JP7613189B2 - Manufacturing method of FeGa alloy single crystal - Google Patents

Description

The present invention relates to a method for producing iron-gallium alloy (FeGa alloy) single crystals, and in particular to a method for producing FeGa alloy single crystals having super magnetostrictive properties formed by the vertical Bridgman method (hereinafter sometimes abbreviated as the "VB method"), in which a melt is solidified in a crucible.

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

Furthermore, since FeGa alloys can exhibit large magnetostriction in a specific crystal orientation, it is believed that their best application is as a single crystal component in which the direction in which magnetostriction is required matches the direction in which the crystal magnetostriction is at its maximum.

Manufacturing methods for FeGa alloy polycrystals include powder metallurgy, rapid solidification (e.g., Patent Document 1), and a method of pressurizing and sintering thin or powdered raw materials produced by liquid rapid solidification (e.g., Patent Document 2). However, all of these manufacturing methods result in polycrystals rather than single crystals within the material, and it is impossible to align all the crystal orientations within the material with the orientation that maximizes magnetostriction, resulting in inferior magnetostriction properties to single crystal materials.

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

Patent No. 4053328 Patent No. 4814085 JP 2016-28831 A

As such, it is difficult to mass-produce FeGa alloy single crystals at low cost using the conventional methods described in Patent Documents 1 to 3.

In comparison, the VB method, in which the melt is solidified in a crucible, allows for the inexpensive manufacture of 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 an FeGa single crystal. When the temperature reaches room temperature, the FeGa single crystal is removed. 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.

However, in the VB method, a mixture of iron and gallium is placed on top of a seed crystal, the mixture is melted, and then the melt is solidified from the seed crystal side while retaining the crystal orientation of the seed crystal. FeGa alloys are incongruently melting crystals, 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 approximately 70-80°C.

As a result, when attempting to grow large FeGa alloy single crystals using the VB method, there are cases where the molten material melts the entire seed crystal, or even if seeding is successful, the crystal becomes polycrystalline during growth, making it impossible to grow a single crystal with the desired crystal orientation.

In view of these circumstances, the present invention aims to provide a method for producing FeGa alloy single crystals using the vertical Bridgman method, which prevents all of the seed crystals from melting during crystal growth and allows stable growth of the single crystal.

In order to solve the above problems, the method for producing a FeGa alloy single crystal of the present invention is 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 seed crystal arranged below the raw material in the crucible is lowered from the first growth furnace to the opening, and the raw material heated and melted by the heater is seeded with the seed crystal, and after the seeding step, a growth step for growing a FeGa alloy single crystal under the condition of a growth speed of 1 mm or less/hour, and the opening of the heat insulating layer is cylindrical and satisfies the condition of height/opening cross-sectional area = 0.0035 or more.

In the seeding process, the temperature in the crucible may be adjusted so that it increases vertically from bottom to top, and the temperature gradient in the crucible is within the range of 2.5 to 5.5°C/mm.

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.

The present invention provides a method for producing FeGa alloy single crystals using the vertical Bridgman method, which prevents all of the seed crystals from melting during crystal growth and allows for stable growth of single crystals.

1 is a schematic cross-sectional view of a growth furnace 1000 for growing a single crystal of an iron-gallium alloy. 3 is a schematic diagram of a thermal insulation layer 300. FIG. 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. 1 is a schematic diagram of a crucible 10 for growing a single crystal. 2 is a schematic cross-sectional side view of a melt receiving tray 30. FIG.

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

[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 Fig. 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.

<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.

(Thermal insulation material 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 (Si ₃ N ₄ ), mullite (3Al ₂ O _{3.2SiO 2} to 2Al ₂ O _{3.SiO 2} ), and alumina (Al ₂ O ₃ ).

(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 as shown in FIG. 3 may be used. 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 more precisely controlled. 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.

<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.

(Thermal insulation material 210)
The heat insulating material 210 can form the second growth furnace 200 into a cylindrical shape. There are no particular limitations on the material of the heat insulating material 210, and examples of the material include carbon, boron nitride (BN), silicon nitride (Si ₃ N ₄ ), mullite (3Al ₂ O _{3.2SiO 2} to 2Al ₂ O _{3.SiO 2} ), and alumina (Al ₂ O ₃ ).

(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.

<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 supporting the single crystal growth crucible 10 to pass through with a small gap. By disposing the heat insulating layer 300 having such a narrow opening 310 between the first growth furnace 100 and the second growth furnace 200, 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, it is possible to suppress the heat generated by the heater 120 from entering the first growth furnace 100 into the second growth furnace 200. 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.

