JP2008076772A - Faraday rotator and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Faraday rotator made of Bi-substituted rare-earth iron garnet eliminating the need for a magnetic field application means for saturating magnetization or capable of sufficiently saturating magnetization with a weak magnetic field. <P>SOLUTION: The Faraday rotator comprises a polycrystalline Bi-substituted rare-earth iron garnet including magneto-optical effect. The polycrystalline body comprises a plurality of crystal grains of Bi-substituted rare-earth iron garnet different in magnetic anisotropy energy. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is a Faraday rotator used in an optical isolator or the like for preventing light emitted from a light source such as a semiconductor laser from returning to the light source due to various causes in the field of optical communication or optical measurement. In particular, the present invention relates to a Faraday rotator which does not require a magnetic field applying means for saturating the magnetization in the light propagation direction or can sufficiently saturate the magnetization with a weak magnetic field.

    FIG. 4 shows a schematic configuration of an optical isolator using a Faraday rotator that is well known in the art. In the figure, 41 is a Faraday rotator, 42 is a polarizer, 43 is an analyzer, 44 is a magnetic field applying means such as a permanent magnet, 45 is a light source composed of a semiconductor laser or the like, 46 is a propagation direction of light emitted from the light source 45. Indicates.

  As a material of the conventional Faraday rotator 41, for example, as described in Patent Document 1, a bismuth-substituted rare earth iron garnet single crystal formed on a nonmagnetic garnet substrate by a liquid phase epitaxial method has been used. In general, the angle between the polarization direction of light incident on the Faraday rotator and the polarization direction of light after passing through the Faraday rotator, that is, the Faraday rotation angle, is the thickness of the light propagation direction of the Faraday rotator. Proportional.

  For example, in the case of an optical isolator, the Faraday rotation angle needs to be 45 degrees, and the thickness of the bismuth-substituted rare earth iron garnet is 400 to 500 μm (hereinafter, for obtaining a Faraday rotation angle of 45 degrees). The thickness is referred to as “propagation length”). Usually, in order to obtain such propagation length, after forming the bismuth-substituted rare earth iron garnet thicker than the above-mentioned propagation length by liquid phase epitaxy, the substrate is removed by polishing, and further, the desired Faraday rotation angle is obtained by precision polishing. A processing method has been adopted in which the film thickness required for obtaining is obtained.

When the Faraday rotator is used for an optical isolator or the like, it is generally used by saturating the magnetization of the Faraday rotator in the light propagation direction by an appropriate magnetic field applying means 44 such as a permanent magnet. Document 2 describes a Faraday rotator that does not require such magnetic field application means. Faraday rotator is described in the publication, Tb formed by the liquid phase epitaxial method _{3-x Bi X Fe 5-} YZ Ga y Al z O 12 ( where, 1.1 ≦ x ≦ 1.5,0.65 ≦ y + z ≦ 1.2 , Z ≦ y) and is composed of a bismuth-substituted rare earth iron garnet single crystal. When the Faraday rotator is magnetized in a magnetic field, the magnetization reversal field is negative (magnetized). Therefore, it is described that the magnetic field applying means such as a permanent magnet is not necessary.
Japanese Patent Laid-Open No. 7-206593 JP 9-328398 A

  As a result of systematic examination of the reversibility of the magnetization reversal magnetic field of the Faraday rotator that does not require an external magnetic field by the inventor, the magnitude of the magnetization reversal magnetic field is determined based on the portion of the single crystal or the cutting or polishing of the single crystal. It has become clear that there is a problem that the reproducibility is difficult to obtain with the conventional method. Therefore, the problem to be solved by the present invention is to provide a Faraday rotator which does not require a magnetic field applying means for saturating magnetization or can sufficiently saturate magnetization with a weak magnetic field.

