JPH0982523A - Faraday rotator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reducing magnetic hysteresis and identifying easily and magnitude of the magnetic hysteresis in a bismuth-substituted rare- earth iron garnet single-crystal film having very low saturation magnetic field but hardly used as a photoswitch or a Faraday rotator for a magnetic field sensor because of its higher magnetic hysteresis. SOLUTION: A bismuth-substituted rare-earth garnet single crystal is grown in such a state that five or more pits remain in a Faraday rotator when the Faraday rotator is formed by cutting the bismuth-substituted rare-earth garnet single crystal. Then, the magnetic hysteresis is reduced in the bismuth-substituted rare-earth garnet single crystal that has been hardly used as an optical switch or a Faraday rotator for a field sensor, and at the same time a Faraday rotator with large magnetic hystreresis can be identified easily. Then, the bismuth- substituted rare-earth garnet single crystal with low saturation magnetization can be utilized as a Faraday rotator for an optical field sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Faraday rotator composed of a bismuth-substituted rare earth iron garnet single crystal film having a very low saturation magnetic field. Specifically, the present invention relates to a method for producing a bismuth-substituted rare earth iron garnet single crystal film having a small magnetic hysteresis despite a very low saturation magnetic field, and a Faraday rotator for an optical magnetic field sensor using the same.

[0002]

2. Description of the Related Art In recent years, a bismuth-substituted rare earth iron garnet single crystal film having a large Faraday effect (hereinafter referred to as "BIG
Devices called "optical film sensors" and optical magnetic field sensors, which are also called photocurrent sensors and optical rotation sensors, have been put to practical use one after another, and BIGs adapted to these applications have been developed.
Membranes are also being actively developed. 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.

Generally, the rotation angle of the plane of polarization in the Faraday rotator is called the Faraday rotation angle, which increases in proportion to the strength of the external magnetic field applied to the Faraday element.
However, the above description regarding the Faraday rotation angle is applicable to the weak magnetic material such as lead glass, and is not necessarily appropriate as the description of the Faraday rotation angle of the BIG film which is a ferromagnetic material. The reason is that the BIG film is a multi-domain material composed of many magnetic domains. Hereinafter, changes in the Faraday rotation angle and the magnetic domain structure in the BIG film with respect to the external magnetic field strength will be described.

FIG. 1 shows changes in the magnetic domain structure of the BIG film in response to an external magnetic field. State 1 in FIG. 1 is BI
The film cross section of the G film is shown, and is composed of magnetic domains having a width of several microns to several tens of microns. The magnetic domains A in which the magnetization direction is upward and the magnetic domains B in which the magnetization direction is downward are alternately arranged. Each magnetic domain has a Faraday rotation angle with a different sign but the same absolute value. That is, assuming that the magnetization of the magnetic domain A is (+ M) and the Faraday rotation angle (+ θf), the magnetization and the Faraday rotation angle of the magnetic domain B are -M and -θf, respectively. For convenience, the plus sign of the Faraday rotation angle indicates that the polarization plane rotates clockwise, and the minus sign indicates the counterclockwise rotation. Further, regarding the magnetization and the Faraday rotation angle, in the following description, the magnetization of the entire material (= BIG film) is distinguished as [magnetization] and the sign (Mt), and the Faraday rotation angle is defined as the [Faraday rotation angle] and the sign [θt]. To do.

In FIG. 1, the state 1 is a case where no external magnetic field is applied. When an upward external magnetic field is applied to this, the magnetic domain structure changes from state 1 to state 2. That is, the area of the magnetic domain A having the same magnetization as the direction of the external magnetic field increases. Then, when the external magnetic field is further strengthened, the state 3 in which the magnetic domain B finally disappears, that is,
It becomes a single magnetic domain. This is the magnetically saturated state. Similarly, when the external magnetic field is directed downward, the state goes through the state 4 to the state 5 and is saturated.

