JP2009147184A

JP2009147184A - Method for manufacturing bismuth-substituted rare-earth iron garnet single crystal

Info

Publication number: JP2009147184A
Application number: JP2007324189A
Authority: JP
Inventors: Yohei Hanaki; 陽平花木
Original assignee: Granopt Ltd
Current assignee: Granopt Ltd
Priority date: 2007-12-17
Filing date: 2007-12-17
Publication date: 2009-07-02

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a bismuth-substituted rare-earth iron garnet single crystal not containing lead by a liquid phase epitaxial method using melt not containing lead in flux components. <P>SOLUTION: The method for manufacturing the bismuth-substituted rare-earth iron garnet single crystal is characterized by generating the melt from a flux consisting of Li<SB>2</SB>O, B<SB>2</SB>O<SB>3</SB>and Bi<SB>2</SB>O<SB>3</SB>and growing the bismuth-substituted rare-earth iron garnet single crystal by the liquid phase epitaxial method on a nonmagnetic garnet single crystal using the melt. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

本発明は、光アイソレータや光サーキュレータなどのファラデー回転子に用いられる希土類鉄ガーネット単結晶に関する。 The present invention relates to a rare earth iron garnet single crystal used for a Faraday rotator such as an optical isolator or an optical circulator.

近年、光ファイバ通信や光計測の発展はめざましいものがある。この光ファイバ通信や光計測では多くの場合、信号源として半導体レーザが使用されている。しかし、半導体レーザは、光ファイバ端面などから反射し、再び半導体レーザ自身に戻ってくるところの所謂反射戻り光があると、発振が不安定になるという重大な欠点がある。そのため半導体レーザの出射側に光アイソレータを設けて、反射戻り光を遮断し、半導体レーザの発振を安定化させることが行われている。 In recent years, the development of optical fiber communication and optical measurement has been remarkable. In this optical fiber communication and optical measurement, a semiconductor laser is often used as a signal source. However, the semiconductor laser has a serious drawback that oscillation is unstable if there is so-called reflected return light that is reflected from the end face of the optical fiber and returns to the semiconductor laser itself. Therefore, an optical isolator is provided on the emission side of the semiconductor laser to block the reflected return light and stabilize the oscillation of the semiconductor laser.

光アイソレータは偏光子、検光子、ファラデー回転子およびファラデー回転子を磁気的に飽和させるための永久磁石からなる。光アイソレータの中心的な機能を担うファラデー回転子には、主に液相エピタキシャル（以下、ＬＰＥと略す）法で育成される厚さが数十μｍから５００μｍ程度のビスマスを置換した希土類鉄ガーネット単結晶（以下、ＲＩＧと適宜略す）、たとえば（ＨｏＴｂＢｉ）_３Ｆｅ_５Ｏ_１２、（ＹｂＴｂＢｉ）_３Ｆｅ_５Ｏ_１２などが提案されている。 The optical isolator includes a polarizer, an analyzer, a Faraday rotator, and a permanent magnet for magnetically saturating the Faraday rotator. The Faraday rotator, which plays a central role in optical isolators, is a rare earth iron garnet single-layered film in which bismuth having a thickness of about several tens to 500 μm, which is grown mainly by liquid phase epitaxy (hereinafter abbreviated as LPE), is substituted. Crystals (hereinafter abbreviated as RIG as appropriate), for example, (HoTbBi) ₃ Fe ₅ O ₁₂ , (YbTbBi) ₃ Fe ₅ O ₁₂ have been proposed.

一般的なＬＰＥ法によるＲＩＧの育成は、フラックス成分であるＰｂＯ−Ｂｉ_２Ｏ_３−Ｂ_２Ｏ_３にガーネット単結晶成分である希土類や鉄を溶かした融液を、ガーネット単結晶が析出する過飽和温度状態に保ち、種結晶基板を該融液に浸漬して、基板上に結晶を成長させるという方法である。この際に、フラックス成分であり、かつファラデー効果の増大をもたらすビスマスが多量に取り込まれ、希土類の一部がビスマスに置換されたＲＩＧが育成されるのである。しかしながら、同じくフラックス成分である鉛も、不純物として０.２重量％〜０.８重量％が取り込まれる。 The growth of RIG by a general LPE method is supersaturation in which a garnet single crystal precipitates a melt obtained by dissolving rare earth or iron as a garnet single crystal component in PbO—Bi ₂ O ₃ —B ₂ O ₃ as a flux component. This is a method in which a seed crystal substrate is immersed in the melt while maintaining a temperature state to grow a crystal on the substrate. At this time, a large amount of bismuth, which is a flux component and causes an increase in the Faraday effect, is taken in, and RIG in which a part of the rare earth is replaced with bismuth is grown. However, 0.2% by weight to 0.8% by weight of lead, which is also a flux component, is incorporated as an impurity.

近年、環境に対する規制が厳しくなってきている。鉛は中枢神経系機能障害やガンを引き起こす物質であることから、例えば、ＲｏＨＳ指令「電気電子機器に含まれる特定有害物質の使用制限に関する欧州議会および理事会指令」での指定物質であり、その最大許容量は０.１重量％と定められている。このＲｏＨＳ指令を満足するための最も有効な手段は、鉛を含まないフラックス成分を使った融液による結晶育成であることは明白である。例えば、鉛を含まないフラックス成分としてＢｉ_２Ｏ_３（特許文献１）、またはＢｉ_２Ｏ_３にアルカリ金属を添加した方法を用いる例（特許文献２）が報告されているが、光通信用途のファラデー回転子に必要な厚さ０.５ｍｍ程度の良質なＲＩＧを、安定に育成する技術は確立されていない。また、困難だとされている。
特開昭５０−１３４０００特公昭５７−４５７１９ In recent years, environmental regulations have become stricter. Since lead is a substance that causes central nervous system dysfunction and cancer, for example, it is a designated substance in the RoHS Directive “European Parliament and Council Directive on Restriction of Use of Specific Hazardous Substances Included in Electrical and Electronic Equipment”. The maximum allowable amount is set at 0.1% by weight. It is clear that the most effective means for satisfying this RoHS directive is crystal growth by a melt using a flux component not containing lead. For example, Bi ₂ O ₃ (Patent Document 1) or an example of using a method of adding an alkali metal to Bi ₂ O ₃ (Patent Document 2) as a flux component not containing lead has been reported. A technique for stably growing a high-quality RIG having a thickness of about 0.5 mm required for a Faraday rotator has not been established. It is also difficult.
JP 50-134000 A Japanese Patent Publication No.57-45719

フラックス成分に鉛を含まないＬＰＥ法にて、安定的に結晶育成が可能で、量産性に富んだＲＩＧの結晶育成技術を提案する。 We propose a crystal growth technique for RIG that is capable of stable crystal growth and is mass-productive by the LPE method that does not contain lead in the flux component.

