JPH05119288A - Magneto-optical film of magneto-optical field sensor - Google Patents

Abstract

PURPOSE:To provide the magneto-optical film which has a high sensitivity and is formed to eliminate the influence of temp. on this sensitivity as the magneto-optical film of the magneto-optical sensor for which a magneto-optical effect is utilized. CONSTITUTION:The magneto-optical film to be used for the magnetic field sensor for which the magneto-optical effect is utilized is a magnetic garnet film which consists of a compsn. expressed by YbXTbYBi3-x-yFe3O12 where (x) and (y) are so determined as to satisfy the following conditions: 1.82-1.27x<=y<=2.02-1.27x.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical film used in an optical magnetic field sensor for measuring the magnetic field strength by utilizing the Faraday effect of a magneto-optical element, and particularly to a magneto-optical film formed around a distribution line supplying electric power. The present invention relates to a magneto-optical film for an optical magnetic field sensor that measures magnetic field strength and detects the magnitude of the current.

[0002]

2. Description of the Related Art In recent years, as a current sensor for detecting the abnormality by measuring the magnitude of the current flowing through a substation, a transmission line, a distribution line, etc. in an electric power transmission path from a power plant to a terminal electric power consumer, A plan is underway to use an optical magnetic field sensor that measures the magnetic field generated around the conducting wire through which the current flows by utilizing the magneto-optical effect and obtains the current value. In particular, when large currents such as substations and high-voltage transmission lines are handled, and damage from an accident spreads over a wide range, practical application has already started in some areas.

Since the optical magnetic field sensor for current measurement is generally used outdoors, it is important that it has a stable sensitivity to changes in the environment, especially in temperature.
Fluctuation rate of the sensitivity in the temperature range of 20~ + 80 ° C (S _R
= ΔS / S (%)) is required to be within ± 1%. The sensitivity here means the rate of change of the sensor output with respect to the change of the magnetic field. As described above, the optical magnetic field sensor used in a substation that handles a large current or a high-voltage power transmission line has a low sensitivity (1 × 10 ⁻⁴ / Oe (Oersted) or less), but a magnetic saturation in a large magnetic field. A paramagnetic material or a diamagnetic material such as lead glass, ZnSe, BGO, BSO, etc., which does not cause the phenomenon is used as the magneto-optical material. And these materials have a small sensitivity variation with temperature,
Good results have been obtained.

On the other hand, recently, a plan to use this kind of optical magnetic field sensor is also progressing in a distribution line handling a small current close to that of a power consumer. In the case of such a distribution line, since the magnetic field generated is small, a high sensitivity of 1 × 10 ⁻⁴ / Oe or more is required. Therefore, the lead glass, ZnSe, BGO,
With magneto-optical materials such as BSO, sufficient sensitivity cannot be obtained, and accurate measurement becomes difficult. Therefore,
As such a distribution line, an optical magnetic field sensor using a magnetic garnet film having high magnetic sensitivity and further a Bi substitution type magnetic garnet film has been developed and studied. The optical magnetic field sensor for the distribution line is required to be inexpensive, except for a part, and normally 0.85.
Light having a wavelength of about μm is used.

[0005]

However, since the above-mentioned magnetic garnet film is a ferromagnetic substance, the above-mentioned ZnS is especially used.
Compared with paramagnetic materials or diamagnetic materials such as e, BGO, and BSO, magnetic characteristics such as the saturation magnetic field Hs and Faraday rotation coefficient θf and magneto-optical characteristics significantly change depending on temperature,
For this reason, there is a problem in that the sensitivity itself can be largely changed due to a change in temperature. As described above, it was not possible to realize a magnetic garnet film for this type of optical magnetic field sensor using the conventional magnetic material as it is.

It is an object of the present invention to provide a magneto-optical film having a high sensitivity in this type of optical magnetic field sensor and eliminating the influence of temperature on this sensitivity.