The [magnetization] of the BIG film in the state 3 is Mt =
+ M, [Faraday rotation angle] is the Faraday rotation angle of domain A
It is equal to + θf and θt = + θf. In the state 5, Mt = -M, θt = -θf. The [magnetization] of the entire BIG film in the state 2 or the state 4 in which the magnetic domains A and B are mixed is expressed by the following equation (1) from the volume ratio (Va) of the magnetic domains A. Mt = + M x Va + (-M) x (1-Va) (1)

On the other hand, state 1 in which magnetic domain A and magnetic domain B are mixed,
BI in 2 or state 4, so-called multi-domain state
What is the formula for the [Faraday rotation angle] for the G film as a whole? The details are given in Tanagzawa et al., Japan Society for Applied Magnetics 14,648-652 (1990), but the [Faraday rotation angle] in state 1, 2 or state 4 in which magnetic domain A and magnetic domain B are mixed is not uniquely determined. It depends on the measurement method.

An ordinary method for measuring the Faraday rotation angle, that is, linearly polarized light is radiated and the transmitted light is received by the analyzer, and the light intensity transmitted through the analyzer is minimized while rotating the analyzer. For the method of determining the rotation position of,
[Θt] is given by the following equation (2) with the saturation magnetization of the material being (Ms). θt = Tan ^-1 (Mt / Ms × tanθf) (2) Mt changes according to the external magnetic field strength. The relationship between θt and the external magnetic field exhibits the behavior as shown in FIG. 2, for example. However, it should be noted that even with the same material, the shape of the curve changes depending on the magnitude of θf. That is, the true Faraday rotation angle in the multi-domain structure cannot be defined except in the saturated state, and is merely an apparent value.

[Faraday rotation angle] in a multi-domain structure such as a BIG film is measured as an apparent value, but it can be understood as a reflection of the magnetic domain structure. Therefore, the change in the apparent Faraday rotation angle of the BIG film with respect to the external magnetic field, that is, the so-called Faraday loop will be described with reference to FIG. In FIG. 2, the Faraday rotation angle of the Faraday rotator when no external magnetic field [strength] is applied is zero.

[0], that is, located at the origin o. This state is state 1 in FIG.

When the external magnetic field is gradually strengthened, the apparent Faraday rotation angle passes through the route a or the route d and gradually approaches the value when it is saturated [route o → a → b or route o → d → e]. This state (route a or route d) is shown in FIG.
Corresponds to the state 2 or the state 4. When the external magnetic field strength reaches a certain strength [Hs], the Faraday rotation angle becomes a saturated value [saturation magnetic field, point b or point e]. Even if the external magnetic field strength increases, it is already saturated, so b to c,
Alternatively, the [Faraday rotation angle] does not change but only changes from d to f. This state corresponds to the state 3 or the state 5 in FIG. Next, when the external magnetic field is gradually weakened, the reverse path, that is, c → b → a → o or f →
The route e → d → o is traced, and finally the origin o is returned to the point where there is no influence of the external magnetic field.

There are optical switches and magnetic field sensors that utilize the external magnetic field dependence characteristics of the state change of the magnetic domains as described above. The optical switch has a saturation point b and a saturation point e in FIG.
The above magnetic field is generated and switched by a magnetic field generator, and the detection of the magnetic field by the photocurrent sensor is performed by detecting the difference in the apparent Faraday rotation angle in the region between the origin o and the saturation point b (or The change in magnetic domain structure) is detected as the light intensity. The detection of the strength of the magnetic field by the optical magnetic field sensor, for example, the use as a rotation sensor is performed by using the origin o and the saturation point b or the saturation point c.
The difference in the apparent Faraday rotation angle (or the change in the magnetic domain structure) between and as the light intensity, or the difference in the apparent Faraday rotation angle between the origin o and the point a or point d reaching the saturation point b or c (or the magnetic domain structure). Change) is detected as the light intensity.

A tachometer using an optical magnetic field sensor, ie,
In the optical signal tachometer, a permanent magnet is attached to the rotating equipment (Applied Optics (Appli
edOptics), Vol. 28, No. 11, p. 1992 (1989)], and the range of influence of the magnetic field formed by this permanent magnet is BIG.
An optical magnetic field sensor made of a film is arranged. With the rotation of the rotating device, the optical magnetic field sensor and the permanent magnet repeat approaching and separating, but there is a difference in the magnetic field strength applied to the Faraday rotator when the permanent magnet approaches and when the permanent magnet separates. That is, due to the rotation of the permanent magnet, the magnetic domain structure changes, and as a result, the intensity of light passing through the analyzer changes. That is,
This is because the number of rotations and the rotation speed of the permanent magnet are captured as a change in light intensity.