本発明者らは、上記課題を解決すべく鋭意検討した結果、フラックス成分がＬｉ_２Ｏ、Ｂ_２Ｏ_３、Ｂｉ_２Ｏ_３により構成された融液を生成し、該融液を用いることが上記課題を解決するために有効であるという知見を見出し、本発明を完成させた。 As a result of intensive studies to solve the above problems, the inventors of the present invention generate a melt whose flux components are composed of Li ₂ O, B ₂ O ₃ , and Bi ₂ O ₃ and use the melt. The present inventors have found the knowledge that it is effective for solving the above problems and completed the present invention.

また上記課題は融液中のＬｉ_２Ｏのモル濃度ｘ（ｍｏｌ％）とＢ_２Ｏ_３のモル濃度ｙ（ｍｏｌ％）とＢｉ_２Ｏ_３のモル濃度ｚ（ｍｏｌ％）が１．２≦（ｘ/ｙ）≦３．５及び０．０５６（ｘ/ｙ）＾１．０７≦（ｘ/ｚ）≦０．２１１（ｘ/ｙ）＾１．２８を満たす融液を生成し、該融液を用いることで達成される。 In addition, the above-mentioned problem is that the molar concentration x (mol%) of Li ₂ O, the molar concentration y (mol%) of B ₂ O _{3 and} the molar concentration z (mol%) of Bi ₂ O _{3 in} the melt are 1.2 ≦ (X / y) ≦ 3.5 and 0.056 (x / y) ^ 1.07 ≦ (x / z) ≦ 0.211 (x / y) ^ 1.28 are produced, This is achieved by using a melt.

環境への規制、例えばＲｏＨＳ指令を満足し、光学特性の優れたファラデー回転子の提供が可能となる。 It is possible to provide a Faraday rotator that satisfies environmental regulations such as the RoHS directive and has excellent optical characteristics.

上記である本発明において、ＲＩＧは、
一般式：Ｒ_３−ａＢｉ_ａＦｅ_５−ｂＭ_ｂＯ_１２
（式中、ＲはＹ、Ｅｕ、Ｇｄ、Ｔｂ、Ｈｏ、ＹｂおよびＬｕからなる群から選ばれる一種または二種以上の元素である。Ｍは、ＧａまたはＡｌ、およびその両方の元素である。また、０．５≦ａ≦２．０、ｂ≦１．６である。）
の式で表されるＲＩＧから選択する。
ここで、ａが０．５未満ではファラデー効果が小さくなり好ましくない。ファラデー効果との観点からは、より大きいことが好ましいが、２．０を超えると結晶欠陥が増加してくるので好ましくない。
ＧａとＡｌにてＦｅを置換する手法は、ＲＩＧの飽和磁界を下げるために用いるが、置換量ｂが１．６を超えるとファラデー効果が小さくなるので好ましくない。 In the present invention as described above, RIG is:
General _{_{_{formula: R 3-a Bi a Fe}}} 5-b M b O 12
(In the formula, R is one or more elements selected from the group consisting of Y, Eu, Gd, Tb, Ho, Yb, and Lu. M is an element of Ga or Al, or both. Also, 0.5 ≦ a ≦ 2.0 and b ≦ 1.6.)
It selects from RIG represented by the type | formula.
Here, if a is less than 0.5, the Faraday effect becomes small, which is not preferable. From the viewpoint of the Faraday effect, it is preferably larger, but if it exceeds 2.0, crystal defects increase, which is not preferable.
The method of substituting Fe with Ga and Al is used to lower the saturation magnetic field of RIG. However, if the substitution amount b exceeds 1.6, the Faraday effect is reduced, which is not preferable.

また、Ｒは、光学特性と磁気特性を考慮し、かつ基板との格子定数の適合性などを考慮して選択するものであるが、具体的には、Ｙ、Ｅｕ、Ｇｄ、Ｔｂ、Ｈｏ、Ｙｂ、Ｌｕの組み合わせが挙げられる。
また、Ｍは、２つのＦｅサイトに置換される置換量が安定となるように選択することが好ましく、具体的には、Ｇａ、Ａｌの組み合わせが挙げられる。 R is selected in consideration of optical characteristics and magnetic characteristics and in consideration of the compatibility of the lattice constant with the substrate. Specifically, Y, Eu, Gd, Tb, Ho, The combination of Yb and Lu is mentioned.
Further, M is preferably selected so that the substitution amount substituted with two Fe sites is stable, and specific examples include a combination of Ga and Al.

上記ＲＩＧをＬＰＥ法にて育成するためのフラックス成分として従来は、ＰｂＯ、Ｂｉ_２Ｏ_３、及びＢ_２Ｏ_３が用いられてきた。しかしながらＰｂＯ、Ｂｉ_２Ｏ_３、及びＢ_２Ｏ_３で構成されるフラックスで上記ＲＩＧ膜をＬＰＥ法にて育成すると、不純物としてＲＩＧにＰｂが混入することは避けがたいという大きな問題があった。 Conventionally, PbO, Bi ₂ O ₃ , and B ₂ O ₃ have been used as flux components for growing the RIG by the LPE method. However, when the RIG film is grown by the LPE method with a flux composed of PbO, Bi ₂ O ₃ , and B ₂ O ₃ , there is a big problem that it is unavoidable that Pb is mixed into the RIG as an impurity.

本発明者らはフラックス成分として、Ｐｂの代替となる元素について鋭意検討を重ねた。その結果、リチウム（Ｌｉ）がＰｂの代替となる元素であることを見出した。すなわち、Ｌｉ_２Ｏ、Ｂ_２Ｏ_３、Ｂｉ_２Ｏ_３で構成されるフラックスで上記ＲＩＧ膜をＬＰＥ法にて育成したところ、結晶性良好で、なおかつＰｂを含まないＲＩＧが得られた。なお、本願実施例においては、Ｌｉ_２Ｏを生成させるために試薬にＬｉＯＨを用いている。用いる試薬が水酸化物や炭酸化合物であっても高温の融液中では、分解されＬｉ_２Ｏとして存在していると考えるのが一般的であるので、Ｌｉ_２ＣＯ_３といった炭酸化物等を用いてもよい。
The inventors of the present invention have made extensive studies on an element that substitutes for Pb as a flux component. As a result, it was found that lithium (Li) is an element that can substitute for Pb. That is, when the RIG film was grown by the LPE method with a flux composed of Li ₂ O, B ₂ O ₃ , and Bi ₂ O ₃ , an RIG having good crystallinity and not containing Pb was obtained. In this embodiment, LiOH is used as a reagent in order to generate Li ₂ O. Even if the reagent to be used is a hydroxide or a carbonate compound, it is generally considered that the reagent is decomposed and present as Li ₂ O in a high-temperature melt. Therefore, a carbonate such as Li ₂ CO ₃ is used. May be.

