JPH1126237A - Alternating-current magnetic field measuring faraday rotor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable an alternating-current magnetic field measuring Faraday rotor to be kept high in sensitivity linearity even to an alternating-current magnetic field of a few oersteds or below, by a method wherein a bismuth- substituted rare earth iron garnet single crystal film is grown on a non-magnetic garnet board tilted at a specific angle to a (111) plane orientation through a liquid phase epitaxial method. SOLUTION: One side of a garnet single crystal board which is possessed of a lattice constant of 1.2495±0.0005 nm and tilted at an angle of 0.5 deg. or below to a (111) board plane orientation is brought into contact with the surface of a melting liquid for growing a bismuth-substituted rare earth iron garnet single crystal to start an epitaxial growth process. At this point, it is preferable that the composition formula of a bismuth-substituted rare earth iron garnet single crystal is represented by (RBi)3 (FeA)5 O12 (R denotes an element selected out of Y, La, Ce, Pr, Nb, Sm and the like). By this setup, an alternating-current magnetic field measuring Faraday rotor can be kept high in linearity of sensitivity to a very weak alternating-current magnetic field.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bismuth-substituted rare earth iron garnet single crystal film used as a Faraday rotator for a current sensor. More specifically, the present invention relates to a bismuth-substituted rare earth iron garnet single crystal film having a wide dynamic range.

[0002]

2. Description of the Related Art In recent years, devices such as an optical-optical isolator using a rare-earth iron garnet single crystal film having a large Faraday effect and an optical magnetic field sensor also called an optical current sensor or an optical rotation sensor have been put into practical use one after another. The development of rare earth iron garnet single crystal films tailored to the application is also being actively pursued. The Faraday effect is a type of magneto-optical effect, and refers to a phenomenon in which the plane of polarization of light transmitted through a material exhibiting the Faraday effect, that is, a Faraday element (Faraday rotator) such as a rare-earth iron garnet single crystal film is rotated. Then, the magnitude of the rotation angle of the polarization plane increases in proportion to the magnetization intensity of the Faraday element. This is shown in FIG. The detection of the magnetic field by the photocurrent sensor is to detect the difference in the Faraday rotation angle in the linear region between the origin o and the saturation point a as the light intensity.

A photocurrent sensor is generally configured as shown in FIG. That is, reference numeral 1 denotes a polarizer made of rutile, etc.
Reference numeral 2 denotes a Faraday rotator made of a rare-earth iron garnet single crystal film or the like, and reference numeral 3 denotes an analyzer made of rutile or the like.
In FIG. 2, the light transmitted through the polarizer 1 becomes linearly polarized light, and then the plane of polarization is rotated by the Faraday rotator 2. The light transmitted through the Faraday rotator 2 then transmits through the analyzer 3, and the light intensity changes according to the Faraday rotation angle. Normally, the rotation of the plane of polarization by the Faraday rotator changes almost linearly below the saturation magnetic field in accordance with the external magnetic field intensity applied to the Faraday rotator (see FIG. 1). Therefore, by measuring the light intensity after transmission through the analyzer, the intensity of the external magnetic field applied to the Faraday rotator is detected.

[0004]

In recent years, a Faraday rotator having good linearity with respect to an external magnetic field has been demanded because of the need for a sensor having a wider dynamic range. However, the bismuth-substituted rare earth iron garnet single crystal film manufactured by the liquid phase epitaxial method has a serious problem that the sensitivity is reduced with respect to an alternating magnetic field of several Oersteds or less. Specifically, 1 Oe to 10 Oe
Within this range, it is desired that the deviation from the linearity of the sensitivity be within 20%, but at present there is a deviation of 20% or more.

The cause of the deterioration of the sensitivity linearity is not clear, but is presumed as follows in connection with the magnetic domain structure of the bismuth-substituted rare earth iron garnet single crystal film. As shown in FIG. 3, the magnetic domain structure of the rare-earth iron garnet has a so-called multi-domain structure in which regions A having upward magnetization directions and regions B having downward magnetization lines are alternately arranged (state 1). The magnetic domain A has a certain Faraday rotation angle (+ θf). On the other hand, the magnetic domain B has the same Faraday rotation angle and the absolute value as the magnetic domain A, but has the opposite sign (−θf).