The material of the heat insulating layer 300 is not particularly limited, and examples thereof include carbon, boron nitride (BN), silicon nitride (Si ₃ N ₄ ), mullite (3Al ₂ O _{3.2SiO 2} to 2Al ₂ O _{3.SiO 2} ), and alumina (Al ₂ O ₃ ).

(Opening 310)
2A is a schematic diagram of the insulating layer 300, and FIG. 2B is a side cross-sectional view of the insulating layer 300. The opening 310 of the 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 calculated by ^πr2 , where r is the radius of the opening.

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 the heat generated by the heater 120 from penetrating from the first growth furnace 100 to the second growth furnace 200. As a result, it is possible to prevent the internal temperature of the second growth furnace 200 from increasing, thereby preventing the seed crystal from being completely melted by heat after seeding.

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 penetrating from the first growth furnace 100 to the second growth furnace 200 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.

<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 receiving tray 30 thereon, an arm 420 for raising and lowering the stage 410, and a storage box 430 for storing the arm 420.

The crucible stand 400 raises and lowers the single crystal growth crucible 10 between the first growth furnace 100 and the second growth furnace 200, so that the FeGa alloy raw material 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 the FeGa alloy single crystal.

(Other configurations)
The growth furnace 1000 may further include components in addition to the above components, such as 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.

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

The lower part of the single crystal growth crucible 10 is filled with an FeGa alloy seed crystal 16, and a mixture of iron and gallium 17 is filled on top of this FeGa alloy seed crystal 16.

The crucible 10 for single crystal growth can be used in the VB method to solidify the molten mixture 17 of iron and gallium in the crucible 10 for single crystal growth, thereby growing a FeGa alloy single crystal.

Figure 4 shows a schematic diagram of an example of a crucible 10 for growing single crystals. Figure 4a is a perspective view, and Figure 4b is a cross-sectional view. The crucible 10 for growing single crystals comprises a portion 10a for inserting raw material, a portion 10c for inserting a seed crystal, and a tapered portion 10b connecting portions 10a and 10c. For example, a crucible with 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 portion 10a of 150 mm, a total height H2 of portions 10a and 10b of 170 mm, and an inner dimension height H4 of 196 mm can be used.

(Support base 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.

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

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 side walls 32 can be used as the melt receiving dish 30, and the outer diameter R can be set to 108 mm.

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, the heat generated by the heater 120 can be prevented from entering the second growth furnace 200 from the first growth furnace 100. As a result, the internal temperature of the second growth furnace 200 can be prevented from rising, and the seed crystal after seeding can be prevented from being completely melted by heat.

[Method for producing FeGa alloy single crystal]
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.

FeGa alloy single crystals having super magnetostrictive properties can be grown, for example, by solidifying a melt of iron and gallium in a crucible. In the present invention, a growth furnace equipped with a first growth furnace, a second growth furnace, an insulating layer, and a crucible stand is used to grow FeGa alloy single crystals by the VB method. The opening of the insulating layer in the growth furnace is cylindrical and satisfies the condition of height/cross-sectional area of opening = 0.0035 or more.

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.

<Growth process>
Furthermore, the manufacturing method of the present invention includes, after the seeding step, a growing step of growing an FeGa alloy single crystal at a growth rate of 1 mm/hour or less.

The method for producing a FeGa alloy single crystal of the present invention may include additional steps in addition to the seeding step and the growing step. Below, the crucible placement step, melting step, bubble removal step, seeding step, and growing step will be described with reference to FIG. 3.

In the VB method, first, an FeGa alloy seed crystal 16 with a principal plane orientation of <100> is placed at the bottom of a crucible 10 for growing single crystals. Then, a required amount of the raw material iron and gallium mixture 17 is placed on top of the FeGa alloy seed crystal 16 (Crucible placement step in FIG. 3(a)), and then the crucible 10 is appropriately covered with a lid.

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, producing the raw material melt 18 (FIG. 3(b) melting process).

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

After the bubble removal process, 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 again, and then an FeGa alloy single crystal is grown inside the single crystal growth crucible 10 (Growth process in FIG. 3(d)). 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 (iron and gallium mixture 17) and is covered with a lid, so that the temperature distribution is high in the upper part of the height direction and low in the lower part. 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 of the height direction by moving the movable rod 13 to raise the crucible 10, and seeding is performed (Seeding process in FIG. 3(c)).

