JP2006225204A - Method for producing bismuth-substituted rare earth iron garnet single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the variation width of magnetic properties to the minimum even when a work for growing a bismuth-substituted rare earth iron garnet single crystal film by an LPE method is repeatedly performed many times. <P>SOLUTION: In a method comprising filling a melt composed of a PbO-B<SB>2</SB>O<SB>3</SB>-Bi<SB>2</SB>O<SB>3</SB>flux component and bismuth-substituted rare earth iron garnet components, and then repeatedly performing the work for growing the bismuth-substituted rare earth iron garnet LPE film on a non-magnetic garnet substrate by the LEC method, after performing the growth work one time or a plurality of times, an element becoming a main constitutive component of the LPE film to be grown and having action making the compensation temperature of the LPE film shift to the high temperature side is added excessively into the melt in addition to the addition of the materials equivalent to the grown crystal components to the melt. Thereby, the shift of the compensation temperature to the low temperature side caused by mixing of platinum into the melt is reduced or canceled out. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for growing a large number of bismuth-substituted rare earth iron garnet single crystal films by an LPE (liquid phase epitaxial) method. More specifically, the present invention relates to an LPE film to be grown after one or a plurality of growth operations. Bismuth-substituted rare earth iron garnet single crystal that can suppress variations in magnetic properties even when the LPE film is repeatedly grown many times by adding an element that shifts the compensation temperature to the high temperature side excessively It is related with the manufacturing method. This technique is useful for manufacturing a Faraday element used in the field of optical communication or optical measurement, for example.

  As is well known, various Faraday rotation devices using the Faraday effect are used in the fields of optical communication and optical measurement. For example, an optical isolator that is a device for preventing reflected return light, a variable optical attenuator that is a device for variably controlling the amount of transmitted light, or an optical switch that is a device for controlling on / off of transmitted light They incorporate a Faraday element (magneto-optic crystal) having a function of rotating the polarization plane. Here, in order to reduce the size and increase the performance of the device, a material having a large Faraday rotation capability is desirable as the Faraday element.

  A typical example of a magneto-optic crystal having a large Faraday rotation ability is a bismuth-substituted rare earth iron garnet single crystal. Therefore, at present, a single crystal film having a thickness of several tens of μm to several hundreds of μm grown by the LPE method is widely used as a Faraday element. This is because the growth of a single crystal film by the LPE method is excellent in productivity and has an advantage that a Faraday element exhibiting a necessary Faraday rotation angle can be provided at a low price.

The growth of the bismuth-substituted rare earth iron garnet single crystal film by the LPE method is performed using an LPE film growth apparatus (LPE furnace). This LPE film growing apparatus has a structure in which a platinum crucible is installed in an electric furnace. A platinum crucible is filled with a predetermined oxide raw material (PbO—B ₂ O ₃ —Bi ₂ O ₃ flux component and bismuth-substituted rare earth iron garnet component), and a uniformly mixed and stirred melt is obtained. By bringing a nonmagnetic garnet substrate suspended in a temperature-controlled state into contact with the melt surface, an LPE single crystal film can be grown on the substrate. A large number of bismuth-substituted rare earth iron garnet single crystal films can be continuously produced by exchanging the substrate and repeating the above-described growing operation.

  However, when the bismuth-substituted rare earth iron garnet single crystal film is continuously and repeatedly grown by such a method, there arises a problem that the magnetic properties (particularly the saturation magnetic field) are greatly different between the first grown film and the last grown film. In designing a magnetic field necessary for a device, a margin of required magnetic characteristics is small (usually, it is desirable that the margin is about 10% or less) in order to reduce costs. If the magnetic characteristics fluctuate greatly, it may not be possible to apply a necessary magnetic field to the Faraday element, and the desired characteristics of the device may not be realized. In order to avoid this, it is necessary to take a large margin, resulting in an unnecessarily large device and an increase in cost.

  By the way, in order to reduce the manufacturing cost of a single crystal, the erosion position of the crucible is changed by intentionally moving the liquid level of the melt in the platinum crucible, thereby preventing the crucible from perforating and continuously for a long period of time. A technique for increasing the number of repetitions of training has been proposed (see Patent Document 1). Here, as a method of moving the liquid level of the melt, a method of adding the same components as the melt and a method of pumping out the melt are disclosed. In addition, a method of putting a crucible material into a melt or taking out a crucible material that has been put into a melt in advance has been proposed (see Patent Document 2).

