JPH03249565A - Magneto-optical film for magnetic field sensor - Google Patents

Abstract

PURPOSE:To obtain the sensor utilizing a magneto-optical effect by forming epitaxially a magnetic garnet film of composition of (GdBi)3(FeAlGa)5O12 on a gadolinium gallium garnet single crystal substrate. CONSTITUTION:On a gadolinium gallium garnet single crystal substrate 3, a magnetic garnet film 4 of composition of (GdBi)3(FeAlGa)5O12 is formed epitaxially. At the time of a magnetic field Hs, a Faraday rotation angle theta, and a transmittance eta required for saturating this film, a sensitivity coefficient =theta.eta/Hs, Hs of the film 4 of this composition is extremely small, and also, theta=thetaF.d, and eta=exp((-alphad), in this regard, there is a relation that thetaF, alpha, and (d) denote a coefficient, an absorption coefficient and film thickness, respectively, and theta and eta depend greatly on the film thickness (d) and wavelength of light. Accordingly, by selecting correct magnetic garnet film thickness (d) in accor dance with wavelength of a use light, a magneto-optical film for a sensor of high sensitivity which can detect ununiformity of a feeble magnetic field and a micro-magnetic field is obtained.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a magnetic field sensor that utilizes the magneto-optical effect, particularly a highly sensitive magnetic field suitable for detecting weak magnetic fields and microscopic non-uniformity of magnetic fields. The present invention relates to a magneto-optical film used in a detection section of a sensor.

[Conventional technology]

Conventionally, magnetic field sensors that utilize the magneto-optical effect of magnetic garnet films have been widely used in the power field. Since this is mainly intended for detecting current in power transmission lines, it is desirable that the magneto-optical properties be stable against changes in the environment.
Therefore, it has been required to use a material whose sensitivity coefficient changes little due to temperature changes. Generally, the sensitivity of a magnetic field sensor is determined by the magnetic field required to saturate the magnetic garnet film.
s, Faraday rotation angle is θ, and light transmittance is η, then
It is expressed by the sensitivity coefficient shown in the formula below.

Sensitivity coefficient = θ・η/Hs However, θ=θ,・d, η=exp (−α・d) θF: Faraday rotation coefficient (deg/cm) d Thickness of nigernet film α: Absorption coefficient (marked − 1).

[Problem to be solved by the invention]

Recently, as the applications of magnetic field sensors have diversified, there has been a demand for magnetic field sensors that use materials with high sensitivity (large sensitivity coefficient) that can detect weak magnetic fields, rather than stability against temperature changes.

That is, it has become necessary to be able to detect a weak magnetic field and to detect slight non-uniformity of the magnetic field. For example, it can be used to detect microscopic inhomogeneities in magnetic fields caused by microscopic defects in permanent magnets.

Therefore, the sensitivity coefficient of the magneto-optical film required for these magnetic field sensors is preferably as large as possible (it is considered to be at least 0.1 or more), but with conventional materials, the sensitivity coefficient is 0.02.
However, a satisfactory magneto-optical film has not yet been obtained.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a highly sensitive magneto-optical film for a magnetic field sensor that can detect weak magnetic fields and microscopic non-uniformity of magnetic fields.

[Means and effects for solving the problem] In order to solve the above problems, the inventors of the present invention have conducted extensive research and examination, and have found that
(GdBi)s(FeAIG) grown by liquid phase epitaxial growth on a cadrinium gallium garnet single crystal substrate
a) A magnetic garnet film with a composition of 50 ++ is a material that requires an extremely small magnetic field Hs for saturation, and
It has also been found that the value varies greatly depending on the thickness of the magnetic garnet film, leading to the present invention.

The larger θ and η, and the smaller Hs, the greater the sensitivity coefficient θ.
- η/Hs increases, resulting in high sensitivity.

However, as can be seen from the sensitivity coefficient equation above, as the thickness d of the magnetic garnet film increases, θ and Hs increase, and η decreases. Therefore, the thickness d of the magnetic garnet film required to obtain a large sensitivity coefficient is θ, Hs,
It is determined by the balance of η. Furthermore, since θ and η largely depend on the film thickness d and the wavelength of light, the appropriate film thickness d of the magnetic garnet film to obtain high sensitivity will also differ if the wavelength of light used in the magnetic field sensor differs. For example, wavelength 0.6
When using light in the μm band, the film thickness is preferably 0.5 μm to 2 μm, and when using light in the 0.8 μm wavelength band, the film thickness is 40 μm.
The film thickness is preferably 90 μm to 1 μm when using light with a wavelength of 1.3 μm.

〔Example〕

Hereinafter, the present invention will be described in detail based on an illustrated embodiment.

X 凰正 221.64 g of PbO using a crucible.

Bit Ox 308.47g, B! 01 1
9.75g as flux, Gdz Oa 7.
45g.

Fes Ox 35.56g, Alz Os 2
．． 98g.

4.14 g of Ga10+ was dissolved to prepare a melt. By rotating the melt at 1.0 rpm while heating the melt to 770°C to 790°C and contacting the melt surface with a gadolinium gallium garnet single crystal substrate having a composition of (cdca)s(MgZrGa)aO12. , (GdBi)3(FeAIGa)sol was deposited on one side of the substrate with a film thickness varying from 0.3 μm to 500 μm.
A magnetic garnet film having a composition of 1 was grown, and this film was used as a sample for measuring the magneto-optic film according to the present invention.