The first means provided by the present invention for solving the above problems is as follows:
A Faraday rotator composed of a Bi-substituted rare earth iron garnet polycrystal having a magneto-optic effect, wherein the polycrystal has a plurality of Bi-substitutions different in at least one of magnetic anisotropy energy and saturation magnetization It is a Faraday rotator characterized by being composed of rare earth iron garnet crystal grains.

The second means provided by the present invention includes
The Faraday rotator is characterized in that the means for differentiating the magnetic anisotropy energy of the crystal grains of the Bi-substituted rare earth iron garnet is a means utilizing the magnetoelastic effect of the Bi-substituted rare earth iron garnet.

The third means provided by the present invention includes
The Bi grain-substituted rare earth iron garnet, its chemical composition is _{(Bi x R 3-x)} (Fe 5-y M y) O 12 ( wherein, R is La, Ce, Pr, Nd, Eu, Gd, At least one of Tb, Ho, Y, Yb, and Lu, M is at least one of Ga and Al, and x and y are 0 <x ≦ 1.6 and 0 ≦ y ≦ 1.0, respectively. The Faraday rotator is characterized in that the polycrystalline body is composed of a plurality of crystal grains that are within the range and have different compositions within the range of the chemical composition.

Furthermore, the fourth means provided by the present invention includes:
A manufacturing method of the Faraday rotator described above,
Raw material fine particles composed of a single composition or a plurality of Bi-substituted rare earth iron garnets having the Faraday effect are mixed with a carrier gas to form an aerosol, and the raw material fine particles are passed through a nozzle together with the carrier gas in a decompression chamber. A method for producing a Faraday rotator comprising an aerosol deposition step of forming a polycrystalline film body made of Bi-substituted rare earth iron garnet by accelerating and spraying the substrate surface.

  In general, the magnetization process of a polycrystalline magnetic material such as a ferromagnetic material or a ferrimagnetic material is roughly divided into a process involving domain wall movement and a process based on magnetization rotation. In a polycrystalline magnetic material, the magnetic exchange interaction acting between the crystal grains is sufficiently smaller than the magnetic exchange interaction acting within the crystal grains (for example, when the grain boundary is made of a non-magnetic material) ) And the size of the crystal grain is smaller than the critical grain size that forms a single magnetic domain structure, the magnetization process is dominated by the magnetization rotation process, and the coercive force of the magnetic material is the magnetism of the crystal grain. It is determined by the anisotropic energy and the magnitude of magnetization.

  On the other hand, when the magnetic exchange interaction between the crystal grains is sufficiently large, in other words, when it can be regarded as magnetically continuous, the domain wall motion becomes dominant in the initial magnetization process, and the magnetic substance The coercive force is determined by the difficulty of domain wall movement. The coercive force determined by the difficulty of domain wall movement is particularly called a domain wall coercive force, and is distinguished from a coercive force based on magnetization rotation.

  Hereinafter, the domain wall coercive force will be described in detail.

  In general, it is known that the domain wall energy is given by the equation (1).

式（１）において、γは磁壁エネルギー、Ａは交換スティフネス定数、Ｋは異方性エネルギーである。

In Expression (1), γ is a domain wall energy, A is an exchange stiffness constant, and K is an anisotropic energy.

  FIG. 5 schematically shows changes in the domain wall energy (γ) depending on the position inside the magnetic body. In an ideal magnetic material, both the exchange stiffness constant (A) and the anisotropic energy (K) are constant regardless of location, and the domain wall energy is a uniform value. In this case, the domain wall coercive force is zero. However, in the case of a polycrystal, for example, the substantial anisotropy energy varies depending on the location due to the change in crystal orientation of the crystal grains depending on the location or the presence of the crystal grain boundary. However, the domain wall coercive force takes a finite value.

  In general, when a magnetic field is not applied to the magnetic material, the domain wall exists at the minimum point of the domain wall energy. In FIG. 5, the position is assumed to be x1. When a magnetic field is applied to the magnetic material, the position of the domain wall changes according to the strength of the applied magnetic field.

