JP3538449B2 - Magneto-optical element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical device, and more particularly to a magneto-optical device made of a magnetic garnet crystal suitable for measuring a magnetic field.

[0002]

2. Description of the Related Art In a magneto-optical element, the Faraday rotation angle is proportional to the magnetic field in a magnetic field smaller than its saturation magnetic field. It is well known that this phenomenon is used to construct a sensor that measures a magnetic field from a magneto-optical element, and is combined with an optical fiber in a transformer or circuit breaker where high voltage is generated, or where insulation is required. Used. Typical magneto-optical element (Faraday element) used for magnetic field sensors
The following are known: According to JP 58-139082, in the magnetic garnet films having the composition represented by the general formula _{Bi x R 3-x (Fe} 5-y M y) O 12,
R is a rare earth element such as Y or La, and M is Ga, Al, Ge
It is described that a material substituted with an element such as has a small change in the temperature of the Verdet constant and is excellent in temperature stability when a device for measuring a magnetic field is configured. Further, according to JP-A-2-196100, especially when limiting the composition as _{(Y 3-xy Ho x Bi} y) Fe 5 O 12, the temperature change rate of the Verdet constant per 100 ° C. is within 2% ± The composition range showing the excellent characteristics is shown. Furthermore, according to Matsushita Electric Industrial: Abstracts of the Lectures of the Japan Society of Applied Magnetics, p.
_{3-xyz Gd x Bi y La} z) when limited as _{Fe 5-u Ga u O 12} , the temperature change rate of the Verdet constant per 100 ° C. is illustrated in composition within 1%. It also shows that the saturation magnetic field is lowered and the sensitivity is increased at a low magnetic field.

[0003]

However, the temperature change rate of the Verdet constant is as large as several percents per 10 ° C. depending on the Bi, R, and M element ratios exemplified in the above-mentioned documents, and is not practical. . In this document, it is described that several kinds of elements that can be used are selected from twenty or more kinds and combined so as to constitute a magnetic garnet structure, and among them, Y, La, Ho, etc. are selected as R. Can,
Although it is described that Ga can be selected as M,
Neither Ho nor Ga is used in the examples of this document,
Furthermore, it does not suggest remarkable thermal stability and high sensitivity due to a synergistic effect when these are coexisted. In fact, the exemplified compositions are quite different from those of the present invention, and the thermal stability is more than 5 times worse than the present invention, as will be explained later.

In the above-mentioned literature, the magnetic field required for the saturation of the Faraday rotation is large. In particular, when a sensor for measuring a low magnetic field of several hundred Oe or less using this magneto-optical element (Faraday element) is used, the sensitivity is high. However, there was a drawback that it was low.

Further, in the above-mentioned literature, the ionic radius of Gd is relatively large, so that the amount of substitution of Bi is limited, and the Faraday rotation angle cannot be increased. Therefore, it is difficult to reduce the film thickness. In the 800 nm wavelength band, the light absorption of the magnetic garnet crystal film is large. Therefore, it is desirable that the absorption loss be as small as possible. However, when Gd is contained, the film thickness is large and the absorption loss is large.

Further, the conventional carnet crystal film for a magnetic field sensor has a small degree of freedom in design, and it is difficult to obtain a magnetic garnet having a low saturation magnetic field even if the composition of the magnetic garnet having a high saturation magnetic field is adjusted. The converse is also true. Another problem is that when the output of the magnetic field sensor is guided to the monitoring place by an optical fiber, if a wavelength of about 800 nm is used as in the past, the loss becomes large because the attenuation of the magneto-optical element and the optical fiber is large, and the detection is difficult. become. Therefore, a magneto-optical element which exhibits high sensitivity when detecting at a wavelength of 1300 nm or more is desired.