本発明者らはフラックス成分におけるＬｉ_２Ｏ、Ｂ_２Ｏ_３、及びＢｉ_２Ｏ_３のモル濃度比を変えて、ＲＩＧの育成を試みた。本発明においては、融液中のＬｉ_２Ｏのモル濃度ｘ（ｍｏｌ％）、Ｂ_２Ｏ_３のモル濃度ｙ（ｍｏｌ％）、Ｂｉ_２Ｏ_３のモル濃度ｚ（ｍｏｌ％）とし、Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）及びＬｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）を融液組成のパラメータとして用いた。 The inventors tried to grow RIG by changing the molar concentration ratio of Li ₂ O, B ₂ O ₃ , and Bi ₂ O _{3 in} the flux component. In the present invention, in the melt Li ₂ O molar concentration x _(mol%), the molar concentration y (mol%) of B 2 _{O 3,} and _Bi 2 _{O 3} molar concentration z (mol%), Li ₂ The molar concentration ratio (x / y) between O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were used as parameters of the melt composition.

本発明者らは、詳細な実験を重ね、良質なＲＩＧを得るためのフラックス組成比を見出し、本発明を完成させるに至った。なお、品質についての判断基準においては、ＲＩＧ内における１００μｍ以上のピット状の欠陥の数とし、１００μｍ以上のピット状の欠陥の数が１０個／ｃｍ^２未満の場合、結晶性は良好、１０個／ｃｍ^２以上の場合、結晶性は悪いと判断した。
図１は、Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）とＬｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）との関係を示すグラフである。図中×は、育成速度が極端に遅い条件、図中△は、ＲＩＧ内に存在する１００μｍ以上のピット状の欠陥が１０個／ｃｍ^２以上であった条件、図中〇はＲＩＧ膜内に存在する１００μｍ以上のピット状の欠陥が１０個／ｃｍ^２未満であった条件を表す。ＬＰＥ法では、フラックス成分の組成比に応じてＲＩＧの成分である上記一般式中のＲやＦｅ、Ｍの成分比を適宜選ぶことで、ＲＩＧを育成することができる。本発明では、図中のフラックス成分に対して、ＲやＦｅ、Ｍの成分比を最適化した結果をもって、その育成されたＲＩＧの結晶性を評価した。まずＬｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）を変えて、融液組成の検討を行った。ｘ/ｙが１．２より小さい場合、ＲＩＧの育成速度が極端に遅くなるか、育成が可能になった場合においてもＲＩＧに欠陥が多く発生し、育成条件的に好ましくないものであった。またｘ/ｙが３．５より大きいと、ＲＩＧを育成する温度において融液中に微結晶が析出してしまい、ＲＩＧに欠陥が多数発生してしまう。よってｘ/ｙにおいては、ＲＩＧを安定的に育成できる条件として、１．２≦ｘ/ｙ≦３．５と定めた（図１の直線ａ、ｂ間）。 The present inventors have repeated detailed experiments, found a flux composition ratio for obtaining a high-quality RIG, and completed the present invention. In addition, in the judgment criteria regarding the quality, the number of pit-like defects of 100 μm or more in the RIG is used, and when the number of pit-like defects of 100 μm or more is less than 10 / cm ² , the crystallinity is good, 10 In the case of / cm ² or more, the crystallinity was judged to be bad.
FIG. 1 is a graph showing the relationship between the molar concentration ratio (x / y) of Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) of Li ₂ O and Bi ₂ O ₃ . Figure × is growth rate is extremely slow condition in FIG △, the condition 100μm or pit-like defects existing in the RIG was 10 / cm ² or more, drawing 〇 is in the RIG film This represents a condition in which the number of existing pit-like defects of 100 μm or more was less than 10 / cm ² . In the LPE method, RIG can be grown by appropriately selecting the component ratio of R, Fe, and M in the above general formula, which is a component of RIG, according to the composition ratio of the flux component. In the present invention, the crystallinity of the grown RIG was evaluated based on the result of optimizing the component ratio of R, Fe, and M with respect to the flux components in the figure. First, the composition of the melt was examined by changing the molar concentration ratio (x / y) between Li ₂ O and B ₂ O ₃ . When x / y is smaller than 1.2, even when the growth rate of RIG is extremely slow or when growth is possible, many defects are generated in RIG, which is not preferable in terms of growth conditions. On the other hand, if x / y is greater than 3.5, microcrystals are deposited in the melt at the temperature at which the RIG is grown, and many defects are generated in the RIG. Therefore, in x / y, it was determined that 1.2 ≦ x / y ≦ 3.5 (between lines a and b in FIG. 1) as a condition for stably growing RIG.

次にＬｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）について検討した。ｘ/ｚが小さいと育成速度が遅くなり、また大きいとＲＩＧに欠陥が多数発生する。組成比と育成条件を詳細に検討した結果、上記ｘ/ｙの範囲であり、なおかつ０．０５６（ｘ/ｙ）＾１．０７≦（ｘ/ｚ）≦０．２１１（ｘ/ｙ）＾１．２８を満たす（図１の直線ｃ、ｄ間）組成において、結晶性の良好なＲＩＧが得られた。 Next, the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ was examined. When x / z is small, the growth rate is slow, and when x / z is large, many defects occur in the RIG. As a result of examining the composition ratio and the growth conditions in detail, it is in the above x / y range, and 0.056 (x / y) ^ 1.07 ≦ (x / z) ≦ 0.211 (x / y) ^ With a composition satisfying 1.28 (between lines c and d in FIG. 1), RIG having good crystallinity was obtained.

本発明に用いる上記ＲＩＧの製造に用いる育成基板としては、公知のものが使用できる。一般には、ＳＧＧＧ基板と称して市販されている格子定数が１．２４９０ｎｍから１．２５１５ｎｍの非磁性ガーネット［（ＧｄＣａ）_３（ＧａＭｇＺｒ）_５Ｏ_１２］基板から適宜選択する。 A well-known thing can be used as a growth board | substrate used for manufacture of said RIG used for this invention. Generally, it is appropriately selected from non-magnetic garnet [(GdCa) ₃ (GaMgZr) ₅ O ₁₂ ] substrates having a lattice constant of 1.2490 nm to 1.2515 nm which are commercially available as SGGG substrates.