  When the applied magnetic field is not sufficiently large, in FIG. 5, assuming that the domain wall has moved from x1 to x2, equation (2) is established.

式（２）において、Isは磁化、Hは印加磁界である。
式（２）と図５とから、印加磁界が一定の場合、磁壁は、磁壁エネルギーの位置に対する微係数の増大と共に、あるいは磁化の減少と共に、移動し難くなることが定性的に理解される。また、 印加磁界が充分大きい場合には、磁壁は磁壁エネルギーの極大を乗り越えて移動し、磁性体の印加磁界に応じて磁化量は増加することになる。

In Equation (2), Is is magnetization and H is an applied magnetic field.
From Equation (2) and FIG. 5, it is qualitatively understood that when the applied magnetic field is constant, the domain wall becomes difficult to move with an increase in the derivative with respect to the position of the domain wall energy or with a decrease in magnetization. When the applied magnetic field is sufficiently large, the domain wall moves over the domain wall energy maximum, and the amount of magnetization increases in accordance with the applied magnetic field of the magnetic material.

  As described above, the domain wall coercivity is caused by the nonuniformity of the domain wall energy, in other words, the nonuniformity of the anisotropic energy, and the value increases the derivative with respect to the position of the domain wall energy. Can be enlarged.

  If the domain wall coercive force increases, the amount of residual magnetization increases, and as a result, sufficient Faraday rotation can be obtained without providing a magnetic field application means such as a permanent magnet.

  In the present invention, in a polycrystalline Bi-substituted rare earth iron garnet magnetic body, the anisotropy energy of crystal grains constituting the polycrystalline body is made different to increase the derivative with respect to the position of the domain wall energy, thereby increasing the high domain wall resistance. Magnetic force is developed.

  According to the present invention, it is possible to provide a Faraday rotator made of a Bi-substituted rare earth iron garnet that does not require a magnetic field applying means for saturating magnetization or can sufficiently saturate magnetization with a weak magnetic field.

  Embodiments of the present invention will be described below.

  FIG. 1 schematically shows the form of a polycrystalline Bi-substituted rare earth iron garnet according to the present invention. In the figure, 1, 2, 11, 12, and 13 are crystal grains constituting the polycrystalline Bi-substituted rare earth iron garnet, 3 is a crystal grain boundary, and 31 and 32 are crystal grain boundaries that exist between the crystal grains 11 and 12, respectively. , And a crystal grain boundary existing between the crystal grains 12 and 13. Further, the magnetic anisotropy energy of the crystal grains 1, 11 and 13 is different from the same energy of the crystal grains 2 and 12.

  Hereinafter, a case where the magnetic anisotropy energy of the crystal grains 11 and 13 is larger than that of the crystal grains 12 will be described as an example. FIG. 2 schematically shows the domain wall energy (see formula (1)) along the line AA ′ in FIG. 1. In the figure, P1 and P2 correspond to the locations where the crystal grain boundaries 31, 32 shown in FIG. Assuming that the exchange stiffness constant (A) is substantially constant, the domain wall energy is proportional to the magnetic anisotropy energy, and therefore is small in the portion corresponding to the crystal grains 12 and large in the portions corresponding to the crystal grains 11 and 13.

  As described above, since the domain wall coercivity is proportional to the differential coefficient with respect to the position of the domain wall energy, the domain wall coercivity increases as the change in domain wall energy, that is, the change in magnetic anisotropy energy becomes steeper. In the case of the polycrystalline Bi-substituted rare earth iron garnet according to the present invention, the region where the magnetic anisotropy energy changes is almost limited to the region of the grain boundary, and the grain boundary is generally very thin, The differential coefficient with respect to the position of the magnetic anisotropy energy, that is, the same coefficient of the domain wall energy becomes very large, and the domain wall coercive force can be increased.