When a magnetic field is applied from the outside in the same direction as the region A, the area of the region A gradually increases (state 2).
Finally, the magnetic domains disappear, and all the magnetizations are aligned in the plus direction (state 3). As described above, the Faraday rotation angle increases in proportion to the external magnetic field. However, the reason for the increase in the Faraday rotation angle is that the area of + θf eventually increases,
This corresponds to the decrease in the area of -θf.
Therefore, it is considered that the decrease in the sensitivity linearity indicates that the magnetic domain width is not increased or decreased linearly with respect to the magnetic field.

[0007]

SUMMARY OF THE INVENTION The present inventors have found that when a bismuth-substituted rare earth iron garnet single crystal film grown on a non-magnetic garnet substrate by a liquid phase epitaxial method is used for a Faraday rotator, a few Oersted or less is obtained. As a result of intensive studies to solve the big problem that the linearity of sensitivity deteriorates with respect to the AC magnetic field, we obtained useful knowledge that the plane orientation of the non-magnetic garnet substrate is a very important factor, Further, the present inventors completed the invention of the present application through research and examination.

That is, the present invention uses a bismuth-substituted rare earth iron garnet single crystal film grown on a non-magnetic garnet substrate having a tilt within 0.5 degrees from the (111) plane orientation by a liquid phase epitaxial method. This is a Faraday rotator for AC magnetic field measurement. A non-magnetic garnet substrate for growing a bismuth-substituted rare earth iron garnet single crystal film must have a plane orientation within 0.5 degrees from (111).
If it exceeds 0.5 degree, the sensitivity of the bismuth-substituted rare earth iron garnet single crystal film in an alternating magnetic field is 20% or more in a magnetic field of 1 Oe to 10 Oe, and deviation from linearity occurs.

In carrying out the present invention, the composition of the Faraday rotator, that is, the bismuth-substituted rare earth iron garnet single crystal film is not particularly limited, but the general formula: (RBi) ₃ (FeA) ₅ O
₁₂ (where R is Y, La, Ce, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, E
r is at least one selected from the group consisting of r, Tm, Yb, and Lu, and A is
It is at least one selected from the group consisting of Ga, Sc, Al, and In. ] Is preferred. When practicing the present invention, the non-magnetic garnet substrate type is not particularly limited, but can be doped with a large amount of bismuth,
And transparent in the near infrared region, lattice constant is 1.2495 ± 0.0005nm
The (GdCa) ₃ (GaMgZr) ₅ O ₁₂ substrate is particularly preferred.

[0010]

The present invention will be specifically described below with reference to examples and comparative examples. Example 1 Lead oxide (PbO, 4N) 4,500 g, bismuth oxide (Bi ₂ O ₃ , 4N) 5,
230 g, ferric oxide (Fe ₂ O ₃ , 4N) 666 g, boron oxide (B ₂ O ₃ , 5N
N) 230 g, terbium oxide (Tb ₂ O ₃ , 3N) 68.0 g and gallium oxide (Ga ₂ O ₃ , 3N) 42.0 g are heated and melted in a 2,000 ml platinum crucible to grow a bismuth-substituted rare earth iron garnet single crystal It was used as a melt. On the surface of the melt obtained here,
According to a conventional method, the thickness is 500 μm and the lattice constant is 1.2497.
One side of a garnet single crystal [(GdCa) ₃ (GaMgZr) ₅ O ₁₂ ] substrate having a tilt of ± 0.0002 nm and a tilt of 0.3 degrees or less from the (111) substrate plane orientation was brought into contact with the substrate to perform epitaxial growth. And
A Tb _1.7 Bi _1.3 Fe _4.6 Ga _0.4 O ₁₂ single crystal film (hereinafter referred to as “G film-1”) having a thickness of 72 μm was obtained. The composition analysis was performed by a plasma emission analysis method.

