JPH0769797A - Low saturation magnetic field bismuth substituted iron garnet single crystal - Google Patents

Abstract

(57) [Abstract] [Purpose] General formula Y _3-xy La _x Bi _y Fe _5-z Ga _z O ₁₂ [where x, y and z are 0.1 ≦ x ≦ 0.4 and 1.0 ≦ y ≦
A bismuth-substituted iron garnet single crystal having a chemical composition of 1.9, 1.0 ≦ z ≦ 1.6] is industrially provided at low cost. [Structure] Using a melt for single crystal growth composed of lead oxide, bismuth oxide, ferric oxide, boron oxide, yttrium oxide, lanthanum oxide, etc., it is grown by liquid phase epitaxial method on a non-magnetic garnet single crystal substrate. . [Effect] Excellent characteristics as a Faraday rotator for an optical magnetic field sensor, in particular, it has become possible to manufacture a bismuth-substituted iron garnet single crystal with a small hysteresis due to cutting and a small saturation magnetic field. The sensor head can be industrially manufactured at low cost and provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bismuth-substituted iron garnet single crystal for an optical magnetic field sensor utilizing the Faraday effect. More specifically, the present invention has excellent properties as a Faraday rotator for an optical magnetic field sensor head,
Moreover, the present invention relates to a bismuth-substituted iron garnet single crystal having a very small saturation magnetic field.

[0002]

2. Description of the Related Art At present, many general-purpose industrial equipments and consumer equipments have rotating devices such as motors and gears and rotating parts. Due to advances in science and technology, global environment protection, and increasing social concern and demand for energy conservation, operation control of industrial equipment, such as aircraft and ships, and consumer equipment, such as rotating equipment and devices such as passenger cars. Attempts have been made specifically to implement the above with higher accuracy.

As one of the concrete measures to meet the social demands for protection of the global environment and energy saving, various experimental studies have been attempted on a more sophisticated and highly accurate control method for rotating equipment and devices. As a result, the method that can achieve this research objective most easily is to measure the accurate rotation speed [number] of the rotating equipment / rotating device continuously and instantly, and control it at the rotation speed [number]. It became clear that it is a method to do. In order to easily achieve highly sophisticated and highly accurate control of rotating equipment / rotating device, in order to easily and accurately measure the rotational speed (number) of the rotating equipment / rotating device, it is simple and easy to measure. Lightweight and compact measuring devices must be provided and supplied at low cost and in large quantities.

Various methods of measuring the rotational speed have already been proposed, but the rotational speed meter utilizing electromagnetic induction is most widely adopted [Sensor Technology, December 1986, 68].
page〕. The tachometer using this electromagnetic induction has already been used for measuring and measuring the rotational speed [number] of aircraft and automobile engines. However, the tachometer using electromagnetic induction has a serious drawback that it is susceptible to electromagnetic influences, that is, noise, between the transmission line [cable] between the measurement terminal and the device body. . Therefore, naturally,
The distance between the installation environment and the signal transmission line, that is, the length of the transmission line [cable] is limited, making it unsuitable for telemetry and operation.
Further, since an electric circuit is used, explosion-proof measures are required when used in an environment where flammable substances such as organic solvents are handled.

Brian J. Z
[ook] proposed a method using an optical magnetic field sensor that utilizes the Faraday effect of a magneto-optical material [Applied
Optics [Applied Optics], Volume 28, No. 11,
1992 (1989)]. In the method using the optical magnetic field sensor utilizing the Faraday effect of the magneto-optical material, when the permanent magnet [magnetic field] approaches the optical magnetic field sensor, the rotation angle of the polarization plane of the magneto-optical material in the optical magnetic field sensor causes It utilizes that it changes depending on the presence or absence. That is, the method using the optical magnetic field sensor is to measure the rotation speed (number) by converting the rotation of the polarization plane of the light passing through the magneto-optical material in the optical magnetic field sensor into a change in the light intensity to detect and count. It is what

The optical magnetic field sensor is classified into a transmission type and a reflection type. Due to the nature of its components, the transmissive type is arranged so that the incident and transmitted directions of signal light are aligned.
Since they must be arranged, there is a restriction on the installation location, and depending on the purpose of use and the installation location, they cannot be installed or adopted.

[0007] Matsui et al. [JP-A-56-55811] proposes a reflection type optical magnetic field sensor as a structure for improving the drawbacks of the transmission type optical magnetic field sensor. In the reflection type optical magnetic field sensor proposed here, the input optical fiber and the output optical fiber of the signal light are on the same side with respect to the Faraday rotator, in other words, the output optical fiber is the input optical fiber. In the same direction as the fiber, in other words, the Faraday rotator is arranged and installed at the tip of the optical magnetic field sensor. Therefore, the reflection type optical magnetic field sensor has a feature that it can be installed in a convoluted and narrow space where the transmission type optical magnetic field sensor cannot be installed due to a small mounting space. However, the reflection type optical magnetic field sensor proposed by Matsui et al. [JP-A-56-55811] is
Since the lens and the polarizer, and the lens and the analyzer have to be arranged in series and in parallel, it is difficult to automate the assembly work, and thus it is difficult to reduce the manufacturing cost. ing.

[0008] Matsumura et al. [Japanese Patent Publication No. 3-22595] describes a problem of the reflection type optical magnetic field sensor head proposed by Matsui et al. [Japanese Patent Laid-Open No. 56-55811], that is, it is difficult to automate the assembling work, and therefore the manufacturing cost is As a method of solving the problem that it is difficult to reduce the above, it is proposed to replace the polarizer and the analyzer with a single polarizer. In addition, Matsumura et al. Propose to use yttrium-iron-garnet (chemical structural formula: Y ₃ Fe ₅ O ₁₂ ) as a Faraday rotator (magneto-optical material).

Yttrium / iron / garnate is generally abbreviated as YIG and can be produced by a known method such as a melt method. Yttrium / Iron / Garnet (YI
G) has a characteristic that the sensitivity is extremely higher than that of paramagnetic glass, zinc selenide (ZnSe), etc., which have been conventionally used as Faraday rotators. Therefore, the proposal of Matsumura et al., Yttrium / Iron / Garnet (YIG)
It can be said that the proposal of using as a Faraday rotator of a reflection type optical magnetic field sensor is a very interesting proposal in terms of its characteristics. However, when considering the properties / characteristics of yttrium / iron / garnet (YIG) with respect to light transmission, the practicality of the magneto-optical sensor as a magneto-optical material, that is, a Faraday rotator, is questioned. That is, yttrium, iron, and garnet (YIG) have already transmitted light in the near-infrared wavelength region with a wavelength of 1.1 μm or more, and have a wavelength region of 0.8 μm.
This is because it is known to have a characteristic property that it absorbs light in the band well.

At present, generally, as a light source of an optical sensor, a semiconductor laser (LD) or a light emitting diode (LED) having a center wavelength of 0.78 μm to 0.85 μm is widely used for awards. The reason that the semiconductor laser (LD) and the light emitting diode (LED) are widely used as the light source of the optical sensor is that they are already commercially available as a light source device at low cost, and the photodetector has high sensitivity. Yttrium / iron / garnet
The fact that (YIG) absorbs light in the 0.8 μm wavelength range well means that when a commercially available light source device is used as the light source,
It means that the detection of the optical signal becomes difficult and / or possible.

The inventors of the present application have conducted various studies and experiments on a method for avoiding the drawbacks of yttrium-iron-garnet (YIG), and as a result, they have relatively easily manufactured by the liquid phase epitaxial (LPE) method. Chemical formula (RBi)
₃ (FeA) ₅ O ₁₂ [wherein R represents yttrium Y or a rare earth element, and A represents aluminum Al or gallium Ga.
Bismuth-substituted iron garnet single crystal represented by (in other words, bismuth-substituted magnetic garnet single crystal, for example, (GdBi) ₃ (FeGaAl) ₅ O ₁₂ or (HoTbBi) ₃
The possibility has been found in (FeGaAl) ₅ O _{12 and the} like [see Japanese Patent Application Laid-Open No. 61-20926 and Japanese Patent Application No. 5-55621].

The Faraday rotation coefficient of bismuth-substituted iron garnet, in other words, the rotation angle of the plane of polarization per unit film thickness when the magnetization is saturated is yttrium.iron.
It is several times more than the Faraday rotation coefficient of garnet (YIG), and more specifically, it is about 10 times larger at a wavelength of 0.8 μm. Therefore, when the same effect as the magneto-optical material is expected, it is possible to reduce the film thickness of the magneto-optical material in proportion to the Faraday rotation coefficient, and as a result, the absorption loss of light is reduced, small,
It suggests that it can be miniaturized. That is, the material of the magneto-optical material is yttrium / iron / garnet (Y
By replacing (IG) with bismuth-substituted iron garnet, the element film thickness will be reduced, light absorption loss will be reduced, and it will be possible to develop an optical magnetic field sensor using light in the wavelength region of 0.8 μm band as a light source. Suggests.