  The mechanism for increasing the domain wall coercive force in the present invention has been described above. This increase in the domain wall coercive force is caused when the magnetic anisotropy energy of the crystal grains 12 is larger than the energy of the crystal grains 11 and 13. Are naturally expressed.

  Also, as a method of changing the magnetic anisotropy energy of the crystal grains constituting the polycrystalline Bi-substituted rare earth iron garnet, <1> a method of changing the chemical composition of the crystal grains, or <2> a method of changing the magnetic anisotropy by the magnetoelastic effect. The method of inducing directionality can be mentioned. Among these methods, the method <1> is a method based on the fact that, in the case of Bi-substituted rare earth iron garnet, the magnetic anisotropy energy differs depending on the chemical composition. A method for inducing magnetic anisotropy by the magnetoelastic effect <2> will be described below.

  Generally, when a force is applied to a magnetic material, magnetic anisotropy is induced by a magnetoelastic effect. The relationship between the stress generated in the magnetic body by applying force and the magnetic anisotropy energy is given by equation (3).

式（３）において、Ｋｕは誘導される磁気異方性エネルギー、λは磁歪定数、σは応力である。一般的に、応力が圧縮応力の場合には、σは負、同引っ張り応力の場合には正で表記される。また、磁歪定数（λ）は正・負いずれの値もとり得、λ・σ積が正の場合には、応力の方向を磁化容易軸とする一軸的な磁気異方性が、λ・σ積が負の場合には、応力の方向と直交する方向を磁化容易軸とする磁気異方性が誘導される。

また、Ｂｉ置換希土類鉄ガーネットのような立方晶に属する磁性体の場合、磁歪定数（λ）は、λ₁₁₁とλ₁₀₀の線型結合で表される。ここで、λ₁₁₁は応力の方向が（１１１）方向の場合の磁歪定数、λ₁₀₀は同（１００）方向の場合の磁歪定数である。一般的に、磁歪定数、λ₁₁₁とλ₁₀₀は互いに異なり、例えばTb₃Fe₅O₁₂の場合、λ₁₁₁は12×10⁶、λ₁₀₀は-3.3×10⁶である。

In Equation (3), Ku is the induced magnetic anisotropy energy, λ is the magnetostriction constant, and σ is the stress. Generally, when the stress is a compressive stress, σ is expressed as negative, and when the stress is the tensile stress, it is expressed as positive. The magnetostriction constant (λ) can be either positive or negative. When the λ · σ product is positive, the uniaxial magnetic anisotropy with the direction of stress as the easy axis of magnetization is the λ · σ product. Is negative, magnetic anisotropy is induced with the easy axis as the direction orthogonal to the direction of stress.

In the case of a magnetic material belonging to a cubic crystal such as Bi-substituted rare earth iron garnet, the magnetostriction constant (λ) is represented by a linear combination of λ ₁₁₁ and λ ₁₀₀ . Here, λ ₁₁₁ is a magnetostriction constant when the stress direction is the (111) direction, and λ ₁₀₀ is a magnetostriction constant when the stress direction is the (100) direction. In general, the magnetostriction constants λ ₁₁₁ and λ ₁₀₀ are different from each other. For example, in the case of Tb ₃ Fe ₅ O ₁₂ , λ ₁₁₁ is 12 × 10 ⁶ and λ ₁₀₀ is −3.3 × 10 ⁶ .

  An example of a method for inducing magnetic anisotropy by the magnetoelastic effect will be described with reference to FIGS. 3a and 3b. FIG. 3a is a schematic cross-sectional side view schematically showing a form in which a Bi-substituted rare earth iron garnet polycrystal is formed on a suitable substrate, and FIG. 3b is a diagram showing magnetism induced by magnetoelastic effect in each crystal grain. It is the figure which showed the anisotropy typically. In the figure, 33 is a substrate, 34 is a Bi-substituted rare earth iron garnet polycrystal, 35 is a crystal grain constituting the polycrystal 34, 351 is a crystal grain having a positive magnetostriction constant, 352 is a crystal grain having a negative magnetostriction constant, Reference numerals 36 and 37 denote arrows indicating the easy axis direction of magnetization, and 38 denotes the direction of stress.