Such a method has an advantage that a larger number of LPE films can be manufactured at a low cost. However, as a larger number of LPE films are continuously and repeatedly grown, as described above, the variation in magnetic characteristics (especially the difference in saturation magnetic field) between the first grown film and the later grown film increases. turn into. That is, a single crystal can be manufactured, but the problem that the device design becomes difficult cannot be solved because the variation in magnetic characteristics is further increased.
JP-A-9-175898 JP-A-10-167894

  The problem to be solved by the present invention is that the fluctuation range of the magnetic properties can be minimized even if the growing operation of the bismuth-substituted rare earth iron garnet single crystal film by the LPE method is repeated continuously many times. It is to be.

In the present invention, a platinum crucible is filled with a melt composed of a PbO—B ₂ O ₃ —Bi ₂ O ₃ flux component and a bismuth-substituted rare earth iron garnet component, and the bismuth-substituted rare earth iron is formed on the nonmagnetic garnet substrate by the LPE method. In the method of repeating the operation of growing the garnet LPE film, after one or a plurality of growth operations, in addition to adding a material corresponding to the crystal component to be grown to the melt, an element which is a main constituent of the LPE film to be grown In addition, there is provided a method for producing a bismuth-substituted rare earth iron garnet single crystal, wherein an element having an action of shifting the compensation temperature of the LPE film to a high temperature side is excessively added to the melt. Here, the “compensation temperature” is a temperature at which the magnetic moment of the magneto-optical crystal is reversed at the temperature. The compensation temperature can be easily obtained because the sign of the Faraday rotation angle is reversed with the temperature as a boundary.

  When a bismuth-substituted rare earth iron garnet single crystal film is continuously and repeatedly grown using a platinum crucible over a long period of time by the LPE method, the magnetic properties vary even though the same work is performed using the same melt. A phenomenon was observed in which (specifically, the difference in saturation magnetic field between the first grown film and the last grown film) increased. An example of the relationship between the temperature and saturation magnetization in the initial film and the repetitively grown film is shown in FIG. As a result of diligent research on such a phenomenon, it was found that platinum was mixed in the grown LPE film, and the amount of the mixed platinum gradually increased with the number of times of growth. This is because the platinum as the crucible material continues to dissolve in the melt during the growth operation for a long time, and the platinum concentration in the melt gradually increases. When the amount of platinum mixed in the LPE film increases, as shown in FIG. 3, the compensation temperature shifts to the low temperature side, and thereby the saturation magnetic field at room temperature increases. Presuming from this, when the compensation temperature becomes room temperature (for example, about 25 ° C.) or higher, it is expected that the compensation temperature approaches the room temperature by repeated growth, the saturation magnetization at room temperature becomes smaller, and the saturation magnetic field becomes smaller. . In that case, the coercive force may be increased. Thus, fluctuation of the compensation temperature is not preferable because the magnetic characteristics change in any case. The present invention has been completed based on the knowledge and investigation of the cause of such a phenomenon.

  In the present invention, an element that is a main constituent of an LPE film to be grown after one or a plurality of growing operations and has an action of shifting the compensation temperature of the LPE film to a high temperature side is added to the melt. Thus, the characteristic fluctuation due to the platinum mixing into the LPE film is reduced or offset. Actually, it is preferable to add the element excessively to the melt every time one growing operation is completed. However, depending on the growing conditions, the element is excessively added to the melt after a plurality of growing operations are completed. The method of adding may be used. Here, the excessively added element is originally a main component of the LPE film, so there is no harmful effect caused by the addition. Tb, Gd, Dy, and Ho are elements having an effect of shifting the compensation temperature of the LPE film to the high temperature side.

  More preferably, after the crystal growth operation, in addition to the material corresponding to the crystal component to be grown and the element having the action of shifting the compensation temperature of the LPE film to be grown to the high temperature side, the same component as the melt is added to the melt. In addition, there is a method of growing a bismuth-substituted rare earth iron garnet single crystal film by moving the liquid level of the melt in the platinum crucible. This method combines the advantage that many single crystals can be grown in one platinum crucible and the advantage that the magnetic properties of many obtained single crystals are aligned.

In these methods, an LPE film to be grown has a bismuth-substituted rare earth iron garnet composition having Tb and Ga as elements as main constituent elements, and has an effect of shifting the compensation temperature of the LPE film to a high temperature side. Is the Tb, and it is preferable to reduce or cancel the shift of the compensation temperature to the low temperature side due to the platinum addition to the melt by the excessive addition of Tb. Tb is usually charged as an oxide into a platinum crucible. A typical composition of the LPE film is (TbYBi) ₃ (FeGa) ₅ O ₁₂ , which is grown on an SGGG substrate.