Accordingly, it is an object of the present invention to provide a magneto-optical element in which the temperature change rate of the Verdet constant is as small as 0.2% or less per 10 ° C. Another object of the present invention is to
An object of the present invention is to provide a magneto-optical element having a low saturation magnetic field, high detection sensitivity to a magnetic field, and a temperature change rate of the Verdet constant as small as ± 0.2% per 10 ° C. Still another object of the present invention is to provide a magneto-optical element which has a small loss when used at an optical wavelength of 1300 nm or more and a temperature change rate of a Verdet constant of ± 0.2% or less per 10 ° C. is there.

[0008]

SUMMARY OF THE INVENTION The present invention relates to compounds of the general formula _{(Y 3-xyz Bi x Ho} y La z) (Fe 5-u Ga u)
Composition represented by O ₁₂ (provided that 1.2 ≦ x ≦ 1.6, 0 ≦ y ≦
1.8, 0 ≦ z ≦ 0.1, 0.01 ≦ u ≦ 1.4, and 4.0 ≦ 8y + 5u, and 1.3y + 1.75u ≦ 2.
The above-mentioned problem is solved by a magneto-optical element for a magnetic field sensor comprising a magnetic garnet crystal having (28). This magneto-optical element has excellent temperature stability, and the temperature change rate of the Verdet constant is as small as ± 0.2% per 10 ° C.

The present invention also solves the above-mentioned problems by a magneto-optical element for a high-sensitivity magnetic field sensor made of a magnetic garnet crystal, wherein the above general formula further satisfies 3.4 ≦ y + 17u. In this magneto-optical element, the temperature change rate of the Verdet constant is ± 0.2% per 10 ° C.
Not only good thermal stability but also a saturation magnetic field of 12
Less than 00 Oe, high sensitivity when used as a magnetic field sensor.

Further, in the above general formula, 3.
Magneto-optical device for a magnetic field sensor comprising a magnetic garnet crystal suitable for an apparatus for measuring a magnetic field using a light source having a high wavelength of 1300 nm or more, satisfying 4 ≦ y + 17u and simultaneously satisfying 7.2 ≦ 9y + 8u. The above problem is solved by an element. This magneto-optical element has not only good thermal stability with a temperature change rate of Verdet constant of 0.2% or less per 10 ° C., but also a saturation magnetic field of 1200 Oe or less, and high sensitivity when used as a magnetic field sensor. Light sources of 1300 nm and above can be used, thereby reducing light loss.

In the present invention, by replacing a part of Bi with Ho, the temperature stability is improved and the temperature change rate of the Verdet constant can be reduced to within ± 0.2% per 10 ° C. At this time, Ho has an ion radius smaller than that of Gd of the above-described conventional example, and the amount of Bi having a large ion radius can be increased as much as possible. Bi has the effect of increasing the Faraday rotation ability, and has the advantage that the film thickness can be reduced in order to obtain the same Faraday rotation angle. Since light absorption of the garnet crystal film is large in the wavelength band of 800 nm, it is desirable that the absorption loss be as small as possible. Therefore, the absorption loss can be suppressed low by making the film thickness smaller by Ho substitution than by Gd substitution. When a rare earth ion having an ion radius smaller than that of Ho is substituted, unlike Ho, it has a negative Verdet constant temperature coefficient, so that it is difficult to reduce the temperature coefficient. In addition, when Ho is used, the film thickness may be smaller than in the case of Gd, so that there is an advantage in manufacturing that defects and cracks generated when forming a thick film are small. Also, the running cost is low.

The uniaxial magnetic anisotropy in the case of Ho substitution is smaller than that in the case of Gd substitution, so that the perpendicular magnetization component of the crystal film is smaller than that of Gd. Generally, when the perpendicular magnetization component is small, hysteresis is less likely to occur. Hysteresis tends to occur when the saturation magnetic field is reduced by Ga substitution.
By the Ho substitution, the saturation magnetic field at which hysteresis occurs can be made lower than that of Gd. This is advantageous for using low magnetic fields,
A stable magnetic field measuring device can be configured.

Next, in the present invention, part of Fe is replaced by Ga. Ga lowers the saturation magnetic field of the magnetic garnet, and when used as a magnetic sensor, can increase the sensitivity of a magneto-optical element made of a magnetic garnet crystal. If the substitution amount of Ga is appropriate, the temperature stability of the magnetic garnet obtained by the substitution of Ho is not affected.