As shown in the figure, when the formation surface of the polycrystal body 34 is warped convexly with the upper surface as the upper surface, compressive stress exists inside the polycrystal body 34. In such a case, since the crystal axes of the crystal grains 35 constituting the polycrystal 34 are disorderly oriented, the magnetostriction constants with respect to the direction of the stress are also different. For example, as shown in FIG. In some cases, the magnetostriction constant is positive, and in some crystal grains, it is negative. For example, in the case of Tb ₃ Fe ₅ O ₁₂ described above, the magnetostriction constant related to the induced magnetic anisotropy is a positive value in the case of crystal grains whose stress direction coincides with the <111> axis. In the case of a crystal grain having only a certain λ ₁₁₁ and the direction of the stress coincides with the <100> axis, the magnetostriction constant related to the induced magnetic anisotropy is only a negative value λ _100. .

  Thus, when the signs of the magnetostriction constants are different, as shown in FIG. 3b, not only the induced magnetic anisotropy energy but also the easy magnetization axis direction differs depending on the crystal grains.

  In the present invention, it is not an essential requirement that the sign of the magnetostriction constant is different. In short, as long as the magnetostriction constant involved in the induced magnetic anisotropy is different in each crystal grain, the domain wall of the present invention. The effect of increasing the coercive force appears. Further, the stress existing in the Bi-substituted rare earth iron garnet is not limited to compressive stress, and the domain wall coercive force increasing effect of the present invention is exhibited even in the case of tensile stress.

  As the method for changing the magnetic anisotropy energy described above, when the method <1>, that is, the method of changing the chemical composition of the crystal grains, is adopted, the chemical composition of each crystal grain is clearly defined at the grain boundary. It is important to distinguish between From such a viewpoint, as a method for forming the Bi-substituted rare earth iron garnet, a film forming method using an aerosol deposition method is suitable.

  The aerosol deposition method (hereinafter referred to as the AD method) is a method in which a raw material composed of fine particles such as ceramics having a particle size of several tens of nanometers to several μm is mixed with a gas to form an aerosol, which is then sprayed onto a substrate through a nozzle to produce ceramics, etc. This is a technique for forming a film. The AD method is a method capable of forming a dense film having a crystal structure similar to that of fine particles as a raw material at a low substrate temperature and at a high film formation rate.

  A film forming apparatus using the AD method will be described with reference to FIG. FIG. 5 is a schematic diagram showing the basic configuration of the film forming apparatus. In the figure, 51 is a deposition substrate, 52 is an XY stage that moves the deposition substrate 51, 53 is a nozzle, 54 is a deposition chamber, 55 is a classifier, 56 is an aerosol generator, 57 is a high-pressure gas, 58 Is a mass flow controller, 59 is a pipeline, and the arrows in the figure schematically show the substrate scanning direction. Raw material fine particles made of ceramics or the like are mixed with a carrier gas (not shown) supplied via a mass flow controller 58 inside the aerosol generator 56 to be aerosolized. The inside of the film forming chamber 54 is decompressed to about 50 Pa by a vacuum pump (not shown), and the raw material fine particles aerosolized by the gas flow generated by the differential pressure between this pressure and the pressure inside the aerosol generator 56. Is introduced into the film forming chamber 54 through the classifier 55, accelerated through the nozzle 53, and sprayed onto the film formation substrate 51. The raw material fine particles conveyed by the gas are accelerated up to several hundred m / s by passing through a nozzle having a minute opening of 1 mm or less. The accelerated raw material fine particles collide with the deposition target substrate 51, and the kinetic energy is released at a stretch to form a film.