以下、本発明を実施例によって、具体的に説明する。
実施例１
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]、酸化イッテリビウム[Ｙｂ_２Ｏ_３]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は７０ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１３．４ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は６．３ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は９ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は１．２ｍｏｌ％、Ｙｂ_２Ｏ_３のモル濃度は０．１ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ１．４３、０．１３であった。
この融液を精密縦型管状電気炉の所定の位置に設置し、１０００℃に加熱溶融し、十分に攪拌混合してＲＩＧ育成用の融液とした。ここに得られた融液の温度を飽和温度以下の温度まで低下させて後、融液表面に、常法に従って、厚さが７６０μmで、格子定数が１．２４９７±０．０００２nmの３インチ（１１１）ガーネット単結晶[(ＧｄＣａ)_３(ＣａＭｇＺｒ)_５Ｏ_１２]基板の片面を接触させ、基板を回転させながらエピタキシャル成長を行った結果、膜厚５３０μmのＲＩＧを得た。１００μｍ以上のピット状の欠陥の数は２個/ｃｍ^２であった。この結晶を蛍光Ｘ線分析法により組成分析した結果、組成はＴｂ_１．９Ｙｂ_０．１Ｂｉ_１．０Ｆｅ_５．０Ｏ_１２であった。またＬｉとＰｂは検出されなかった。ファラデー回転角は１５５０ｎｍ波長にて９８０ｄｅｇ／ｃｍであった。 Hereinafter, the present invention will be specifically described by way of examples.
Example 1
In a platinum crucible, bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ], A total of 6000 g of ytterbium oxide [Yb ₂ O ₃ ] was charged to obtain a melt. The molar concentration of Bi ₂ O ₃ in the melt is 70 mol%, the molar concentration of Fe ₂ O ₃ is 13.4 mol%, the molar concentration of B ₂ O ₃ is 6.3 mol%, and the molar concentration of Li ₂ O is 9 mol%. The molar concentration of Tb ₄ O ₇ was 1.2 mol%, and the molar concentration of Yb ₂ O ₃ was 0.1 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 1.43 and 0.13, respectively.
This melt was placed at a predetermined position in a precision vertical tubular electric furnace, heated and melted to 1000 ° C., and sufficiently stirred and mixed to obtain a melt for RIG growth. After the temperature of the melt thus obtained is lowered to a temperature equal to or lower than the saturation temperature, the surface of the melt is 3 inches (thickness: 760 μm, lattice constant: 1.2497 ± 0.0002 nm according to a conventional method) One side of a 111) garnet single crystal [(GdCa) ₃ (CaMgZr) ₅ O ₁₂ ] substrate was brought into contact and epitaxial growth was performed while rotating the substrate. As a result, an RIG having a film thickness of 530 μm was obtained. The number of pit-like defects of 100 μm or more was 2 / cm ² . As a result of analyzing the composition of this crystal by X-ray fluorescence analysis, the composition was Tb _1.9 Yb _0.1 Bi _1.0 Fe _5.0 O ₁₂ . Li and Pb were not detected. The Faraday rotation angle was 980 deg / cm at a wavelength of 1550 nm.

実施例２
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]、酸化ホルミウム[Ｈｏ_２Ｏ_３] 、酸化ガリウム[Ｇａ_２Ｏ_３]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は７２ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１３．６ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は４．８ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は７．２ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は０．７ｍｏｌ％、Ｈｏ_２Ｏ_３のモル濃度は０．３ｍｏｌ％、Ｇａ_２Ｏ_３のモル濃度は１．４ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ１．５０、０．１０であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、膜厚５7０μmのＲＩＧを得た。１００μｍ以上のピット状の欠陥の数は３個/ｃｍ^２であった。この結晶を蛍光Ｘ線分析法により組成分析した結果、組成はＴｂ_１．３Ｈｏ_０．６Ｂｉ_１．１Ｆｅ_４．３Ｇａ_０．７Ｏ_１２であった。またＬｉとＰｂは検出されなかった。ファラデー回転角は１５５０ｎｍ波長にて８７０ｄｅｇ／ｃｍであった。 Example 2
In a platinum crucible, bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ], A total of 6000 g of holmium oxide [Ho ₂ O ₃ ] and gallium oxide [Ga ₂ O ₃ ] were charged to obtain a melt. The molar concentration of Bi ₂ O ₃ in the melt is 72 mol%, the molar concentration of Fe ₂ O ₃ is 13.6 mol%, the molar concentration of B ₂ O ₃ is 4.8 mol%, and the molar concentration of Li ₂ O is 7. 2 mol%, the molar concentration of _Tb 4 _{O 7} is 0.7 mol%, the molar concentration of _Ho 2 _{O 3} is 0.3 mol%, the molar concentration of _Ga 2 _{O 3} was 1.4 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 1.50 and 0.10, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1. As a result, an RIG with a thickness of 570 μm was obtained. The number of pit-like defects of 100 μm or more was 3 / cm ² . As a result of analyzing the composition of this crystal by X-ray fluorescence analysis, the composition was Tb _1.3 Ho _0.6 Bi _1.1 Fe _4.3 Ga _0.7 O ₁₂ . Li and Pb were not detected. The Faraday rotation angle was 870 deg / cm at a wavelength of 1550 nm.

実施例３
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]、酸化イッテリビウム[Ｙｂ_２Ｏ_３]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は７２ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１３．４ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は４．８ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は８．４ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は１．３ｍｏｌ％、Ｙｂ_２Ｏ_３のモル濃度は０．１ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ１．７５、０．１２であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、膜厚５５０μmのＲＩＧを得た。１００μｍ以上のピット状の欠陥の数は４個/ｃｍ^２であった。この結晶を蛍光Ｘ線分析法により組成分析した結果、組成はＴｂ_１．９Ｙｂ_０．１Ｂｉ_１．０Ｆｅ_５．０Ｏ_１２であった。またＬｉとＰｂは検出されなかった。ファラデー回転角は１５５０ｎｍ波長にて９６０ｄｅｇ／ｃｍであった。 Example 3
In a platinum crucible, bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ], A total of 6000 g of ytterbium oxide [Yb ₂ O ₃ ] was charged to obtain a melt. The molar concentration of Bi ₂ O ₃ in the melt is 72 mol%, the molar concentration of Fe ₂ O ₃ is 13.4 mol%, the molar concentration of B ₂ O ₃ is 4.8 mol%, and the molar concentration of Li ₂ O is 8. 4 mol%, the molar concentration of _Tb 4 _{O 7} is 1.3 mol%, the molar concentration of _Yb 2 _{O 3} was 0.1 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 1.75 and 0.12, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1. As a result, an RIG having a thickness of 550 μm was obtained. The number of pit-like defects of 100 μm or more was 4 / cm ² . As a result of analyzing the composition of this crystal by X-ray fluorescence analysis, the composition was Tb _1.9 Yb _0.1 Bi _1.0 Fe _5.0 O ₁₂ . Li and Pb were not detected. The Faraday rotation angle was 960 deg / cm at a wavelength of 1550 nm.

実施例４
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]、酸化イッテリビウム[Ｙｂ_２Ｏ_３]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は６５ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１３．１ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は７．４ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は１３．０ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は１．４ｍｏｌ％、Ｙｂ_２Ｏ_３のモル濃度は０．１ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ１．７６、０．２０であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、膜厚５７０μmのＲＩＧを得た。１００μｍ以上のピット状の欠陥の数は２個/ｃｍ^２であった。この結晶を蛍光Ｘ線分析法により組成分析した結果、組成はＴｂ_１．９Ｙｂ_０．１Ｂｉ_１．０Ｆｅ_５．０Ｏ_１２であった。またＬｉとＰｂは検出されなかった。ファラデー回転角は１５５０ｎｍ波長にて９５０ｄｅｇ／ｃｍであった。 Example 4
In a platinum crucible, bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ], A total of 6000 g of ytterbium oxide [Yb ₂ O ₃ ] was charged to obtain a melt. The molar concentration of Bi ₂ O ₃ in the melt is 65 mol%, the molar concentration of Fe ₂ O ₃ is 13.1 mol%, the molar concentration of B ₂ O ₃ is 7.4 mol%, and the molar concentration of Li ₂ O is 13. The molar concentration of 0 mol%, Tb ₄ O ₇ was 1.4 mol%, and the molar concentration of Yb ₂ O ₃ was 0.1 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 1.76 and 0.20, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1. As a result, an RIG having a thickness of 570 μm was obtained. The number of pit-like defects of 100 μm or more was 2 / cm ² . As a result of analyzing the composition of this crystal by X-ray fluorescence analysis, the composition was Tb _1.9 Yb _0.1 Bi _1.0 Fe _5.0 O ₁₂ . Li and Pb were not detected. The Faraday rotation angle was 950 deg / cm at a wavelength of 1550 nm.