The G film-1 was cut into 2 mm × 2 mm, and FIG.
The magnetic characteristics were measured by using the AC magnetic field characteristic evaluation device of the above. In FIG. 4, reference numeral 4 denotes a semiconductor laser light source having a wavelength of 830 nm, reference numeral 5 denotes a Glan-Thompson prism as a polarizer, reference numeral 6 denotes a G film-1 cut into 2 mm × 2 mm, reference numeral 7 denotes a Helmholtz coil, and reference numeral 8 denotes Ammeter, reference numeral 9 is a stabilized power supply, reference numeral 10 is a fan cushion generator,
Reference numeral 11 denotes a Gauss meter for measuring a magnetic field, reference numeral 12 denotes a Glan-Thompson prism as an analyzer, reference numeral 13 denotes a photodiode, reference numeral 14 denotes a voltmeter, reference numeral 15 denotes an amplifier, and reference numeral 16 denotes an oscilloscope. The Glan-Thompson prism 5 and the Glan-Thompson prism 12 are arranged at an angle of 45 degrees with respect to each other.

830 emitted from the semiconductor laser light source 4
The light of nm passes through the Glan-Thompson prism 5 to become linearly polarized light, and enters the G film-1. Current is supplied to the Helmholtz coil 7 from a stabilized power supply, and as a result, an AC magnetic field is applied to the G film-1. This alternating magnetic field is measured by the Gauss meter 11. The laser beam transmitted through the G film-1 then passes through the Glan-Thompson prism 12 and reaches the photodiode 13. The voltage generated by the photodiode 13 is taken into an oscilloscope via the amplifier 14 and detected as an output value. The above is the measurement method. The measurement results are shown in FIG. Figure 5 shows the alternating magnetic field (Oe) at a frequency of 230 Hz
3 shows the output (mV) with respect to. FIG. 6 shows the deviation from the sensitivity (= output / magnetic field) normalized at 20 Oe. In the G film-1, the maximum deviation in sensitivity in a magnetic field of 1 Oe or more was -15%.

Example 2 Lead oxide (PbO, 4N) 1,66 was added to a platinum crucible having a capacity of 1,000 ml.
0 g, bismuth oxide (Bi ₂ O ₃ , 4N) 1,160 g, ferric oxide (Fe ₂
O ₃ , 4N) 175 g, boron oxide (B ₂ O ₃ , 5N) 74.0 g, gadolinium oxide (Gd ₂ O ₃ , 3N) 10.3 g, yttrium oxide (Y ₂ O ₃ , 3
N) 6.4 g and gallium oxide (Ga ₂ O ₃ , 3N) 39.0 g were charged. This is installed at a predetermined position in a precision vertical tubular electric furnace,
The mixture was sufficiently dissolved and stirred at 1,000 ° C to obtain a melt for growing a bismuth-substituted rare earth iron garnet single crystal.

A garnet single crystal [(GdCa) having a thickness of 500 μm, a lattice constant of 1.2497 ± 0.0002 nm, and a tilt of less than 0.3 ° from the (111) substrate plane orientation is formed on the surface of the melt obtained in a conventional manner. ) ₃ (GaMgZr) ₅ O ₁₂ ]
Epitaxial growth was performed. And Gd with a thickness of 65 μm
_0.8 Y _0.8 Bi _1.4 Fe _4.0 Ga _1.0 O ₁₂ single crystal film (hereinafter “G film-2”)
To be described). The composition analysis was performed by a plasma emission analysis method. Next, the G film-2 was cut into 2 mm × 2 mm, applied to the magnetometer shown in FIG. 4, and the sensitivity was measured exactly as in Example 1. As a result, the maximum sensitivity shift in a magnetic field of 1 Oe or more was -18%.

