adjustment of the lattice constant.

The thus obtained Gd _3-s Eu _s S
_{c t Ga 5-t O 12} ( however, 0 <s <3,1.8 <t <
The nonmagnetic garnet single crystal represented by 2.2) has a lattice constant of 1.256 nm (when s = 0) or less depending on the amount of s.
It can be adjusted within a range of about 1.262 nm (when s = 3). Further, since the segregation coefficient of each component is almost equal to 1, the fluctuation of the lattice constant in the grown single crystal is very small. Further, it is transparent in a wavelength band from about 800 nm to around 1800 nm. From these characteristics, it is extremely useful as a substrate for growing a bismuth heavily substituted rare earth iron garnet LPE single crystal film for use as a magneto-optical element.

[0014]

EXAMPLE First, an example of a nonmagnetic garnet single crystal used as a substrate for producing an LPE film will be described. The crystal was grown by the pulling method.

(Example A1) Gd ₂ O was used as a starting material.
₃ : Eu ₂ O ₃ : Sc ₂ O ₃ : Ga ₂ O ₃ 1.8:
Weighed to a molar ratio of 1.2: 1.9: 3.1,
Wet mixing using a ball mill, isostatic press 1000
Pellets were produced at a pressure of kg / cm ² , and then fired at 1300 ° C. for 20 hours in an air atmosphere to synthesize polycrystalline garnet. Its composition is Gd
_1.8 Eu _1.2 Sc _1.9 Ga _3.1 O ₁₂ . About 400 g of this calcined raw material is put into an iridium crucible having an outer diameter of 50 mm and a height of 50 mm, and under an atmosphere of 99% nitrogen and 1% oxygen,
Melted at about 1700 ° C. by high frequency induction heating. NGSGG was used as a seed crystal, immersed in the melt while rotating at 30 rpm, and pulled up at a rate of 1 mm / h to grow a single crystal having a diameter of 1 inch. When the solidification rate reached 50%, the crystals were separated from the melt and slowly cooled.
As a result, a single crystal having a brownish-brown color and free from cracks and crystal distortion could be obtained. The lifting direction is <
111>, but the orientation does not have to be particularly limited.

Next, a wafer was cut out from the upper and lower portions of the grown single crystal, and the crystal quality was measured by an etching method and an X-ray topography method. As a result, it was found that the single crystal had almost no dislocation and good crystallinity. It could be confirmed. When the lattice constant of the crystal was measured by the X-ray bonding method, it was 1.2576 nm in the upper part of the crystal and 1.2577 nm in the lower part. The composition of the crystals was measured by ICP emission spectroscopy. Since both the upper and lower parts of the crystal had almost the same composition as the charged composition, it was found that the segregation coefficient of each component was almost equal to 1. The light transmittance was measured with a spectrophotometer after mirror polishing both surfaces of the wafer.
The result is shown in FIG. The horizontal axis is the wavelength (nm), and the vertical axis is the transmittance (%). For comparison, a conventional product (NGSG
The transmittance of G) is also shown. It can be seen that the product of the present invention (EGGSGG) is transparent in the wavelength range of 800 to 1800 nm.

(Example A2) The charged composition is Gd _2.9 Eu.
Example A except for _0.1 Sc _1.8 Ga _3.2 O ₁₂
Crystals were grown and evaluated in the same manner as in Example 1. The lattice constant of the crystal was 1.2564 nm, and there was no difference between the upper and lower portions of the crystal. The crystal quality was also good.

(Example A3) The charged composition is Gd _0.1 Eu.
Example A except for _2.9 Sc _2.1 Ga _2.9 O ₁₂
Crystals were grown and evaluated in the same manner as in Example 1. The lattice constant of the crystal was 1.2611 nm, and there was no difference between the upper and lower portions of the crystal. The crystal quality was also good.

Next, the nonmagnetic garnet single crystal of the present invention having a diameter of 25 mm and a thickness of 500 μm was used as a substrate,
A magnetic garnet single crystal film was grown by the PE method. The embodiment will be described. For comparison, a magnetic garnet single crystal film was grown by LPE using a conventional substrate crystal. Then, the magneto-optical characteristics of each LPE film at wavelengths of 980 nm and 1550 nm, that is, the Faraday rotation coefficient θ
(Deg / cm) and absorption coefficient α (dB / cm 2) were measured, and a 45 ° rotation loss L (dB) was calculated and evaluated.

[0020] (Example B1) substrate crystal used was composition with _{Gd 1.8 Eu 1.2 Sc 1.9 Ga 3.1} O 12, a non-magnetic garnet single crystal in lattice constant 1.2576Nm (above in Example A1), Gd _1.1 La _0.1 Bi _1.8 Fe ₅ O
Fostered ₁₂ For details of the breeding method,
₂ O ₃ , La ₂ O ₃ , Bi ₂ O ₃ , Fe ₂ O ₃ , Pb
500 g of a raw material composed of O and B ₂ O ₃ is placed in a platinum crucible,
The mixture was melted at 950 ° C. for 10 hours, subsequently stirred at 950 ° C. for 3 hours, and then cooled to 690 ° C., and the substrate crystal was brought into contact with the melt and grown for 25 hours. L cultivated
The thickness of the PE film was 250 μm. This LPE single crystal film was mirror-finished and an antireflection film was deposited, and then the magneto-optical characteristics were measured.