実施例５
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]、酸化イッテリビウム[Ｙｂ_２Ｏ_３]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は６３ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１２．８ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は１０ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は１２．５ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は１．６ｍｏｌ％、Ｙｂ_２Ｏ_３のモル濃度は０．１ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ１．２５、０．２０であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、膜厚５３０μmのＲＩＧを得た。１００μｍ以上のピット状の欠陥の数は８個/ｃｍ^２であった。この結晶を蛍光Ｘ線分析法により組成分析した結果、組成はＴｂ_１．９Ｙｂ_０．１Ｂｉ_１．０Ｆｅ_５．０Ｏ_１２であった。またＬｉとＰｂは検出されなかった。ファラデー回転角は１５５０ｎｍ波長にて９４０ｄｅｇ／ｃｍであった。 Example 5
In a platinum crucible, bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ], A total of 6000 g of ytterbium oxide [Yb ₂ O ₃ ] was charged to obtain a melt. The molar concentration of Bi ₂ O ₃ in the melt is 63 mol%, the molar concentration of Fe ₂ O ₃ is 12.8 mol%, the molar concentration of B ₂ O ₃ is 10 mol%, and the molar concentration of Li ₂ O is 12.5 mol%. The molar concentration of Tb ₄ O ₇ was 1.6 mol%, and the molar concentration of Yb ₂ O ₃ was 0.1 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 1.25 and 0.20, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1. As a result, RIG having a film thickness of 530 μm was obtained. The number of pit-like defects of 100 μm or more was 8 / cm ² . As a result of analyzing the composition of this crystal by X-ray fluorescence analysis, the composition was Tb _1.9 Yb _0.1 Bi _1.0 Fe _5.0 O ₁₂ . Li and Pb were not detected. The Faraday rotation angle was 940 deg / cm at a wavelength of 1550 nm.

実施例６
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]、酸化イッテリビウム[Ｙｂ_２Ｏ_３]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は５９ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１３．３ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は１２ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は１４．４ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は１．２ｍｏｌ％、Ｙｂ_２Ｏ_３のモル濃度は０．１ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ１．２０、０．２４であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、膜厚５２０μmのＲＩＧを得た。１００μｍ以上のピット状の欠陥の数は８個/ｃｍ^２であった。この結晶を蛍光Ｘ線分析法により組成分析した結果、組成はＴｂ_１．９Ｙｂ_０．１Ｂｉ_１．０Ｆｅ_５．０Ｏ_１２であった。またＬｉとＰｂは検出されなかった。ファラデー回転角は１５５０ｎｍ波長にて９４０ｄｅｇ／ｃｍであった。 Example 6
In a platinum crucible, bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ], A total of 6000 g of ytterbium oxide [Yb ₂ O ₃ ] was charged to obtain a melt. The molar concentration of Bi ₂ O ₃ in the melt is 59 mol%, the molar concentration of Fe ₂ O ₃ is 13.3 mol%, the molar concentration of B ₂ O ₃ is 12 mol%, and the molar concentration of Li ₂ O is 14.4 mol%. The molar concentration of Tb ₄ O ₇ was 1.2 mol%, and the molar concentration of Yb ₂ O ₃ was 0.1 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 1.20 and 0.24, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1. As a result, an RIG having a thickness of 520 μm was obtained. The number of pit-like defects of 100 μm or more was 8 / cm ² . As a result of analyzing the composition of this crystal by X-ray fluorescence analysis, the composition was Tb _1.9 Yb _0.1 Bi _1.0 Fe _5.0 O ₁₂ . Li and Pb were not detected. The Faraday rotation angle was 940 deg / cm at a wavelength of 1550 nm.

実施例７
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]、酸化ホルミウム[Ｈｏ_２Ｏ_３]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は３９ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１５．４ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は１０ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は３５ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は０．２ｍｏｌ％、Ｈｏ_２Ｏ_３のモル濃度は０．４ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ３．５０、０．９０であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、膜厚５００μmのＲＩＧを得た。１００μｍ以上のピット状の欠陥の数は６個/ｃｍ^２であった。この結晶を蛍光Ｘ線分析法により組成分析した結果、組成はＴｂ_０．７Ｈｏ_１．１Ｂｉ_１．２Ｆｅ_５．０Ｏ_１２であった。またＬｉとＰｂは検出されなかった。ファラデー回転角は１５５０ｎｍ波長にて１１５０ｄｅｇ／ｃｍであった。
Example 7
In a platinum crucible, bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ], A total of 6000 g of holmium oxide [Ho ₂ O ₃ ] was charged to obtain a melt. The molar concentration of Bi ₂ O ₃ in the melt is 39 mol%, the molar concentration of Fe ₂ O ₃ is 15.4 mol%, the molar concentration of B ₂ O ₃ is 10 mol%, the molar concentration of Li ₂ O is 35 mol%, Tb The molar concentration of ₄ O ₇ was 0.2 mol%, and the molar concentration of Ho ₂ O ₃ was 0.4 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 3.50 and 0.90, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1, and as a result, a RIG having a thickness of 500 μm was obtained. The number of pit-like defects of 100 μm or more was 6 / cm ² . As a result of analyzing the composition of this crystal by X-ray fluorescence analysis, the composition was Tb _0.7 Ho _1.1 Bi _1.2 Fe _5.0 O ₁₂ . Li and Pb were not detected. The Faraday rotation angle was 1150 deg / cm at a wavelength of 1550 nm.

実施例８

白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]、酸化イッテリビウム[Ｙｂ_２Ｏ_３]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は５５ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１５ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は６．９ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は２２．１ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は０．８ｍｏｌ％、Ｙｂ_２Ｏ_３のモル濃度は０．１ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ３．２０、０．４０であった。

この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、膜厚５５０μmのＲＩＧを得た。１００μｍ以上のピット状の欠陥の数は６個/ｃｍ^２であった。この結晶を蛍光Ｘ線分析法により組成分析した結果、組成はＴｂ_１．９Ｙｂ_０．１Ｂｉ_１．０Ｆｅ_５．０Ｏ_１２であった。またＬｉとＰｂは検出されなかった。ファラデー回転角は１５５０ｎｍ波長にて９５０ｄｅｇ／ｃｍであった。 Example 8

In a platinum crucible, bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ], A total of 6000 g of ytterbium oxide [Yb ₂ O ₃ ] was charged to obtain a melt. The molar concentration of Bi ₂ O ₃ in the melt is 55 mol%, the molar concentration of Fe ₂ O ₃ is 15 mol%, the molar concentration of B ₂ O ₃ is 6.9 mol%, and the molar concentration of Li ₂ O is 22.1 mol%. The molar concentration of Tb ₄ O ₇ was 0.8 mol%, and the molar concentration of Yb ₂ O ₃ was 0.1 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 3.20 and 0.40, respectively.

