JP2022146327A - MANUFACTURING METHOD OF FeGa ALLOY SINGLE CRYSTAL - Google Patents

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

The FeGa alloy can be machined and exhibits a large magnetostriction of about 100 to 350 ppm, so it is suitable as a material for magnetostrictive vibration power generation, actuators, and the like, and has been attracting attention in recent years.

Furthermore, since the FeGa alloy can produce a large magnetostriction in a specific crystal orientation, a single-crystal member in which the direction requiring magnetostriction of the magnetostrictive member and the orientation in which the crystal magnetostriction is maximized are aligned. It is considered that the use as is most suitable.

In the method for producing a polycrystal of an FeGa alloy, a flaky or powdery raw material produced by a powder metallurgy method, a rapid solidification method (for example, Patent Document 1), or a liquid rapid solidification method is sintered under pressure. A method (for example, Patent Document 2) has been proposed. However, in any of these various manufacturing methods, the inside of the member becomes polycrystalline instead of single crystal, and it is impossible to match all the crystal orientations in the member with the orientation that maximizes magnetostriction. The magnetostrictive property is inferior to that of the member of

On the other hand, there is a pulling method for the production of single crystals. For example, Patent Document 3 describes a method for growing a single crystal by a pulling method (Czochralski method). However, in this method, the raw material is melted by a high-frequency induction heating system, which increases the power supply cost. In addition, the structure of the apparatus is complicated and the cost of the apparatus is high, so that the pull-up method results in high manufacturing costs.

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

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

Compared to these methods, the VB method, in which the melt is solidified in a crucible, can produce a FeGa alloy single crystal having giant magnetostriction at a low cost. In the VB method, a crucible containing an FeGa alloy seed crystal and an FeGa mixed raw material is heated with a heater to melt the FeGa mixed raw material. The liquid is solidified to grow an FeGa single crystal, and when the temperature reaches room temperature, the FeGa single crystal is taken out. After that, the FeGa alloy single crystal is cut into a desired size to obtain a magnetostrictive plate. That is, the larger the grown FeGa alloy single crystal, the more magnetostrictive plates can be obtained.

However, in the VB method, it is necessary to place a mixture of iron and gallium on top of the seed crystal, melt the mixture, and then solidify the melt from the seed crystal side while inheriting the crystal orientation of the seed crystal. FeGa alloys are inconsistent melting crystals, the solidus line and the liquidus line in the phase diagram do not match, and when the gallium content is 17 to 19% in terms of atomic weight, the temperature between the solidus line and the liquidus line is The difference is about 70-80°C.

Therefore, when trying to grow a large FeGa alloy single crystal by the VB method, the molten material melts all the seed crystals, resulting in a situation where the single crystal cannot be grown in the desired crystal orientation.

Therefore, in view of such circumstances, the present invention provides a method for producing an FeGa alloy single crystal by the vertical Bridgman method, which is capable of preventing the entire seed crystal from melting during crystal growth. The purpose is to provide a method.

In order to solve the above-mentioned problems, the method for producing an FeGa alloy single crystal of the present invention includes a first growth furnace surrounded by a heat insulating material and equipped with a cylindrical heater, and a furnace positioned vertically below the first growth furnace. a second growth furnace surrounded by a heat insulating material and not equipped with a heater; a heat insulation layer having a cylindrical opening connecting the first growth furnace and the second growth furnace; and a crucible through the opening. A method for producing a FeGa alloy single crystal by the vertical Bridgman method using a growth furnace comprising a crucible table for raising and lowering the first growth furnace and the second growth furnace, wherein a seeding step of lowering the arranged seed crystal from the first growth furnace to the opening and seeding the raw material heated and melted by the heater with the seed crystal; The part has a cylindrical shape that satisfies the condition of height/opening cross-sectional area=0.0035 or more.

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

The crucible may have an outer dimension of 74 mm square, a height of 200 mm, an inner dimension of 66 mm square, a height of 196 mm, and a thickness of 4 mm.

According to the present invention, it is possible to provide a method for producing a FeGa alloy single crystal by the vertical Bridgman method, which is capable of preventing the entire seed crystal from melting during crystal growth. can.

