Manufacturing method for FeGa alloy single crystal

Abstract

To provide a manufacturing method of an FeGa alloy single crystal by a vertical Bridgman method, the manufacturing method being capable of preventing all seed crystals from melting in a crystal growth.SOLUTION: An FeGa alloy single crystal is manufactured by a vertical Bridgeman method using a growth furnace that includes a first growth furnace that is surrounded by a heat insulation material and includes a cylindrical heater, a second growth furnace that is located in a lower part of the first growth furnace in a vertical direction, is surrounded by the heat insulation material, and includes no heater, a heat insulation layer that has an opening part connecting the first growth furnace and the second growth furnace, and a crucible table that lifts / lowers a crucible through the opening part between the first growth furnace and the second growth furnace. The manufacturing method includes a seeding process where a seed crystal arranged in a lower part of a raw material in the crucible is lowered from the first growth furnace to the opening part, and the raw material molten by heating by the heater and the seed crystal are seeded. The opening part of the heat insulation layer has a cylindrical shape that satisfies a condition that a height / an opening area is 0.0035 or more.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing an iron-gallium alloy (FeGa alloy) single crystal, and more particularly to a method for producing an FeGa alloy single crystal having giant magnetostrictive properties formed by the Vertical Bridgman method (hereinafter sometimes abbreviated as "VB method"), in which a melt is solidified in a crucible. [Background technology]

[0002] FeGa alloys can be machined and exhibit large magnetostriction of about 100 to 350 ppm, making them suitable as materials for magnetostrictive vibration power generators, actuators, and the like, and have been attracting attention in recent years.

[0003] Furthermore, since FeGa alloys can exhibit large magnetostriction in a specific crystal orientation, it is believed that they are best used as single crystal components in which the direction in which magnetostriction is required matches the direction in which the crystal magnetostriction is at its maximum.

[0004] As a method for producing polycrystalline FeGa alloy, powder metallurgy, rapid solidification (e.g., Patent Document 1), and a method for producing by pressure sintering a flake-like or powder-like raw material produced by liquid rapid solidification (e.g., Patent Document 2) have been proposed. However, in all of these various production methods, the inside of the material is not single crystal but polycrystalline, and it is impossible to match all the crystal orientations in the material with the orientation that maximizes magnetostriction, resulting in inferior magnetostriction properties to those of single crystal materials.

[0005] On the other hand, there is a pulling method for producing single crystals. For example, Patent Document 3 describes a method for growing single crystals by the pulling method (Czochralski method). However, this method requires high power costs because the raw material is melted using a high-frequency induction heating method. In addition, the device configuration is complex and the device costs are high, so the pulling method ultimately results in high production costs. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4053328 [Patent Document 2] Patent No. 4814085 [Patent Document 3] JP 2016-28831 A Summary of the Invention [Problem to be solved by the invention]

[0007] As described above, it is difficult to mass-produce FeGa alloy single crystals at low cost by the conventional methods described in Patent Documents 1 to 3.

[0008] In comparison, the VB method, in which the melt is solidified in a crucible, can inexpensively produce FeGa alloy single crystals with giant magnetostrictive properties. In the VB method, a crucible containing a FeGa alloy seed crystal and a FeGa mixed raw material is heated with a heater to melt the FeGa mixed raw material, and then the crucible is lowered at a constant speed to move the crucible away from the heater to solidify the melt and grow a FeGa single crystal, and when it reaches room temperature, the FeGa single crystal is taken out. The FeGa alloy single crystal is then cut to the desired size to obtain a magnetostrictive plate. In other words, the larger the grown FeGa alloy single crystal, the more magnetostrictive plates can be obtained.

[0009] However, in the VB method, a mixture of iron and gallium is placed above a seed crystal, the mixture is melted, and then the melt is solidified from the seed crystal side while inheriting the crystal orientation of the seed crystal. FeGa alloy is a non-congruent melting crystal, and the solidus and liquidus do not coincide in the phase diagram. When the gallium content is 17-19% by atomic weight, the temperature difference between the solidus and liquidus is about 70-80°C.

[0010] Therefore, when attempting to grow a large FeGa alloy single crystal using the VB method, the molten material may completely melt the seed crystal, making it impossible to grow a single crystal with the desired crystal orientation.