(Example B2) As a substrate crystal, the composition was G
A nonmagnetic garnet single crystal having a lattice constant of 1.2564 nm (Example A2 described above) of d _2.9 Eu _0.1 Sc _1.8 Ga _3.2 O ₁₂ was used, and Gd _1.3 La _0.2 Bi _1.5 Fe ₅ O ₅ was used.
Fostered ₁₂ The breeding method is the same as in Example B1. However, the growth temperature was 730 ° C., and the film thickness was 350 μm.
A sample was prepared in the same manner as in Example B1, and the magneto-optical characteristics were measured.

Example B3 A substrate crystal having a composition of G
d _0.1 Eu _2.9 Sc _2.1 Ga _2.9 In O _12, lattice constant using a non-magnetic garnet single crystal 1.2611Nm (the Example _{A3), Gd 0.8 La 0.5 Bi} 1.7 Fe 5 O
Fostered ₁₂ The breeding method is the same as in Example B1. However, the growth temperature was 700 ° C., and the film thickness was 300 μm.
A sample was prepared in the same manner as in Example B1, and the magneto-optical characteristics were measured.

(Comparative Example 1) As a substrate crystal, the composition was Nd
_1.21 Gd _1.74 Sc _2.07 Ga _2.98 O ₁₂ with a lattice constant of 1.
Using a non-magnetic garnet single crystal of 2619 nm, Nd
_1.69 Bi _1.31 Fe ₅ O ₁₂ was grown. The breeding method is the same as in Example B1. A sample was prepared in the same manner as in Example B1, and the magneto-optical characteristics were measured.

(Comparative Example 2) As a substrate crystal, the composition was (C
aGd) ₃ (ZrMgGa) ₅ O ₁₂ with a lattice constant of 1.
Using a non-magnetic garnet single crystal of 2496 nm, Tb
_1.85 Bi _1.15 Fe _4. was grown ₇₅ Al _0.25 O _12. The breeding method is the same as in Example B1. A sample was prepared in the same manner as in Example B1, and the magneto-optical characteristics were measured.

Table 1 shows the measurement results and the evaluation results of the above Examples and Comparative Examples.

[0026]

[Table 1]

The criterion for determining whether the characteristic is acceptable is 4 at a wavelength of 980 nm.
The 5-degree rotation loss was 4 dB, and the 45-degree rotation loss at a wavelength of 1550 nm was 0.2 dB. The reason is as follows. Light having a wavelength of 980 nm is used as an excitation light source for an optical amplifier. The input power to the optical amplifier requires about 30 mW, and the output is about 120 mW. Therefore, if the coupling loss is 2 dB, 4 dB
Is the upper limit of tolerance. Light having a wavelength of 1550 nm is used as communication light, and it is generally considered that the upper limit is about 0.2 dB. In particular, at a wavelength of 980 nm, the Faraday rotation coefficient is large, so that the LPE film thickness can be made small. On the contrary, the substrate crystal cannot be ground because it is too thin, so that it remains as it is. Therefore, as in the present invention, a wavelength of about 800
A substrate crystal transparent between nm and 1800 nm is very convenient when used as a magneto-optical element while leaving the substrate crystal.

[0028]

The non-magnetic garnet single crystal according to the present invention has a good crystal quality, is transparent in the optical communication wavelength band, and is varied from about 1.256 nm to 1.
There is an effect that an arbitrary lattice constant can be set in a range up to 262 nm. Therefore, it is particularly useful as a substrate crystal for growing a rare earth iron garnet LPE film that replaces bismuth in a large amount.

The magnetic garnet single crystal according to the present invention has a wide range of wavelengths from about 980 nm to about 1550 nm.
Good magneto-optical characteristics and a high-performance magneto-optical element can be obtained. In particular, there is an advantage that it can be easily manufactured because a single composition can be used even in a wide wavelength range.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the wavelength and the transmittance of a product of the present invention and a conventional product.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hiromitsu Umezawa 5-36-11 Shimbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. F-term (reference) 4G077 AA02 AA03 BC21 BC23 BC27 BC28 CF10 QA71 5E049 AB06 AB09 AC03 BA22 MC09

Claims (3)

[Claims] 1. At least a cation is Gd, Eu, S
A non-magnetic garnet single crystal made of an oxide containing all of c and Ga. 2. A substrate material used in the liquid phase epitaxial method, a composition formula _{Gd 3-s Eu s Sc t} Ga 5-t O 12
(However, a nonmagnetic garnet single crystal represented by 0 <s <3, 1.8 <t <2.2). 3. A lattice constant of 1.256 nm to 1.262 nm.
As a substrate a non-magnetic garnet single crystal according to claim 1 or 2 is, was a liquid phase epitaxial growth on the substrate, a composition formula _{Gd 3-xy La x Bi y} Fe 5 O 12 ( where 0.1 ≦ x ≦ 0.5, 1.5 ≦ y ≦ 1.8) A magnetic garnet single crystal for a magneto-optical element.