JPH0443316A - Magneto-optical thin-film material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Application Field of the Invention) The present invention enables control of magnetic anisotropy in magneto-optic thin film materials, more specifically in magneto-optic materials used in magneto-optic elements such as optical isolators. and relates to materials with a large Faraday effect.

(Prior art) As optical communications and optical information processing become more sophisticated, magneto-optical devices such as isolators that utilize the Faraday effect are used to prevent instability and noise increase in laser light sources induced by returned light. elements are becoming important. The main requirements for materials used in magneto-optical elements include having a large Faraday effect at the wavelength used, having low light absorption, and having magnetic properties that match the structure of the element. As materials used in the near-infrared wavelength region, materials having a garnet-type crystal structure such as Y3Fes○]2 or Gd5Fe5012 are known.

In order to increase the Faraday effect of these Ganinet materials, a portion of Y or Gd is replaced with Bi. This i-substituted garnet is produced by liquid phase epitaxial method, etc., but in this method, Bi
There is a limit to the amount of substitution, and the increase in the Faraday effect is limited by this amount of substitution. Additionally, various elements are substituted to control magnetic anisotropy, but this generally reduces the Faraday effect.

(Problems to be Solved by the Invention) In order to replace a large amount of Bi, thin films have recently been formed using ECR plasma sputtering, ion beam sputtering, or RF magnetron sputtering, and Bi5Fe50t2 epitaxy in which all Y or Gd has been replaced with Bi has been developed. A thin film was obtained. The Faraday rotation coefficient of this thin film was shown to be about 20 times larger than that of Y3Fes○12 at a wavelength of 1.55 μm. However, the magnetic anisotropy of this thin film is oriented perpendicular to the film surface;
When applied to an element that requires magnetic anisotropy in a direction other than the perpendicular direction, such as a waveguide type element, there is a drawback that the magnetic anisotropy cannot be controlled.

The present invention solves the above-mentioned drawbacks of the Bi3Fe5O12 thin film, and aims to provide a magneto-optic thin film material that allows control of magnetic anisotropy and has a large Faraday effect.

(Summary of the Invention) In order to solve the above-mentioned problems, the magneto-optic thin film material according to the present invention has a compound having a garnet-type crystal structure represented by the composition formula Bi3-XCeXFe5Ot2, in which the amount of Ce is 0 and X
It is characterized by being in the range of ≦2.

That is, the present invention is based on the discovery that in a compound with a garnet crystal structure represented by Bi3-xcexFeso12, by changing the amount of Ce, it is possible to control the magnetic anisotropy and that the faraday effect is large. It is characterized in that the amount of Ce is in the range of x≦2.

(Detailed Description of the Invention) The sign and magnitude of the uniaxial magnetic anisotropy of a single crystal garnet film formed by sputtering mainly depends on stress and magnetostriction.

The perpendicular magnetic anisotropy constant (Ku) is determined by the magnetostriction (λ), Young's modulus (E), Poisson's ratio (μ), and the difference between the lattice constant (a,) of the substrate and the lattice constant (ap) of the thin film (Δa= as-
ap) and K.

−(3/2>[E/(1+μ)] (Δa/a p
) is expressed as λ. Among these parameters, the difference in lattice constant and the magnetostriction both take positive or negative values depending on the material, and the positive or negative value of the perpendicular magnetic anisotropy constant is determined by the combination of these positive and negative values. Bi3-XCe
The lattice constant of the XFe5Ox2 thin film is 12.62,
The maximum lattice constant of commonly available garnet substrates is 12.
．． Since there are 55 people, the lattice constant difference is greater than -0.07. From this, the above relational expression -(3/2)[E/(1
+μ)](Δa/ap) is positive, that is, tension acts in the direction perpendicular to the film surface, and the sign of the perpendicular magnetic anisotropy constant is controlled only by the sign of magnetostriction.