[0011] In view of the above circumstances, the present invention aims to provide a method for producing a FeGa alloy single crystal by a vertical Bridgman method, which can prevent all of the seed crystal from melting during crystal growth. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention provides a method for producing a FeGa alloy single crystal by a vertical Bridgman method using a growth furnace including a first growth furnace surrounded by a heat insulating material and equipped with a cylindrical heater, a second growth furnace located below the first growth furnace in the vertical direction, surrounded by a heat insulating material and not equipped with a heater, a heat insulating layer having a cylindrical opening connecting the first growth furnace and the second growth furnace, and a crucible stand for raising and lowering a crucible between the first growth furnace and the second growth furnace through the opening, the method including a seed crystal disposed below a raw material in the crucible being lowered from the first growth furnace to the opening, and seeding the raw material heated and melted by the heater with the seed crystal, the opening of the heat insulating layer being cylindrical and satisfying a condition of height / cross-sectional area of ​​opening=0.0035 or more.

[0013] In the seeding step, the temperature inside the crucible may be adjusted so that it increases vertically from bottom to top, and so that the temperature gradient inside the crucible is within a range of 2.5 to 5.5° C. / mm.

[0014] The crucible may have outer dimensions of 74 mm square and 200 mm height, and inner dimensions of 66 mm square and 196 mm height and 4 mm thickness. Effect of the Invention

[0015] According to the present invention, there can be provided a method for producing an FeGa alloy single crystal by the vertical Bridgman method, which can prevent all of the seed crystal from melting during crystal growth. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic cross-sectional view of a growth furnace 1000 for growing a single crystal of an iron-gallium alloy. [Diagram 2] FIG. 3 is a schematic diagram of a thermal insulation layer 300. [Diagram 3] 1 is a schematic cross-sectional view showing the arrangement of a single crystal growth crucible 10 and a resistance heater 120 in each step of a method for producing a FeGa alloy single crystal by the VB method. [Figure 4] FIG. 1 is a schematic diagram of a crucible 10 for growing a single crystal. [Diagram 5] 2 is a schematic cross-sectional side view of a melt receiving tray 30. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, the method for producing a FeGa alloy single crystal according to one embodiment of the present invention will be described in more detail with reference to the drawings. Note that the present invention is not limited to the following examples, and can be arbitrarily modified without departing from the gist of the present invention.

[0018] [Single crystal growth equipment] The method for producing a FeGa alloy single crystal of the present invention can use, for example, a growth furnace 1000 for growing an iron-gallium alloy single crystal, as shown in Figure 1. The growth furnace 1000 includes a first growth furnace 100, a second growth furnace 200, a heat insulating layer 300, and a crucible stand 400.

[0019] <First growth furnace 100> The first growth furnace 100 is surrounded by a heat insulating material 110 and includes a cylindrical heater 120. This furnace is used to melt the raw material of the FeGa alloy placed in the single crystal growth crucible 10 and then perform seeding.

[0020] (Insulation 110) The heat insulating material 110 can form the first growth furnace 100 into a cylindrical shape, and a heater 120 is further disposed inside the first growth furnace, and the crucible 10 for growing a single crystal is disposed inside the heater 120. There are no particular limitations on the material of the heat insulating material 110, and examples of the material include carbon, boron nitride (BN), silicon nitride (Si3N4), mullite (3Al2O3·2SiO2 to 2Al2O3·SiO2), and alumina (Al2O3).

[0021] (Heater 120) The heater 120 is disposed inside the heat insulating material 110, and may be a carbon resistance heater. When growing the FeGa alloy single crystal, the heater 120 can form a hot zone. As the heater 120, a heater composed of an upper heater 120a, a middle heater 120b, and a lower heater 120c may be used as shown in FIG. 3. By adjusting the input power to each of these heaters 120a to 120c, a hot zone can be formed inside the heater 120, and the temperature gradient in the hot zone can be controlled more precisely. For example, it is possible to realize a temperature distribution in which the upper part of the first growth furnace 100 is high temperature and the lower part is low temperature.

[0022] <Second growth furnace 200> The second growth furnace 200 is located vertically below the first growth furnace 100, is surrounded by a heat insulating material 210, and is a furnace that does not include a heater. This furnace is used to cool and solidify the FeGa alloy raw material after seeding.