The saturation magnetic field [500-1200 Oe] of bismuth-substituted iron garnet is about half of the saturation magnetic field [about 1800 Oe] of yttrium-iron-garnet (YIG).
Therefore, it is expected that a weak magnetic field can be measured. The fact that a weak magnetic field can be measured means that the distance / interval between the permanent magnet and the optical magnetic field sensor can be made longer. This means that the degree of freedom and flexibility of arrangement and installation of the optical magnetic field sensor is improved, which suggests the possibility of expanding the field of application of the optical magnetic field sensor.

From the results of these examinations, the present inventors
Magneto-optical material of bismuth-substituted iron garnet, i.e., with the conviction that it is possible to develop a reflection type optical magnetic field sensor using a Faraday rotator, further, earnestly conducting detailed basic experiments and development experiments, We have completed and proposed a reflective optical magnetic field sensor using a Faraday rotator made of bismuth-substituted iron garnet [Japanese Patent Application No. 0-090976, Japanese Patent Application No. 4-320379, etc.].

[0015]

The international public opinion on the protection of the global environment and energy saving, that is, the response and efforts of the industrial world in response to the social demand, progresses unexpectedly and rapidly. Optical magnetic field sensors that utilize the Faraday effect of magneto-optical materials are rapidly being put into practical use and generalized. With the widespread use of tachometers that use optical magnetic field sensors, the requirements for their performance have also become more sophisticated,
It is becoming more severe and not only improving the sensitivity but also developing and providing a small optical magnetic field sensor head for weak magnetic field measurement.

In a tachometer using an optical magnetic field sensor utilizing the Faraday effect of a magneto-optical material, that is, a tachometer based on an optical signal, a permanent magnet is attached to a rotating device as illustrated in FIG. Applied Optics, Volume 28, No. 11, p. 1992 (1989
Year) 〕. The longer the distance between the permanent magnet and the optical magnetic field sensor head, the weaker the magnetic field formed by the permanent magnet. Therefore, in order to further improve the sensitivity and accuracy of the tachometer,
A permanent magnet and a magnetic field sensor head are selected by using a permanent magnet having a stronger magnetic force to cope with the weakening of the magnetic field formed by the permanent magnet, or to select an optical magnetic field sensor head that exhibits a sufficient function even in a weak magnetic field. It is necessary to shorten the distance between and. 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, which places restrictions on the installation location. As a result, the distance from the head becomes long, and the substantial improvement effect cannot be obtained.

The inventors of the present application consider the simplest method of the optical magnetic field sensor to specifically meet the social demands and expectations for the tachometer using the optical magnetic field sensor utilizing the Faraday effect of the magneto-optical material. Various experimental studies were carried out in order to obtain data for further improvement of the sensitivity of the head and the possibility of developing a compact optical magnetic field sensor head for weak magnetic field measurement.

At present, optical magnetic field sensors having various configurations and structures have already been proposed. From the viewpoint of further miniaturization of the optical magnetic field sensor head, a glass polarizer and a Faraday rotator, that is,
It will be easily understood that a so-called reflection type magneto-optical sensor head having a bismuth-substituted iron garnet single crystal is preferable. Reflective magnetic field sensor head [Japanese Patent Application No. 4-116141]
Has a simple structure and structure, and has already been confirmed to have a certain size and weight reduction effect, and is also excellent in productivity and mass productivity. Therefore, the inventors of the present application first examined the possibility of further miniaturization of the Faraday rotator constituting the reflective optical magnetic field sensor head, that is, the bismuth-substituted iron garnet single crystal.

The Faraday rotator, ie, the bismuth-substituted iron garnet single crystal, which is currently used in the commercially available reflection type optical magnetic field sensor head is mainly used because of its easy handling, more specifically, the single crystal. Considering the ease of cutting and assembling and fine-tuning operations of the crystal, it is selected as a square with a side length of 2.5 mm to 3.0 mm. Based on the principle of optics, it is sufficient that the size of the bismuth-substituted iron garnet single crystal is about several times the core diameter of the optical fiber. Therefore, theoretically, even considering the ease of handling of the bismuth-substituted iron garnet single crystal, further downsizing is possible, the side length is 2.0 mm or less, more specifically, It is estimated that it can be 1.5 mm to 2.0 mm.

In order to experimentally confirm the possibility of downsizing a bismuth-substituted iron garnet single crystal, the inventors of the present invention:
The chemical structural formula (HoTbBi) ₃ Fe ₅ O that has already been adopted as a Faraday rotator for optical isolators and magnetic field sensors
₁₂ [saturation magnetic field 1100 Oe, refer to JP-A-63-041979] and chemical structural formula (HoTbBi) ₃ (FeGaAl) ₅ O ₁₂ [saturation magnetic field 600 Oe or less, see Japanese Patent Application No. 5-055621], and chemical structural formula (GdB
i) ₃ (FeGaAl) ₅ O ₁₂ (saturation magnetic field 600 Oe, JP-A 61-020926
The bismuth-substituted iron garnet single crystal described in [1] is cut into a square shape with a side length of 1.5 mm to 3.0 mm to produce a reflection type optical magnetic field sensor head [see Japanese Patent Application No. 4-090976]. Installed in a rotation speed tester so that the magnetic field strength of the part becomes the saturation magnetic field [maximum value], the size of the bismuth-substituted iron garnet single crystal and the reflection type optical magnetic field sensor, that is,
The relationship with the performance as a rotation speed (number) sensor was tested and examined. Chemical structural formula (HoTbBi) ₃ Fe ₅ O ₁₂ [Saturation magnetic field
1100 Oe] bismuth-substituted iron garnet single crystal is used as a Faraday rotator in a reflection type optical magnetic field sensor head, the size of the single crystal, that is, even if the side length is 1.5 mm, it is 3.0 mm.
It could detect a magnetic field similar to the one described above, and functioned as a rotation speed (number) sensor. However, the chemical structural formula (Ho
TbBi) ₃ (FeGaAl) ₅ O ₁₂ (saturation magnetic field 600 Oe or less) and chemical structural formula (GdBi) ₃ (FeGaAl) ₅ O ₁₂ (saturation magnetic field 600 O
The reflective optical magnetic field sensor head using the bismuth-substituted iron garnet single crystal of [e] as a Faraday rotator has a single crystal size, that is, a side length of 2.0 mm or less, as shown in Table 1. Sometimes, it could not detect the magnetic field and did not function as a rotational speed (number) sensor.

[0021]

[Table 1]

The experimental results obtained here show that the sensitivity of a reflection type optical magnetic field sensor head using a bismuth-substituted iron garnet single crystal as a Faraday rotator, in other words, the detection limit value of the magnetic field strength is bismuth-substituted iron garnet single crystal. Type of crystal, in other words, chemical structural formula, and size of Faraday rotator, that is, bismuth-substituted iron garnet single crystal [dimension]
It shows that it changes greatly by. This means that the magnetization characteristics of the bismuth-substituted iron garnet single crystal having a low saturation magnetic field with respect to the external magnetic field greatly change depending on its shape and size. The present inventors
I do not know the whereabouts of the documents that describe / report this phenomenon.

Next, the inventors of the present invention have prepared the bismuth-substituted iron garnets of the chemical structural formula (HoTbBi) ₃ (FeGaAl) ₅ O ₁₂ and the chemical structural formula (GdBi) ₃ (FeGaAl) ₅ O _{12 which} were prototyped here. A reflection type optical magnetic field sensor head that uses a crystal as a Faraday rotator distinguishes between a state in which the saturation magnetic field is applied and a state in which the saturation magnetic field is not applied, in other words, functions as a rotation speed (number) sensor. In order to clarify the reason why it is not possible, various basic examination experiments were conducted.

As a result, the above phenomenon, that is, the main cause of not being able to discriminate between the state in which the magnetic field is applied to the same degree as the saturation magnetic field and the state in which the magnetic field is hardly applied, is caused by the cutting of the single crystal. I knew it was due to an increase in magnetic hysteris. This means that the bismuth-substituted iron garnet single crystal having a low saturation magnetic field, more specifically, the chemical structural formula (HoTbBi) ₃ (FeGaAl) ₅ O ₁₂ and the chemical structural formula (GdBi) ₃ (FeGaAl) ₅ O _{In order for} the bismuth-substituted iron garnet single crystal of ₁₂ to function as an optical magnetic field sensor, for example, a rotation speed (number) sensor, its size, that is, the dimension has a limit value, and that value is the side length. This means about 2.0 mm.