  As described above, since the ceramic film having the same crystal structure as that of the raw material fine particles can be formed at a low substrate temperature by using the AD method, for example, fine particles made of a plurality of types of Bi-substituted rare earth iron garnets having different compositions are previously prepared. A Bi-substituted rare earth iron garnet polycrystal having a distinct chemical composition at the grain boundary is formed by mixing at a desired ratio and forming the composite fine particles as raw material fine particles using the AD method. Obtainable.

  Hereinafter, the present invention will be described in more detail with reference to examples.

<Example 1>
A Bi _1.0 Gd _2.0 Fe ₅ O ₁₂ film having a thickness of 300 μm was formed on the surface of the sapphire substrate by the AD method. The average particle diameter of the raw material fine particles used here was 0.8 μm, the carrier gas was oxygen, and the flow rate was 5 liters / minute. The opening diameter of the injection nozzle was 0.6 mmφ. The shape of the sapphire substrate used was 10 mm square and the thickness was 0.6 mm.

The thermal expansion coefficient of the sapphire substrate is about 5 × 10 ⁻⁶ / ° C., which is smaller than the thermal expansion coefficient (about 10 × 10 ⁻⁶ / ° C.) of the Bi-substituted rare earth iron garnet used in this example.

After film formation, heat treatment was performed in an oxygen atmosphere at 700 ° C. for 1 hour. The sample after the heat treatment warped in a concave shape when the film formation surface was the upper surface, and it was confirmed that tensile stress remained in the Bi _1.0 Gd _2.0 Fe ₅ O ₁₂ film. Moreover, as a result of measuring the X-ray diffraction of the Bi _1.0 Gd _2.0 Fe ₅ O ₁₂ film after the heat treatment by the powder X-ray diffraction method, the film is a polycrystal and the specific crystal axis is preferentially oriented. Not confirmed.

The sample after the heat treatment was cut into a rectangular parallelepiped shape having a width of 300 μm and a length of 450 μm, and a magnetization curve and a Faraday rotation were measured. (The Bi _1.0 Gd _2.0 Fe ₅ O ₁₂ film thickness of the cuboid sample is 300 μm, and when the thickness of the sapphire substrate: 0.6 mm is included, the thickness of the cuboid sample is 0.9 mm.)
As a result of measuring the saturation Faraday rotation angle by transmitting light having a wavelength of 1.55 μm in the longitudinal direction of the rectangular parallelepiped sample, the value was 54 degrees. Further, as a result of measuring the magnetization curve by sweeping the magnetic field in the longitudinal direction of the sample with a VSM (vibrating magnetometer), the coercivity of the Bi _1.0 Gd _2.0 Fe ₅ O ₁₂ film is 170 Oe, and the Mr square ratio is about 0. .85.
<Example 2>
A Bi-substituted rare earth iron garnet mixed film composed of a mixture of Bi _1.0 Gd _2.0 Fe ₅ O ₁₂ and Bi _1.0 Tb _2.0 Fe ₅ O ₁₂ is formed on the surface of the sapphire substrate in a manner substantially similar to the method described in Example 1. A thick film was formed. The raw material fine particles used were fine particles in which powders of Bi _1.0 Gd _2.0 Fe ₅ O ₁₂ and Bi _1.0 Tb _2.0 Fe ₅ O _{12 having} an average particle diameter of 0.8 μm were mixed at a weight ratio of 1: 1.

As a result of measuring the X-ray diffraction of the heat-treated sample by the powder X-ray diffraction method, the formed Bi-substituted rare earth iron garnet mixed film is a polycrystal and the specific crystal axis is preferential as in Example 1. It was confirmed that they were not oriented. In addition, the diffraction located on the high diffraction angle side due to the garnet structure is clearly separated and formed based on each of Bi _1.0 Gd _2.0 Fe ₅ O ₁₂ and Bi _1.0 Tb _2.0 Fe ₅ O ₁₂ The film was confirmed to be a mixture of two types of Bi-substituted rare earth iron garnets with distinctly different compositions.