[0023] (Insulation 210) The heat insulating material 210 can form a cylindrical shape of the second growth furnace 200. There is no particular limitation on the material of the heat insulating material 210, and examples thereof include carbon, boron nitride (BN), silicon nitride (Si3N4), mullite (3Al2O3·2SiO2 to 2Al2O3·SiO2), and alumina (Al2O3).

[0024] (electrode 220) An electrode 220 for applying a current to the heater 120 is disposed in the second growth furnace 200. The heater 120 is fixed to the electrode 220 by a screw 130. The electrode 220 and the screw 130 may be made of carbon, for example.

[0025] <Thermal insulation layer 300> The insulating layer 300 has a cylindrical opening 310 connecting the first growth furnace 100 and the second growth furnace 200 (FIGS. 1 and 2). The insulating layer 300 is disposed between the first growth furnace 100 and the second growth furnace 200 in the vertical direction, and the diameter of the opening 300 is smaller than the diameters of the cylindrical first growth furnace 100 and the second growth furnace 200, and is open enough to allow the melt tray 30 carrying the support stand 20 that supports the single crystal growth crucible 10 to pass through with a small gap. By disposing the insulating layer 300 having such a narrow opening 310 between the first growth furnace 100 and the second growth furnace 200, it is possible to suppress the heat generated by the heater 120 from entering the second growth furnace 200 from the first growth furnace 100 when the single crystal growth crucible 10 is moved from the first growth furnace 100 to the second growth furnace 200, particularly while the single crystal growth crucible 10 is passing through the opening 300. As a result, it is possible to suppress an increase in the internal temperature of the second growth furnace 200, and it is possible to prevent the seed crystal after seeding from being completely melted by heat.

[0026] The material of the heat insulating layer 300 is not particularly limited, and examples thereof include carbon, boron nitride (BN), silicon nitride (Si3N4), mullite (3Al2O3·2SiO2 to 2Al2O3·SiO2), and alumina (Al2O3).

[0027] (Opening 310) 2 is a schematic diagram of the heat insulating layer 300, where Fig. 2(a) is a plan view of the heat insulating layer 300 and Fig. 2(b) is a side cross-sectional view of the heat insulating layer 300. The opening 310 of the heat insulating layer 300 is cylindrical and satisfies the condition of height H / opening cross-sectional area = 0.0035 or more. The opening cross-sectional area is expressed as πr 2 It is calculated as follows.

[0028] By satisfying the condition of height H / opening cross-sectional area=0.0035 or more, when the single crystal growth crucible 10 is moved from the first growth furnace 100 to the second growth furnace 200, particularly while the single crystal growth crucible 10 is passing through the opening 310, it is possible to prevent heat generated by the heater 120 from entering the second growth furnace 200 from the first growth furnace 100. As a result, it is possible to suppress an increase in the internal temperature of the second growth furnace 200, and it is possible to prevent the seed crystal after seeding from being completely melted by heat.

[0029] Furthermore, if the height H / opening cross-sectional area is less than 0.0035, the insulating effect of the insulating layer 300 becomes insufficient, and the heat generated by the heater 120 cannot be sufficiently prevented from entering the second growth furnace 200 from the first growth furnace 100 while the single crystal growth crucible 10 is passing through the opening 310, and the seed crystal after seeding may be completely melted by the heat.

[0030] 〈Crucible stand 400〉 The crucible stand 400 is a stand that can raise and lower the single crystal growth crucible 10 between the first growth furnace 100 and the second growth furnace 200 through an opening 310. The crucible stand 400 includes a stage 410 for placing the melt tray 30 thereon, an arm 420 for raising and lowering the stage 410, and a storage box 430 for storing the arm 420.

[0031] The crucible stand 400 raises and lowers the crucible 10 for growing single crystals between the first growth furnace 100 and the second growth furnace 200, so that the raw material for the FeGa alloy is melted in the first growth furnace 100, which has a heater 120, and seeded with a seed crystal, and then the raw material is solidified in the second growth furnace 200, which does not have a heater, to grow a FeGa alloy single crystal.