Thus, according to the present invention, by combining Ho and Ga, the saturation magnetic field of the magnetic garnet magneto-optical element used as a magnetic field sensor can be relatively freely designed according to the measured magnetic field while maintaining stable temperature characteristics. .
FIG. 1 is a graph showing the composition points of the examples (horizontal axis: formula amount of Ga, vertical axis: formula amount of Ho). . In the black frame, λ = 80
It represents a composition range in which the temperature change rate of the Verdet constant measured using a light source of 0 or 1300 nm is within ± 0.2% / 10 ° C. This range is defined as x, y, z,
When u is in the predetermined range, it is in the range of 4.0 ≦ 8y + 5u and 1.3y + 1.75u ≦ 2.28. FIG.
Shows the relationship between the temperature change rate of the Verdet constant measured using a light source having a wavelength of 800 nm and the saturation magnetic field. From now on, ±
It can be seen that the saturation magnetic field can be arbitrarily set in the range of 380 Oe to 1670 Oe at a temperature change rate within 0.2% / 10 ° C. FIG. 3 is a graph showing the composition points of the examples, and the sample numbers are indicated above the points. The wavelength within the dotted frame is 800 or 13
The temperature change rate of the Verdet constant measured using a light source of 00 nm is within ± 0.2% / 10 ° C. and the saturation magnetic field is 1.2 k
The composition range is within Oe. This condition is satisfied when x, y, z, and u in the above general formula are within a predetermined range.
4.0 ≦ 8y + 5u, 1.3y + 1.75u ≦ 2.28
And 3.4 ≦ y + 17u is satisfied. Thus, a magneto-optical element suitable as a high-sensitivity magnetic field sensor is obtained. Highly sensitive sensors measure magnetic fields of 1200 Oe or less in most cases. The black frame in FIG. 3 indicates a composition range in which the temperature change rate of the Verdet constant is within ± 0.2% / 10 ° C. and the saturation magnetic field is within 1.2 kOe when measured using a light source having a wavelength of 1300 nm. Represent. This range is 7.2 when x, y, z, u are within a predetermined range in the above general formula.
≦ 9y + 8u, 1.3y + 1.75u ≦ 2.28, and 3.4 ≦ y + 17u. Thus, a magneto-optical element suitable as a low-loss magnetic field sensor is obtained.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing embodiments of the present invention, a method for measuring the temperature change rate of the Verdet constant and the temperature change rate per 10 ° C. will be defined. Samples at -20 ° C to 80 ° C
The Verdet constant is measured in the range. Measurements are -20 ° C, 25
C. and 80.degree. Based on the Verdet constant at 25 ° C., this is set as V ₂₅ . Assuming that the Verdet constants at −20 ° C. and 80 ° C. are V ₋₂₀ and V ₈₀ , the average deviation of the Verdet constant from V ₂₆ is (V ₈₀ −V ₋₂₀ ) / V ₂₅ (% / ° C.). Is the deviation per 1 ° C.
Multiply and define the rate of change per 10 ° C.

[0016] Example _{1 Bi 2 O 3, PbO,} Y 2 O 3 and B ₂ O ₃ in the flux _{mainly, Bi 2 O 3, Ho 2} O 3, La 2 O 3,
Fe ₂ O ₃ and Ga ₂ O ₃ were melted, and a garnet single crystal film of about 100 μm was grown on a calcium, magnesium, and zirconium substituted GGG substrate by LPE. When this film was mirror-polished to a thickness of about 90 μm and subjected to fluorescent X-ray analysis, (Y _0.82 , Bi _1.31 , Ho _0.83 , La
_0.04) (Fe _4.83, was composition represented by Ga _0.17) O _12. A peak wavelength of 1300 nm in a direction perpendicular to the film surface
And a perpendicular magnetic field was applied to the film surface, and an optical measurement was performed. As a result, the saturation magnetic field at the Faraday rotation angle was 1175 Oe. Furthermore, when the value of the Verdet constant was measured in the temperature range of -20 to 80 ° C., the rate of change per 10 ° C. was 0.14%, which was extremely stable. Next, this film is mirror-polished to a thickness of about 25 μm, and a peak wavelength of 800
Similar measurements were made using a nm light source. As a result, the saturation magnetic field showed almost the same value as that of the case of 1300 nm, but the temperature change rate of the Verdet constant was −0.1 / ° C.
10% had shifted to the negative side.