1 is a schematic cross-sectional view of a growth furnace 1000 for growing a single crystal of an iron-gallium alloy; FIG. 3 is a schematic diagram of a heat insulating layer 300; FIG. 1 is a schematic cross-sectional view showing the arrangement of a crucible 10 for single crystal growth and a resistance heater 120 in each step of a method for producing a FeGa alloy single crystal by the VB method; FIG. 1 is a schematic diagram of a single-crystal-growing crucible 10. FIG. 3 is a schematic side cross-sectional view of a melt receiving tray 30; FIG.

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

[Single crystal growth device]
The FeGa alloy single crystal production method of the present invention can use, for example, a growth furnace 1000 for growing an iron-gallium alloy single crystal shown in FIG. The growing furnace 1000 includes a first growing furnace 100 , a second growing furnace 200 , a heat insulating layer 300 and a crucible base 400 .

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

(Insulation material 110)
The heat insulating material 110 can form the first growth furnace 100 in a cylindrical shape. ing. _{The material} of the _{heat insulating material 110} is not _{particularly limited} . Alumina _{( Al2O3} ) etc. are mentioned.

(Heater 120)
The heater 120 is arranged inside the heat insulating material 110, and a resistance heating heater made of carbon can be used. A hot zone can be formed by the heater 120 during the growth of the FeGa alloy single crystal. 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 electric power supplied to 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 strictly. ing. For example, it is possible to realize a temperature distribution in which the upper portion of the first growth furnace 100 is high temperature and the lower portion 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 does not have a heater. This furnace is used to cool and solidify the FeGa alloy raw material after seeding.

(Insulation material 210)
The heat insulating material 210 can form the second growth furnace 200 into a cylindrical shape. _{The material} of the _{heat insulating material 210} is not _{particularly limited} . Alumina _{( Al2O3} ) etc. are mentioned.

(electrode 220)
An electrode 220 for applying current to the heater 120 is arranged in the second growth furnace 200 . Heater 120 is fixed to electrode 220 by screws 130 . Electrodes 220 and screws 130 can be made of carbon, for example.

<Heat insulation layer 300>
The heat insulating layer 300 has a cylindrical opening 310 connecting the first growing furnace 100 and the second growing furnace 200 (FIGS. 1 and 2). The heat insulating layer 300 is arranged vertically between the first and second growth furnaces 100 and 200, and the diameter of the opening 300 is smaller than the diameters of the cylindrical first and second growth furnaces 100 and 200. A melt receiving plate 30 on which a support base 20 for supporting the crucible 10 for single crystal growth is placed is opened to the extent that it can pass through with a slight gap. By arranging the heat insulating layer 300 having such a narrow opening 310 between the first growth furnace 100 and the second growth furnace 200, the single crystal growth crucible 10 is separated from the first growth furnace 100 to the second growth furnace 200. , especially while the crucible 10 for single crystal growth is passing through the opening 300, the heat generated by the heater 120 can be suppressed from entering the second growth furnace 200 from the first growth furnace 100. can. As a result, it is possible to suppress the rise in the internal temperature of the second growth furnace 200, thereby preventing the seed crystals 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 _{( Si3N4} ) _, mullite _{( 3Al2O3.2SiO2} to _2Al2O3.SiO2 ) _, and Alumina _{( Al2O3} ) etc. are mentioned.

(Opening 310)
2A and 2B are schematic diagrams of the heat insulating layer 300, FIG. 2A is a plan view of the heat insulating layer 300, and FIG. The opening 310 of the heat insulating layer 300 has a cylindrical shape that satisfies the condition of height H/opening cross-sectional area=0.0035 or more. The cross-sectional area of the opening is calculated by πr ² , where r is the radius of the opening.

By satisfying the condition of height H/opening cross-sectional area=0.0035 or more, when single crystal growth crucible 10 is moved from first growth furnace 100 to second growth furnace 200, single crystal growth crucible 10 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 while the heat is passing through the opening 310 . As a result, it is possible to suppress the rise in the internal temperature of the second growth furnace 200, thereby preventing the seed crystals after seeding from being completely melted by heat.