Further, the experimental results shown in Table 1 show that the bismuth-substituted iron garnet single crystal used in the present experiment has a magnetization characteristic with respect to an external magnetic field, in other words, a magnetic hysteresis shows that the side length of the single crystal is small. It means that it greatly increases due to such a decrease, and it does not function as an optical magnetic field sensor, for example, a rotation speed (number) sensor.

A bismuth-substituted iron garnet single crystal [(HoTbBi) ₃ Fe ₅ O ₁₂ ] having a large saturation magnetic field and a sufficient side length of 2.5
Bismuth-substituted iron garnet single crystal with a small saturation magnetic field of mm or more [(HoTbBi) ₃ (FeGaAl) ₅ O ₁₂ , (GdBi) ₃ (FeGaAl)
₅ O ₁₂ ] as a Faraday rotator, for example, the magnetization characteristics of a Faraday rotator of a rotation speed [number] sensor with respect to an external magnetic field, that is, the relationship between the external magnetic field strength and the Faraday rotation angle is shown in FIG. It seems

In FIG. 2, when an external magnetic field [strength] is not applied, in other words, when the magnetic field of the permanent magnet does not exert an influence on the Faraday rotator, the Faraday of the bismuth-substituted iron garnet single crystal is The rotation angle is zero

[0], that is, located at the origin O. The rotating body rotates,
When the permanent magnet fixed to the rotating body approaches the Faraday rotator, the externally applied magnetic field gradually strengthens and the absolute value of the Faraday rotation angle of the Faraday rotator (θ _F or −θ
_F ] gradually increases through the route a or the route d [route O → a → b or route O → d →
e]. When the rotating body further rotates and the distance between the permanent magnet and the Faraday rotator reaches a certain value, in other words, the external magnetic field strength reaches a certain strength [Hs], the Faraday rotation angle of the Faraday rotator becomes , A saturated value [saturation magnetic field: point b or point e]. Even if the rotating body further rotates, the permanent magnet approaches the Faraday rotator, and the externally applied magnetic field strength further increases, the Faraday rotation angle of the Faraday rotator is already saturated. Therefore, b to c or e Only the shift from f to f does not change the Faraday rotation angle. When the permanent magnet comes closest to the Faraday rotator and the external magnetic field strength reaches its maximum value, and then moves away, the externally applied magnetic field gradually weakens, and the reverse path, that is, c → b → a →
O or f → e → d → O is traced, the influence of the external magnetic field disappears, and the process returns to the origin O. The detection of the magnetic field by the reflective optical magnetic field sensor is intended to detect the difference in Faraday rotation angle between the origin O and the saturation point b or the saturation point e as the light intensity.

A bismuth-substituted iron garnet single crystal that is currently commonly used as a Faraday rotator, for example, a chemical structural formula (HoTbBi) ₃ (FeGaAl) ₅ O ₁₂ or a chemical structural formula (GdBi)
Bismuth-substituted iron garnet single crystal of ₃ (FeGaAl) ₅ O ₁₂
When cut into small pieces with a side length of 2.0 mm or less, a phenomenon occurs that the optical magnetic field sensor does not function as illustrated in Table 1. This means that the bismuth-substituted iron garnet single crystal [(HoTbBi) ₃ (FeGa
It is suggested that the relationship between the external magnetic field strength and the Faraday rotation angle of (Al) ₅ O ₁₂ and (GdBi) ₃ (FeGaAl) ₅ O ₁₂ ] is not as shown in FIG.

The inventors of the present invention have made a detailed study on the relationship between the external magnetic field strength and the Faraday rotation angle of the bismuth-substituted iron garnet single crystal. As a result, the above-mentioned phenomenon is caused by the cutting of the bismuth-substituted iron garnet single crystal. We have found that it can be easily understood and explained by considering the hysteresis effect of the magnetization characteristics. That is, an optical magnetic field sensor using a bismuth-substituted iron garnet single crystal as a Faraday rotator cannot sometimes detect an external magnetic field, and does not function as an optical magnetic field sensor because it is a Faraday rotator, that is, bismuth-substituted iron garnet. By cutting the single crystal to a side length of 2.0 mm or less, the magnetization characteristics change, and the relationship between the external magnetic field strength and the Faraday rotation angle is not shown in FIG. 2 but as shown in FIG. 3 [path O → a → b → c → b
→ b '→ a → O]. That is, when the bismuth-substituted iron garnet single crystal is cut into small pieces with a side length of 2.0 mm or less, when the strength of the external magnetic field is strengthened [route
O → a → b → c], when weakening [Route c → b →
b ′ → a → O], the route is different as seen in FIG.

In FIG. 3, the magnetic fields at points b and e are called saturation magnetic field Hs, and the magnetic fields at points b'and e'caused by the hysteresis of the magnetization characteristic due to cutting are called nucleation magnetic fields Hn. The difference between the magnetic field Hs and the nucleation magnetic field Hn (Hs-Hn) is defined as the size of hysteresis. The difference in the paths seen in FIG. 3 is due to the hysteresis of the magnetization characteristics due to cutting. For simplicity and ease of explanation, the saturation magnetic field Hs at the point b is represented by Hs ₁ , the nucleation magnetic field Hn at the point b ′ is represented by Hn _1, and the saturation magnetic field Hs at the point e is represented by Hs ₂ , e. The nucleation magnetic field Hn at the 'point is denoted by Hn ₂ . When the hysteresis of the Faraday rotator increases and the nucleation magnetic field Hn approaches the origin O, the magnetically saturated state is maintained until the external magnetic field becomes almost zero, as shown in FIG. become. That is, c → b
In the path of → b 'or f → e → e', the output signal reflected from the sensor head does not change because the Faraday rotation angle of the Faraday rotator does not change even though the externally applied magnetic field strength changes. The light intensity of the light will not change. Therefore, in order to detect the strength of the magnetic field using the optical magnetic field sensor head composed of the Faraday rotator with large hysteresis,
The magnetic field strength in the periphery should be almost zero.

When the hysteresis of the Faraday rotator is further increased, as shown in FIG. 4, the nucleation magnetic field is increased.
Hn ₁ goes over the origin O and enters the negative side. When the hysteresis further increases, the nucleation magnetic field Hn ₁
Becomes smaller than the saturation magnetic field Hs ₂ , and finally, a hysteresis curve of a quadrangle is drawn [Fig. 5], and once saturated, only a loop of this quadrangle is drawn.

As a practical matter, the rotational speed [number] of the rotating body
In many cases, the installation location / environment of the optical magnetic field sensor head for measuring is inside the mechanical device. Therefore, a large number of metal parts exist around it. It is a well-known fact that the metal parts constituting the mechanical device are magnetized in some way. Based on the current state of the art in this technical field, it is extremely difficult to make the magnetic field strength at the installation location / site of the magnetic field sensor head zero.

The experimental results obtained here can achieve the miniaturization of the reflection type optical magnetic field sensor head simply by reducing the shape and size of the Faraday rotator, that is, the bismuth-substituted iron garnet single crystal. It shows that it is impossible. That is, the bismuth-substituted iron garnet having a large hysteresis is unsuitable as a Faraday rotator for a magnetic field sensor for the purpose of detecting and measuring a weak magnetic field, and is not practical. In addition, Table 1 and FIGS. 2 to 5 show bismuth-substituted iron garnets that have conventionally been commonly used as Faraday rotators, such as the chemical structural formula (HoTbBi) ₃ (FeGaAl) ₅ O ₁₂ and the chemical structural formula ( GdBi) ₃ (FeGaA
l) ₅ O ₁₂ bismuth-substituted iron garnet single crystal cannot be used to manufacture a small optical magnetic field sensor head for weak magnetic field measurement, and has desired sensitivity and magnetization characteristics for an external magnetic field suitable for that purpose, More specifically,
This means that a new bismuth-substituted iron garnet with a low saturation magnetic field and a low hysteresis must be developed.