[0007]

The magneto-optical film of the present invention comprises:
Made in the composition of _{Yb X Tb Y Bi 3-XY} Fe 3 O 12, x and y is obtained so as to satisfy the following equation (1). 1.82-1.27x ≦ y ≦ 2.02-1.27x (1)

In the magneto-optical film of the present invention, x is in the range of 0.8 to 1.1 and the film thickness is 10 to 30 μm.
It is characterized by being m.

[0009]

First, the sensitivity S of the optical magnetic field sensor using the magnetic garnet film is expressed by the following equation (2), where L is the thickness of the magnetic garnet film. S = sin (2θf · L) / Hs (2) In the above formula (2), the saturation magnetic field Hs and the Faraday rotation coefficient θf change depending on the temperature. Therefore, in the formula (2), sin (2θf · L) with respect to temperature change is expressed as By making the change of Hs the same, the ratio (2)
The sensitivity represented by the formula can be made constant even when the temperature changes. Further, if the composition of the magnetic garnet film is determined, the Faraday rotation coefficient θf and the saturation magnetic field H
Since each temperature change rate of s is also determined, the variation rate S _R of the sensitivity S with respect to temperature depends on the composition of the magnetic garnet film. Further, the fluctuation rate S _R also depends on the film thickness L because the sensitivity S has a problem of the sin function of θf · L. That is, even in the case of the magnetic garnet film having the same composition, the variation rate S _R changes depending on the film thickness L.

According to the present invention, the composition of the magnetic garnet film is designed in consideration of the above points, and the film thickness L for reducing the variation rate S _R is determined, which is suitable for this type of optical magnetic field sensor. A magneto-optical film can be obtained. And, in particular, from the saturation magnetization and the Faraday rotation coefficient θf of the Bi-substituted iron garnet when changing the rare earth element and the test results of the change with respect to the temperature, (Yb Tb Bi) ₃ Fe ₃ O ₁₂
The materials of the system have proved to be suitable.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The light according to the present invention will be described below with reference to FIGS. 1 and 2.
An example of the magneto-optical film of the magnetic field sensor will be described. The present invention
The magneto-optical film of Yb_XTb_YBi_3-XYFe₃O₁₂The composition of
However, this magnetic garnet film is suitable for liquid phase epitaxial method.
More above Yb_XTb_YBi_3-XYFe₃O₁₂X and y in
Different types were produced with different compositions. That is,
First, PbO, Bi in the platinum crucible₂0₃, B₂0₃The
Yb as a Lux₂0₃, Tb₂0₃, Fe₂0₃To
A melt was prepared by melting. The melt is heated to a temperature of 77
While heating to 0 to 790 ° C, gadly on the surface of the melt
Ni-Gallium garnet single crystal substrate (hereinafter GGG
Substrate) and spin at 100 rpm
As a result, Yb with a thickness of 70 μm is formed on one surface of the GGG substrate._X
Tb _YBi_3-XYFe₃O₁₂A magnetic garnet film was grown.

In the above case, Yb ₂ O ₃ and Tb _{2 in the} melt are
By changing the content ratio of 0 ₃ , the above x and the above y can be obtained.
Samples with different compositions are produced. In the liquid phase epitaxial method, the lattice constant of the magnetic garnet film and the lattice constant of the GGG substrate (12.496A) need to be substantially equal to each other. Satisfaction conditions are added. Therefore, if x of x and y is determined, y is also uniquely determined. Further, the film thickness L of the magnetic garnet film prepared was set to 70 μm. However, when the film thickness L is 70 μm or more, the loss becomes large in the case of light having a wavelength of 0.85 μm. This is because it cannot be used as a magnetic field sensor.

Next, 30 samples of each magnetic garnet film having different x and y were taken out as samples, and formed by polishing so that L = 5 to 65 μm. That is, in the range of 5 to 65 μm for each of the above x compositions, 3
Samples with 0 kinds of film thickness were manufactured. Furthermore, GGG of each sample
The substrate surface and the magnetic garnet film surface were coated with a non-reflective coating consisting of a SiO ₂ single layer for a wavelength of 0.85 μm.