  The present invention is an LPE in which an element which is a main constituent of an LPE film to be grown and has an action of shifting the compensation temperature of the LPE film to a high temperature side after the growing operation is excessively added to the melt. Because it is a method for producing bismuth-substituted rare earth iron garnet single crystals by the method, it is possible to reduce or cancel out characteristic fluctuations due to platinum inclusion in the LPE film, so that the magnetic properties can be obtained even if the growth operation is repeated many times in succession. The fluctuation range of (for example, a saturation magnetic field) can be minimized (specifically, 10% or less). In this way, LPE films with uniform magnetic properties can be mass-produced, the cost can be reduced, and the design of the magnetic field in the device is facilitated.

The growth of the bismuth-substituted rare earth iron garnet single crystal film by the LPE method is performed as follows using, for example, an LPE film growth apparatus (LPE furnace) as shown in FIG. A support base 14 equipped with a platinum crucible 12 is inserted from below into a vertical three-zone electric furnace 10. The platinum crucible 12 is filled with predetermined oxide raw materials (PbO—B ₂ O ₃ —Bi ₂ O ₃ flux component and bismuth-substituted rare earth iron garnet component), and the melt 16 uniformly mixed and stirred To do. Note that the melt temperature can be measured and controlled by the thermocouple 18. From above, the nonmagnetic garnet single crystal substrate 22 is suspended by the support member 20 so that it can be rotated, lowered and raised. By placing the substrate 22 at an appropriate position in the electric furnace 10, the substrate temperature is controlled and the melt 16 can be contacted and separated. Thereby, an LPE single crystal film can be grown on the substrate 22. As the substrate 22, a nonmagnetic garnet single crystal having the same crystal structure as that of the single crystal film to be grown is used. After growing the LPE film, the substrate is taken out, a new substrate is mounted, and the above-described growing operation is repeated. In this way, a large number of bismuth-substituted rare earth iron garnet single crystal films can be continuously produced.

In the present invention, a PbO—B ₂ O ₃ —Bi ₂ O ₃ flux component and a bismuth-substituted rare earth iron garnet component having Tb and Ga are charged into a platinum crucible and heated and stirred to obtain a uniform molten state. When PbO—B ₂ O ₃ —Bi ₂ O ₃ is used as a flux component, platinum as a crucible material gradually dissolves in the melt. The platinum dissolved in the melt is mixed into the growing LPE film, and the compensation temperature is shifted to the low temperature side, thereby increasing the saturation magnetic field at room temperature. Therefore, in the present invention, after one growth operation, in addition to adding a material corresponding to the grown crystal component to the melt, Tb (actually Tb having the effect of shifting the compensation temperature of the LPE film to be grown to the high temperature side) Oxide) is added to the melt in excess. This reduces or cancels the shift of the compensation temperature to the low temperature side due to the platinum mixture in the LPE film. Therefore, according to the method of the present invention, the platinum concentration and the Tb concentration in the LPE film increase as the number of times of growing work increases. The composition of the LPE film is typically (TbYBi) ₃ (FeGa) ₅ O ₁₂ , which is grown on the SGGG substrate.

  As a more preferable growth method, in addition to the material corresponding to the grown crystal component and the element having the action of shifting the compensation temperature of the grown LPE film to the high temperature side after one growth operation, the same component as the melt Is added to the melt to move the level of the melt in the platinum crucible. The platinum crucible is locally eroded at the liquid surface position of the melt. The range of erosion at one time is about 5 mm, and if the liquid level is moved by about 0.5 mm for each growth, the erosion position gradually shifts. Can continue to use. By the way, if the erosion position is not changed, a hole is opened by about 15 times of growth work, and melt leakage occurs. However, if the erosion position is moved, the growth work of about 40 to 80 times becomes possible. As described above, since the growing operation can be performed many times, the present invention capable of suppressing the fluctuation of the magnetic characteristics is more effective in mass production.

  Note that the change in the saturation magnetic field tends to be large at the initial stage where the number of continuous growths is small, and small at the stage where the number of growths is large, and the change width tends to be stable. For this reason, it is preferable to add a large amount of elements having an effect of shifting the compensation temperature to the high temperature side in the initial stage and then to change the amount in small amounts. In addition, since the change in the magnetic characteristics at the initial stage is large, the effect of stabilizing the magnetic characteristics is very large even with a normal growth method in which the same components as the melt are not added to the melt.