Since the sign of the magnetostriction of the Bi3Fes○12 thin film is negative, the perpendicular magnetic anisotropy constant is negative, indicating perpendicular magnetic anisotropy.

When a portion of Bi in this thin film is replaced with Ce, the amount of substitution increases and the magnetostriction decreases, and then the sign reverses from negative to positive. The lattice constant of Ce-substituted FNiM is larger than that of the garnet substrate, as in the case of the B i 3Fe5012 thin film.

For these reasons, the sign of the perpendicular magnetic anisotropy constant is reversed from negative to positive, and the in-plane magnetic anisotropy component becomes stronger.

On the other hand, Ce of B i 3-XCexF e 5012
Thin films with a JLX of up to 2 have a single garnet phase, but thin films with a higher amount of Ce have a mixture of different phases in the garnet phase. When different phases coexist, light absorption increases, so
Thin films are not suitable as magneto-optic materials.

The Faraday rotation coefficient of this garnet single-phase thin film is 0.9
In the wavelength range of 5 to 1.6 μm, Bi3Fes○1
Since the value is larger than that of 2 thin films, it is suitable as a material for magneto-optical elements used in the near-infrared region.

From the above, it is possible to control the magnetic anisotropy, and the Faraday effect is large, so that the amount of Ce in the garnet thin film of 13-xCexFesO12 is in the range of O<X≦2.

(Example) A Bi3-xCexFes○12 thin film was formed on a Nd3Ga5012 substrate with a lattice constant of 12.51 by RF sputtering using a ceramic target consisting of Bi3-xCexFes012 and Bi2O3. The substrate temperature at this time was 500°C.

Table 1 shows the amount of Ce, phase state, magnetostriction, and Faraday rotation coefficient at a wavelength of 1.55 μm of the thin film thus formed. Sample No. 11 is a comparative example of a Bi3Fe5O12 thin film containing no Ce. Sample N092
．． Samples 3.4 and 5 are examples of the present invention in which the amount of Ce is changed, and samples No. 6 and 6 are comparative examples.

The thin films containing Ce in Samples Nos. 12, 3, 4, and 5 are all single-phase garnet. It was confirmed that the lattice constants of these thin films were all larger than that of the substrate. The sign of the magnetostriction of the thin film of sample No. 2 in which the amount of Ce is 0.2 is negative.

The sign of the magnetostriction of the thin films of samples No. 3.4 and 5 having a larger amount of Ce is positive, and the larger the amount of Ce, the larger the value of the magnetostriction. The sign of the Faraday rotation coefficient of the thin film of each of these Examples is negative, and its value is that of sample No.
-B200deg which is the value of Bi5FesOt2 film of 1
/cm larger. Ce amount X of sample N096 is 2.5
The thin film contains phases other than the garnet phase, and is not a single phase.

From the above Examples and Comparative Examples, it is clear that B in which Bi in Bi3Fe5O12 is partially replaced with Ce.
13-xcexFeso12 garnet thin film), the sign and magnitude of strain changed depending on the amount of Ce, and it was confirmed that the magnetic anisotropy could be controlled.

It was also confirmed that the Faraday rotation coefficient was larger than that of the Bi5FesO12 thin film. The effective amount of Ce for obtaining these effects is O<X≦2.

The magnetic anisotropy can be controlled by adjusting the amount of Ce in the 13-xcexFesot2 thin film shown in Table 1B. Further, the Faraday effect is larger than that of Bi3Fe5O12. For these reasons, the magneto-optic thin film material of the present invention is useful as a material for magneto-optical elements that require control of magnetic anisotropy.

Fist: Bi>XCeXFe5O12 1. : Light wavelength 1.55μm

Claims (1)

[Claims] (1) Composition formula Bi_3_-_XCe_XFe_5O_1
A magneto-optical thin film material, characterized in that in a compound having a garnet-type crystal structure represented by _2, the amount of Ce is in the range of 0<X≦2.