[0017] Example _{2 Bi 2 O 3, PbO,} Y 2 O 3 and B ₂ O ₃ in the flux _{mainly, Bi 2 O 3, Ho 2} O 3, La 2 O 3,
Fe ₂ O ₃ and Ga ₂ O ₃ were melted, and a garnet single crystal film having a thickness of about 200 μm was grown on a calcium, magnesium, and zirconium substituted GGG substrate by using the LPE method. This film was mirror-polished to a thickness of about 90 μm, and subjected to fluorescent X-ray analysis. (Y _1.43 , Bi _1.43 , Ho _0.10 , La
_0.04 ) (Fe _4.18 , Ga _0.82 ) O ₁₂ . A peak wavelength of 1300 nm in a direction perpendicular to the film surface
And a perpendicular magnetic field was applied to the film surface, and an optical measurement was performed. As a result, the saturation magnetic field at the Faraday rotation angle was 500 Oe. Furthermore, when the value of the Verdet constant was measured in a temperature range of -20 to 80 ° C, the rate of change per 10 ° C was 0.18%, which was extremely stable. Next, this film is mirror-polished to a thickness of about 25 μm, and the peak wavelength is 800 n.
The same measurement was performed using m light sources. as a result,
The saturation magnetic field showed almost the same value as that at 1300 nm, but the temperature change rate of the Verdet constant was 0.02% per 10 ° C.
And had shifted to the negative side.

Example 3 The growth time was extended at the same compounding ratio as in Example 2 to a thickness of about 5
A garnet single crystal of 00 μm was obtained. 1300
Optical measurement using a light source of nm gave a Faraday rotation capability of 1900 deg / cm. Saturation field is 500 Oe
The temperature characteristics of the Verdet constant were the same as in Example 2.
When this film was mirror-polished to a thickness of 420 μm, the Faraday rotation angle was about 80 °. Using this film, a change in the amount of light was measured while applying a DC magnetic field (polarizer,
The analyzer is arranged at 45 °). As a result, the measured magnetic field is ± 150
Within Oe, the linearity of the light quantity change was within ± 2%. Further, the temperature change of the light amount under a magnetic field of 30 Oe is -20 ° C.
It was stable at 0.2% per 10 ° C. in the range of 80 ° C.
The sensitivity was also excellent. When this was mirror-polished to a thickness of 210 μm, the Faraday rotation angle was about 40 °. When the similar light quantity change characteristics were measured, the linearity of the light quantity change was ± 1.8% when the measured magnetic field was within ± 300 Oe.
Was within. If the crystal film is thickened, the Faraday rotation angle is increased, and the maximum measurement magnetic field is determined so that the Faraday rotation angle is about 25 °, the linearity error of the light amount is within 2% and the sensitivity is low and the magnetic field is low. A good magnetic field measuring device was constructed. As described above, it was possible to quickly and inexpensively respond to the market required magnetic field only by controlling the film thickness.

Example 4 The composition shown in Table 1 (in terms of Fe ₂
A magnetic garnet of 5.00 in total of O ₃ and Ga ₂ O ₃ was produced. Table 1 shows the measurement results of the temperature change rate (λ = 800 nm and λ = 1300 nm) of the Verdet constant and the saturation magnetization of the obtained sample.