[0032] (Other configurations) The growth furnace 1000 may further include components in addition to the above components. For example, the growth furnace 1000 may include a thermocouple 15 capable of measuring the temperature of the single crystal growth crucible 10 to grasp the temperatures of the raw material, the seed crystal, and the solidified FeGa alloy single crystal in the single crystal growth crucible 10, a vacuum pump capable of adjusting the inside of the growth furnace 1000 to a vacuum atmosphere, a chamber capable of covering the growth furnace 1000 to maintain the atmosphere in the furnace, and an inert gas introducing means capable of introducing an inert gas such as argon or nitrogen into the chamber.

[0033] <Crucible 10 for single crystal growth> The material of the crucible 10 for single crystal growth is preferably alumina, which has low chemical reactivity with the FeGa alloy single crystal and has a high melting point. Magnesia and pyrolitic boron nitride may also be used. The crucible 10 for single crystal growth, which is open at the top, may be covered with a lid of the same material.

[0034] An FeGa alloy seed crystal 16 is filled in the lower part of a crucible 10 for growing a single crystal, and a mixture 17 of iron and gallium is filled on top of this FeGa alloy seed crystal 16 .

[0035] By using the single crystal growth crucible 10 in the VB method, a melt 17 of a mixture of iron and gallium is solidified in the single crystal growth crucible 10, whereby a FeGa alloy single crystal can be grown.

[0036] FIG. 4 shows a schematic diagram of an example of a crucible 10 for growing a single crystal. FIG. 4a is a perspective view, and FIG. 4b is a cross-sectional view. The crucible 10 for growing a single crystal includes a portion 10a for introducing a raw material, a portion 10c for introducing a seed crystal, and a tapered portion 10b connecting the portion 10a and the portion 10c. For example, a crucible having an outer dimension W1 of 74 mm square, an inner dimension W2 of 66 mm, a uniform thickness of the crucible, a height H1 of 200 mm, a height H3 of the portion 10a of 150 mm, a total height H2 of the portions 10a and 10b of 170 mm, and an inner dimension height H4 of 196 mm can be used.

[0037] (Support stand 20) The support stand 20 is a stand that supports the single crystal growth crucible 10 so that it does not fall over. The single crystal growth crucible 10 is tapered toward the bottom and has a high center of gravity, making it prone to falling over, so the support stand 20 prevents the single crystal growth crucible 10 from falling over. For example, a cylindrical stand made of alumina can be used as the support stand 20.

[0038] (Melt tray 30) The melt tray 30 serves to receive the raw material melt that leaks from the crucible in the event that the single crystal growth crucible 10 is damaged during melting or seeding of the raw material for the FeGa alloy single crystal or during growth of the single crystal.

[0039] For example, as shown in the schematic side cross-sectional view of FIG. 5, a dish made of alumina and having a bottom 31 and a side wall 32 can be used as the melt receiving dish 30, and the outer diameter R can be set to 108 mm.

[0040] In addition, the difference between the diameter R of the melt tray 30 and the diameter of the opening 310 of the insulating layer 300 can be set to 5 mm to 15 mm. If the difference is within this range, when the single crystal growth crucible 10 is moved from the first growth furnace 100 to the second growth furnace 200, particularly while the single crystal growth crucible 10 is passing through the opening 310, it is possible to prevent the heat generated by the heater 120 from entering the second growth furnace 200 from the first growth furnace 100. As a result, it is possible to prevent the internal temperature of the second growth furnace 200 from increasing, and thus it is possible to prevent the seed crystal after seeding from being completely melted by the heat.

[0041] [Method of manufacturing FeGa alloy single crystals] Next, a method for producing a FeGa alloy single crystal according to one embodiment of the present invention will be described, which uses a growth furnace 1000 shown in FIG.

[0042] The FeGa alloy single crystal having the giant magnetostrictive property can be grown, for example, by solidifying a melt of iron and gallium in a crucible, and in the present invention, a growth furnace including a first growth furnace, a second growth furnace, a heat insulating layer, and a crucible stand is used to grow the FeGa alloy single crystal by the VB method. Note that the opening of the heat insulating layer in the growth furnace is cylindrical and satisfies the condition of height / cross-sectional area of ​​opening=0.0035 or more.

[0043] Seeding process The manufacturing method of the present invention includes a seeding step in which a FeGa alloy seed crystal 16 arranged below a raw material (a mixture of iron and gallium 17) in a crucible 10 for growing a single crystal is lowered from a first growth furnace 100 to an opening 310, and the raw material that has been heated and melted by a heater 120 is seeded with the FeGa alloy seed crystal 16.

