JPH0375516B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a magneto-optical material used for optical isolators, optical circulators, etc. that utilize the Faraday effect, and in particular has a small temperature coefficient of the Faraday rotation angle and a low saturation magnetization. This invention relates to materials for small magneto-optical elements.

(Prior Art) In optical communication using a laser, an optical isolator is required to block light returning to the light source, and a magnetic garnet material with a Faraday effect is used for the optical isolator. However, with the conventional Faraday rotator made of bulk magnetic garnet material, there are limits to the reduction in size, weight, and cost.
Various alternative materials have been researched, and on a garnet single crystal substrate represented by the formula: (GdCa) ₃ (GaMgZr) ₅ O ₁₂ , a so-called high lattice constant GGG substrate, for example, a material with the formula: (GdBi) ₃ (FeAlGa) ₅ is used. Epitaxially grown Bi-substituted rare earth iron garnets such as O ₁₂ have been proposed. In Bi-substituted rare earth iron garnet, the Faraday rotation coefficient is increased by replacing some of the rare earth sites with Bi, and the increase in the lattice constant due to Bi substitution is adjusted by replacing some of the Fe sites with Al and Ga. There is. Matching the lattice constants of the substrate and film is extremely important in epitaxial growth.

(Problem to be Solved by the Invention) In addition to having a large Faraday rotation coefficient, the Faraday rotator has a temperature range of -20 to 60°C in order to keep the performance of the optical isolator constant.
It is required that the temperature coefficient of the Faraday rotation angle at (°C) be small. Furthermore, in order to make the optical isolator smaller and lighter, it is required that the saturation magnetization be small. The reason for this is that the external dimensions of the optical isolator are mainly determined by the magnet, and in order to make the magnet smaller, a Faraday rotator with low saturation magnetization is required. However, a material that satisfies all of the above conditions has not yet been reported.

An object of the present invention is to provide a material for a magneto-optical element that satisfies all the conditions required for a Faraday rotator, such as a large Faraday rotation coefficient, a small temperature coefficient of the Faraday rotation angle, and a small saturation magnetization. It is in.

(Means for solving the problem) In order to achieve this object, the magneto-optical element material of the present invention is formed on the high lattice constant GGG substrate by the following formula:
Bi-substituted rare earth iron garnet represented by Yb _x Tb _y Bi _3-xy Fe ₅ O ₁₂ is epitaxially grown, and in the above formula, x and y are x+Y≦2.2,
It is characterized in that it is selected so as to satisfy the following conditions: x≦y and y=−2.3x+21×(12.62−a) (where a is the lattice constant of the substrate).

The magneto-optical element material of the present invention uses a garnet single crystal substrate with a known high lattice constant GGG, that is, (GdCa) ₃ (GaMgZr) ₅ O ₁₂ , and this substrate material has Gd sites and Ga sites. Since the lattice constant changes in the range of 12.48 to 12.53 Å depending on the amount of substitution,
The lattice constant is measured in advance so that the composition of the Bi-substituted rare earth iron garnet matches this lattice constant within a range of ±0.001 Å.

1 of the rare earth components of Bi-substituted rare earth iron garnet
The reason why Yb is selected as the material is that Yb has a small ionic radius, and the amount of Bi substitution can be sufficiently increased within the range where the lattice constant matches the substrate without replacing Fe sites. If the Fe site is replaced with Al, Ga, etc., the temperature coefficient of the Faraday rotation angle increases, but in the present invention, by using Yb as one of the rare earth components, the replacement of the Fe site is not necessary, and the temperature coefficient of the Faraday rotation angle increases. We succeeded in minimizing the Faraday rotation coefficient and increasing the Faraday rotation coefficient.

Further, the reason why Tb was selected as one of the other rare earth components is that Tb does not undergo magnetization reversal at the operating environment temperature (-20 to 60° C.), and its saturation magnetization can be made small. The rare earth element that can minimize saturation magnetization is Gd, but Gd has the fatal drawback of magnetization reversal occurring in the above-mentioned operating temperature range, and cannot be used.

In Yb _x Tb _y Bi _3-xy Fe ₅ O ₁₂ , x and y are values determined by the Faraday rotation coefficient, target value of saturation magnetization, and lattice constant matching with the substrate material. First, in the above composition system, the Faraday rotation coefficient is proportional to the amount of Bi substitution, and the target Faraday rotation coefficient is -
In order to achieve 1000 degrees/cm or more (at a wavelength of 1.3 μm), the content (fu) per molecular formula of Bi needs to be 0.8 or more. Based on this experimental result, 3-x-y≧
0.8, that is, x+y≦2.2. Next, the magnitude of saturation magnetization is proportional to the Yb/Tb molar ratio, and in order to set the target saturation magnetization magnitude to 1500 Oe or less, the Yb/Tb molar ratio must be 50% or less. Based on this experimental result, it is necessary to satisfy the relationship of fu of Yb and Tb, that is, x and y=x≦y. Furthermore, it is necessary that the lattice constants of the substrate and the film having the above composition be matched. This matching condition is theoretically determined from the lattice constants of Yb ₃ Fe ₅ O ₁₂ , Tb ₃ Fe ₅ O ₁₂ , Bi ₃ Fe ₅ O ₁₂ and the lattice constants of fu and the substrate. That is, the lattice constants of Yb ₃ Fe ₅ O ₁₂ and Tb ₃ Fe ₅ O ₁₂ are 12.291 Å and 12.477 Å, and the theoretical lattice constant of Bi ₃ Fe ₅ O ₁₂ is 12.620 Å, so the lattice constant of the substrate is a Å Then, the following formula holds true.

