JPH0727823B2 - Magnetic material for magneto-optical element - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic garnet material for a magneto-optical element.

[Conventional technology]

The optical fiber communication has an advantage that a large amount of data can be transmitted at high speed and with low loss as compared with the conventional telecommunication, and its practical application is rapidly progressing at present. However, when part of the laser light propagating in the fiber is reflected by optical devices such as optical fiber connection points, connectors, and switches and returns to the semiconductor laser of the light source, laser oscillation becomes unstable,
It will reduce the transmission quality. Therefore, in performing highly reliable communication and measurement, an optical isolator is known as an optical element that allows emitted light to pass but blocks reflected light from passing.

The optical isolator is generally composed of a polarizer, a Faraday rotator and an analyzer. The light traveling in the forward direction has its polarization component selected by polarization, and when it enters the Faraday rotator, the plane of polarization is rotated by 45 degrees due to the Faraday effect. Since the polarization plane of the analyzer is set to be inclined by 45 degrees with respect to the polarization plane of the polarizer, light in the forward direction passes with low loss. On the other hand, with respect to the incident light from the opposite direction, the light of the polarization plane inclined by 45 degrees with respect to the polarizer is selected by the analyzer and further rotated by 45 degrees by the Faraday rotator.
Only the polarized components that are 90 degrees apart will enter the polarizer, and therefore the passage will be blocked.

Conventionally, as a material for Faraday rotator, yttrium-iron-garnet Y ₃ Fe ₅ O ₁₂ (YI
The bulk single crystal of G) has been used, but YIG has a small Faraday rotation coefficient, so the thickness must be increased to 2-3 mm to obtain the required Faraday effect.
However, since YIG is expensive, such thickening poses a problem in terms of device manufacturing cost.

Therefore, in recent years, as a material for the Faraday rotator, a material in which a relatively thin magnetic garnet film is epitaxially grown on a non-magnetic garnet substrate has been proposed. In the case of such a material, the magnetic garnet film has a large Faraday rotation coefficient so that the desired Faraday effect can be obtained even if the film thickness is small, and the lattice constant matches that of the nonmagnetic garnet to be the substrate. Is required. It is known that the Faraday rotation coefficient is remarkably increased when a part of the rare earth component of the magnetic garnet is replaced with bismuth (Bi), and gadolinium gallium garnet Gd ₃ Ga ₅ is used as the above magnetic material utilizing this. A material in which a magnetic garnet film represented by (GdBi) ₃ (FeAlGa) ₅ O ₁₂ is grown on an O ₁₂ (GGG) substrate is known.

[Problems to be solved by the invention]

By the way, the environment where elements such as optical isolators are used,
In order to have stable operation characteristics in a situation, the Faraday rotation coefficient of the magnetic material used as the Faraday rotator is required to have a small temperature coefficient in a temperature range as wide as possible.

However, in the film having the composition of (GdBi) ₃ (FeAlGa) ₅ O ₁₂ described above, Bi also has an action of increasing the lattice constant,
In order to match the lattice constant with the substrate GGG, it is necessary to replace a part of Fe with an element having a smaller ionic radius such as Al or Ga.
Since these Al and Ga have the effect of increasing the temperature coefficient of the Faraday rotation coefficient of the obtained material, the above materials have a problem that the temperature characteristics are deteriorated.

Therefore, an object of the present invention is to solve the above problems, and to provide a magnetic garnet material for a magneto-optical element that is thin and has a large Faraday rotation ability, and has a small Faraday rotation coefficient temperature coefficient in a wide temperature range. is there.

[Means for solving problems]

MEANS TO SOLVE THE PROBLEM This invention solves the above-mentioned problems, and a garnet single crystal substrate having a composition represented by the formula: (GdCa) ₃ (GaMgZr) ₅ O ₁₂ , and a general formula (I) epitaxially grown on the substrate. during _{R 3-x Bi x Fe 5} -y M y O 12 ... (I) [wherein, R is at least one rare earth element selected Yb, Tm, Er, Ho, and Dy, M is, Al And at least one element selected from Ga, x is a number of 0 <x <2, and y is a number of 0 ≦ y <0.5]. A magnetic garnet material for a magneto-optical element is provided.

The garnet single crystal substrate (hereinafter referred to as “high lattice constant GGG substrate”) having a composition of the formula (GdCa) ₃ (GaMgZr) ₅ O ₁₂ used as a substrate in the present invention is G
It is known that Gd and Ga of GG are partially substituted with Ca, Mg, and Zr, respectively, and that the lattice constant is 12.498Å, which is larger than that of GGG. The thickness of the substrate is 400-500 μm
Good.