After that, while maintaining the temperature gradient in the growth furnace 1000, the descent speed of the single crystal growth crucible 10 is set to 1 mm/hour or less, and the arm 420 is moved at a constant speed to lower the single crystal growth crucible 10 to grow the FeGa alloy single crystal 16 (growth process in FIG. 4(d)), and all of the melt is solidified. Note that if the descent speed of the single crystal growth crucible 10 is made faster than 1 mm/hour, polycrystallization will occur, and it will not be possible to grow the FeGa alloy single crystal.

After the lowering of the crucible 10 is completed and the growth of the single crystal is completed (Figure 3 (e)), the mixture is cooled at a predetermined rate to obtain the FeGa alloy 19 (cooling process).

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 removed to remove the grown single crystal from the single crystal growth crucible 10.

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.

If the temperature gradient in the single crystal growth crucible 10 is less than 2.5°C/mm, the FeGa alloy seed crystal 16 may become too hot and melt completely. On the other hand, to prevent an increase in power consumption due to an increase in heater output and to prevent the generation of gallium vapor from the top surface of the melt, the temperature gradient is set to 5.5°C/mm or less. In addition, we attempted 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.

The method for producing a FeGa alloy single crystal of the present invention can prevent the iron gallium alloy seed crystal 16 from melting completely. Since the FeGa alloy is a non-uniform melting crystal, when the gallium content in the FeGa alloy is 18% by atomic weight, 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 in order to provide a temperature difference of 75°C or more in the vertical direction of the iron gallium alloy seed crystal 16.

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 wider range of descending speed of the crucible 10 for single crystal growth. 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 it 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.

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.

[Example 1]
First, in an environment of room temperature 20 ° C., a granular iron raw material (purity: 99.9%) and a gallium raw material (purity: 99.99%) having a median diameter of about 1 mm were weighed so that the ratio of iron to gallium was 82:18 in the stoichiometric ratio, that is, the gallium content was 18.0% in atomic weight %. The weighed gallium raw material was put into a Teflon (registered trademark) container and melted in a hot water bath. Furthermore, the iron raw material was put into the molten gallium raw material, stirred in the container, and then cooled to room temperature to prepare a mixture 17 of iron and gallium, which is a mixed raw material.

Then, in the lower part of the crucible 10 for growing single crystals made of dense alumina, which has 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, as shown in FIG. 4, a FeGa alloy seed crystal 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 was filled, and a mixture 17 of iron and gallium was filled on top of the FeGa alloy seed crystal 16. At this time, a crystal with a main surface orientation of the <100> orientation was used for the FeGa alloy seed crystal 16.

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 tray 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 tray 30 was made of alumina, had a bottom 31 and sidewall 32, was 90 mm high, and had an outer diameter R of 108 mm. The insulating materials 110, 210, and the insulating layer 300 were made of alumina.

In the growth furnace 1000 shown in FIG. 1, the heat insulating layer 300 had a height H of 40 mm, an opening 310 with a radius of 60 mm, an opening cross-sectional area of 11,300 mm ² , and height H/opening cross-sectional area=0.0035.

Next, the arm 420 was driven to set the stage 410 at the bottom of 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. In addition, the upper heater 120a, the middle heater 120b, and the lower heater 120c, which were made of carbon resistance heaters 120, were independently controllable.

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 inside the growth furnace 1000 was raised. After the temperature rise was completed and the temperature inside the growth furnace 1000 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, with a high temperature at the top and a low temperature at the bottom, the temperature inside the single crystal growth crucible 10 rose as it moved to the top of the first growth furnace 100, and the mixture 17 of iron and gallium melted to form a molten material.

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 3.0°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 is such that the gallium content in the FeGa alloy single crystal is 18% in atomic weight percent, and the solidification temperature of the FeGa alloy in this case is approximately 1450°C. Therefore, the position of the single crystal growth crucible 10 when the measured temperature at the tip of the thermocouple 15 is 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.

When the mixed raw materials were almost melted and turned into 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 approximately 30 minutes. Next, the pressure was gradually reduced at a gradient of 2.5 Pa/min over 60 minutes until the pressure reached 200 Pa or less, and air bubbles in the molten material were removed (air bubble removal process). After the air bubble removal process, the introduction of argon gas was resumed, and the inside of the growth furnace 1000 was adjusted to an inert atmosphere of 1 atmosphere.