[0034]

The inventors of the present invention industrially manufacture a new bismuth-substituted iron garnet suitable for a Faraday rotator for a small optical magnetic field sensor head for weak magnetic field measurement in response to social demands. As a result of conducting various experimental studies in order to provide the above, on a non-magnetic garnet single crystal substrate,
General formula Y _3-xy La _x grown by liquid phase epitaxial method
Bi _y Fe _5-z Ga _z O ₁₂ [where x, y, and z are 0.1
≤ x ≤ 0.4, 1.0 ≤ y ≤ 1.9, 1.0 ≤ z ≤ 1.6], the bismuth-substituted iron garnet single crystal has excellent magnetization characteristics with respect to an external magnetic field, and has an optical magnetic field even in a weak magnetic field. Based on the knowledge that the sensor functions sufficiently as a sensor and is suitable for the purpose of further miniaturization of the optical magnetic field sensor, further intensive research experiments were conducted to complete the present invention. That is, according to the present invention, by substituting gallium for part of the iron element of the yttrium-lanthanum-bismuth-substituted iron garnet single crystal, the magnetization characteristic with respect to the external magnetic field is improved, and moreover, the desired magnetization characteristic value is controlled. Based on the knowledge that it can be done, further detailed experimental study was conducted and it was completed as an industrial manufacturing technology.

With the completion of the present invention, it has become possible to industrially manufacture a smaller optical magnetic field sensor head for measuring a weak magnetic field and to provide it at a low cost.

The bismuth-substituted iron garnet single crystal of the present invention is required for a Faraday rotator for an optical magnetic field sensor, for example, a rotation speed (number) sensor, even if it is cut into a side length of 1.5 mm to 2.0 mm. Even if the performance, that is, the magnetic hysteresis is small and the strength of the external magnetic field is weak, the value at which the Faraday rotation angle is saturated is easily reached, in other words, the saturation magnetic field [θ _F or −θ _F ] is reached. Therefore, it is possible to detect the presence of a weak magnetic force, that is, a weak magnetic field [magnet].
Moreover, the magnetization characteristic value of the bismuth-substituted iron garnet single crystal of the present invention is in the practical temperature range [range] of the optical magnetic field sensor head, more specifically, from about -50 ° C to 70 ° C.
It is maintained and maintained over the temperature range of, and can fully meet the social demands and expectations.

Bismuth-substituted iron garnet single bond of the present invention
Crystal, more specifically, the general formula Y _3-xyLa_xBi_yFe
_5-zGa_zO₁₂[However, x, y, and z are each 0.1 ≤ x ≤
 The numbers are 0.4, 1.0 ≤ y ≤ 1.9, and 1.0 ≤ z ≤ 1.6.
Below, bismuth-substituted iron garnet [Y_3-xyLa_xBi_yFe
_5-zGa_zO₁₂] Single crystal or YLaBiFeGa garnet single
Abbreviated as crystal]]
The single crystal is formed by the well-known liquid phase epitaxial (LPE) method.
By growing it on a non-magnetic garnet single crystal substrate.
Can be manufactured.

When carrying out the present invention, the substitution amount x of the lanthanum La element constituting the bismuth-substituted iron garnet [Y _3-xy La _x Bi _y Fe _5-z Ga _z O ₁₂ ] single crystal is 0.1 to 0.4,
In particular, it is preferable to select it within the range of 0.1 to 0.25. If the value of the substitution amount x of the lanthanum La element is selected to be 0.1 or less, crystal defects, that is, pits, swirls, and cracks increase, and sometimes the light transmittance decreases due to the crystal defects. For Faraday rotator,
It is inconvenient.

The decrease in the light transmittance of the Faraday rotator means that the intensity of the signal light reaching the photodetector is decreased, and therefore high precision is required in manufacturing the optical magnetic field sensor, and the signal light This is disadvantageous in terms of manufacturing cost, such as the electronic circuit for increasing the amplification factor becomes more complicated. Therefore, the higher the light transmittance of the Faraday rotator, the more preferable. The optical transmittance of the Faraday rotator required for an optical magnetic field sensor varies depending on the light intensity of the light source used and the configuration of the optical magnetic field sensor, but in general, the Faraday rotation angle
At a thickness of 45 degrees, the optical loss (transmission loss) is 5 dB or less. In the reflection type optical magnetic field sensor head, the incident light emitted from the light source passes through the polarizer and the Faraday rotator to reach the reflection film, is reflected by the reflection film surface, and is reflected light.
Once again, the light passes through the Faraday rotator and the polarizer to reach the photodetector. Therefore, the optical loss of the reflective magneto-optical sensor head is
Double the transmission loss. However, in the present invention,
In accordance with convention in the art, all Faraday rotator optical losses shall be expressed as transmission losses.

Also, bismuth-substituted iron garnet [Y _3-xy
La _x Bi _y Fe _5-z Ga _z O ₁₂ ] Lanthanum La constituting a single crystal
If the element replacement amount x is selected to be 0.4 or more, single crystal growth
During the growth operation, fine crystals are precipitated in the melt, making it difficult to grow a single crystal, and a single crystal film having a predetermined thickness cannot be obtained.

When carrying out the present invention, the amount y of the bismuth Bi element constituting the bismuth _- substituted iron garnet [Y _3-xy La _x Bi _y Fe _5-z Ga _z O ₁₂ ] single crystal is 1.0 to 1.9, particularly , 1.2 to 1.7 is preferable. If the value y of the bismuth Bi element is selected to be 1.0 or less, the Faraday rotation coefficient (also called sensitivity constant), more specifically,
There arises such a problem that the rotation angle [Faraday rotation angle] of the polarization plane per unit film thickness of the Faraday rotator becomes small. The film thickness of the Faraday rotator becomes thinner as the Faraday rotation coefficient becomes larger. Therefore, the larger the Faraday rotation coefficient of the Faraday rotator, the more preferable.
Further, as the film thickness of the Faraday rotator increases, the insertion loss increases accordingly. Therefore, it is unsuitable as the Faraday rotator of the small-sized optical magnetic field sensor head for weak magnetic field measurement, that is, the bismuth-substituted iron garnet single crystal, which is the object of the present invention. Also, if the amount y of the bismuth Bi element that constitutes the bismuth _- substituted iron garnet [Y _3-xy La _x Bi _y Fe _5-z Ga _z O ₁₂ ] single crystal is selected to be 1.9 or more, the growth and growth operation of the single crystal is performed. Inside, crystallites are precipitated in the melt,
It becomes impossible to grow and grow single crystals.

When the present invention is carried out, the amount z of gallium Ga constituting the bismuth-substituted iron garnet [Y _3-xy La _x Bi _y Fe _5-z Ga _z O ₁₂ ] single crystal is in the range of 1.0 to 1.6. It is preferable to select. When the amount z of gallium Ga is selected to be 1.0 or less, the saturation magnetic field of the bismuth-substituted iron garnet single crystal grown here becomes 600 Oe or more, and as a Faraday rotator for a small optical magnetic field sensor head for weak magnetic field measurement, Is inappropriate. Also, bismuth-substituted iron garnet [Y _3-xy
If the amount z of gallium Ga that composes the La _x Bi _y Fe _5-z Ga _z O ₁₂ ] single crystal is selected to be 1.6 or more, the Curie temperature of the bismuth-substituted iron garnet single crystal grown here, that is, the Faraday rotation The temperature at which the angle becomes 0 is reduced to 50 ° C. to 60 ° C., which is unsuitable from a practical point of view.

When carrying out the present invention, the type of garnet used as a substrate for growing a bismuth-substituted iron garnet single crystal is not particularly limited. Bismuth-substituted iron garnet for growth [Y _3-xy La _x Bi _y Fe _5-z Ga _z O ₁₂ ]
Considering the quality required for a single crystal, it may be appropriately selected from garnets having a crystal orientation [111] that are generally used. Generally, the prevention / suppression of internal pits, swirls, and concentric cracks, and
From the viewpoint of simplicity, a non-magnetic garnet single crystal commercially available as a substrate for liquid phase epitaxial growth, for example, calcium / magnesium / zirconium substituted gadolinium / gallium / gallium / gallium with a lattice constant of 12.492 Å to 12.503 Å
It may be appropriately selected from the garnet (CaGd) ₃ (MgZrGa) ₅ O ₁₂ single crystal [SGGG] substrate, if desired.