If the height H/opening cross-sectional area is less than 0.0035, the heat insulating effect of the heat insulating layer 300 becomes insufficient, and the heat generated by the heater 120 while the crucible 10 for single crystal growth is passing through the opening 310. In some cases, it is not possible to sufficiently prevent the heat from entering the second growth furnace 200 from the first growth furnace 100, and the seed crystal after seeding is completely melted by the heat.

<Crucible stand 400>
The crucible table 400 is a table on which the crucible 10 for single crystal growth can be moved up and down between the first growth furnace 100 and the second growth furnace 200 through the opening 310 . The crucible table 400 includes a stage 410 on which the melt tray 30 is placed, an arm 420 for raising and lowering the stage 410 , and a storage box 430 for storing the arm 420 .

The crucible 400 raises and lowers the crucible 10 for single crystal growth between the first growth furnace 100 and the second growth furnace 200, thereby melting the raw material of the FeGa alloy in the first growth furnace 100 having the heater 120, and producing a seed crystal. After seeding, the raw material is solidified in the second growth furnace 200 without a heater to grow the FeGa alloy single crystal.

(other configurations)
The growth furnace 1000 may have a further configuration in addition to the configuration described above. For example, a thermocouple 15 capable of measuring the temperature of the crucible 10 for single crystal growth and grasping the temperature of the raw material, the seed crystal, and the solidified FeGa alloy single crystal in the crucible 10 for single crystal growth, and the inside of the growth furnace 1000. A vacuum pump capable of adjusting the vacuum atmosphere, a chamber capable of covering the growth furnace 1000 to maintain the atmosphere inside the furnace, and an inert gas introduction capable of introducing an inert gas such as argon or nitrogen into the chamber. Means and the like can be provided.

<Single crystal growth crucible 10>
The crucible 10 for single crystal growth is preferably made of alumina, which has low chemical reactivity with the FeGa alloy single crystal and has a high melting point. Also, magnesia and pyrolitic boron nitride may be used. Further, the crucible 10 for single crystal growth, which is open on the upper side, may be covered with a lid made of the same material.

A FeGa alloy seed crystal 16 is filled in the lower portion of the crucible 10 for single crystal growth, and a mixture 17 of iron and gallium is filled on top of the FeGa alloy seed crystal 16 .

A FeGa alloy single crystal can be grown by solidifying a melt 17 of a mixture of iron and gallium in the crucible 10 for single crystal growth in the VB method.

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

(Support table 20)
The support base 20 is a base for supporting the crucible 10 for single crystal growth so that it does not fall down. Since crucible 10 for single crystal growth tapers toward the bottom and has a high center of gravity, it tends to topple over. For example, a cylindrical table made of alumina can be used as the support table 20 .

(Melt receiver 30)
The melt receiver 30 serves to receive the raw material melt that leaks from the crucible in the event that the single crystal growth crucible 10 should break during the melting and seeding of the raw material of the FeGa alloy single crystal and the growth of the single crystal. responsible for

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

Also, the difference between the diameter R of the melt receiving tray 30 and the diameter of the opening 310 of the heat insulating layer 300 can be set to 5 mm to 15 mm. If the difference is within this range, heater It is possible to suppress the heat generated by 120 from entering the second growth furnace 200 from the first growth furnace 100 . As a result, it is possible to suppress the rise in the internal temperature of the second growth furnace 200, thereby preventing the seed crystals after seeding from being completely melted by heat.

[Method for producing FeGa alloy single crystal]
Next, a manufacturing method using the growth furnace 1000 shown in FIG. 1 will be described as a method for manufacturing an FeGa alloy single crystal according to one embodiment of the present invention.

A FeGa alloy single crystal having giant magnetostriction can be grown by solidifying a melt of iron and gallium in a crucible, for example. , a crucible stand, and a FeGa alloy single crystal is grown by the VB method. The opening of the heat insulating layer in the growth furnace has a cylindrical shape that satisfies the condition of height/opening cross-sectional area=0.0035 or more.