Using this melt, epitaxial growth was performed in the same manner as in Example 1. As a result, an RIG having a thickness of 550 μm was obtained. The number of pit-like defects of 100 μm or more was 6 / cm ² . As a result of analyzing the composition of this crystal by X-ray fluorescence analysis, the composition was Tb _1.9 Yb _0.1 Bi _1.0 Fe _5.0 O ₁₂ . Li and Pb were not detected. The Faraday rotation angle was 950 deg / cm at a wavelength of 1550 nm.

比較例１
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]、酸化イッテリビウム[Ｙｂ_２Ｏ_３]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は７６ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１２．８ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は４．９ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は４．９ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は１．３ｍｏｌ％、Ｙｂ_２Ｏ_３のモル濃度は０．１ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ１．００、０．０６であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、ＲＩＧの育成は確認できなかった。 Comparative Example 1
In a platinum crucible, bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ], A total of 6000 g of ytterbium oxide [Yb ₂ O ₃ ] was charged to obtain a melt. The molar concentration of Bi ₂ O ₃ in the melt is 76 mol%, the molar concentration of Fe ₂ O ₃ is 12.8 mol%, the molar concentration of B ₂ O ₃ is 4.9 mol%, and the molar concentration of Li ₂ O is 4. 9 mol%, the molar concentration of Tb ₄ O ₇ was 1.3 mol%, and the molar concentration of Yb ₂ O ₃ was 0.1 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 1.00 and 0.06, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1. As a result, no growth of RIG could be confirmed.

比較例２
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は３１ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１２．３ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は９．３ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は４６．８ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は０．６ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ５．０３、１．５１であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、膜厚５６０μmのＲＩＧを得た。１００μｍ以上のピット状の欠陥の数は３２個/ｃｍ^２であった。この結晶を蛍光Ｘ線分析法により組成分析した結果、組成はＴｂ_２．１Ｂｉ_０．９Ｆｅ_５．０Ｏ_１２であった。またＬｉとＰｂは検出されなかった。ファラデー回転角は１５５０ｎｍ波長にて９００ｄｅｇ／ｃｍであった。 Comparative Example 2
Bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ] in a platinum crucible A total of 6000 g charged melt was obtained. The molar concentration of Bi ₂ O ₃ in the melt is 31 mol%, the molar concentration of Fe ₂ O ₃ is 12.3 mol%, the molar concentration of B ₂ O ₃ is 9.3 mol%, and the molar concentration of Li ₂ O is 46. The molar concentration of 8 mol% and Tb ₄ O ₇ was 0.6 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 5.03 and 1.51, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1. As a result, RIG having a thickness of 560 μm was obtained. The number of pit-like defects of 100 μm or more was 32 / cm ² . As a result of analyzing the composition of this crystal by X-ray fluorescence analysis, the composition was Tb _2.1 Bi _0.9 Fe _5.0 O ₁₂ . Li and Pb were not detected. The Faraday rotation angle was 900 deg / cm at a wavelength of 1550 nm.

比較例３
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]、酸化イッテリビウム[Ｙｂ_２Ｏ_３]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は４０ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１６．４ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は１２．３ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は３０．６ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は０．６５ｍｏｌ％、Ｙｂ_２Ｏ_３のモル濃度は０．０５ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ２．４９、０．７７であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、膜厚５６０μmのＲＩＧを得た。１００μｍ以上のピット状の欠陥の数は１５個/ｃｍ^２であった。この結晶を蛍光Ｘ線分析法により組成分析した結果、Ｔｂ_１．９Ｙｂ_０．１Ｂｉ_１．０Ｆｅ_５．０Ｏ_１２であった。またＬｉとＰｂは検出されなかった。ファラデー回転角は１５５０ｎｍ波長にて９４０ｄｅｇ／ｃｍであった。 Comparative Example 3
In a platinum crucible, bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ], A total of 6000 g of ytterbium oxide [Yb ₂ O ₃ ] was charged to obtain a melt. The molar concentration of Bi ₂ O ₃ in the melt is 40 mol%, the molar concentration of Fe ₂ O ₃ is 16.4 mol%, the molar concentration of B ₂ O ₃ is 12.3 mol%, and the molar concentration of Li ₂ O is 30. The molar concentration of 6 mol%, Tb ₄ O ₇ was 0.65 mol%, and the molar concentration of Yb ₂ O ₃ was 0.05 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 2.49 and 0.77, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1. As a result, RIG having a thickness of 560 μm was obtained. The number of pit-like defects of 100 μm or more was 15 / cm ² . As a result of analyzing the composition of this crystal by X-ray fluorescence analysis, it was Tb _1.9 Yb _0.1 Bi _1.0 Fe _5.0 O ₁₂ . Li and Pb were not detected. The Faraday rotation angle was 940 deg / cm at a wavelength of 1550 nm.

比較例４
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]、酸化イッテリビウム[Ｙｂ_２Ｏ_３]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は７０ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１３．６ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は３．４ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は１１．９ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は１．０ｍｏｌ％、Ｙｂ_２Ｏ_３のモル濃度は０．１ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ３．５０、０．１７であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、ＲＩＧの育成は確認できなかった。 Comparative Example 4
In a platinum crucible, bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ], A total of 6000 g of ytterbium oxide [Yb ₂ O ₃ ] was charged to obtain a melt. The molar concentration of Bi ₂ O ₃ in the melt is 70 mol%, the molar concentration of Fe ₂ O ₃ is 13.6 mol%, the molar concentration of B ₂ O ₃ is 3.4 mol%, and the molar concentration of Li ₂ O is 11. 9 mol%, the molar concentration of Tb ₄ O ₇ was 1.0 mol%, and the molar concentration of Yb ₂ O ₃ was 0.1 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 3.50 and 0.17, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1. As a result, no growth of RIG could be confirmed.

比較例５
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]、酸化イッテリビウム[Ｙｂ_２Ｏ_３]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は５３ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１６．２ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は１３．３ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は１６ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は１．４ｍｏｌ％、Ｙｂ_２Ｏ_３のモル濃度は０．１ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ１．２０、０．３０であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、膜厚５３０μmのＲＩＧを得た。１００μｍ以上のピット状の欠陥の数は１５個/ｃｍ^２であった。この結晶を蛍光Ｘ線分析法により組成分析した結果、Ｔｂ_１．９Ｙｂ_０．１Ｂｉ_１．０Ｆｅ_５．０Ｏ_１２であった。またＬｉとＰｂは検出されなかった。ファラデー回転角は１５５０ｎｍ波長にて９５０ｄｅｇ／ｃｍであった。 Comparative Example 5
In a platinum crucible, bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ], A total of 6000 g of ytterbium oxide [Yb ₂ O ₃ ] was charged to obtain a melt. The molar concentration of Bi ₂ O ₃ in the melt is 53 mol%, the molar concentration of Fe ₂ O ₃ is 16.2 mol%, the molar concentration of B ₂ O ₃ is 13.3 mol%, and the molar concentration of Li ₂ O is 16 mol%. The molar concentration of Tb ₄ O ₇ was 1.4 mol%, and the molar concentration of Yb ₂ O ₃ was 0.1 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 1.20 and 0.30, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1. As a result, RIG having a film thickness of 530 μm was obtained. The number of pit-like defects of 100 μm or more was 15 / cm ² . As a result of analyzing the composition of this crystal by X-ray fluorescence analysis, it was Tb _1.9 Yb _0.1 Bi _1.0 Fe _5.0 O ₁₂ . Li and Pb were not detected. The Faraday rotation angle was 950 deg / cm at a wavelength of 1550 nm.