(Example)
As initial charge materials, Tb ₄ O ₇ : 34.5 g, Y ₂ O ₃ : 14.6 g, Fe ₂ O ₃ : 375 g, Ga ₂ O ₃ : 83.7 g, PbO: 2696 g, B ₂ O ₃ : 168. A total of 9000 g of ₂ g, Bi ₂ O ₃ : 5628 g was put in a platinum crucible and melted at a temperature of 950 ° C. for 60 hours. Thereafter, the mixture was stirred at the same 950 ° C. for 24 hours, and the temperature was lowered to 730 ° C. to grow an LPE film on the SGGG substrate. This SGGG substrate is a (CaGd) ₃ (MgZrGa) ₅ O ₁₂ substrate having a shape of 3 inches and a lattice constant of 1.2497 ± 0.0003 nm. After the growth, the substrate was cooled to room temperature and taken out. The weight of the LPE film was calculated from the difference between the weight of the SGGG substrate before growing the LPE film and the weight of (SGGG substrate + LPE film) after growing the LPE, and it was 15.84 g. The main component composition of the grown crystal (excluding impurities such as platinum and lead oxide) was Tb _1.0 Y _0.6 Bi _1.4 Fe _4.1 Ga _0.9 O ₁₂ . Next, this LPE film was cut into 7.6 mm square and the substrate was removed, followed by heat treatment in the atmosphere at 1100 ° C. for 24 hours. Then, both surfaces were mirror-polished and processed into chips having a length of 1 mm, a width of 1.2 mm, and a thickness of 0.34 mm. The saturation magnetic field at room temperature in the direction perpendicular to the mirror surface of this chip was 9.5 kA / m.

まず、１枚目に育成した結晶組成とその重量（１５．８４ｇ）から各酸化物原料の重量を求め、白金坩堝に追加した（表１の「結晶成分」）。また、初期仕込材料と同じ材料を同じ重量比で合計５０ｇとなるように求め、白金坩堝に追加した（表１の「融液と同じ成分」）。更に、Ｔｂの酸化物１ｇを過剰に追加した（表１の「磁気特性相殺分」）。 Next, as shown in Table 1, the material was weighed (unit: g) and replenished to the platinum crucible.

First, the weight of each oxide raw material was determined from the crystal composition grown on the first sheet and its weight (15.84 g), and added to the platinum crucible (“Crystal component” in Table 1). Further, the same materials as the initial charge materials were obtained so as to have a total weight of 50 g and added to the platinum crucible ("Same components as melt" in Table 1). Furthermore, 1 g of Tb oxide was added in excess (“Magnetic property offset” in Table 1).

  Thereafter, the temperature was raised again to 950 ° C. and melted for 20 hours. And after stirring for 12 hours at the same 950 ° C., the temperature was lowered to 730 ° C. to grow an LPE film on the SGGG substrate. At this time, the weight of the LPE film was 15.53 g. Moreover, as a result of processing into a chip and measuring the saturation magnetization as in the first sheet, it was 9.8 kA / m.

In the same manner as after the growth of the first sheet, 15.53 g of “crystal component” obtained by determining the weight of each oxide raw material from the crystal weight of the second sheet and the composition of the grown film, “the same component as the melt” 50 g, “ As shown in Table 2, 0.1 g of Tb oxide was added to the platinum crucible as “magnetic property offset”.

  A series of operations after the second LPE film growth was repeated to grow 35 LPE films. The “crystal component” is adjusted each time by obtaining the weight of each oxide raw material from the crystal weight and the composition of the grown film. The excess amount of oxide of Tb as “magnetic property offset” is constant at 0.1 g. The saturation magnetic field of the 35th single crystal chip was 10.5 kA / m, and the difference from the first was 1.0 kA / m.

(Comparative example)
The same initial charge 9000 g as in the above example was placed in a platinum crucible and melted at a temperature of 950 ° C. for 60 hours. Thereafter, the mixture was stirred at the same 950 ° C. for 24 hours, and the temperature was lowered to 730 ° C. to grow an LPE film on the SGGG substrate. After the growth, the substrate was cooled to room temperature and taken out. The weight of the LPE film was 15.93 g. Further, the main component composition of the grown crystal (excluding impurities such as platinum and lead oxide) was the same as in the above example. Similarly to the example, this LPE film was processed to obtain a chip having a length of 1 mm, a width of 1.2 mm, and a thickness of 0.34 mm. The saturation magnetic field of this chip at room temperature was 9.5 kA / m.