As a result of measuring the saturation Faraday rotation angle of the sample after the heat treatment by the same method as described in Example 1, the value was 50 degrees. The coercive force was 200 Oe and the Mr squareness ratio was about 0.82.
<Example 3>
A Bi-substituted rare earth iron garnet film composed of a mixture of Bi _1.0 Gd _2.0 Fe ₅ O ₁₂ and Bi _1.0 Gd _2.0 Fe _4.5 Al _0.5 O ₁₂ was formed in the same manner as in Example 2. The mixing ratio of both is 1: 1 as in Example 2.

As a result of measuring the X-ray diffraction of the heat-treated sample by the powder X-ray diffraction method, the formed Bi-substituted rare earth iron garnet mixed film is a polycrystal and the specific crystal axis is preferential as in Example 1. It was confirmed that they were not oriented. In addition, the diffraction located on the high diffraction angle side due to the garnet structure is clearly separated into diffraction based on each of Bi _1.0 Gd _2.0 Fe ₅ O ₁₂ and Bi _1.0 Gd _2.0 Fe _4.5 Al _0.5 O ₁₂ , It was confirmed that the formed film was a mixture of two types of Bi-substituted rare earth iron garnets with clearly different compositions.

The sample after the heat treatment was measured for saturated Faraday rotation angle by the same method as described in Example 1, and as a result, the value was 48 degrees. The coercive force was 200 Oe and the Mr squareness ratio was about 0.85.
<Example 4>
A Bi-substituted rare earth iron garnet film composed of a mixture of Bi _1.0 Gd _2.0 Fe ₅ O ₁₂ and Bi _1.0 Gd _2.0 Fe _4.5 Ga _0.5 O ₁₂ was formed in the same manner as in Example 2. The mixing ratio of both is 1: 1 as in Example 2.

As a result of measuring the X-ray diffraction of the heat-treated sample by the powder X-ray diffraction method, the formed Bi-substituted rare earth iron garnet mixed film is a polycrystal and the specific crystal axis is preferential as in Example 1. It was confirmed that they were not oriented. In addition, the diffraction located on the high diffraction angle side due to the garnet structure is clearly separated into diffraction based on each of Bi _1.0 Gd _2.0 Fe ₅ O ₁₂ and Bi _1.0 Gd _2.0 Fe _4.5 Gal _0.5 O ₁₂ It was confirmed that the formed film was a mixture of two types of Bi-substituted rare earth iron garnets with clearly different compositions.

  The sample after the heat treatment was measured for saturation Faraday rotation angle by the same method as described in Example 1, and as a result, the value was 49 degrees. The coercive force was 210 Oe and the Mr squareness ratio was about 0.85.

As mentioned above, as an example, the case of Bi-substituted Gd iron garnet has been mainly described in detail, but the present invention is not limited to the garnet composition. That is, as described above, the requirement for expressing the domain wall coercivity increasing effect, which is the effect of the present invention, is different in the magnetic anisotropy energy of the crystal grains constituting the Bi-substituted rare earth iron garnet polycrystal. it, and the within this range, the general _{formula: (Bi x R 3-x} ) (Fe 5-y M y) to R of Bi substituted rare earth iron garnet represented by _{O 12 La, Ce, Pr,} Nd, At least one of Eu, Gd, Tb, Ho, Y, Yb, and Lu can be used, and M can be at least one of Ga and Al. However, in the case of Bi-substituted rare earth iron garnet, if the Bi substitution amount increases, the garnet structure itself becomes unstable. Therefore, the range of the substitution amount: x is preferably 0 <x ≦ 1.6. Further, since M, which is a substitution element of iron, is a nonmagnetic element, the substitution causes a decrease in Faraday rotation. Therefore, from this viewpoint, the range of the substitution amount: y is preferably 0 ≦ y ≦ 1.0.

  Furthermore, the film formation conditions, heat treatment conditions, and substrate types of the AD method when forming the Bi-substituted rare earth iron garnet film are not limited to the conditions and types described in the above-described embodiments.