比較例６
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]、酸化イッテリビウム[Ｙｂ_２Ｏ_３]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は７９ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１１．６ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は３．６ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は４．３ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は１．４ｍｏｌ％、Ｙｂ_２Ｏ_３のモル濃度は０．１ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ１．２０、０．０６であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、ＲＩＧの育成は確認できなかった。 Comparative Example 6
In a platinum crucible, bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ], A total of 6000 g of ytterbium oxide [Yb ₂ O ₃ ] was charged to obtain a melt. The molar concentration of Bi ₂ O ₃ in the melt is 79 mol%, the molar concentration of Fe ₂ O ₃ is 11.6 mol%, the molar concentration of B ₂ O ₃ is 3.6 mol%, and the molar concentration of Li ₂ O is 4. 3 mol%, the molar concentration of _Tb 4 _{O 7} molar concentration of 1.4mol%, _Yb 2 _{O 3} was 0.1 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 1.20 and 0.06, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1. As a result, no growth of RIG could be confirmed.

比較例７
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は７４．５ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１２．７ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は３．３ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は８．２ｍｏｌ％、Ｔｂのモル濃度は１．３ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ２．４８、０．１１であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、ＲＩＧの育成は確認できなかった。 Comparative Example 7
Bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ] in a platinum crucible A total of 6000 g charged melt was obtained. The molar concentration of Bi ₂ O ₃ in the melt is 74.5 mol%, the molar concentration of Fe ₂ O ₃ is 12.7 mol%, the molar concentration of B ₂ O ₃ is 3.3 mol%, and the molar concentration of Li ₂ O is The molar concentration of 8.2 mol% and Tb was 1.3 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 2.48 and 0.11, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1. As a result, no growth of RIG could be confirmed.

比較例８
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]、酸化ホルミウム[Ｈｏ_２Ｏ_３]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は７１ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１２．１ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は７．８ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は７．８ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は０．４ｍｏｌ％、Ｈｏ_２Ｏ_３のモル濃度は０．９ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ１．００、０．１１であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、膜厚５００μmのＲＩＧを得た。１００μｍ以上のピット状の欠陥の数は１７個/ｃｍ^２であった。この結晶を蛍光Ｘ線分析法により組成分析した結果、組成はＴｂ_０．７Ｈｏ_１．１Ｂｉ_１．２Ｆｅ_５．０Ｏ_１２であった。またＬｉとＰｂは検出されなかった。ファラデー回転角は１５５０ｎｍ波長にて１１５０ｄｅｇ／ｃｍであった。 Comparative Example 8
In a platinum crucible, bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ], A total of 6000 g of holmium oxide [Ho ₂ O ₃ ] was charged to obtain a melt. The molar concentration of Bi ₂ O ₃ in the melt is 71 mol%, the molar concentration of Fe ₂ O ₃ is 12.1 mol%, the molar concentration of B ₂ O ₃ is 7.8 mol%, and the molar concentration of Li ₂ O is 7. 8 mol%, the molar concentration of _Tb 4 _{O 7} is 0.4 mol%, the molar concentration of _Ho 2 _{O 3} was 0.9 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 1.00 and 0.11, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1, and as a result, a RIG having a thickness of 500 μm was obtained. The number of pit-like defects of 100 μm or more was 17 / cm ² . As a result of analyzing the composition of this crystal by X-ray fluorescence analysis, the composition was Tb _0.7 Ho _1.1 Bi _1.2 Fe _5.0 O ₁₂ . Li and Pb were not detected. The Faraday rotation angle was 1150 deg / cm at a wavelength of 1550 nm.

比較例９
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]、酸化イッテリビウム[Ｙｂ_２Ｏ_３]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は５２ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１５ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は６．４ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は２５．７ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は０．８ｍｏｌ％、Ｙｂ_２Ｏ_３のモル濃度は０．１ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ４．０２、０．４９であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、膜厚５１０μmのＲＩＧを得た。１００μｍ以上のピット状の欠陥の数は１６個/ｃｍ^２であった。この結晶を蛍光Ｘ線分析法により組成分析した結果、Ｔｂ_１．９Ｙｂ_０．１Ｂｉ_１．０Ｆｅ_５．０Ｏ_１２であった。またＬｉとＰｂは検出されなかった。ファラデー回転角は１５５０ｎｍ波長にて９５０ｄｅｇ／ｃｍであった。 Comparative Example 9
In a platinum crucible, bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ], A total of 6000 g of ytterbium oxide [Yb ₂ O ₃ ] was charged to obtain a melt. The molar concentration of Bi ₂ O ₃ in the melt is 52 mol%, the molar concentration of Fe ₂ O ₃ is 15 mol%, the molar concentration of B ₂ O ₃ is 6.4 mol%, and the molar concentration of Li ₂ O is 25.7 mol%. The molar concentration of Tb ₄ O ₇ was 0.8 mol%, and the molar concentration of Yb ₂ O ₃ was 0.1 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 4.02 and 0.49, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1. As a result, a RIG having a thickness of 510 μm was obtained. The number of pit-like defects of 100 μm or more was 16 / cm ² . As a result of analyzing the composition of this crystal by X-ray fluorescence analysis, it was Tb _1.9 Yb _0.1 Bi _1.0 Fe _5.0 O ₁₂ . Li and Pb were not detected. The Faraday rotation angle was 950 deg / cm at a wavelength of 1550 nm.

比較例１０
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]、酸化イッテリビウム[Ｙｂ_２Ｏ_３]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は５３ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１３．７ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は１５．９ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は１５．９ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は１．４ｍｏｌ％、Ｙｂ_２Ｏ_３のモル濃度は０．１ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ１．００、０．３であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、膜厚５４０μmのＲＩＧを得た。１００μｍ以上のピット状の欠陥の数は２０個/ｃｍ^２であった。この結晶を蛍光Ｘ線分析法により組成分析した結果、Ｔｂ_１．９Ｙｂ_０．１Ｂｉ_１．０Ｆｅ_５．０Ｏ_１２であった。またＬｉとＰｂは検出されなかった。ファラデー回転角は１５５０ｎｍ波長にて９６０ｄｅｇ／ｃｍであった。 Comparative Example 10
In a platinum crucible, bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ], A total of 6000 g of ytterbium oxide [Yb ₂ O ₃ ] was charged to obtain a melt. The molar concentration of Bi ₂ O ₃ in the melt is 53 mol%, the molar concentration of Fe ₂ O ₃ is 13.7 mol%, the molar concentration of B ₂ O ₃ is 15.9 mol%, and the molar concentration of Li ₂ O is 15. 9 mol%, the molar concentration of Tb ₄ O ₇ was 1.4 mol%, and the molar concentration of Yb ₂ O ₃ was 0.1 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 1.00 and 0.3, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1. As a result, RIG having a thickness of 540 μm was obtained. The number of pit-like defects of 100 μm or more was 20 / cm ² . As a result of analyzing the composition of this crystal by X-ray fluorescence analysis, it was Tb _1.9 Yb _0.1 Bi _1.0 Fe _5.0 O ₁₂ . Li and Pb were not detected. The Faraday rotation angle was 960 deg / cm at a wavelength of 1550 nm.