In practicing the present invention, non-magnetic garnet
For the melt to grow on the substrate by liquid phase epitaxial method
Is not particularly limited, but especially lead oxide, bismuth oxide
, Ferric oxide, boron oxide, yttrium oxide, and
And it is preferable to use a melt of lanthanum oxide.
The composition of the melt for single crystal growth is the target bismuth-substituted iron.
Garnet [Y_3-xyLa _xBi_yFe_5-zGa_zO₁₂] Single crystal products
It is selected appropriately considering the quality and growing conditions, but usually
Generally, lead oxide PbO 30% to 50% by weight,
Suma Bi₂O₃35% to 60% by weight, boron oxide B₂O₃ 2.4
Wt% to 3.3 wt%, ferric oxide Fe₂O ₃5.5% by weight
Up to 7% by weight, in addition to the sum of ferric oxide and gallium oxide
Ratio of yttrium oxide to lanthanum oxide [[Fe₂O
₃+ Ga₂O₃) / (Y₂O₃+ La₂O₃)] In the range 10 to 25
Is preferred. Lead oxide, bismuth oxide, ferric oxide, oxidation
Each concentration of boron and the sum of ferric oxide and gallium oxide
Ratio of the sum of yttrium oxide and lanthanum oxide to
Molar ratio [(Fe₂O₃+ Ga₂O₃) / (Y₂O₃+ La₂O₃)] Is outside the above range
The target bismuth-substituted iron garnet single crystal
The outer crystal grows, or the crystallite grows during the crystal growth.
Yttrium, lanthanum, and bismuth
Normal epitaxial of iron, gallium and garnet
It becomes impossible to grow.

When carrying out the present invention, the growth temperature of the bismuth-substituted iron garnet single crystal is set so that the lattice constant of the bismuth-substituted iron garnet single crystal, which is the object of the present invention, matches the lattice constant of the substrate. It is selected in consideration of the composition of the growing melt and the lattice constant of the substrate. Generally, the growth temperature of a bismuth-substituted magnetic garnet single crystal is
A temperature within a commonly known temperature range, more specifically 72
If the temperature is selected within the range of 0 ° C to 860 ° C, the intended purpose can be achieved.

When carrying out the present invention, the liquid phase epitaxial growth rate is not particularly limited. However, considering the productivity and mass productivity of the single crystal and the amount of crystal defects, it is preferable to select within the range of 10 μm / hour to 40 μm / hour, particularly 15 μm / hour to 30 μm / hour. When the liquid phase epitaxial growth rate is selected to be 10 μm / hour or less, the time required for liquid phase epitaxial growth, in other words, the required film growth time, becomes long, which is not preferable from the viewpoint of productivity. On the other hand, if the liquid phase epitaxial growth rate is selected to be 40 μm / hour or more,
Since the number of swirls increases and the length of the swirl, that is, the striped pattern becomes long, it is not preferable from the viewpoint of product yield.

When carrying out the present invention, the non-magnetic substrate for forming the YLaBiFeGa garnet thin film need not be removed. Rather, when the YLaBiFeGa garnet single crystal film has a very small thickness of several tens of μm, it is preferable to leave the substrate as a support in terms of strength. On the other hand, when the YLaBiFeGa garnet has a very large film thickness of several hundreds of μm, it is not necessary as a support in terms of strength, and may be removed by a polishing method from the viewpoint of miniaturization.

The wavelength of the light source of the optical magnetic field measuring device is selected in consideration of the sensitivity of the Faraday rotator, the light transmittance, the performance and cost of the light source, the sensitivity of the detector, and the like.
When the present invention is carried out, the wavelength of the light source is: -A high-power short-wavelength semiconductor laser or a light-emitting diode is commercially available at a low price-The photodetector has a high sensitivity and is available at a low price. It is preferable to select near infrared light having a wavelength of 780 nm to 850 nm. In addition, as a suboptimal measure, it is possible to select light in the wavelength bands of 1300 nm and 1550 nm, which are practically used in optical fiber communication, or in the wavelength band of 1060 nm in which a YAG laser can be used. However, if the wavelength of the light source deviates from the above range, the light absorption becomes large, or the Faraday rotation coefficient of YLaBiFeGa garnet becomes small, which makes it difficult to detect the signal light, or , And the Faraday rotator must be made thicker, which is not preferable.

The embodiments and effects of the present invention will be specifically described in detail below with reference to Examples and Comparative Examples, but the following examples are for specific description. It is not intended to limit the embodiments of the present invention or the scope of the invention.

[0050]

【Example】

 Example 1 A platinum crucible having a capacity of 300 ml was charged with lead oxide [PbO 4N] 450.
g, bismuth oxide (Bi₂O ₃, 4N] 400 g, ferric oxide [Fe₂
O₃, 4N] 55 g, boron oxide [B₂O₃, 5N] 24g, oxide
Thorium [Y₂O₃, 3N] 3.60 g, lanthanum oxide [La
₂O₃, 3N] 2.50 g, gallium oxide [Ga₂O₃, 3N] 12g
Was charged. Place this in place on the precision vertical tubular electric furnace.
Install, heat and melt at 1000 ° C, stir well and mix evenly.
After combining, cool to melt temperature 756 ℃ and add bismuth.
A melt for growing a substituted iron garnet single crystal was obtained. Then this
On the surface of the melt thus obtained, a thickness of 400 μm
Substrate for growing single crystal of [[111] Garnet single crystal [(GdCa)
₃(GaMgZr)_FiveO₁₂, Lattice constant: 12.490 ± 0.002 Å, 1 in
[H] and keep the melt temperature at 756 ℃.
Epitaxial growth for 130 minutes to grow single crystal
On one side of the circuit board (YLaBi)₃(FeGa)_FiveO₁₂Has a single crystal film
 (YLaBi)₃(FeGa)_FiveO₁₂Single crystal (hereinafter, YLaBiFeGa single crystal
1). Then, the YLaBi obtained here
The FeGa single crystal 1 was made into a predetermined size (8.3 mm × 8.
3 mm] was cut to obtain a test piece [1-1] [4 pieces]. here
Select one randomly from the obtained test pieces [1-1], and
Single crystal composition of aBiFeGa single crystal 1 and its characteristic value [single crystal
Crystal composition, film thickness, saturation magnetic field, Faraday rotation angle]
When done, single crystal composition: Y_1.32La_0.11Bi_1.57Fe_3.84Ga
_1.16O₁₂ Film thickness: 68 μm Saturation magnetic field: 470 Oe Faraday rotation angle: 47 ° [degree]. Then, according to the usual method,
Specimen [1-1] is cut into a specified size and Specimen [1-2]
[4.0 mm x 4.0 mm, 4 pieces], test piece [1-3] [2.0 mm x 2.
0mm, 16 pieces] and test piece [1-4] [1.5mm × 1.5mm
 , 25 pieces] were obtained. Test piece obtained here [1-2] and test
Randomly from piece [1-3] and test piece [1-4]
Select four and change the applied magnetic field strength while changing the magnetic field strength.
And the Faraday rotation angle are measured and drawn on the diagram.
When the amount of stersis was calculated, the test piece [1-2] [4.0mm × 4.0mm]: 10 Oe test piece [1-3] [2.0mm × 2.0mm]: 15 Oe test piece [1-4] [1.5 mm × 1.5 mm]: A result of 15 Oe was obtained [see FIG. 3].

It should be noted that YLaBiFeGa single crystal, that is, YLaBiFeG
a The garnet crystal composition was obtained by randomly selecting one from the test pieces [1-1] obtained here, removing the single crystal growth substrate by the polishing method, and then dissolving it in phosphoric acid to obtain YLaBiFe.
The Ga garnet-phosphoric acid solution was used as an analytical sample and measured and quantified by the ICP analysis method. In addition, the magnetization characteristics of the single crystal film,
That is, the magnitude of the hysteresis was measured by a method which is generally adopted and determined from the dependence of the Faraday rotation angle on the externally applied magnetic field. That is, a test piece was attached to a sample holding device of a magnetic field application device (MAGNET) manufactured by Magnetic Corporation and set at a predetermined position, that is, in a [gap] between electromagnetic coils. Next, while changing the applied magnetic field strength, laser light having a wavelength of 0.786 μm was made incident from the light source, and the rotation angle of the plane of polarization of the laser light transmitted through the test piece, that is, the Faraday rotation angle was measured.