In this case, as the distance between the permanent magnet and the optical magnetic field sensor head becomes longer, the magnetic field formed by the permanent magnet becomes weaker. Therefore, when a permanent magnet having a stronger magnetic force is used as a means for further increasing the sensitivity and accuracy of the tachometer utilizing the Faraday effect, selecting an optical magnetic field sensor head that exhibits a sufficient function even in a weak magnetic field, Furthermore, the distance between the permanent magnet and the optical magnetic field sensor head may be shortened.

Not only is it economically disadvantageous to replace the permanent magnet with one having a stronger magnetic force, but sometimes the shape of the permanent magnet becomes large and the installation place is restricted. The distance from the magnetic field sensor head becomes long, and the adverse effect such as the substantial improvement effect is not likely to occur. From these, a bismuth-substituted rare earth iron garnet single crystal film that is magnetically saturated at a lower magnetic field is required.
As described above, in the optical magnetic field sensor, a BIG film that saturates at a magnetic field as low as possible is desired from the viewpoint of performance or manufacturing cost.

On the other hand, the chemical formula R ₃ (FeA) ₅ O ₁₂ [wherein R means yttrium (Y), bismuth (Bi), or other rare earth elements, A is aluminum (Al), gallium (Ga), etc. The BIG film represented by [1] can be relatively easily manufactured by the liquid phase epitaxial (LPE) method. In particular, it is known that a bismuth-substituted iron garnet single crystal in which a part of rare earth is replaced with bismuth exhibits a very large Faraday effect.

The rare earth iron garnet single crystal used in the optical magnetic field sensor is desired to have a saturation magnetic field as low as possible from the viewpoint of sensitivity or manufacturing cost. Therefore, iron is usually replaced with an element such as aluminum or gallium. It is widely practiced. For example, (GdBi) ₃ (FeGaA
l) ₅ O ₁₂ and (HoTbBi) ₃ (FeGaAl) ₅ O ₁₂ etc.
6, see Japanese Patent Application No. 5-55621]. However, in the BIG film, the composition ratio of Al or Ga and Fe is changed,
When the saturation magnetic field is lowered, the magnetic hysteresis gradually increases, which is a very serious problem in practical use.

The magnetic hysteresis will be described below. In the description, the relationship between the external magnetic field strength and the apparent Faraday rotation angle as shown in FIG. 2 is used for the reason that it is easy to understand. Rare earth iron garnet single crystal with relatively high saturation magnetic field, for example (HoTbBi) ₃ F
The magnetization characteristic of the F ₅ O ₁₂ of the Faraday rotator with respect to the external magnetic field, that is, the relationship between the external magnetic field strength and the apparent Faraday rotation angle is represented by almost one curve with respect to the external magnetic field as shown in FIG. .

However, a rare earth-substituted iron garnet single crystal having a small saturation magnetic field, for example, (GdBi) ₃ (FeAlGa) ₅ O ₁₂ has a relationship between the external magnetic field strength and the Faraday rotation angle as shown in FIG.
, The path is o → a → b → c → b → b '→ a → o
Draw a hysteresis loop like. That is, when increasing the strength of the external magnetic field [path o → a → b → c]
And when weakening [route c → b → b ′ → a → o], the route is different. When weakening the external magnetic field, what should normally have a multi-domain structure like the state 2 or the state 4 in FIG. 1 in the region below the saturation magnetic field is the structure of the state 3 or the state 5 (single domain). Structure) is maintained temporarily.

In FIG. 3, the magnetic fields at the points b and e are called the saturation magnetic field Hs, and the magnetic fields at the points b'and e'caused by the hysteresis of the magnetization characteristic are called the nucleation magnetic field Hn. The difference from Hn (Hs-Hn) is defined as the size of hysteresis. The saturation magnetic field Hs at the point b is represented by Hs1, the nucleation magnetic field Hn at the point b'is represented by Hn1, the saturation magnetic field Hs at the point e is represented by Hs2, and the nucleation magnetic field Hn at the point e'is represented by Hn2. Here, the term “nucleation” means that some nuclei for transitioning from a single magnetic domain structure to multiple magnetic domains are generated.