<Seeding process>
In the manufacturing method of the present invention, the FeGa alloy seed crystal 16 placed under the raw material (the mixture 17 of iron and gallium) in the crucible 10 for single crystal growth is lowered from the first growth furnace 100 to the opening 310, A seeding step of seeding the raw material heated and melted by the heater 120 and the FeGa alloy seed crystal 16 is included.

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, the melting step, the bubble removal step, the seeding step, and the growing step will be described below with reference to FIG.

In the VB method, first, an FeGa alloy seed crystal 16 having a <100> principal plane orientation is arranged in the lower portion of the crucible 10 for single crystal growth. Then, a required amount of a mixture 17 of iron and gallium as 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.

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 gallium nitride or the like is likely to be 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, which are arranged so as to surround the crucible 10 for single crystal growth, are actuated to raise the temperature of iron and gallium. Melting of the mixture 17 is started to form a raw material melt 18 (Fig. 3(b) melting step).

When the mixture 17 of iron and gallium is almost melted to form a melt, the vacuum pump is operated to reduce the pressure in the growth furnace 1000 and remove bubbles in the melt (bubble removal step).

After the bubble removing step, an inert gas such as argon or nitrogen is flowed into the growth furnace 1000 to adjust the atmosphere inside the growth furnace 1000 again to an inert atmosphere, and then the FeGa alloy single crystal is grown inside the crucible 10 for single crystal growth. (FIG. 3(d) growth step). Specifically, using the heater 120, the FeGa alloy seed crystal 16 and the melt (mixture 17 of iron and gallium) are accommodated, and the single crystal growth crucible 10 covered with a lid is moved upward in the height direction. Heating is performed so that the temperature is high and the lower temperature is low. In this state, the temperature in the growth furnace 1000 is changed to a position where the FeGa alloy seed crystal 16 melts up to about half in the height direction, and the crucible 10 is raised by moving the movable rod 13 to perform seeding (Fig. 3(c) seeding step).

Thereafter, while maintaining the temperature gradient in the growth furnace 1000, the lowering speed of the crucible 10 for single crystal growth is set within the range of 1 to 10 mm/hour, and the arm 420 is moved at a constant speed to move the crucible 10 for single crystal growth. is lowered to grow the FeGa alloy single crystal 16 (FIG. 4(d) growing step), and solidify all the melt. Although the single crystal can be grown even if the descent speed of the crucible 10 for single crystal growth is set to 1 mm/hour or less, the growing period becomes longer and the productivity drops. In order to suppress changes in the crystal composition, the descent rate of the single crystal growth crucible 10 is preferably 5 mm/hour or more.

After the descent of the crucible 10 is completed and the growth of the single crystal is completed (FIG. 3(e)), cooling is performed at a predetermined rate to obtain the FeGa alloy 19 (cooling step).

Next, after confirming that the temperature in the growth furnace 1000 has reached room temperature, the crucible 10 for single crystal growth containing the grown single crystal is removed from the crucible stand 400, and the lid is removed to grow the single crystal. A grown single crystal is taken out from the crucible 10 for use.

Here, the temperature inside single-crystal-growing crucible 10 during seeding is increased vertically from the bottom to the top, and the temperature gradient during seeding inside single-crystal-growing crucible 10 is 2.5 to 2.5. The seeding position and the input power of the heater 120 are adjusted so as to obtain 5.5° C./mm. Such a temperature gradient can more reliably prevent the FeGa alloy seed crystal 16 from completely melting.

If the temperature gradient in single crystal growth crucible 10 is less than 2.5° C./mm, FeGa alloy seed crystal 16 may reach a high temperature and be completely melted. On the other hand, the temperature gradient is set to 5.5° C./mm or less in order to suppress an increase in power consumption due to an increase in heater output and generation of gallium vapor from the upper surface of the melt. Further, an attempt was made to investigate the seeding position where the temperature gradient is 6.5° C./mm, but the thermocouple 50 made of platinum rhodium broke during temperature measurement due to the high temperature, so the investigation was discontinued.