12.291x+12.477y+12.620×(3-x-y)=3a
From this equation, y=-2.3x+21×(12.62-a) is derived. (As mentioned above, a is in the range of 12.48 to 12.53 Å.) Therefore, once the lattice constant of the substrate is determined, the relationship between x and y is uniquely determined.

As mentioned above, the fu of Yb and Tb, that is, x and y, are
x+y≦2.2, x≦y, y=−2.3x+21×(12.62−
It is necessary to select so as to satisfy the three equations a).

(Examples) Example 1 Using (GbCa) ₃ (GaMgZr) ₅ O ₁₂ with a lattice constant of 12.498 Å as a substrate, Yb _0.5 Tb _1.3 Bi _1.2 Fe ₅ O ₁₂ was grown by a liquid phase epitaxial method. In this liquid phase epitaxial method, the melt composition is
Yb ₂ O ₃ 2.3 g, Tb ₂ O ₃ 4.3 g, Fe ₂ O ₃ 41.8 g,
After melting 206.7 g of PbO, 150.5 g of Bi ₂ O ₃ and 3.5 g of B ₂ O ₃ in a platinum crucible at 1000°C,
The temperature was lowered to .degree. C. to create a supercooled state, and the substrate was brought into contact with this melt while rotating at 100 rpm.

The growth rate was 1 μm/min, and the film was grown to a thickness of 300 μm. This material has a Faraday rotation coefficient of -1700 degrees/cm at room temperature when measured at a wavelength of 1.3 μm, and a temperature coefficient of Faraday rotation angle of 0.064 degrees/℃ at 30 degrees Celsius.
The saturation magnetization was 1100 Oe.

Example 2 Melt composition: Yb ₂ O ₃ 1.5 g, Tb ₂ O ₃ 5.0 g,
Fe ³ O ₃ 41.8g, PbO206.8g, Bi ₂ O ₃ 150.5g,
An epitaxial film was grown to a thickness of 400 μm on a high lattice constant GGG substrate in the same manner as in Example 1, except that 3.5 g of B ₂ O ₃ was used and the growth temperature was 820° C. The obtained film composition was Yb _0.4 Tb _1.5 Bi _1.1 Fe ₅ O ₁₂ , and the wavelength was 1.3 μm.
The Faraday rotation coefficient at room temperature is −
The temperature coefficient at 30°C of the Faraday rotation angle was 0.060°/°C, and the saturation magnetization was 1000 Oe.

Example 3 Melt composition: Yb ₂ O ₃ 3.4 g, Tb ₂ O ₃ 3.2 g,
Fe ₂ O ₃ 41.8g, PbO206.7g, Bi ₂ O ₃ 150.5g,
Epitaxial growth was carried out in the same manner as in Example 1 except that 3.5 g of B ₂ O ₃ was used and the growth temperature was 800°C.
A Yb _0.7 Tb _0.9 Bi _1.4 Fe ₅ O ₁₂ film with a thickness of 200 μm was obtained.
The material with this epitaxial film has a wavelength of 1.3 μm.
The Faraday rotation coefficient at room temperature is −
The temperature coefficient at 2600 degrees/cm, the Faraday rotation angle at 30 degrees Celsius was 0.062 degrees/℃, and the saturation magnetization was 1300 Oe.

(Effects of the Invention) The present invention provides an extremely well-balanced structure with an absolute value of the Faraday rotation coefficient of 1000 degrees/cm or more at a wavelength of 1.3 μm, a temperature change in the Faraday rotation angle of 0.065 degrees/℃ or less, and a saturation magnetization of 1500 Oe or less. A material for magneto-optical elements could be obtained. According to such materials, it is possible to make optical isolators, optical circulators, etc. smaller and lighter, and to reduce costs.

Claims (1)

[Claims] 1. A garnet single crystal substrate having a composition represented by the formula: (GdCa) ₃ (GaMgZr) ₅ O ₁₂ and a garnet single crystal substrate epitaxially grown on the substrate, the formula: Yb _x Tb _y Bi _{3- xy} Fe ₅ O ₁₂ , and x and y are x+y≦2.2, x≦y
and y = -2.3x + 21 x (12.62 - a) (a is the lattice constant of the above substrate, a value in the range of 12.48 to 12.53, unit A) for a magnetic optical element comprising a magnetic garnet single crystal film that satisfies the following conditions. material.