COMPARATIVE EXAMPLE 1 Except that the [(GdCa) ₃ (GaMgZr) ₅ O ₁₂ ] substrate has a (110) plane orientation, a thickness of 60
A Tb _1.7 Bi _1.3 Fe _4.6 Ga _0.4 O ₁₂ single crystal film (hereinafter, referred to as “G film-C1”) having a thickness of μm was obtained.
And the sensitivity was measured in exactly the same manner as in Example 1. As a result, the maximum sensitivity shift in a magnetic field of 1 Oe or more was -44%.

Comparative Example 2 A thickness of 75 μm was obtained in exactly the same manner as in Example 1 except that the plane orientation of the [(GdCa) ₃ (GaMgZr) ₅ O ₁₂ ] substrate was inclined at 5 degrees from (111). Thus, a Tb _1.7 Bi _1.3 Fe _4.6 Ga _0.4 O ₁₂ single crystal film (hereinafter referred to as “G film-C2”) was obtained.
Was cut into 2 mm × 2 mm, and the sensitivity was measured exactly as in Example 1. As a result, the maximum sensitivity shift in a magnetic field of 1 Oe or more was -36%.

Comparative Example 3 The [(GdCa) ₃ (GaMgZr) ₅ O ₁₂ ] substrate has a plane orientation of 0.5 from (111).
A Tb _1.7 Bi _1.3 Fe _4.6 Ga _0.4 O ₁₂ single crystal film (hereinafter, referred to as “G film-C3”) having a thickness of 75 μm was obtained in exactly the same manner as in Example 1 except that the film was tilted. Then, G film-C3
Was cut into 2 mm × 2 mm, and the sensitivity was measured exactly as in Example 1. As a result, the maximum sensitivity shift in a magnetic field of 1 Oe or more was -23%.

Comparative Example 4 The [(GdCa) ₃ (GaMgZr) ₅ O ₁₂ ] substrate has a plane orientation of 0.5 from (111).
A Gd _0.8 Y _0.8 Bi _1.4 Fe _4.0 Ga _1.0 O ₁₂ single crystal film (hereinafter referred to as “G film-C4”) having a thickness of 63 μm was obtained in exactly the same manner as in Example 2 except that the film was tilted. Then, the G film-C4 was cut into 2 mm × 2 mm, and the sensitivity was measured in exactly the same manner as in Example 1. As a result, the maximum sensitivity deviation in a magnetic field of 1 Oe or more was −25%. Was.

[0019]

According to the present invention, the linearity of sensitivity is maintained even at an extremely low AC magnetic field, so that an optical magnetic field sensor having a wide dynamic range can be constructed.

[Brief description of figures]

FIG. 1 is a schematic diagram showing a change in a Faraday rotation angle with respect to an external magnetic field in a Faraday rotator.

FIG. 2 is a diagram illustrating an example of a current sensor using the Faraday effect.

FIG. 3 is a schematic view showing a state of magnetic domains of a bismuth-substituted rare earth iron garnet single crystal film.

FIG. 4 is a schematic diagram showing an apparatus for measuring the sensitivity of a bismuth-substituted rare earth iron garnet single crystal film in an alternating magnetic field.

FIG. 5 is a schematic diagram showing an example of a relationship between an AC magnetic field and an output when a bismuth-substituted rare earth iron garnet single crystal film is used as a Faraday rotator.

FIG. 6 is a schematic diagram illustrating an example of a relationship between an AC magnetic field and sensitivity when a bismuth-substituted rare earth iron garnet single crystal film is used as a Faraday rotator.

[Explanation of symbols]

1: polarizer, 2: Faraday rotator, 3: analyzer, 4:
Semiconductor laser, 5: Glan Thompson prism, 6: G
Membrane, 7: Helmholtz coil, 8: ammeter, 9: stabilized power supply, 10: fan cushion generator, 11: Gauss meter, 12: Glan-Thompson prism, 13: photodiode, 14: amplifier, 15: oscilloscope

Claims (1)

[Claims] An alternating magnetic field using a bismuth-substituted rare earth iron garnet single crystal film grown on a nonmagnetic garnet substrate having a tilt within 0.5 degrees from the (111) plane orientation by a liquid phase epitaxial method. Faraday rotator for measurement.