Further, in the garnet of the general formula (I) used as the magnetic single crystal film in the present invention, the rare earth element R is Yb, T
It is selected from m, Er, Ho and Dy. Since these have a smaller ionic radius than Gd and the like, the Faraday rotation coefficient can be increased by increasing the Bi substitution amount while suppressing the increase of the lattice constant.

That is, Bi increases the Faraday rotation coefficient as described above, but also acts to increase the lattice constant. However, in the present invention, since a rare earth element having a small ionic radius as described above is selected as R, the lattice constant does not increase as much as in the case of Gd or the like, and Bi substitution of the R site is suppressed while suppressing the increase. The quantity (x) can be increased and the Faraday rotation coefficient can be increased. Moreover, since the substrate has a larger lattice constant than GGG as described above, the lattice constant of the obtained single crystal film matches (matches) the lattice constant of the substrate within the allowable range (± 0.001Å). It is easy to do. As a result, the need to replace the Fe site with Al or Ga is extremely small, and y may be 0 ≦ y <0.5,
It is also possible to set y = 0.

The ionic radius of the rare earth element R increases in the order of Yb, Tm, Er, Ho, Dy, and therefore the value of x necessary for matching the lattice constants decreases in the order of this element sequence. For example, if y = 0,
The value of x is 1.888 for Yb, 1.759 for Tm, 1.649 for Er and 1.4 for Ho.
It is 75 and Dy is 1.274.

In the present invention, X in the general formula (I) (substitution amount of Bi)
Must be a number 0 <X <2.

That is, there is a linear relationship between X and the Faraday rotation coefficient,
The Faraday rotation coefficient increases as X increases. The larger the Faraday rotation coefficient, the thinner the film can be used in the optical isolator, and the more compact the optical isolator can be. Also, the thinner the film, the shorter the time required for crystal growth. From this point of view, X needs to be larger than zero.

Further, when a crystal is grown on a substrate having a high lattice constant, the lattice constant of the crystal is restricted by the lattice constant of the substrate, and if the difference between the crystal and the lattice constant of the substrate is 0.005 Å or more, a good crystal cannot be obtained. That is, when growing a crystal using the substrate,
When Yb having the smallest ion radius is selected as R, X becomes maximum. Therefore, Example 3 described later
From the result of (selecting Yb as R), X was set to a range smaller than 2 in consideration of the allowable width of the difference in lattice constant.

The magnetic garnet material of the present invention can be manufactured by growing the magnetic single crystal of the general formula (I) on a high lattice constant GGG substrate by a liquid phase epitaxial growth method.

That is, according to a known method, the raw material components and the flux components are charged and melted at an appropriate ratio, and the temperature of the melt is, for example, in the range of 750 to 950 ° C., the temperature at which the lattice constants of the substrate and the single crystal film are the same. (Lattice constant matching temperature) is selected, and a magnetic single crystal film is grown while rotating the substrate with one surface of the polished substrate in contact with the melt.

The substrate thus obtained, on which a magnetic single crystal film has been grown, is polished to a required thickness and then used for device production.

〔Example〕

 Hereinafter, the present invention will be specifically described with reference to examples.

Example 1 Raw materials and flux components were used in the following melt preparation composition (molar ratio).

_{Fe 2 O 3 / Dy 2 O} 3 = 15.0 PbO / (Bi 2 O 3 + B 2 O 3) = 1.30 (Dy 2 O 3 + Fe 2 O 3) / (Dy 2 O 3 + Fe 2 O 3 + PbO + B 2 O 3 + Bi
₂ O ₃ ) ＝ 0.145 A high lattice constant GGG substrate (diameter 50 mm, thickness 0.450 mm) was formed by Dy _1.726 Bi _1.274 Fe ₅ O ₁₂ on one side of a high lattice constant matching temperature of 820 ° C. by liquid phase epitaxial growth method. A single crystal garnet film having a thickness of about 500 μm was grown.

The Faraday rotation coefficient (room temperature) of the obtained magnetic material is 1500.
The temperature coefficient (room temperature) is -0.06 degrees / ° C.
Met.

Example 2 In the same manner as in Example 1, the lattice constant matching temperature was 770 ° C. and the composition was Yb _1.112 Bi on the high lattice constant GGG substrate.
A single crystal garnet film having a thickness of about 300 μm represented by _1.888 Fe ₅ O ₁₂ was grown.