  For example, in the case of utilizing the induced magnetic anisotropy due to the magnetoelastic effect described in Example 1, from the viewpoint of the magnetostriction constant of Bi-substituted rare earth iron garnet and the necessary internal stress, ordinary experimental means are used. The substrate type or heat treatment conditions can be selected as appropriate. Also, the carrier gas flow rate or the average particle diameter of the raw material fine particles, which are film formation conditions of the AD method, can be appropriately selected by ordinary experimental means.

Schematic view of polycrystalline Bi-substituted rare earth iron garnet according to the present invention Schematic diagram showing changes in domain wall energy along the line AA 'in FIG. Schematic side sectional view schematically showing the form when a Bi-substituted rare earth iron garnet polycrystal is formed on a suitable substrate Diagram showing magnetic anisotropy induced in crystal grains by magnetoelastic effect Schematic diagram of optical isolator using Faraday rotator Schematic diagram showing changes in domain wall energy depending on position Schematic showing the basic configuration of the film deposition system using the AD method

Explanation of symbols

1, 2, 11, 12, 13 Crystal grains constituting polycrystalline Bi-substituted rare earth iron garnet 3 Grain boundary 31 Grain boundary existing between crystal grains 11 and 12,
32 Grain boundary existing between crystal grains 12 and 13
P1 Location where the crystal grain boundary 31 shown in FIG. 1 exists P2 Location where the crystal grain boundary 32 shown in FIG. 1 exists
33 Substrate 34 Bi-substituted rare earth iron garnet polycrystal 35 Crystal grains constituting the polycrystal 34 351 Crystal grains having a positive magnetostriction constant 352 Crystal grains having a negative magnetostriction constant 36, 37 Arrows indicating the easy axis of magnetization 38 Stress Directional arrow 41 Faraday rotator 42 Polarizer 43 Analyzer 44 Magnetic field applying means such as a permanent magnet 45 Light source composed of a semiconductor laser or the like 46 Propagation direction of light emitted from the light source 45 51 Deposition substrate 52 Deposition substrate XY stage for moving 51 53 Nozzle 54 Deposition chamber 55 Classifier 56 Aerosol generator 57 High pressure gas 58 Mass flow controller 59 Pipeline

Claims (4)

  A Faraday rotator composed of a polycrystalline body of Bi-substituted rare earth iron garnet having a magneto-optical effect, wherein the polycrystalline body is composed of a plurality of grains of Bi-substituted rare earth iron garnet having different magnetic anisotropy energies Faraday rotator characterized by being.   2. The Faraday rotator according to claim 1, wherein the means for differentiating the magnetic anisotropy energy of the crystal grains of the Bi-substituted rare earth iron garnet is a means utilizing the magnetoelastic effect of the Bi-substituted rare earth iron garnet. .   The crystal grains of the Bi-substituted rare earth iron garnet have a chemical composition of (BixR3-x) (Fe5-yMy) O12 (where R is La, Ce, Pr, Nd, Eu, Gd, Tb, Ho, Y, Yb , Lu, M is at least one of Ga and Al, and x and y are in the range of 0 <x ≦ 1.6 and 0 ≦ y ≦ 1.0, respectively, and The Faraday rotator according to claim 1, wherein the polycrystal is composed of a plurality of crystal grains having different compositions within the range of the chemical composition.   5. A method for producing a Faraday rotator according to claim 1, wherein raw material fine particles comprising a plurality of Bi-substituted rare earth iron garnets having a single composition or different compositions having the Faraday effect are mixed with a carrier gas to form an aerosol. And an aerosol deposition step of forming a polycrystalline film body made of Bi-substituted rare earth iron garnet by accelerating the raw material fine particles together with the carrier gas in a reduced pressure chamber through a nozzle and injecting them toward the substrate surface. A method for producing a Faraday rotator, comprising:

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