Next, the test results of the sensitivity of the magneto-optical film manufactured as described above to temperature changes will be described.
For each sample of the magnetic garnet film, the temperature is -20 to +
Its sensitivity is measured in the temperature range of 80 ° C., and FIG. 1 shows an example of the configuration of a measurement system for performing such a test. In the figure, light having a wavelength of 0.85 μm emitted from the laser diode 1 passes through the lens 2 and the polarizer 3 to become linearly polarized light, and enters the magnetic garnet film 4. Then, the light that has been subjected to the optical rotatory action according to the strength of the magnetic field to be measured (hereinafter, simply referred to as magnetic field) when passing through the magnetic garnet film 4 further passes through the lens 5 and the polarizer 6 and the strength of the magnetic field. It becomes the strength corresponding to. After that, the intensity of the light incident on the silicon photodiode 7 from the polarizer 6 is detected. In the above case, ± 300 Oe
Is applied in parallel to the optical path, and the temperature of the magnetic garnet film 4 is changed by a Peltier device (not shown).

-20 of each magnetic garnet film sample
The sensitivity S in the temperature range of + 80 ° C is investigated, and the variation S _R is within ± 1% Yb _X Tb _Y Bi _3-XY Fe ₃ O
_When x and the film thickness L in ₁₂ were obtained, the results shown in FIG. 2 were obtained. That is, in the case of the region surrounded by the straight lines a, b and c in the graph of FIG.
The variation rate S _R of the sensitivity S is within ± 1% in the range of 0 to + 80 ° C. In the graph, in the region below the straight line d, the sensitivity S itself is already 1 × 10 ⁻⁴ / Oe or less. That is, in the region surrounded by the straight lines a, b, c and d (hatched part), the variation rate S _R of the sensitivity S in the temperature range of −20 to + 80 ° C. is within ± 1%, and the sensitivity S itself. Is 1 × 10 ⁻⁴ to 4 × 10 ⁻⁴ / Oe.

Therefore, in the Yb _X Tb _Y Bi _3-XY Fe ₃ O ₁₂ magnetic garnet film, the range of x corresponding to such a region is 0.8 to 1.1 and the film thickness L of the magnetic garnet film is L.
Is 10 to 30 μm, the temperature is −20 to +80.
In the range of ° C, the variation rate S _R of the sensitivity S is within ± 1%, and the sensitivity S itself becomes 1 × 10 ^-4 to 4 × 10 ^-4 / Oe.
An optical magnetic field sensor using such a magnetic garnet film can stably measure a minute magnetic field with high accuracy even if the temperature changes considerably.

[0017]

As described above, the magneto-optical film of the present invention has a high sensitivity, and this sensitivity is extremely stable with respect to changes in temperature. In particular, it is harsh when detecting a current value of a distribution line or the like. It is possible to realize an optical magnetic field sensor of this kind that can measure a minute magnetic field with high accuracy under various environments.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a sensitivity measurement system for a sensitivity test on a magneto-optical film of the present invention.

FIG. 2 is a graph showing the relationship between film composition and film thickness based on the results of sensitivity measurement for the magneto-optical film of the present invention.

[Explanation of symbols]

 1 Laser diode 2 Lens 3 Polarizer 4 Magnetic garnet film 5 Lens 6 Polarizer 7 Silicon photodiode

Claims (2)

[Claims] 1. A magneto-optical film used in a magnetic field sensor utilizing a magneto-optical effect, comprising: Yb _X Tb _Y Bi _3-XY Fe ₃ O
A magneto-optical film having a composition of ₁₂ , wherein x and y are magnetic garnet films satisfying the following conditional expressions. 1.82-1.27x ≦ y ≦ 2.02-1.27x 2. The above x is in the range of 0.8 to 1.1,
The magneto-optical film according to claim 1, wherein the magnetic garnet film has a thickness of 10 to 30 μm.