When the hysteresis of the BIG film increases and the nucleation magnetic field Hn approaches the origin o, the magnetically saturated state (state 3 or state 5 in FIG. 1) is maintained until the external magnetic field becomes almost zero. Will be retained. Therefore, in the optical rotation sensor composed of the Faraday rotator having a large hysteresis, in order to detect the strength of the magnetic field strength, the magnetic field strength around and around the optical magnetic field sensor must be set to almost zero. However, the rotation sensor is generally installed inside the mechanical device, and the mechanical device material has a slight magnetic force. Therefore, it is quite difficult to use the magnetic field strength around and around the optical magnetic field sensor in a state where the magnetic field strength is substantially zero.

When the hysteresis of the BIG film is further increased, the nucleation magnetic field Hn1 enters the minus side beyond the origin o (FIG. 4) and the nucleation magnetic field Hn1 is saturated magnetic field Hs.
It is larger than 2 and draws a quadratic hysteresis curve (Fig. 5), and once it is saturated, it only draws this quadrangle loop, and the magnetic field required for saturation is larger than the original saturation magnetic field Hs of the BIG film. There is also. As described above, since the BIG film having a large hysteresis has a large magnetic field necessary for its saturation, it is very difficult to use it for the optical magnetic field sensor.

[0022]

DISCLOSURE OF THE INVENTION The present inventors have earnestly studied to develop a BIG film having no magnetic hysteresis.
As a result, we have found (YLaBi) ₃ (FeGa) ₅ O ₁₂ as having a very small magnetic hysteresis despite a low saturation magnetic field, as compared with the conventional BIG film. This is a general formula Y _3-xy La _x Bi _y Fe _5-z Ga _z O ₁₂ grown on a non-magnetic garnet single crystal substrate by a liquid phase epitaxial method (where x, y, z are 0.1 ≦ x ≦ 0.4, 1.0 ≦ y ≦ 1.9, 1.0 ≦
z ≦ 1.6] is a bismuth-substituted rare earth iron garnet single crystal film.

However, the above (YLaBi) ₃ (FeGa) ₅ O ₁₂
Was manufactured and finely cut into actual sizes (for example, 2 mm × 2 mm) for use as a Faraday rotator for magnetic field sensors, and the magnetic hysteresis of each cut product was measured. Or mixed. Then, it was found that the ratio of large magnetic hysteresis was different depending on the (YLaBi) ₃ (FeGa) ₅ O _{12 produced} .

When manufacturing a Faraday rotator, defective products having large magnetic hysteresis can be removed by measurement. However, since the measurement time of magnetic hysteresis is long, there is a problem in mass productivity (actually, the magnetic field strength applied to the Faraday rotator is gradually increased, and then the Faraday rotation angle is measured while weakening the magnetic field strength. There is a need). Further, since the device is relatively large in size, it leads to an increase in manufacturing cost. Therefore, it is desirable to be able to check defective products by a very simple method that does not rely on measurement of magnetic hysteresis. Furthermore, there is a strong demand for the development of a method for directly reducing the magnetic hysteresis as much as possible.

As described above in detail, since the BIG film having a low saturation magnetic field has a large magnetic hysteresis, when it is used for a Faraday rotator for an optical magnetic field sensor, a magnetic field generator for switching magnetic fields becomes large. At present, there are obstacles and restrictions such as increasing the strength of the permanent magnet attached to the rotating body and the very narrow magnetic field measurement range.

[0026]

Means for Solving the Problems The present inventors
As a result of measuring the magnetic hysteresis of each Faraday rotator in detail by manufacturing a large number of Faraday rotators by cutting the film, as described above, the magnitude of the magnetic hysteresis between Faraday rotators cut out from the same BIG film was increased. We obtained an interesting fact that the BIG films have different magnetic properties, or the ratio of occurrence of large magnetic hysteresis differs among several BIG films. As a result of a detailed study of the results, the inventors of the present invention have found that the magnetic hysteresis becomes large when the Faraday rotator for magnetic field sensor cut out from the BIG film has few or no pits (a kind of defects). I got a very interesting finding. Further, experiments and measurements were repeated to complete the present invention.