The FeGa alloy single crystal production method of the present invention can prevent the iron-gallium alloy seed crystal 16 from completely melting. Since the FeGa alloy has inconsistent melting crystals, the temperature difference between the solidus line and the liquidus line on the phase diagram is about 75° C. when the gallium content in the FeGa alloy is 18% in terms of atomic weight. Therefore, in order to prevent the iron-gallium alloy seed crystal 16 from completely melting, a temperature difference of 75° C. or more is required in the vertical direction of the iron-gallium alloy seed crystal 16 . Normally, the length of the iron-gallium alloy seed crystal 16 in the vertical direction is set to 30 mm. In order to provide a temperature difference of 2.5° C./mm or more, it is necessary to set the temperature gradient in the crucible 10 for single crystal growth to 2.5° C./mm or more.

By setting a high temperature gradient in single crystal-growing crucible 10 during seeding, it is possible to grow a single crystal at a lowering speed of single-crystal-growing crucible 10 in a wider range. However, if the temperature gradient inside the crucible 10 for single crystal growth during seeding is set high, the heater output will be high. As a result, the amount of melted material evaporated increases and adheres to the heat insulating material 110, the heater 120, the crucible base 400, etc., requiring cleaning. It is preferable to cover the crucible 10 for single crystal growth with a lid in order to suppress the evaporation amount of the melt. When the temperature gradient in the crucible 10 for single crystal growth during seeding is set to 6.0° C./mm or more, the amount of evaporation of the melted material increases due to the output of the heater. Therefore, it is preferable to set the temperature gradient within the crucible 10 for single crystal growth during seeding to 5.5° C./mm or less.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

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

As shown in FIG. 4, the outer dimension W1 is 74 mm square, the inner dimension W2 is 66 mm, and the thickness of the crucible is uniform. A FeGa alloy seed crystal 16 having a gallium content adjusted in advance (the gallium content is atomic weight % 17%, cylindrical shape of 5 mm diameter and 30 mm length) was filled, and a mixture 17 of iron and gallium was filled on top of the FeGa alloy seed crystal 16 . At this time, as the FeGa alloy seed crystal 16, a crystal having a main plane orientation of <100> orientation was used.

Next, the opening 10d of the crucible 10 for single crystal growth was covered with a lid made of sintered compact alumina. Then, as shown in FIG. 1, the crucible 10 for single crystal growth filled with the FeGa alloy seed crystal 16 and the mixture 17 of iron and gallium is placed on the support base arranged on the melt receiving tray 30 placed on the stage 410. 20 , and the tip of the thermocouple 15 was brought into contact with the side surface of the crucible 10 for single crystal growth. The melt receiver 30 is made of alumina, has a bottom 31 and side walls 32, has a height of 90 mm and an outer diameter R of 108 mm. Also, the heat insulating materials 110 and 210 and the heat insulating layer 300 are made of alumina.

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, an opening cross-sectional area of 11300 mm ² , and a heat insulating layer of height H/opening cross-sectional area=0.0035. was used.

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 to adjust the inside of the growth furnace 1000 to an argon atmosphere of atmospheric pressure. As the upper heater 120a, the middle heater 120b, and the lower heater 120c made of carbon resistance heaters 120, heaters capable of being controlled independently were used.

Then, the temperature in the growth furnace 1000 was raised by setting the temperature of the upper heater 120a to 1500° C., the temperature of the middle heater 120b to 1400° C., and the temperature of the lower heater 120c to 1300° C. After the temperature rise is completed and the temperature in the growth furnace 1000 is stabilized, the stage 410 is raised by driving the arm 420 to raise the crucible 10 for single crystal growth to the first growth furnace 100 at a moderate speed. rice field. A temperature gradient is created in the first growth furnace 100 in which the temperature in the upper part is high and the temperature in the lower part is low. Then the iron-gallium mixture 17 melted to form the melt.

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

When the mixed raw material was almost melted and turned into a melt, the introduction of argon gas into the growth furnace 1000 was suppressed, and the pressure inside the growth furnace 1000 was reduced to 350 Pa using a vacuum pump, and the mixture was kept as it was for about 30 minutes. Next, the pressure was gradually reduced to 200 Pa or less at a gradient of 2.5 Pa/min over 60 minutes to remove bubbles in the melt (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.