Example 2 A platinum crucible having a capacity of 300 ml was charged with lead oxide [PbO 4, 4N] 500.
g, bismuth oxide (Bi₂O ₃, 4N] 380g, ferric oxide [Fe₂
O₃, 4N] 70 g, boron oxide [B₂O₃, 5N] 26g, oxide
Thorium [Y₂O₃, 3N] 0.80 g, lanthanum oxide [La
₂O₃, 3N] 12.0 g, gallium oxide [Ga₂O₃, 3N] 14g
Was charged. Place this in place on the precision vertical tubular electric furnace.
Install, heat and melt at 1000 ° C, stir well and mix evenly.
After combining, cool to a melt temperature of 827 ℃ and add bismuth.
A melt for growing a substituted iron garnet single crystal was obtained. Then this
On the surface of the melt thus obtained, a thickness of 400 μm
Substrate for growing single crystal of [[111] Garnet single crystal [(GdCa)
₃(GaMgZr)_FiveO₁₂, Lattice constant: 12.490 ± 0.002 Å, 1 in
Contact the other side to maintain the melt temperature at 827 ℃.
Epitaxial growth for 130 minutes to grow single crystal
On one side of the circuit board (YLaBi)₃(FeGa)_FiveO₁₂Has a single crystal film
 (YLaBi)₃(FeGa)_FiveO₁₂Single crystal (hereinafter, YLaBiFeGa single crystal
2). Then, the YLaBi obtained here
FeGa single crystal 2 was sized according to the usual method (8.3 mm × 8.
3 mm] was cut to obtain a test piece [2-1] [4 pieces]. here
Select one randomly from the obtained test pieces [2-1], and
Single crystal composition of aBiFeGa single crystal 2 and its characteristic value [single crystal
Crystal composition, film thickness, saturation magnetic field, Faraday rotation angle]
When done, single crystal composition: Y_1.57La_0.37Bi_1.06Fe_3.95Ga
_1.05O₁₂ The following results were obtained: film thickness: 65 μm Saturation magnetic field: 580 Oe Faraday rotation angle: 43 ° [degrees]. Then, according to the usual method,
Specimen [2-1] is cut into a specified size and Specimen [2-2]
[4.0 mm x 4.0 mm, 4 pieces], test piece [2-3] [2.0 mm x 2.
0mm, 16 pieces] and test piece [2-4] [1.5mm × 1.5mm
 , 25 pieces] were obtained. Test piece obtained here [2-2] and test
Randomly from piece [2-3] and test piece [2-4]
Select four and change the applied magnetic field strength while changing the magnetic field strength.
And the Faraday rotation angle are measured and drawn on the diagram.
When the amount of stersis was calculated, the test piece [2-2] [4.0 mm × 4.0 mm]: 5 Oe test piece [2-3] [2.0 mm × 2.0 mm]: 10 Oe test piece [2-4] [1.5 mm × 1.5 mm]: A result of 10 Oe was obtained.

Example 3 A platinum crucible having a capacity of 300 ml was charged with lead oxide [PbO 4N] 400.
g, bismuth oxide (Bi₂O ₃, 4N] 470 g, ferric oxide [Fe₂
O₃, 4N] 65 g, boron oxide [B₂O₃, 5N] 25g, oxide
Thorium [Y₂O₃, 3N] 3.50 g, lanthanum oxide [La
₂O₃, 3N] 2.60 g, gallium oxide [Ga₂O₃, 3N] 17g
Was charged. Place this in place on the precision vertical tubular electric furnace.
Install, heat and melt at 1000 ° C, stir well and mix evenly.
After combining, cool to melt temperature 775 ℃ and add bismuth.
A melt for growing a substituted iron garnet single crystal was obtained. Then this
On the surface of the melt thus obtained, a thickness of 400 μm
Substrate for growing single crystal of [[111] Garnet single crystal [(GdCa)
₃(GaMgZr)_FiveO₁₂, Lattice constant: 12.490 ± 0.002 Å, 1 in
[H] and keep the melt temperature at 775 ℃.
Epitaxial growth for 180 minutes to grow a single crystal
On one side of the circuit board (YLaBi)₃(FeGa)_FiveO₁₂Has a single crystal film
 (YLaBi)₃(FeGa)_FiveO₁₂Single crystal (hereinafter, YLaBiFeGa single crystal
3). Then, the YLaBi obtained here
The FeGa single crystal 3 was made into a predetermined size (8.3 mm × 8.
3 mm] was cut to obtain a test piece [3-1] [4 pieces]. here
Select one randomly from the obtained test pieces [3-1], and
Single crystal composition of aBiFeGa single crystal 3 and its characteristic value [single crystal
Crystal composition, film thickness, saturation magnetic field, Faraday rotation angle]
When done, single crystal composition: Y_1.37La_0.14Bi_1.49Fe_3.69Ga
_1.31O₁₂ Film thickness: 70 μm Saturation magnetic field: 320 Oe Faraday rotation angle: 46 ° [degree] Then, according to the usual method,
Specimen [3-1] is cut into a specified size and Specimen [3-2]
[4.0 mm x 4.0 mm, 4 pieces], test piece [3-3] [2.0 mm x 2.
0mm, 16 pieces] and test piece [3-4] [1.5mm × 1.5mm
 , 25 pieces] were obtained. Test piece [3-2] obtained here and test
Randomly from piece [3-3] and test piece [3-4]
Select four and change the applied magnetic field strength while changing the magnetic field strength.
And the Faraday rotation angle are measured and drawn on the diagram.
When the size of stersis was calculated, the test piece [3-2] [4.0mm × 4.0mm]: 15 Oe test piece [3-3] [2.0mm × 2.0mm]: 20 Oe test piece [3-4] [1.5 mm × 1.5 mm]: A result of 30 Oe was obtained.

Example 4 A platinum crucible having a capacity of 300 ml was charged with lead oxide [PbO 4, 4N] 400.
g, bismuth oxide (Bi₂O ₃, 4N] 470 g, ferric oxide [Fe₂
O₃, 4N] 60 g, boron oxide [B₂O₃, 5N] 25g, oxide
Thorium [Y₂O₃, 3N] 3.20 g, lanthanum oxide [La
₂O₃, 3N] 3.20 g, gallium oxide [Ga₂O₃, 3N] 17.5g
And prepared. This is the position of the precision vertical tubular electric furnace.
Installed in a container, heat and melt to 1000 ° C, and stir well to homogenize
After mixing, cool to melt temperature 785 ℃ and
A melt for growing a single crystal of S-substituted iron garnet was obtained. Then
On the surface of the melt obtained here, according to the usual method, a thickness of 400μ
m single crystal growth substrate [(111) Garnet single crystal [(GdC
a)₃(GaMgZr)_FiveO₁₂, Lattice constant: 12.510 ± 0.002 Å, 1 b
Contact one side to maintain the melt temperature at 785 ° C.
While performing epitaxial growth for 190 minutes, single crystal growth
On one side of the production substrate (YLaBi)₃(FeGa)_FiveO₁₂Has a single crystal film
(YLaBi)₃(FeGa)_FiveO₁₂Single crystal (hereinafter referred to as YLaBiFeGa single crystal
Abbreviated as crystal 4] was obtained. Then YLa obtained here
The BiFeGa single crystal 4 was made into a predetermined size [8.3 mm ×
8.3 mm], and a test piece [4-1] was obtained [4 pieces]. here
We randomly selected one from the test pieces [4-1] obtained in
Single crystal composition of YLaBiFeGa single crystal 4 and characteristic value [single crystal
Crystal composition, film thickness, saturation magnetic field, Faraday rotation angle]
Was carried out, the single crystal composition: Y_1.11La_0.18Bi_1.77Fe_3.54Ga
_1.46O₁₂ The film thickness: 70 μm, saturation magnetic field: 230 Oe, Faraday rotation angle: 44 ° [degrees] were obtained. Then, according to the usual method,
The test piece [4-1] is cut into a predetermined size, and the test piece [4-2]
[4.0 mm x 4.0 mm, 4 pieces], test piece [4-3] [2.0 mm x 2.
0mm, 16 pieces] and test piece [4-4] [1.5mm × 1.5mm
 , 25 pieces] were obtained. Test piece obtained here [4-2] and test
Randomly from piece [4-3] and test piece [4-4]
Select four and change the applied magnetic field strength while changing the magnetic field strength.
And the Faraday rotation angle are measured and drawn on the diagram.
When the size of the stersis was calculated, the test piece [4-2] [4.0 mm × 4.0 mm]: 20 Oe test piece [4-3] [2.0 mm × 2.0 mm]: 40 Oe test piece [4-4] [1.5 mm × 1.5 mm]: A result of 45 Oe was obtained.