[0020]

[Table 1]

The results in Table 1 are shown in FIGS. FIG.
Is a graph showing the composition point of the example (horizontal axis: formula weight of Ga,
The vertical axis is the formula weight of Ho), and the sample numbers are shown on the dots. In the black frame, the temperature change rate of the Verdet constant measured using a light source of λ = 800 or 1300 nm is ± 0.2% / 10 ° C.
Represents the composition range within. This range is 4.0 ≦ 8y + 5u and 1.3y + 1.75u ≦ in the above general formula.
It is in the range of 2.28. FIG. 2 shows the relationship between the temperature change rate of the Verdet constant measured using a light source having a wavelength of 800 nm and the saturation magnetic field. FIG. 3 is a graph showing the composition points of the examples, and the sample numbers are indicated above the points. The saturation magnetic field is 1.2 kOe in the dotted frame.
Within the range, the temperature change rate of the Verdet constant measured using a light source having a wavelength of 800 or 1300 nm is ± 0.2%.
/ 10 ° C. This range is 4.0 ≦ 8y + 5u and 1.3y + 1.7 in the above general formula.
In addition to the range of 5u ≦ 2.28, 3.4 ≦ y + 17
satisfies u. The black frame in FIG. 3 indicates a composition range in which the saturation magnetic field is within 1.2 kOe and the temperature change rate of the Verdet constant is within ± 0.2% / 10 ° C. measured using a light source having a wavelength of 1300 nm. This range in the above general formula,
7.2 ≦ 9y + 8u, 1.3y + 1.75u ≦ 2.2
8, and 3.4 ≦ y + 17u.

[0022]

When a sensor device for measuring a magnetic field is constructed using the magneto-optical element (Faraday element) according to the present invention, an extremely stable measured value can be obtained with respect to a change in ambient temperature. In particular, the composition region in the frame of FIG. 1 is stable against a temperature change over a wide range of measurement wavelengths. Further, since the saturation magnetization can be arbitrarily selected as shown in FIG. 2, it satisfies the market requirements such as being used for measurement of a high magnetic field and performing high-sensitivity measurement at a low magnetic field as shown in FIG. Furthermore, high sensitivity and low loss measurement can be performed as shown by the black frame in FIG.

[Brief description of the drawings]

FIG. 1 is a graph showing composition points of Examples (horizontal axis: Ga formula amount, vertical axis: Ho formula amount), sample numbers are shown on the dots. In the black frame, the temperature change rate of the Verdet constant is ± 0.2% / 10 ° C.
Represents the composition range within.

FIG. 2 shows the relationship between the temperature change rate of the Verdet constant measured using a light source with a wavelength of 800 nm and the saturation magnetic field.

FIG. 3 is a graph showing the composition points of the examples, and the sample numbers are indicated above the points. The area within the dotted frame indicates the range of claim 2 when the saturation magnetic field is within 1.2 kOe. In the black frame, the temperature change rate of the Verdet constant is ± 0.2 measured using a light source having a wavelength of 1300 nm.
% / 10%.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-69797 (JP, A) JP-A-3-223199 (JP, A) JP-A-5-27207 (JP, A) JP-A-3-27207 282414 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/09 501 C30B 29/28 G01R 33/032

Claims (3)

(57) [Claims] 1. A general formula _{(Y 3-xyz Bi x Ho} y La z) (Fe 5-u Ga u)
Composition represented by O ₁₂ (provided that 1.2 ≦ x ≦ 1.6, 0 ≦ y ≦
1.8, 0 ≦ z ≦ 0.1, 0.01 ≦ u ≦ 1.4, and 4.0 ≦ 8y + 5u, and 1.3y + 1.75u ≦ 2.
28) A magneto-optical element for a magnetic field sensor comprising a magnetic garnet crystal having the above (28). 2. The method according to claim 1, further comprising: 3.4 ≦ y +
A highly sensitive magneto-optical element for a magnetic field sensor comprising a magnetic garnet crystal, which satisfies 17u. 3. The method according to claim 2, further comprising: 7.2 ≦ 9y.
+ 8u, high wavelength 1300nm
A magneto-optical element for a magnetic field sensor comprising a magnetic garnet crystal suitable for an apparatus for measuring a magnetic field using a light source in the above wavelength band.