The magnetic field Hs required for saturation of magnetic garnet films (magneto-optical films) with different film thickness is EG & G Pr1nceton
The measurement was performed using a vibrating sample magnetometer manufactured by Applied Research. FIG. 1 shows the relationship between the thickness of the magnetic garnet film and the measured Hs. As is clear from this figure, Hs decreases as the film thickness decreases, and in particular, it decreases rapidly at a thickness of 50 μm or less. Moreover, Hs hardly changes when the film thickness is 200 μm or more.

The Faraday rotation coefficient θ and absorption coefficient α of the magnetic garnet film were measured at wavelengths of 0.63 μm, 0.78 μm, and 1.3.
The test was performed using 1 μm light. He-Ne laser light is used for light with a wavelength of 0.63 pm, 0.78 μm, and 1.31 μm.
The light used was a laser diode light. A Faraday effect measuring device manufactured by Mizojiri Optical Industries was used to measure θF. or,
A self-recording spectrophotometer manufactured by Hitachi, Ltd. was used to measure α. θ
Prior to the measurement of F and α, the Sin
A non-reflective coating of (GdBi)+(
It was applied to the surface of a magnetic Carnet film having a composition of FeAIGa) 501□. The table below shows the measured θ and α at each wavelength. Both become larger as the wavelength becomes shorter.

Table Faraday rotation angle θ and transmittance η can be determined from θF, α and the film thickness of the magnetic garnet film in this table.

The wavelengths calculated using these θ, η and Hs obtained from Fig. 1 are 0.63 μm, 0.78 μm, and 1°31 μm.
Figures 2 and 3 show the relationship between the film thickness and the sensitivity coefficient for light of m.
As shown in the figure.

However, FIGS. 2 and 3 show the case where the magnetic garnet film is used in a magnetic field sensor having the structure shown in FIG. 4. In general, there are two types of magnetic field sensors: one uses reflection as shown in Figure 4, and the other uses transmission as shown in Figure 5.However, it is better to use reflection to obtain θ. The film thickness of the magnetic garnet film is 1 when using transmission.
/2, so the method using reflection is more advantageous in terms of reducing Hs and improving mass productivity. In Figures 4 and 5, ■ is a light source, 2 is a polarizer, 3 is a gadolinium-gallium garnet single crystal substrate, 4 is a magnetic garnet film, 5 is a reflective film, 6 is an analyzer, and 7 is a detector. It is.

From Figure 2, when using light with a wavelength of 0.63 μm, the sensitivity coefficient tends to increase as the thickness of the magnetic garnet film decreases, and the sensitivity coefficient is 0.1 when the film thickness is 2 μm or less.
It can be seen that high characteristics of 2 or more can be obtained. However, if the film thickness is smaller than 0.5 μm, it becomes difficult to control the film thickness, so from the viewpoint of ease of controlling the film thickness, the film thickness should be between 0.5 μm and 2 μm.
m is preferred.

Furthermore, when using light with a wavelength of 0.78 μm, the sensitivity coefficient peaks when the thickness of the magnetic garnet film is 55 μm, and high characteristics with a sensitivity coefficient of 0.12 or more can be obtained in the range of 40 μm to 80 μm. .

Furthermore, from FIGS. 2 and 3, when using light with a wavelength of 131 μm, the sensitivity coefficient tends to increase as the thickness of the magnetic garnet film increases, and when the film thickness is 90 μm or more, the sensitivity coefficient is 0.12. The above high characteristics can be obtained. but,
The crystallinity of the magnetic garnet film deteriorates as the film thickness increases, for example, pits are formed, so the film thickness must be 1+am or less. More preferably, the film thickness is 500 μm.
It is preferable to do the following.

〔Effect of the invention〕

As described above, the magneto-optical film for a magnetic field sensor according to the present invention has a practically important advantage in that it can constitute a highly sensitive magnetic field sensor that can detect weak magnetic fields and microscopic non-uniformities in magnetic fields.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the film thickness of a magnetic garnet film, which is an embodiment of the magneto-optical film for a magnetic field sensor according to the present invention, and the magnetic field Hs required for saturation of the film, and FIGS. 2 and 3 are as described above. A diagram showing the relationship between the film thickness of the magnetic garnet film and the sensitivity coefficient,
FIG. 4 and FIG. 5 are configuration diagrams of a reflection type magnetic field sensor and a transmission type magnetic field sensor, respectively. DESCRIPTION OF SYMBOLS 1... Light source, 2... Polarizer, 3... Gadolinium gallium garnet single crystal substrate, 4... Magnetic garnet film, 5... Reflective film, 6... Analyzer, 7...detector. fl Illustration R()Jm)

Claims (4)

[Claims] (1) In a magneto-optical film used in a magnetic field sensor using the magneto-optic effect, the film is grown by liquid phase epitaxial growth on a gadolinium gallium garnet single crystal substrate (GdBi)_3(FeAlGa)_5O_1_2
A magneto-optical film characterized by being a magnetic garnet film having a composition of (2) The magneto-optical film according to claim 1, wherein the film has a thickness of 0.5 μm to 2 μm when the light used for the magnetic field sensor has a wavelength of 0.6 μm. (3) The magneto-optical film according to claim 1, wherein the film has a thickness of 40 μm to 80 μm when the light used in the magnetic field sensor has a wavelength of 0.8 μm. (4) The magneto-optical film according to claim 1, wherein the film has a thickness of 90 μm to 1 mm when the light used in the magnetic field sensor has a wavelength of 1.3 μm.