[0044] The method for producing a FeGa alloy single crystal of the present invention may include additional steps in addition to the seeding step. Each step of the crucible placement step, melting step, bubble removal step, seeding step, and growth step will be described below with reference to FIG.

[0045] In the VB method, first, a single crystal growth crucible 10 is placed at the bottom of which a crystal having a principal surface orientation is placed. <100> A FeGa alloy seed crystal 16 having a desired orientation is placed in the crucible 10. A required amount of a mixture 17 of iron and gallium raw materials is placed on the FeGa alloy seed crystal 16 (FIG. 3(a) crucible placement step), and then the crucible 10 is appropriately covered with a lid.

[0046] Next, an inert gas such as argon or nitrogen is flowed into the growth furnace 1000 to adjust the inside of the growth furnace 1000 to an inert atmosphere. If there is a risk of gallium nitride or the like being generated, it is preferable to introduce argon gas. After the inside of the growth furnace 1000 becomes an inert atmosphere, the upper heater 120a, the middle heater 120b, and the lower heater 120c arranged to surround the single crystal growth crucible 10 are operated to raise the temperature and start melting the mixture 17 of iron and gallium to produce a raw material melt 18 (FIG. 3(b) melting step).

[0047] When the mixture 17 of iron and gallium is almost melted and becomes a molten material, the vacuum pump is operated to reduce the pressure inside the growth furnace 1000 and remove air bubbles in the molten material (air bubble removal process).

[0048] After the bubble removal process, inert gas such as argon or nitrogen is flowed into the growth furnace 1000 to adjust the inside of the growth furnace 1000 to an inert atmosphere again, and then a FeGa alloy single crystal is grown inside the single crystal growth crucible 10 (FIG. 3(d) growth process). Specifically, the heater 120 is used to heat the single crystal growth crucible 10, which contains the FeGa alloy seed crystal 16 and the melt (a mixture of iron and gallium 17) and is covered with a lid, so that the temperature distribution is high at the top in the height direction and low at the bottom. In this state, the temperature inside the growth furnace 1000 is changed to a position where the FeGa alloy seed crystal 16 is melted to about the upper half in the height direction by moving the movable rod 13 to raise the crucible 10, and seeding is performed (FIG. 3(c) seeding process).

[0049] Thereafter, while maintaining the temperature gradient in the growth furnace 1000, the descending speed of the crucible 10 for single crystal growth is set in the range of 1 to 10 mm / hour, and the arm 420 is moved at a constant speed to descend the crucible 10 for single crystal growth to grow the FeGa alloy single crystal 16 (growth step in FIG. 4(d)), and all the melt is solidified. It is possible to grow a single crystal even if the descending speed of the crucible 10 for single crystal growth is set to 1 mm / hour or less, but the growth period will be longer and the productivity will decrease. In order to suppress changes in the crystal composition, it is preferable that the descending speed of the crucible 10 for single crystal growth is 5 mm / hour or more.

[0050] After the lowering of the crucible 10 is completed and the growth of the single crystal is completed (FIG. 3(e)), the mixture is cooled at a predetermined rate to obtain an FeGa alloy 19 (cooling step).

[0051] Next, after confirming that the temperature inside the growth furnace 1000 has reached approximately room temperature, the single crystal growth crucible 10 containing the grown single crystal is removed from the crucible stand 400, and the lid is then removed to remove the grown single crystal from the single crystal growth crucible 10.

[0052] Here, the seeding position and the input power of the heater 120 are adjusted so that the temperature in the single crystal growth crucible 10 during seeding increases vertically from bottom to top, and the temperature gradient during seeding in the single crystal growth crucible 10 is 2.5 to 5.5°C / mm. By setting such a temperature gradient, it is possible to more reliably prevent the FeGa alloy seed crystal 16 from melting completely.

[0053] If the temperature gradient in the crucible 10 for single crystal growth is less than 2.5°C / mm, the FeGa alloy seed crystal 16 may become too hot and melt completely. On the other hand, the temperature gradient is set to 5.5°C / mm or less to suppress the increase in power consumption due to the increase in heater output and the generation of gallium vapor from the upper surface of the melt. In addition, we tried to investigate the seeding position where the temperature gradient would be 6.5°C / mm, but the platinum-rhodium thermocouple 50 broke during temperature measurement due to the high temperature, so we had to discontinue the experiment.