That is, the present invention provides a Faraday rotator manufactured from a bismuth-substituted rare earth iron garnet single crystal film grown by a liquid phase epitaxial method on a non-magnetic garnet single crystal substrate. The Faraday rotator is characterized by including at least five pits, which are a type of crystal defect. In addition, the bismuth-substituted rare earth iron garnet single crystal film was grown by a liquid phase epitaxial method on a non-magnetic garnet single crystal substrate; R _3-x Bi _x Fe _5-y A _y O ₁₂ [where R Is at least one selected from Y and rare earth elements, and A is at least one selected from Ga and Al. x and y are 0.8 ≦ x ≦ 1.9 and 0.5 ≦ y ≦, respectively.
It has a chemical composition of 1.6.

The present invention will be described below. First, the background of the phenomenon that the magnitude of magnetic hysteresis differs depending on the presence or absence of pits is not clear, and future research and experiment results
We have to wait for results. But anyway,
The knowledge that the size of magnetic hysteresis can be estimated by the number of pits is very significant in industrial production. That is, it is possible to distinguish between a good product and a defective product of the Faraday rotator by the number of pits, and a bismuth-substituted rare earth iron garnet single crystal film (BIG film) with less magnetic hysteresis.
This means that the manufacturing index of

The number of pits in the Faraday rotator can be observed with a microscope or an infrared microscope. If the BIG film is thin, specifically 100 μm or less, the pits can be easily observed with a microscope. Also, the BIG film is 100 μm
With the above thickness, some pits are buried and cannot be observed with an ordinary microscope. However, pits inside the crystal can be observed with an infrared microscope.

In the present invention, the pit is a Faraday rotator obtained by cutting the BIG film (normal size is 1 mm × 1 m).
There should be at least 5 or more in 5 mm x 5 mm from m.
If the number is 5 or less, defective products due to magnetic hysteresis [In the present invention, magnetic hysteresis (saturation magnetic field Hs and nucleation magnetic field Hn
Difference) is 80% or more of the saturation magnetic field is defined as a defective product. As a Faraday rotator with reduced magnetic hysteresis, there is no particular upper limit on the number of pits. However, if the number of pits increases, the light transmittance will decrease and the light scattering will increase. Therefore, it is appropriately determined according to the system of the optical magnetic field sensor.

The BIG film of the present invention has a general formula of R _3-x Bi _x Fe _5-y A _y O ₁₂ grown on a non-magnetic garnet single crystal substrate by a liquid phase epitaxial method; 1 or 2 selected from the group consisting of Y and rare earth elements
More than one element, A is at least one selected from Ga and Al. Also, x and y are 0.8 ≦ x ≦ 1.9, respectively.
, 0.5 ≦ y ≦ 1.6] is preferable, and the Faraday effect is large and the saturation magnetic field is low. Further, as a BIG film, a general formula: Y
_3-xy La _x Bi _y Fe _5-z Ga _z O ₁₂ (However, x, y, z are
0.1 ≦ x ≦ 0.4, 1.0 ≦ y ≦ 1.9, 1.0 ≦ z ≦ 1.6], which has a large Faraday effect and a low saturation magnetic field and is suitable as a Faraday rotator material for magnetic field sensors. is there.

In the present invention, there is no particular limitation as long as it is a method capable of causing a predetermined pit to appear in the manufactured BIG film. However, empirically, contamination of the BIG film growth substrate, liquid phase epitaxial growth with an increased degree of supersaturation,
For example, the difference in lattice constant with the substrate is enlarged. When the substrate for growth is contaminated, normal epitaxial growth cannot be performed from the contaminated part, and pits increase. It is well known that pits increase with increasing supersaturation. Further, if the lattice constant difference from the substrate for growth is increased, stress is generated between the substrate and the BIG film, and pits are likely to appear.

Hereinafter, the present invention will be described in detail and specifically by way of its embodiments and effects, and the following examples will specifically describe the embodiments and effects of the present invention. It is not intended to limit the scope of the invention.