Example 5 A platinum crucible having a capacity of 300 ml was charged with lead oxide [PbO 4, 4N] 330.
g, bismuth oxide (Bi₂O ₃, 4N] 570 g, ferric oxide [Fe₂
O₃, 4N] 60 g, boron oxide [B₂O₃, 5N] 30g, oxide
Thorium [Y₂O₃, 3N] 1.20 g, lanthanum oxide [La
₂O₃, 3N] 5.50 g, gallium oxide [Ga₂O₃, 3N] 20.0 g
And prepared. This is the position of the precision vertical tubular electric furnace.
Installed in a container, heat and melt to 1000 ° C, and stir well to homogenize
After mixing, cool to melt temperature 760 ℃ and
A melt for growing a single crystal of S-substituted iron garnet was obtained. Then
On the surface of the melt obtained here, according to the usual method, a thickness of 400μ
m single crystal growth substrate [(111) Garnet single crystal [(GdC
a)₃(GaMgZr)_FiveO₁₂, Lattice constant: 12.510 ± 0.002 Å, 1 b
Contact one side to maintain the melt temperature at 760 ° C.
While performing epitaxial growth for 150 minutes, single crystal growth
On one side of the production substrate (YLaBi)₃(FeGa)_FiveO₁₂Has a single crystal film
(YLaBi)₃(FeGa)_FiveO₁₂Single crystal (hereinafter referred to as YLaBiFeGa single crystal
Abbreviated as crystal 5]. Then YLa obtained here
The BiFeGa single crystal 5 was made into a prescribed size [8.3 mm ×
8.3 mm] was cut to obtain a test piece [5-1] [4 pieces]. here
Select one randomly from the test pieces [5-1] obtained in
Single crystal composition of YLaBiFeGa single crystal 5 and its characteristic value [single crystal
Crystal composition, film thickness, saturation magnetic field, Faraday rotation angle]
Was carried out, the single crystal composition: Y_0.89La_0.25Bi_1.86Fe_3.43Ga
_1.57O₁₂ Film thickness: 74 μm Saturation magnetic field: 190 Oe Faraday rotation angle: 45 ° [degrees]. Then, according to the usual method,
Specimen [5-1] is cut into a specified size and Specimen [5-2]
[4.0 mm x 4.0 mm, 4 pieces], test piece [5-3] [2.0 mm x 2.
0mm, 16 pieces], and test piece [5-4] [1.5mm × 1.5mm
 , 25 pieces] were obtained. Test piece obtained here [5-2] and test
Randomly from piece [5-3] and test piece [5-4]
Select four and change the applied magnetic field strength while changing the magnetic field strength.
And the Faraday rotation angle are measured and drawn on the diagram.
When the size of the sterisis was calculated, the test piece [5-2] [4.0 mm × 4.0 mm]: 40 Oe test piece
[5-3] [2.0 mm × 2.0 mm]: 60 Oe test piece [5-4] [1.5 mm × 1.5 mm]: 75 Oe.

Comparative Example 1 Lead oxide [PbO 4N] 400 was added to a platinum crucible having a capacity of 300 ml.
g, bismuth oxide (Bi₂O ₃, 4N] 470 g, ferric oxide [Fe2
O3, 4N] 55 g, boron oxide [B₂O₃, 5N] 27g, oxide
Thorium [Y₂O₃, 3N] 4.00 g, lanthanum oxide [La
₂O₃, 3N] 2.00 g, gallium oxide [Ga₂O₃, 3N] 12.0 g
And prepared. This is the position of the precision vertical tubular electric furnace.
Installed in a container, heat and melt to 1000 ° C, and stir well to homogenize
After mixing, cool to melt temperature 748 ℃ and
A melt for growing a single crystal of S-substituted iron garnet was obtained. Then
On the surface of the melt obtained here, according to the usual method, a thickness of 400μ
m single crystal growth substrate [(111) Garnet single crystal [(GdC
a)₃(GaMgZr)_FiveO₁₂, Lattice constant: 12.510 ± 0.002 Å, 1 b
Contact one side to maintain the melt temperature at 748 ° C.
While performing epitaxial growth for 130 minutes, single crystal growth
On one side of the production substrate (YLaBi)₃(FeGa)_FiveO₁₂Has a single crystal film
(YLaBi)₃(FeGa)_FiveO₁₂Single crystal (hereinafter referred to as YLaBiFeGa single crystal
Crystal 6] is obtained. Then YLa obtained here
The BiFeGa single crystal 6 was made into a prescribed size [8.3 mm ×
8.3 mm], and a test piece [6-1] was obtained [4 pieces]. here
Select one randomly from the test pieces [6-1] obtained in
Single crystal composition of YLaBiFeGa single crystal 6 and characteristic value [single crystal
Crystal composition, film thickness, saturation magnetic field, Faraday rotation angle]
Was carried out, the single crystal composition: Y_0.98La_0.07Bi_1.95Fe_3.80Ga
_1.20O₁₂ The film thickness: 68 μm, saturation magnetic field: 500 Oe, Faraday rotation angle: 47 ° [degree] were obtained. Then, according to the usual method,
The test piece [6-1] is cut into a predetermined size, and the test piece [6-2]
[4.0 mm x 4.0 mm, 4 pieces], test piece [6-3] [2.0 mm x 2.
0mm, 16 pieces] and test piece [6-4] [1.5mm × 1.5mm
 , 25 pieces] were obtained. Test piece [6-2] obtained here and test
Randomly from piece [6-3] and test piece [6-4]
Select four and change the applied magnetic field strength while changing the magnetic field strength.
And the Faraday rotation angle are measured and drawn on the diagram.
When the size of the stersis was calculated, the test piece [6-2] [4.0 mm × 4.0 mm]: 5 Oe test piece [6-3] [2.0 mm × 2.0 mm]: 10 Oe test piece [6-4] [1.5 mm × 1.5 mm]: A result of 10 Oe was obtained. The optical insertion loss is 7 dB.
It was

Comparative Example 2 Lead oxide [PbO, 4N] 400 was added to a platinum crucible having a capacity of 300 ml.
g, bismuth oxide (Bi₂O ₃, 4N] 470 g, ferric oxide [Fe₂
O₃, 4N] 60 g, boron oxide [B₂O₃, 5N] 30g, oxide
Thorium [Y₂O₃, 3N] 3.50 g, lanthanum oxide [La
₂O₃, 3N] 2.60 g, gallium oxide [Ga2O3, 3N] 22.0 g
And prepared. This is the position of the precision vertical tubular electric furnace.
Installed in a container, heat and melt to 1000 ° C, and stir well to homogenize
After mixing, cool to melt temperature 759 ℃ and
A melt for growing a single crystal of S-substituted iron garnet was obtained. Then
On the surface of the melt obtained here, according to the usual method, a thickness of 400μ
m single crystal growth substrate [(111) Garnet single crystal [(GdC
a)₃(GaMgZr)_FiveO₁₂, Lattice constant: 12.496 ± 0.002 Å, 1 b
Contact one side to maintain the melt temperature at 759 ° C.
While performing epitaxial growth for 160 minutes, single crystal growth
On one side of the production substrate (YLaBi)₃(FeGa)_FiveO₁₂Has a single crystal film
(YLaBi)₃(FeGa)_FiveO₁₂Single crystal (hereinafter referred to as YLaBiFeGa single crystal
Abbreviated as crystal 7.] Then YLa obtained here
The BiFeGa single crystal 6 was made into a prescribed size [8.3 mm ×
8.3 mm], and a test piece [7-1] was obtained [4 pieces]. here
Select one randomly from the test pieces [7-1] obtained in
Single crystal composition of YLaBiFeGa single crystal 6 and characteristic value [single crystal
Crystal composition, film thickness, saturation magnetic field, Faraday rotation angle]
Was carried out, the single crystal composition: Y_1.27La_0.14Bi_1.59Fe_3.35Ga
_1.65O₁₂ The film thickness: 72 μm, saturation magnetic field: 150 Oe, Faraday rotation angle: 44 ° [degrees] were obtained. Then, according to the usual method,
The test piece [7-1] is cut into a predetermined size, and the test piece [7-2]
[4.0 mm x 4.0 mm, 4 pieces], test piece [7-3] [2.0 mm x 2.
0mm, 16 pieces] and test piece [7-4] [1.5mm × 1.5mm
 , 25 pieces] were obtained. Test piece obtained here [7-2] and test
Randomly from piece [7-3] and test piece [7-4]
Select four and change the applied magnetic field strength while changing the magnetic field strength.
And the Faraday rotation angle are measured and drawn on the diagram.
When the amount of stersis was calculated, the test piece [7-2] [4.0mm × 4.0mm]: 100 Oe test piece [7-3] [2.0mm × 2.0mm]: 150 Oe test piece [7-4] [1.5 mm × 1.5 mm]: A result of 230 Oe was obtained.