[0054] In the method for producing the FeGa alloy single crystal of the present invention, the iron gallium alloy seed crystal 16 can be prevented from melting completely. Since the FeGa alloy is a non-uniform melting crystal, when the gallium content in the FeGa alloy is 18% in atomic weight percent, the temperature difference between the solidus and liquidus on the phase diagram is about 75°C. Therefore, in order to prevent the iron gallium alloy seed crystal 16 from melting completely, a temperature difference of 75°C or more is required in the vertical direction of the iron gallium alloy seed crystal 16. Since the length of the iron gallium alloy seed crystal 16 in the vertical direction is usually 30 mm, in order to prevent the iron gallium alloy seed crystal 16 from melting completely, the temperature gradient in the single crystal growth crucible 10 needs to be 2.5°C / mm or more to provide a temperature difference of 75°C or more in the vertical direction of the iron gallium alloy seed crystal 16.

[0055] By setting the temperature gradient in the crucible 10 for single crystal growth at the time of seeding high, it becomes possible to grow a single crystal at a lowering speed of the crucible 10 for single crystal growth in a wider range. However, if the temperature gradient in the crucible 10 for single crystal growth at the time of seeding is set high, the heater output becomes high. As a result, the amount of evaporation of the molten material increases, and the molten material adheres to the insulation material 110, the heater 120, the crucible stand 400, etc., and cleaning is required. In order to suppress the amount of evaporation of the molten material, it is preferable to cover the crucible 10 for single crystal growth with a lid. When the temperature gradient in the crucible 10 for single crystal growth at the time of seeding is set to 6.0 ° C. / mm or more, the amount of evaporation of the molten material becomes intense due to the output of the heater. Therefore, it is preferable to set the temperature gradient in the crucible 10 for single crystal growth at the time of seeding to 5.5 ° C. / mm or less. EXAMPLES

[0056] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples in any way.

[0057] [Example 1] First, in an environment of room temperature 20°C, granular iron raw material (purity: 99.9%) and gallium raw material (purity: 99.99%) with a median diameter of about 1 mm were weighed out so that the stoichiometric ratio of iron to gallium was 82:18, that is, the gallium content was 18.0% in atomic weight percent. The weighed gallium raw material was placed in a Teflon (registered trademark) container and melted in a hot water bath. Furthermore, the iron raw material was added to the melted gallium raw material, and after stirring in the container, it was cooled to room temperature to produce a mixture 17 of iron and gallium, which is a mixed raw material.

[0058] The crucible 10 for growing single crystals was made of dense alumina and had an outer dimension W1 of 74 mm square, an inner dimension W2 of 66 mm, a uniform crucible thickness, a height H1 of 200 mm, a height H3 of the portion 10a of 150 mm, a total height H2 of the portions 10a and 10b of 170 mm, and an inner dimension height H4 of 196 mm. The lower part of the crucible was filled with FeGa alloy seed crystals 16 (gallium content of 17% in atomic weight %, cylindrical shape with a diameter of 5 mm and a length of 30 mm) whose gallium content had been adjusted in advance, and a mixture 17 of iron and gallium was filled on the FeGa alloy seed crystals 16. At this time, the FeGa alloy seed crystals 16 had a main surface orientation of <100> A crystal with the same orientation was used.

[0059] Next, the opening 10d of the single crystal growth crucible 10 was covered with a lid made of dense alumina sinter. Then, the single crystal growth crucible 10 filled with the FeGa alloy seed crystal 16 and the mixture 17 of iron and gallium was placed on the support 20 arranged on the melt pan 30 placed on the stage 410 as shown in FIG. 1, and the tip of the thermocouple 15 was brought into contact with the side of the single crystal growth crucible 10. The melt pan 30 was made of alumina and had a bottom 31 and a side wall 32, a height of 90 mm, and an outer diameter R of 108 mm. The heat insulating materials 110, 210 and the heat insulating layer 300 were made of alumina.

[0060] In the growth furnace 1000 shown in FIG. 1, the heat insulating layer 300 has a height H of 40 mm, a radius of the opening 310 of 60 mm, and a cross-sectional area of ​​the opening of 11,300 mm. 2 A heat insulating layer with a height H / opening cross-sectional area of ​​0.0035 was used.