[0034]

【Example】

Example 1 A platinum crucible having a capacity of 1,000 ml (milliliter) was charged with lead oxide (PbO,
4N) 1,260 g, bismuth oxide (Bi ₂ O ₃ , 4N) 1,260 g, ferric oxide (Fe ₂ O ₃ , 4N) 195 g, boron oxide (B ₂ O ₃ , 5N) 68 g, yttrium oxide (Y ₂ O ₃ , 3N) 10.8 g, lanthanum oxide (La
₂ O _3, 3N) 11.0g, was charged with gallium oxide _{(Ga 2 O 3, 3N)} 52g. This was placed in a predetermined position in a precision vertical tubular electric furnace, heated and melted at 1000 ° C, thoroughly stirred and uniformly mixed, and then cooled to a melt temperature of 761 ° C to cool the bismuth-substituted rare earth magnetic garnet unit. The melt was used for crystal growth.

On the surface of the melt thus obtained, the thickness was 500 μm and the lattice constant was 1.2497 ± 0.0002 n according to a conventional method.
2-inch (111) Garnet Single Crystal [(GdCa) ₃ (GaMgZr) of m
One side of the ₅ O ₁₂ ] substrate was brought into contact with the substrate, and epitaxial growth was performed for 2 hours while maintaining the melt temperature at 761 ° C. and the substrate rotation speed at 60 rpm. 65 μm thick (YLaBi) ₃ (FeGa) ₅ O ₁₂
A single crystal film (= YLBG film-1) was obtained.

Next, this YLBG film-1 was divided into a size of 10.5 mm × 10.5 mm to obtain 12 pieces. Select any 4 pieces out of 12 pieces of 10.5 mm x 10.5 mm divided product, and have a wavelength of 0.78μ on both sides.
An antireflection film corresponding to m was applied, and then cut into 2 mm x 2 mm to obtain a Faraday rotator for the 0.78 µm wavelength band. A total of 100 Faraday rotators were obtained. For these 100 Faraday rotators, the pit count and magnetic properties were measured and the relationship between them was investigated.

For magnetic measurement, the following method was adopted. First, 2
A Faraday rotator having a size of mm × 2 mm was placed at the center of a magnetic field generator composed of Helmholtz coils manufactured by Magnetec Co., Ltd., and a semiconductor laser beam of 0.786 μm was applied to the Faraday rotator while applying a magnetic field. Then, the dependence of the Faraday rotation angle on the applied magnetic field was investigated by measuring the rotation angle of the plane of polarization of the laser light transmitted through the Faraday rotator. The results are shown together in FIG. 5 (data with more than 10 pits is omitted).

The saturation magnetic field of the YLBG film-1 was 250 Oe (Oersted). In order to distinguish good products from bad products by magnetic hysteresis, the line where the nucleation magnetic field Hn shows 20% of the saturation magnetic field,
That is, Hn of 44 Oe or more was determined as a good product, and Hn of less than 44 Oe was determined as a defective product. When the number of pits is 4 or less, rejected products occur, whereas when the number of pits is 5 or more, rejected products are not seen at all (the data for 11 or more pits are not listed, but the rejected products are There was none). After all, out of 100 Faraday rotators measuring 2 mm x 2 mm, 85 contained 5 or more pits, which were all good products.

Example 2 Lead oxide (PbO, 4N) 1,26 was added to a platinum crucible having a capacity of 1,000 ml.
0 g, bismuth oxide (Bi ₂ O ₃ , 4N) 1,260 g, ferric oxide (Fe ₂
O _3, 4N) 190g, boron oxide _{(B 2 O 3, 5N)} 45g, gadolinium oxide _{(Gd 2 O 3, 3N)} 21.0g, gallium oxide (Ga ₂ O _3, 3N)
4.0 g and 8.5 g of aluminum oxide (Al ₂ O ₃ , 3N) were charged.
Place this in a predetermined position in a precision vertical tubular electric furnace and
The mixture was heated and melted at 0 ° C., sufficiently stirred and uniformly mixed, and then cooled to a melt temperature of 776 ° C. to obtain a bismuth-substituted rare earth magnetic garnet single crystal growing melt.