比較例１１
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は３１ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１６．９ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は１１．４ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は３９．８ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は０．９ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ３．４９、１．２８であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、膜厚５４０μmのＲＩＧを得た。１００μｍ以上のピット状の欠陥の数は２３個/ｃｍ^２であった。この結晶を蛍光Ｘ線分析法により組成分析した結果、Ｔｂ_２．１Ｂｉ_０．９Ｆｅ_５．０Ｏ_１２であった。またＬｉとＰｂは検出されなかった。ファラデー回転角は１５５０ｎｍ波長にて９００ｄｅｇ／ｃｍであった。 Comparative Example 11
Bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ] in a platinum crucible A total of 6000 g charged melt was obtained. The molar concentration of Bi ₂ O ₃ in the melt is 31 mol%, the molar concentration of Fe ₂ O ₃ is 16.9 mol%, the molar concentration of B ₂ O ₃ is 11.4 mol%, and the molar concentration of Li ₂ O is 39. The molar concentration of 8 mol% and Tb ₄ O ₇ was 0.9 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 3.49 and 1.28, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1. As a result, RIG having a thickness of 540 μm was obtained. The number of pit-like defects of 100 μm or more was 23 / cm ² . As a result of analyzing the composition of this crystal by X-ray fluorescence analysis, it was Tb _2.1 Bi _0.9 Fe _5.0 O ₁₂ . Li and Pb were not detected. The Faraday rotation angle was 900 deg / cm at a wavelength of 1550 nm.

比較例１２
白金製ルツボに酸化ビスマス[Ｂｉ_２Ｏ_３]、酸化第２鉄[Ｆｅ_２Ｏ_３]、酸化ほう素[Ｂ_２Ｏ_３]、水酸化リチウム[ＬｉＯＨ]、酸化テルビウム[Ｔｂ_４Ｏ_７]、酸化イッテリビウム[Ｙｂ_２Ｏ_３]を計６０００ｇ仕込み融液とした。融液中のＢｉ_２Ｏ_３のモル濃度は４３ｍｏｌ％、Ｆｅ_２Ｏ_３のモル濃度は１５ｍｏｌ％、Ｂ_２Ｏ_３のモル濃度は１５．１ｍｏｌ％、Ｌｉ_２Ｏのモル濃度は２５．７ｍｏｌ％、Ｔｂ_４Ｏ_７のモル濃度は１．１ｍｏｌ％、Ｙｂ_２Ｏ_３のモル濃度は０．１ｍｏｌ％であった。Ｌｉ_２ＯとＢ_２Ｏ_３のモル濃度比（ｘ/ｙ）、Ｌｉ_２ＯとＢｉ_２Ｏ_３のモル濃度比（ｘ/ｚ）はそれぞれ１．７、０．６であった。
この融液を用い、実施例１と同様にエピタキシャル成長を行った結果、膜厚５８０μmのＲＩＧを得た。１００μｍ以上のピット状の欠陥の数は１７個/ｃｍ^２であった。この結晶を蛍光Ｘ線分析法により組成分析した結果、Ｔｂ_１．９Ｙｂ_０．１Ｂｉ_１．０Ｆｅ_５．０Ｏ_１２であった。またＬｉとＰｂは検出されなかった。ファラデー回転角は１５５０ｎｍ波長にて９５０ｄｅｇ／ｃｍであった。
Comparative Example 12
In a platinum crucible, bismuth oxide [Bi ₂ O ₃ ], ferric oxide [Fe ₂ O ₃ ], boron oxide [B ₂ O ₃ ], lithium hydroxide [LiOH], terbium oxide [Tb ₄ O ₇ ], A total of 6000 g of ytterbium oxide [Yb ₂ O ₃ ] was charged to obtain a melt. The molar concentration of Bi ₂ O ₃ in the melt is 43 mol%, the molar concentration of Fe ₂ O ₃ is 15 mol%, the molar concentration of B ₂ O ₃ is 15.1 mol%, and the molar concentration of Li ₂ O is 25.7 mol%. The molar concentration of Tb ₄ O ₇ was 1.1 mol%, and the molar concentration of Yb ₂ O ₃ was 0.1 mol%. The molar concentration ratio (x / y) between Li ₂ O and B ₂ O _{3 and} the molar concentration ratio (x / z) between Li ₂ O and Bi ₂ O ₃ were 1.7 and 0.6, respectively.
Using this melt, epitaxial growth was performed in the same manner as in Example 1. As a result, an RIG having a film thickness of 580 μm was obtained. The number of pit-like defects of 100 μm or more was 17 / cm ² . As a result of analyzing the composition of this crystal by X-ray fluorescence analysis, it was Tb _1.9 Yb _0.1 Bi _1.0 Fe _5.0 O ₁₂ . Li and Pb were not detected. The Faraday rotation angle was 950 deg / cm at a wavelength of 1550 nm.

有害物質である鉛を含まず、安定に結晶育成可能で量産性に富んだビスマス置換希土類鉄ガーネット単結晶を得ることができ、その産業上の意義は極めて高い。 A bismuth-substituted rare earth iron garnet single crystal that does not contain lead, which is a harmful substance, can be stably grown and has high mass productivity can be obtained, and its industrial significance is extremely high.

融液中のＬｉ_２Ｏ/Ｂ_２Ｏ_３のモル濃度比とＬｉ_２Ｏ/Ｂｉ_２Ｏ_３のモル濃度比との関係を表した図。Diagram showing the relation between the molar ratio of Li ₂ O / _B molar ratio of 2 _{O 3} and Li ₂ O / _Bi 2 _{O 3} in the melt.

Claims

A melt is generated from a flux composed of Li ₂ O, B ₂ O ₃ and Bi ₂ O _3, and a bismuth-substituted rare earth iron garnet single crystal is formed on the nonmagnetic garnet single crystal by liquid phase epitaxy using the melt. A process for producing a bismuth-substituted rare earth iron garnet single crystal, characterized in that:

According to claim 1, Li ₂ O molar concentration x (mol%) in the melt and _B 2 _{O 3} molar concentration y (mol%) and _Bi 2 _{O 3} molar concentration z (mol%) is the formula 1 and A method for producing a bismuth-substituted rare earth iron garnet single crystal, wherein the condition of Formula 2 is satisfied.
Formula 1: 1.2 ≦ x / y ≦ 3.5
Formula 2: 0.056 (x / y) ^ 1.07 ≦ (x / z) ≦ 0.211 (x / y) ^ 1.28