Comparative Example 3 Lead oxide [PbO 4N] 843 was placed in a platinum crucible having a capacity of 500 ml.
g, bismuth oxide (Bi₂O ₃, 4N] 978g, ferric oxide [Fe₂
O₃, 4N] 128 g, boron oxide [B₂O₃, 5N] 38g,
Rubium (Tb_FourO₇, 3N] 5.0 g, holmium oxide [Ho
₂O₃, 3N] 8.0 g, gallium oxide [Ga₂O₃, 3N] 13 g, acid
Aluminum chloride (Al₂O₃, 3N] 1.0 g. this
Installed at a predetermined position in a precision vertical tubular electric furnace and heated to 1000 ° C.
After melting by heating and stirring thoroughly to mix uniformly, melt
Cooled to 792 ℃, bismuth-substituted iron garnet
A melt for growing a single crystal was obtained. Then, the melt obtained here
A 400 μm-thick single crystal growth substrate was formed on the surface according to the usual method.
Plate [(111) Garnet single crystal [(GdCa)₃(GaMgZr)_FiveO₁₂,
Lattice constant: 12.493 ± 0.002 Å, 1 inch] contact on one side
And maintain the melt temperature at 792 ° C for 120 minutes.
Performs epitaxial growth on one side of the single crystal growth substrate
(HoTbBi)₃(FeGaAl)_FiveO₁₂Has a single crystal film (HoTbBi)₃(Fe
GaAl)_FiveO₁₂Single crystal (hereinafter referred to as HoTbBiFeGaAl single crystal
I got] Then, the HoTbBiFeGaAl single crystal obtained here was
The crystal is made into a prescribed size [8.3 mm × 8.3 mm] by a conventional method.
It cut and obtained the test piece [8-1] [4 pieces]. Got here
Select one randomly from the test pieces [8-1] and select HoTbBiFeGa
Single crystal composition of Al single crystal 8 and characteristic value [single crystal set
Film thickness, film thickness, saturation magnetic field, Faraday rotation angle)
After a while, single crystal composition: Ho_0.99Tb_0.61Bi_1.40Fe_4.39Ga
_0.51Al_0.10O₁₂ Film thickness: 63 μm Saturation magnetic field: 480 Oe Faraday rotation angle: 43 ° [degrees]. Then, according to the usual method,
The test piece [8-1] is cut into a predetermined size, and the test piece [8-2] is cut.
[4.0 mm x 4.0 mm, 4 pieces], test piece [8-3] [2.0 mm x 2.
0mm, 16 pieces] and test piece [8-4] [1.5mm × 1.5mm
 , 25 pieces] were obtained. Test piece [8-2] obtained here and test
Randomly from piece [8-3] and test piece [8-4]
Select four and change the applied magnetic field strength while changing the magnetic field strength.
And the Faraday rotation angle are measured and drawn on the diagram.
When the size of the stersis was calculated, the test piece [8-2] [4.0 mm × 4.0 mm]: 260 Oe test piece [8-3] [2.0 mm × 2.0 mm]: 350 Oe test piece [8-4] [1.5 mm × 1.5 mm]: A result of 440 Oe was obtained.

Comparative Example 4 A platinum crucible having a capacity of 300 ml was charged with lead oxide [PbO, 4N] 420.
g, bismuth oxide (Bi₂O ₃, 4N] 490 g, ferric oxide [Fe₂
O₃, 4N] 65 g, boron oxide [B₂O₃, 5N] 15g, oxidized gas
Dolinium (Ga₂O₃, 3N] 7.1 g, gallium oxide [Ga
₂O₃, 3N] 0.9 g, aluminum oxide [Al₂O₃, 3N] 2.8g
And prepared. This is the position of the precision vertical tubular electric furnace.
Installed in a container, heat and melt to 1000 ° C, and stir well to homogenize
After mixing, cool to melt temperature 831 ℃ and
A melt for growing a single crystal of S-substituted iron garnet was obtained. Then
On the surface of the melt obtained here, according to the usual method, a thickness of 400μ
m single crystal growth substrate [(111) Garnet single crystal [(GdC
a)₃(GaMgZr)_FiveO₁₂, Lattice constant: 12.506 ± 0.002 Å, 1 b
Contact the other side to maintain the melt temperature at 831 ° C.
While performing epitaxial growth for 110 minutes, single crystal growth
On one side of the production substrate (GdBi)₃(FeGaAl)_FiveO₁₂Has a single crystal film
(GdBi)₃(FeGaAl)_FiveO₁₂Single crystal (hereinafter, GdBiFeGaAl single crystal
Abbreviated as crystal]. Then GdBiF obtained here
The eGaAl single crystal was prepared in a standard size (8.3 mm × 8.
3 mm] was cut to obtain a test piece [9-1] [4 pieces]. here
Select one randomly from the obtained test pieces [9-1], and
BiFeGaAl single crystal 9 single crystal composition and characteristic value [single crystal
Crystal composition, film thickness, saturation magnetic field, Faraday rotation angle]
As a result, single crystal composition: Gd_1.70Bi_1.30Fe_4.70Ga_0.11Al
_0.59O₁₂ The following results were obtained: film thickness: 73 μm Saturation magnetic field: 230 Oe Faraday rotation angle: 46 ° [degree]. Then, according to the usual method,
The test piece [9-1] is cut into a predetermined size, and the test piece [9-2] is cut.
[4.0 mm x 4.0 mm, 4 pieces], test piece [9-3] [2.0 mm x 2.
0mm, 16 pieces] and test piece [9-4] [1.5mm × 1.5mm
 , 25 pieces] were obtained. Test piece obtained here [9-2] and test
Randomly from piece [9-3] and test piece [9-4]
Select four and change the applied magnetic field strength while changing the magnetic field strength.
And the Faraday rotation angle are measured and drawn on the diagram.
When the size of the sterisis was obtained, the test piece [9-2] [4.0 mm × 4.0 mm]: 320 Oe test piece [9-3] [2.0 mm × 2.0 mm]: 390 Oe test piece [9-4] [1.5 mm × 1.5 mm]: A result of 420 Oe was obtained.

[0060]

As a result of the completion of the present invention, it is possible to produce a bismuth-substituted iron garnet single crystal having excellent characteristics as a Faraday rotator for an optical magnetic field sensor, particularly, a small hysteresis due to cutting and a small saturation magnetic field. A small optical magnetic field sensor head for measuring a weak magnetic field can be industrially manufactured and provided at low cost.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram showing an example of a rotational speed (number) meter using an optical magnetic field sensor that utilizes the Faraday effect of a magneto-optical material [Applied Optics (Applied Optics)
tics), vol.28, 1991-1994 (1989)].

FIG. 2 is a schematic diagram showing a magnetization characteristic of a Faraday rotator with respect to an external magnetic field, that is, a relationship between a Faraday rotation angle and an external magnetic field strength.

FIG. 3 is a schematic diagram showing the relationship between the Faraday rotation angle of a Faraday rotator having a relatively small hysteresis due to the cutting of the magneto-optical material, the external magnetic field strength, and the hysteresis.

FIG. 4 is a schematic diagram showing the relationship between the Faraday rotation angle of a Faraday rotator having a relatively large hysteresis due to the cutting of the magneto-optical material, the external magnetic field strength, and the hysteresis.

FIG. 5 is a schematic diagram showing a relationship between a Faraday rotation angle of a Faraday rotator having an extremely large hysteresis due to cutting of a magneto-optical material, an external magnetic field strength, and hysteresis.

Claims (4)

[Claims] 1. A general formula Y _3-xy La _x Bi _y grown by a liquid phase epitaxial method on a non-magnetic garnet single crystal substrate.
Fe _5-z Ga _z O ₁₂ [where x, y, and z are each 0.1 ≦ x
≤ 0.4, 1.0 ≤ y ≤ 1.9, 1.0 ≤ z ≤ 1.6] bismuth-substituted iron garnet single crystal having a chemical composition. 2. A crystal grown on a non-magnetic garnet single crystal substrate by a liquid phase epitaxial method using a melt composed of lead oxide, bismuth oxide, ferric oxide, boron oxide, yttrium oxide, and lanthanum oxide. 1. A bismuth-substituted iron garnet according to 1. 3. A non-magnetic garnet single crystal substrate is calcium-magnesium-zirconium-substituted gadolinium.
_{3. A} gallium garnet (CaGd) ₃ (MgZrGa) ₅ O ₁₂ substrate, and / or claim 2.
The bismuth-substituted iron garnet single crystal described. 4. A general formula Y _3-xy La _x Bi _y grown by a liquid phase epitaxial method on a non-magnetic garnet single crystal substrate.
Fe _5-z Ga _z O ₁₂ [where x, y, and z are each 0.1 ≦ x
≤ 0.25, 1.2 ≤ y ≤ 1.7, 1.0 ≤ z ≤ 1.6], and / or
The bismuth-substituted iron garnet single crystal according to claim 3.