[0061] Next, the arm 420 was driven to set the stage 410 at the lowest position in the second growth furnace 200. After that, argon gas was introduced into the growth furnace 1000, and the inside of the growth furnace 1000 was adjusted to an argon atmosphere at atmospheric pressure. Furthermore, the upper heater 120a, the middle heater 120b, and the lower heater 120c, which were made of carbon resistance heaters 120, were independently controllable.

[0062] Then, the temperature of the upper heater 120a was set to 1500°C, the temperature of the middle heater 120b to 1400°C, and the temperature of the lower heater 120c to 1300°C, and the temperature in the growth furnace 1000 was increased. After the temperature increase was completed and the temperature in the growth furnace 1000 was stabilized, the arm 420 was driven to raise the stage 410, and the single crystal growth crucible 10 was raised at a gentle speed to the first growth furnace 100. Since a temperature gradient was created in the first growth furnace 100, in which the temperature in the upper part was high and the temperature in the lower part was low, the temperature in the single crystal growth crucible 10 increased as it moved to the upper part of the first growth furnace 100, and the mixture 17 of iron and gallium was melted to form a melt.

[0063] The temperature of the upper heater 120a was set to 1500°C so that the temperature gradient of the single crystal growth crucible 10 was 2.5°C / mm. At this time, the temperature of the middle heater 120b was set to 1400°C, the temperature of the lower heater 120c was set to 1300°C, and the moving speed of the single crystal growth crucible 10 was set to 2 mm / hour. The FeGa composition has a gallium content of 18% in atomic weight percent in the FeGa alloy single crystal, and the solidification temperature of the FeGa alloy in this case is about 1450°C, so the position of the single crystal growth crucible 10 when the measured temperature at the tip of the thermocouple 15 becomes 1450°C was set as the seeding position. As a result, it was found that the temperature of the upper heater 12a should be set to 1500°C.

[0064] When the mixed raw materials were almost melted to form a molten material, the introduction of argon gas into the growth furnace 1000 was stopped, and the pressure inside the growth furnace 1000 was reduced to 350 Pa using a vacuum pump, and this was maintained for about 30 minutes. Next, the pressure was gradually reduced at a gradient of 2.5 Pa / min over 60 minutes until the pressure was 200 Pa or less, and bubbles in the molten material were removed (bubble removal step). After the bubble removal step, the introduction of argon gas was resumed, and the inside of the growth furnace 1000 was adjusted to an inert atmosphere of 1 atm.

[0065] While monitoring the temperature at the contact point of the thermocouple 15 near the location of the single crystal growth crucible 10 where the melt was formed, the arm 420 was driven to maintain a temperature gradient of 2.5°C / mm in the single crystal growth crucible 10, and the single crystal growth crucible 10 was raised several mm to the seeding position to stabilize the temperature. This process was repeated to raise the single crystal growth crucible 10 so that the temperature of the thermocouple 15 was in a stable state and in the range of 1350 to 1400°C. Once the position for holding the single crystal growth crucible 10 was determined, the crucible was held for 3 hours to perform seeding. After the seeding, the upper heater 120a was kept at a temperature of 1500° C., the middle heater 120b at a temperature of 1400° C., and the lower heater 120c at a temperature of 1300° C., while the arm 420 was driven to lower the crucible 10 for single crystal growth at a descending speed of 2 mm / hour, and the growth of the FeGa alloy single crystal was started. After the descending distance of the crucible 10 for single crystal growth reached 100 mm, the growth was terminated.

[0066] In Example 1, from melting of the raw material to seeding, the crucible 10 for single crystal growth was placed in the first growth furnace 100 equipped with a heater 120, and single crystal growth after seeding started when the upper end position (liquid level) of the raw material melt 18 moved to near the bottom of the first growth furnace 100, and ended when the upper end position moved to near the lower end of the opening 310 of the insulating layer 300. The moving speed of the crucible when descending from the first growth furnace 100 to the second growth furnace was also set to 2 mm / hour.

[0067] After the growth of the single crystal was completed, the grown ingot was removed from the single crystal growth crucible 10. No melting was observed at the lower end of the FeGa alloy seed crystal 16, and none of the FeGa alloy seed crystal 16 melted, confirming that seeding had been performed normally.