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 3.0°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 stable and in the range of 1350 to 1400°C. Once the position to hold the single crystal growth crucible 10 was determined, it was held there for 3 hours to perform seeding. After 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. The arm 420 was driven to lower the crucible 10 for single crystal growth at a rate of 1 mm/hour, i.e., the growth rate of the FeGa alloy single crystal was set to 1 mm/hour, and the growth of the FeGa alloy single crystal was started. After the lowering distance of the crucible 10 for single crystal growth reached 100 mm, the growth was terminated.

In Example 1, the crucible 10 for growing single crystals was placed in the first growth furnace 100 equipped with a heater 120 from melting the raw material to seeding, and the growth of the single crystal 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 bottom 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 1 mm/hour.

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 bottom end of the FeGa alloy seed crystal 16, and the entire FeGa alloy seed crystal 16 had not melted, confirming that seeding had been performed normally. Furthermore, the grown FeGa alloy single crystal was cut and the inside of the crystal was observed, but no defects such as voids that could be seen with the naked eye were found, confirming that the single crystal had been grown without any problems.

The above process was repeated 10 times to produce 10 ingots of FeGa alloy single crystal. The results were the same for each ingot, showing that seeding was successful and that ingots of FeGa alloy single crystal could be stably produced.

[Comparative Example 1]
The lowering speed of the crucible 10 for growing the single crystal was 2 mm/hour, that is, the growth speed of the FeGa alloy single crystal was 2 mm/hour. The other conditions were the same as in Example 1, and the FeGa alloy single crystal was produced.

After the above single crystal growth was completed, the grown ingot was removed from the single crystal growth crucible 10 and cut. The inside of the ingot was observed, and grain boundaries were observed, indicating that the ingot had become polycrystalline. The above growth process was repeated 10 times, and all 10 ingots had become polycrystalline.

[Comparative Example 2]
The lowering speed of the crucible 10 for growing the single crystal was 5 mm/hour, that is, the growth speed of the FeGa alloy single crystal was 5 mm/hour. The other conditions were the same as in Example 1, and the FeGa alloy single crystal was produced.

After the above single crystal growth was completed, the grown ingot was removed from the single crystal growth crucible 10 and cut. The inside of the ingot was observed, and grain boundaries were observed, indicating that the ingot had become polycrystalline. The above growth process was repeated 10 times, and all 10 ingots had become polycrystalline.

[Comparative Example 3]
In the growth furnace 1000 shown in Fig. 1, a heat insulating layer 300 having a height H of 20 mm, a radius of the opening 310 of 60 mm, an opening cross-sectional area of 11300 ^mm2 , and a height H/opening cross-sectional area = 0.0018 was used. The descending speed of the crucible 10 for single crystal growth was 5 mm/hour, i.e., the growth speed of the FeGa alloy single crystal was 5 mm/hour. Other than these, a mixture 17 of iron and gallium was prepared in the same manner as in Example 1, and a single crystal was grown.

After the above single crystal growth was completed, the grown ingot was removed from the single crystal growth crucible 10 and cut. The inside of the ingot was observed, and grain boundaries were observed, indicating that the ingot had become polycrystalline. The above growth process was repeated 10 times, and all 10 ingots had become polycrystalline.

The dimensions of the opening 310 of the insulating layer 300, the growth rate of the FeGa alloy single crystal, the temperature gradient of the crucible 10 for single crystal growth during the seeding process, and the growth results in Example 1 and Comparative Examples 1 to 3 are shown in Table 1.

As a result, the opening 310 of the insulating layer 300 was cylindrical, satisfying the condition of height H/cross-sectional area of the opening = 0.0035 or more, and by setting the growth speed to 1 mm/hour, it was possible to grow FeGa alloy single crystals without any problems.

[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 and can stably grow the single crystal.

10 Single crystal growth crucible, 10a part, 10b part, 10c part,
10d opening, 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 material, 120 Heater, 120a Upper heater,
120b middle heater, 120c lower heater, 130 screw,
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 Inner Dimension

Claims (3)

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;
a growing step of growing a FeGa alloy single crystal at a growth rate of 1 mm/hour or less after the seeding step;
Including,
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 mm2, ^the height/cross-sectional area of the opening is 0.0035 or more;
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 a temperature gradient in the crucible is within a range of 2.5 to 5.5° C./mm . 2. The method for producing an FeGa alloy single crystal according to claim 1, wherein the heat insulating layer is made of at least one of carbon, mullite, and alumina . The method for producing a FeGa alloy single crystal according to claim 1 or 2, 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.

Images