While monitoring the temperature at the contact point of the thermocouple 15 in the vicinity of the position of the single crystal growing crucible 10 where the melt is formed, the arm 420 is driven to create a temperature gradient 2 in the single crystal growing crucible 10 . While maintaining the temperature at 5° C./mm, the crucible 10 for single crystal growth was raised several mm to the seeding position to stabilize the temperature. By repeating this process, the crucible 10 for single crystal growth was raised so that the temperature of the thermocouple 15 was stabilized in the range of 1350 to 1400.degree. When the position to hold the crucible 10 for single crystal growth was determined, the crucible was held for 3 hours for seeding. After seeding, the temperature of the upper heater 120a is maintained at 1500° C., the temperature of the middle heater 120b is maintained at 1400° C., and the temperature of the lower heater 120c is maintained at 1300° C., and the arm 420 is driven to produce the crucible 10 for single crystal growth. The single crystal growth crucible 10 was lowered at a rate of 2 mm/hour to start the growth of the FeGa alloy single crystal. After the descent distance of crucible 10 for single crystal growth reached 100 mm, the growth was terminated.

In Example 1, the crucible 10 for single crystal growth is arranged in the first growth furnace 100 having a heater 120 from the melting of the raw material to seeding, and the single crystal growth after seeding is performed at the upper end of the raw material melt 18 It started when the position (liquid level) 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 heat 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.

After the growth of the single crystal was completed, the grown ingot was taken out from the crucible 10 for single crystal growth. Therefore, it was confirmed that the seeding was performed normally.

Also, the above steps were repeated 10 times to produce 10 ingots. In both cases, the same results as above were obtained, confirming that seeding was performed normally.

[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, an opening cross-sectional area of 11300 mm ² , and a heat insulating layer of height H/opening cross-sectional area=0.0018. was used. Except for this, a mixture 17 of iron and gallium was produced in the same manner as in Example 1, and a single crystal was grown.

After the growth of the single crystal was completed, the grown ingot was taken out from the crucible 10 for single crystal growth, and the seed crystal portion was cut to confirm the orientation. was

Also, the above steps were repeated 10 times to produce 10 ingots, but all the seed crystals were similarly melted.

Table 1 shows the dimensions of the opening 310 of the heat insulating layer 300 and the presence or absence of complete melting of the FeGa alloy seed crystal 16 in Example 1 and Comparative Example 1.

As a result, the opening 310 of the heat insulating layer 300 has a cylindrical shape that satisfies the condition of height H/opening cross-sectional area=0.0035 or more. I was able to ding.

[summary]
As described above, the present invention provides a method for producing a FeGa alloy single crystal by the vertical Bridgman method, which is capable of preventing the entire seed crystal from melting during crystal growth. Clearly it can be done.

10 crucible for single crystal growth, 10a part, 10b part, 10c part,
10d opening, 15 thermocouple, 16 FeGa alloy seed crystal,
17 iron and gallium mixture, 18 raw material melt, 19 FeGa alloy,
20 support stand, 30 melt tray, 31 bottom, 32 side wall, 100 first growth furnace,
110 heat insulating 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 base, 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 heat insulating material and equipped with a cylindrical heater;
a second growing furnace located vertically below the first growing furnace, 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 the crucible between the first growth furnace and the second growth furnace through the opening;
A method for producing a FeGa alloy single crystal by the vertical Bridgman method using a growth furnace comprising
A seeding step of lowering the seed crystal placed under the raw material in the crucible from the first growth furnace to the opening to seed the raw material heated and melted by the heater and the seed crystal. including
The method for producing a FeGa alloy single crystal, wherein the opening of the heat insulating layer has a cylindrical shape that satisfies the condition of height/opening cross-sectional area=0.0035 or more. In the seeding step, the temperature inside the crucible is adjusted so that it increases vertically from bottom to top, and the temperature gradient inside the crucible is within the range of 2.5 to 5.5° C./mm. The method for producing a FeGa alloy single crystal according to claim 1, wherein 3. The method for producing a FeGa alloy single crystal according to claim 1, wherein the crucible has an outer dimension of 74 mm square, a height of 200 mm, an inner dimension of 66 mm square, a height of 196 mm, and a thickness of 4 mm.

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