The Faraday rotation coefficient (room temperature) of the obtained magnetic material is 2900.
The temperature coefficient (room temperature) is as high as -0.04 degrees / ° C.
Met.

Example 3 In the same manner as in Example 1, the lattice constant matching temperature was 780 ° C. and the composition was Tm _1.241 Bi on a high lattice constant GGG substrate.
A single crystal garnet film represented by _1.759 Fe ₅ O _{12 and} having a thickness of about 300 μm was grown.

The Faraday rotation coefficient (room temperature) of the obtained magnetic material is 2700.
The temperature coefficient (room temperature) is as large as -0.045 degrees / ° C.
Met.

Example 4 In the same manner as in Example 1, the lattice constant matching temperature was 795 ° C. and the composition was Er _1.451 Bi on the high lattice constant GGG substrate.
A single crystal garnet film represented by _1.549 Fe ₅ O _{12 and} having a thickness of about 300 μm was grown.

The Faraday rotation coefficient (room temperature) of the obtained magnetic material is 2300.
The temperature coefficient (room temperature) is -0.05 degrees / ° C.
Met.

Example 5 In the same manner as in Example 1, the lattice constant matching temperature was 805 ° C. and the composition was Ho _1.525 Bi on a high lattice constant GGG substrate.
A single crystal garnet film represented by _1.475 Fe ₅ O _{12 and} having a thickness of about 300 μm was grown.

The Faraday rotation coefficient (room temperature) of the obtained magnetic material is 2100.
The temperature coefficient (room temperature) is as large as −0.055 degrees / ° C.
Met.

Comparative Example Raw materials and flux components were used in the following melt preparation composition (molar ratio).

(Fe ₂ O ₃ + Al ₂ O ₃ + Ga ₂ O ₃ ) / Gd ₂ O ₃ = 13.3 PbO / (Bi ₂ O ₃ + B ₂ O ₃ ) = 1.05 (Gd ₂ O ₃ + Fe ₂ O ₃ ) / (Gd ₂ O _{3 + Fe 2 O 3 + PbO} + B 2 O 3 + Bi 2 O 3) = 0.132 in the same manner as in example 1, the high lattice constant GGG substrate, with the lattice constant matching temperature 822 ° C., composition Gd _2.01 Bi _0.99 Fe _4.09 (a
l, Ga) _0.91 O ₁₂ A single crystal garnet film having a thickness of about 500 μm was grown.

The Faraday rotation coefficient (room temperature) of the obtained magnetic material is 15
It was 00 degrees / cm, but its temperature coefficient (room temperature) was -0.11 degrees / ° C.

〔The invention's effect〕

Since the magnetic garnet material for a magneto-optical element of the present invention has a large Faraday rotation coefficient, the desired Faraday effect can be obtained even if it is thin. Moreover, since the Faraday rotation coefficient has a small temperature coefficient, it is possible to manufacture a magneto-optical element such as an optical isolator having stable operation characteristics in a wide temperature range.

Front page continuation (72) Inventor Kenichi Hino 1-6-1, Suehirocho, Ome, Tokyo Sumitomo Metal Mining Co., Ltd. Electronic Materials Research Laboratory (72) Inventor Shuji Ozumi 1-6, Suehirocho, Ome-shi, Tokyo 1 Sumitomo Metal Mining Co., Ltd. Electronic Materials Research Laboratory (72) Inventor Katsumi Machida 1-6-1, Suehirocho, Ome-shi, Tokyo Sumitomo Metal Mining Co., Ltd. Electronic Materials Research Laboratory (56) Reference JP-A-57-200295 (JP, A) JP 59-87805 (JP, A) Spring 1985 (Showa 60) Spring Proceedings of the 32nd Joint Lecture on Applied Physics Page 72 30 p-N-4 J. Appl. Phys. 55 (4) 15 February 1984 P. 1052-1061

Claims (1)

[Claims] 1. A garnet single crystal substrate having a composition represented by the formula: (GdCa) ₃ (GaMgZr) ₅ O ₁₂ , and a general formula: R _3-x Bi _x Fe _5-y epitaxially grown on the substrate. M _y O ₁₂ [wherein, R is at least one element selected from Yb, Tm, Er, Ho and Dy, M is at least one element selected from Al and Ga, and X is Is a number 0 <X <2,
y is a number of 0 ≦ y <0.5], and a garnet material for a magneto-optical element comprising a magnetic single crystal film having a composition represented by