まず、１枚目に育成した結晶組成とその重量（１５．９３ｇ）から各酸化物原料の重量を求め、白金坩堝に追加した（表３の「結晶成分」）。また、初期仕込材料と同じ材料を同じ重量比で合計５０ｇとなるように求め、白金坩堝に追加した（表１の「融液と同じ成分」）。 Next, as shown in Table 3, the material was weighed (unit: g) and replenished to the platinum crucible.

First, the weight of each oxide raw material was determined from the crystal composition grown on the first sheet and its weight (15.93 g), and added to the platinum crucible ("Crystal component" in Table 3). Further, the same materials as the initial charge materials were obtained so as to have a total weight of 50 g and added to the platinum crucible ("Same components as melt" in Table 1).

  Thereafter, the temperature was raised again to 950 ° C. and melted for 20 hours. And after stirring for 12 hours at the same 950 ° C., the temperature was lowered to 730 ° C. to grow an LPE film on the SGGG substrate. As a result of processing into a chip and measuring saturation magnetization in the same manner as the first sheet, it was 10.5 kA / m. Next, as in the case after the growth of the first sheet, 50 g of “crystal component” and “the same component as the melt” obtained from the weight of the crystal of the second sheet and the composition of the grown film were obtained in a platinum crucible. Added.

  This second series of growth and measurement series was repeated to grow 35 LPE films. The saturation magnetic field of the 35th sheet was 14.3 kA / m, and the difference from the first sheet was 4.8 kA / m.

  The difference between the work of the example and the comparative example is that in the example (the method of the present invention), 1 g of Tb oxide is added excessively for the first time every time the growing work is performed, and 0.1 g is added excessively after the second time. On the other hand, the comparative example (prior art) is not doing so. Here, the liquid level is raised by about 0.5 mm by adding 50 g at the same weight ratio as the initial charge material. Note that the amount of the raw material of the crystal component corresponding to the single crystal grown last time varies depending on the grown film thickness.

Table 4 shows the relationship of the saturation magnetic field of the grown LPE film with respect to the number of times of continuous growth. FIG. 2 is a graph of this.

  At the time of growing 35 sheets, about 50% of the fluctuation occurred in the comparative example, but it was confirmed that it was within the fluctuation range of about 10% in the example. The saturation magnetic field tends to change greatly when the number of continuous growths is small, and changes little and the range of change is stable where the number of growths is large. Therefore, if the amount of Tb is controlled more finely, the amount of fluctuation of the saturation magnetic field can be further reduced.

Explanatory drawing which shows an example of the LPE film | membrane growing apparatus used by this invention. Explanatory drawing which shows an example of a magnetic characteristic fluctuation | variation. The relationship diagram of the temperature and saturation magnetization in the initial film and the repetitively grown film.

Explanation of symbols

10 Electric furnace 12 Platinum crucible 16 Melt 22 Substrate

Claims (3)

A platinum crucible is filled with a melt composed of a PbO—B ₂ O ₃ —Bi ₂ O ₃ flux component and a bismuth-substituted rare earth iron garnet component, and a bismuth-substituted rare earth iron garnet LPE film is formed on the nonmagnetic garnet substrate by the LPE method. In a method of repeating the training work,
In addition to adding a material corresponding to the grown crystal component to the melt after one or a plurality of growth operations, it is an element which is a main component of the LPE film to be grown, and the compensation temperature of the LPE film is set to the high temperature side. A process for producing a bismuth-substituted rare earth iron garnet single crystal, wherein an element having an action of shifting to an excessive amount is added to the melt.   In addition to the material corresponding to the grown crystal component and the element having the action of shifting the compensation temperature of the grown LPE film to the high temperature side after one or more growth operations, the same component as the melt is added to the melt. In addition, the method for producing a bismuth-substituted rare earth iron garnet single crystal according to claim 1, wherein the liquid level of the melt in the platinum crucible is moved. The LPE film to be grown is a bismuth-substituted rare earth iron garnet composition having Tb and Ga as the main constituent elements, and the element having the action of shifting the compensation temperature of the LPE film to the high temperature side is Tb, The method for producing a bismuth-substituted rare earth iron garnet single crystal according to claim 1 or 2, wherein a shift of the compensation temperature to a low temperature side due to platinum mixing in the melt is reduced or offset by excessive addition of Tb oxide.

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