On the surface of the melt thus obtained, 2 having a thickness of 500 μm and a lattice constant of 1.2497 ± 0.0002 nm was prepared by a conventional method.
Inch (111) garnet single crystal [(GdCa) ₃ (GaMgZr) ₅ O ₁₂ ]
One side of the substrate was brought into contact with each other, and epitaxial growth was carried out for 2 hours while maintaining the melt temperature at 776 ° C and the substrate rotation speed at 60 rpm. However, the substrate rotation speed was set to 75 rpm for 10 minutes 1 hour after the start of crystal growth. 49 μm thick (GdBi) ₃
A (FeGaAl) ₅ O ₁₂ single crystal film (= GBGA film-1) was obtained.

Next, this GBGA film-1 was divided into a size of 10.5 mm × 10.5 mm to obtain 12 pieces. Select any 4 pieces out of 12 pieces of 10.5mm x 10.5mm, wavelength 0.78μm on both sides
A corresponding antireflection film was applied and then cut into 2 mm x 2 mm to prepare a Faraday rotator for the 0.78 µm wavelength band. A total of 100 Faraday rotators were obtained. The saturation magnetic field of GBGA film-1 is
It was 290 Oe. With respect to the 100 Faraday rotators, the number of pits and magnetic characteristics were measured by the same method as in Example 1. As a result, of 100 Faraday rotators measuring 2mm x 2mm, 78 contained 5 or more pits,
Everything was good. On the other hand, 32 Faraday rotators with less than 5 pits were obtained, of which 26 were defective.

Example 3 Lead oxide (PbO, 4N) 4,20 was added to a platinum crucible having a capacity of 3,000 ml.
0g, bismuth oxide (Bi ₂ O ₃ , 4N) 4,900g, ferric oxide (Fe ₂
O _3, 4N) 650g, boron oxide _{(B 2 O 3, 5N)} 150g, gadolinium oxide _{(Gd 2 O 3, 3N)} 80g, gallium oxide _{(Ga 2 O 3, 3N)} 61
Charged g. This was placed in a predetermined position in a precision vertical tubular electric furnace, heated and melted at 1,000 ° C, sufficiently stirred and mixed uniformly, and then cooled to a melt temperature of 790 ° C and cooled to a bismuth-substituted rare earth magnetic garnet unit. The melt was used for crystal growth.

On the surface of the melt thus obtained, 2 having a thickness of 500 μm and a lattice constant of 1.2497 ± 0.0002 nm was prepared by a conventional method.
Inch (111) garnet single crystal [(GdCa) ₃ (GaMgZr) ₅ O ₁₂ ]
Epitaxial growth was carried out for 22 hours while contacting one surface of the substrate and maintaining the melt temperature at 790 ° C and the substrate rotation speed at 60 rpm. However, when 16 hours passed after starting the crystal growth, the substrate rotation speed was set to 75 rpm for 10 minutes.
385 μm thick (TbBi) ₃ (FeGa) ₅ O ₁₂ single crystal film (= TBG film)
I got

Next, this TBG film was divided into a size of 10.5 mm × 10.5 mm to obtain 12 pieces. Arbitrary 3 pieces were selected from 12 pieces of 10.5 mm × 10.5 mm pieces, the substrate was removed by polishing, and the thickness was set to 324 μm. Wavelength 1.31μ on both sides
An antireflection film corresponding to m was applied, and then cut into 1.6 mm × 1.6 mm to obtain a Faraday rotator for a wavelength band of 1.31 μm. A total of 108 Faraday rotators were obtained. The saturation magnetic field of the TBG film was 340 Oe. With respect to the 108 Faraday rotators, the number of pits was counted (using an infrared microscope) and the magnetic properties were measured in the same manner as in Example 1. As a result, a Faraday rotator with a size of 1.6 mm × 1.6 mm 1
Of the 08 pieces, 92 pieces contained 5 or more pits, which were all good products. On the other hand, 8 Faraday rotators with less than 5 pits were obtained, of which 5 were defective.