[0068] The above process was repeated 10 times to produce 10 ingots. In each case, the results were the same as above, confirming that seeding was successful.

[0069] [Comparative Example 1] In the growth furnace 1000 shown in FIG. 1, the heat insulating layer 300 has a height H of 20 mm, a radius of the opening 310 of 60 mm, and a cross-sectional area of ​​the opening of 11,300 mm. 2 A heat insulating layer having a height H / opening cross-sectional area of ​​0.0018 was used. Except for this, a mixture 17 of iron and gallium was prepared in the same manner as in Example 1, and a single crystal was grown.

[0070] After the growth of the single crystal was completed, the grown ingot was removed from the single crystal growth crucible 10, and the seed crystal portion was cut to confirm the orientation. <100> The orientation was significantly off and the seed crystals were completely melted.

[0071] The above process was repeated 10 times to produce 10 ingots, but all of the seed crystals were melted in the same manner.

[0072] Table 1 shows the dimensions of the opening 310 of the heat insulating layer 300 and whether the FeGa alloy seed crystal 16 was completely melted in Example 1 and Comparative Example 1.

[0073] [Table 1]

[0074] As a result, since the opening 310 of the heat insulating layer 300 was cylindrical and satisfied the condition of height H / cross-sectional area of ​​opening=0.0035 or more, the FeGa alloy seed crystal 16 did not melt at all, and normal seeding was possible.

[0075] [summary] From the above, it is clear that the present invention can provide a method for producing an FeGa alloy single crystal by the vertical Bridgman method, which can prevent all of the seed crystals from melting during crystal growth. [Explanation of symbols]

[0076] 10 Single crystal growth crucible, 10a portion, 10b portion, 10c portion, 10d aperture, 15 thermocouple, 16 FeGa alloy seed crystal, 17 Mixture of iron and gallium, 18 Raw material melt, 19 FeGa alloy, 20 support stand, 30 melt tray, 31 bottom, 32 side wall, 100 first growth furnace, 110 insulation, 120 heater, 120a upper heater, 120b middle heater, 120c lower heater, 130 screws, 200 second growth furnace, 210 heat insulating material, 220 electrode, 300 heat insulating layer, 310 opening, 400 crucible stand, 410 stage, 420 arm, 430 Storage box, 1000 Growth furnace, H height, H1 height, H2 total height, H3 height, H4 inner height, R outer diameter, W1 outer dimension, W2 inside dimension

Claims

1. a first growth furnace surrounded by a thermal insulating material and equipped with a cylindrical heater; a second growth furnace located below the first growth furnace in the vertical direction, surrounded by a heat insulating material, and not equipped with a heater; a heat insulating layer having a cylindrical opening connecting the first growth furnace and the second growth furnace; a crucible stand for raising and lowering a crucible between the first growth furnace and the second growth furnace through the opening; A support stand for supporting the crucible; a melt receiving tray on which the support stand is placed; A method for producing a FeGa alloy single crystal by a vertical Bridgman method using a growth furnace comprising: A seeding step of lowering a seed crystal disposed under the raw material in the crucible from the first growth furnace to the opening and seeding the raw material heated and melted by the heater with the seed crystal, The thermal conductivity of the heat insulating layer is equal to or lower than the thermal conductivity of alumina; The opening of the heat insulating layer is cylindrical and satisfies the condition that, when the height is expressed in mm and the cross-sectional area of ​​the opening is expressed in mm 2 , the height / cross-sectional area of ​​the opening is equal to or greater than 0.0035; the difference between the diameter of the melt tray and the diameter of the opening of the heat insulating layer is 15 mm or less; In the seeding step, the temperature in the crucible is adjusted so as to increase vertically from bottom to top, and so that the temperature gradient in the crucible is within a range of 2.5 to 5.5 ° C. / mm.

2. A method for producing an FeGa alloy single crystal as described in claim 1, wherein the material of the insulating layer is at least one of carbon, mullite, and alumina.

3. 3. The method for producing an FeGa alloy single crystal according to claim 1, wherein the crucible has outer dimensions of 74 mm square and 200 mm height, and inner dimensions of 66 mm square and 196 mm height and 4 mm thickness.

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