Comparative Example 1 A platinum crucible having a capacity of 1,000 ml was charged with lead oxide (PbO, 4N) 1,26
0 g, bismuth oxide (Bi ₂ O ₃ , 4N) 1,470 g, ferric oxide (Fe ₂
O ₃ , 4N) 195 g, boron oxide (B ₂ O ₃ , 5N) 38 g, yttrium oxide (Y ₂ O ₃ , 3N) 10.8 g, lanthanum oxide (La ₂ O ₃ , 3N) 1
1.0 g and gallium oxide (Ga ₂ O ₃ , 3N) 36 g were charged. This is installed in the predetermined position of the precision vertical tubular electric furnace, and 1,000
After melting by heating to ℃ and stirring thoroughly to mix uniformly,
The melt was cooled to 755 ° C. to obtain a melt for growing a bismuth-substituted rare earth magnetic garnet single crystal.

On the surface of the melt thus obtained, 2 with a thickness of 500 μm and a lattice constant of 1.2497 ± 0.0002 nm was used according to a conventional method.
Inch (111) garnet single crystal [(GdCa) ₃ (GaMgZr) ₅ O ₁₂ ]
One surface of the substrate was brought into contact with the substrate, the melt temperature was maintained at 755 ° C., and the epitaxial rotation was performed for 2 hours while the substrate rotation speed was 60 rpm. A 57 μm thick (YLaBi) ₃ (FeGa) ₅ O ₁₂ single crystal film (= YLBG film-2) was obtained.

Next, this YLBG film-2 was treated in exactly the same manner as in Example 1 to obtain 100 Faraday rotators of 2 mm × 2 mm. The number of pits and the magnetic properties of the 100 Faraday rotators were measured. As a result, there were 10 Faraday rotators containing 5 or more pits, which were all good products. There were 90 Faraday rotators with 4 or less pits, of which 12 were good.

Comparative Example 2 In Example 2, the substrate rotation speed during crystal growth was 60 r.p.
The thickness is 43 μm under exactly the same conditions except that the m.
A (GdBi) ₃ (FeGaAl) ₅ O ₁₂ single crystal film (= GBGA film-2) was obtained.
Next, this GBGA film-2 was processed in exactly the same manner as in Example 2, and the number of pits and magnetic characteristics were measured. As a result, the number of Faraday rotators containing 5 or more pits was 5, and all were good products. Also, Faraday rotator with 4 or less pits is 95
Of these, 5 were good products.

[0049]

According to the present invention, even if a bismuth-substituted rare earth iron garnet single crystal film having a low saturation magnetic field, magnetic hysteresis is suppressed, and a defective product having a large magnetic hysteresis is simply identified by measuring the number of pits. This facilitates the manufacture of a Faraday rotator for an optical magnetic field sensor.

[Brief description of drawings]

FIG. 1 Bismuth-substituted rare earth iron garnet single crystal film (B
FIG. 4 is a schematic diagram showing an example of a change in magnetic domain structure of an IG film) with respect to an external magnetic field strength.

FIG. 2 is a schematic diagram showing an example of magnetic characteristics of a BIG film showing no magnetic hysteresis.

FIG. 3 is a schematic diagram showing an example of magnetic characteristics of a BIG film showing magnetic hysteresis.

FIG. 4 is a schematic view showing an example of magnetic characteristics of a BIG film showing a large magnetic hysteresis.

FIG. 5 is a schematic diagram showing an example of magnetic characteristics of a BIG film forming a square hysteresis because the magnetic hysteresis is very large.

FIG. 6 is a schematic diagram showing the relationship between the number of pits and the nucleation magnetic field in the Faraday rotator in the first embodiment.

Claims (2)

[Claims] 1. A Faraday rotator manufactured from a bismuth-substituted rare earth iron garnet single crystal film grown by a liquid phase epitaxial method on a non-magnetic garnet single crystal substrate, wherein a type of crystal defect is present in the Faraday rotator. A Faraday rotator characterized by including at least 5 or more pits. 2. A general formula in which the bismuth-substituted rare earth iron garnet single crystal film is grown on a non-magnetic garnet single crystal substrate by a liquid phase epitaxial method; R _3-x Bi _x Fe _5-y A _y O ₁₂ [ However, R is one or more elements selected from the group consisting of Y and rare earth elements, and A is at least one selected from Ga and Al. Also, x and y are
Faraday rotator according to claim 1, having a chemical composition of 0.8≤x≤1.9 and 0.5≤y≤1.6.