JP2020200226A - Single crystal growth method of iron-gallium alloy - Google Patents

Abstract

To provide a single crystal growth method of an iron-gallium alloy capable of removing bubbles existing in melt of a mixture of iron and gallium or the like without generating scatter of the melt caused by sudden boiling.SOLUTION: In a single crystal growth method of an iron-gallium alloy, including a bubble removal step for removing bubbles in melt by decompressing the melt of a mixture of iron and gallium placed under an inert atmosphere, the decompression has the first decompression for decompressing the melt to 300-500 Pa, and the second decompression for decompressing the melt from a pressure obtained by the first decompression to 200 Pa or lower at a decompression gradient of 2-6 Pa/min.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for growing a single crystal of an iron-gall alloy (FeGa alloy), in particular, a vertical Bridgman method (hereinafter sometimes abbreviated as "VB method") and a vertical temperature gradient solidification method (Vertical Grade). A method for growing a FeGa alloy single crystal having supermagnetic strain characteristics formed by a unidirectional solidification crystal growth method, in which a melt typified by Freeze method (hereinafter sometimes abbreviated as "VGF method") is solidified in a pit. Regarding.

The FeGa alloy is machinable and exhibits a large magnetostriction of about 100 to 350 ppm, and is therefore suitable as a material used for magnetostrictive vibration power generation and actuators, and has been attracting attention in recent years.

Further, since the FeGa alloy can cause a large magnetostriction to appear in a specific orientation of the crystal, the single crystal member in which the direction in which the magnetostriction is required and the orientation in which the magnetostriction of the crystal is maximized are matched. It is considered that the application as is optimal.

In the method for producing a polycrystal of FeGa alloy, a flaky or powdery raw material produced by a powder metallurgy method, a quenching solidification method (for example, Patent Document 1), or a liquid quenching solidification method is pressure-sintered. Methods (eg, Patent Document 2) and the like have been proposed. However, in all of these various manufacturing methods, the inside of the member does not become a single crystal but becomes a polycrystal, and it is impossible to match all the crystal orientations in the member with the orientation in which the magnetostriction is maximized. The magnetostrictive characteristics are inferior to those of the members of.

On the other hand, there is a pull-up method for producing a single crystal, but this single crystal production method has a problem that the production cost is extremely high. 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 the high frequency induction heating method, so that the power supply cost is high. In addition, since the device configuration is complicated and the device cost is high, the manufacturing cost is high as a result of the pulling method.

Further, Patent Document 4 describes a method for growing polycrystals by a one-way solidification method. In this method, general melting equipment and casting equipment, which are relatively inexpensive, can be used. However, since Patent Document 4 is a method for growing a polycrystal, a single crystal portion is separated from the polycrystal in order to obtain a single crystal, so that the production efficiency is very low. Further, since the FeGa alloy is used as the starting material, it is necessary to first prepare the FeGa alloy, and the raw material cost is high, which leads to an increase in the manufacturing cost.

Japanese Patent No. 4053328 Japanese Patent No. 4814085 Japanese Unexamined Patent Publication No. 2016-28831 Japanese Unexamined Patent Publication No. 2016-138028

As described above, it is difficult to inexpensively and mass-produce a single crystal of an iron-gallium alloy by the conventional methods described in Patent Documents 1 to 4 and the like.

Compared with these, a FeGa alloy single crystal having supermagnetic strain characteristics can be produced at a low cost by a unidirectional solidification crystal growth method in which the melt is solidified in a crucible, which is represented by the VB method and the VGF method.

In the one-way solidification crystal growth method, a mixture of iron and gallium is placed on top of the seed crystal, the mixture is melted, and then the melt is solidified from the seed crystal side upward while inheriting the crystal orientation of the seed crystal. There is a need to. Therefore, there is a problem that bubbles are generated between the seed crystal and the melt and inside the melt.

To remove these bubbles, it is effective to reduce the pressure after melting the mixture. However, when the pressure is reduced in a short time, the melt may be scattered from the open portion of the upper part of the crucible due to the sudden boiling of the melt. In this case, the melt adheres to the constituents in the furnace and the single crystal production is interrupted. It will be. On the other hand, when the pressure is gradually reduced over a long period of time, the supply amount of the inert gas decreases, so that the temperature of the melt gradually rises and the seed crystal melts, resulting in a state in which seeding cannot be performed. There is a risk.

In view of these circumstances, the present invention is a single crystal of an iron-gallium alloy capable of removing bubbles existing in a melt of a mixture of iron and gallium without causing scattering of the melt due to sudden boiling. The purpose is to provide a training method.

The melt of the mixture of iron and gallium placed in an inert atmosphere was depressurized, the bubble removal step of removing the bubbles in the melt was performed under various conditions, and the melt was repeatedly observed. It was found that when the pressure was reduced to around 250 Pa, the liquid level of the melt shook and bubbles were removed. In addition, the seed crystals are melted by depressurization for a long time, and if the depressurization is continued for more than about 3 hours, especially under a low pressure of 500 Pa or less, the seed crystals under the melt may be completely melted. It turned out that there is.

Based on the above findings, in the bubble removal step, the pressure inside the furnace is reduced to 500 Pa or less, and then slowly reduced to a pressure of 200 Pa or less to prevent the melt from scattering due to bumping and to prevent the seed crystal from scattering. We have found that air bubbles can be removed while simultaneously achieving complete prevention of melting, and have come up with the present invention.

That is, in order to solve the above problems, the method for growing a single crystal of an iron-gallium alloy of the present invention depressurizes a melt of a mixture of iron and gallium placed in an inert atmosphere and removes air bubbles in the melt. The depressurization includes a first depressurization of depressurizing the melt to 300 to 500 Pa and a depressurization gradient of 2 to 6 Pa / min to 200 Pa or less from the pressure of the first decompression. Has a second decompression to decompress.

The gallium content of the mixture may be 18.0% to 23.0% in terms of atomic weight%.

The single crystal of the iron-gallium alloy may be grown by the vertical Bridgeman method or the vertical temperature gradient solidification method.

According to the method for growing a single crystal of an iron-gallium alloy of the present invention, a single crystal of an iron-gallium alloy can be produced at low cost and in a large amount.

It is the schematic sectional drawing of the growth apparatus which grows a single crystal of an iron-gallium alloy.

Hereinafter, a method for growing a single crystal of an iron-gallium alloy according to an embodiment of the present invention will be described.

A single crystal of an iron-gallium alloy having supermagnetic strain characteristics can be grown by solidifying a melt of iron and gallium in a crucible, and specifically, one direction represented by the VB method and the VGF method. It can be grown by the solidification crystal growth method.

[Bubble removal process]
In the growth of a single crystal of an iron-gallium alloy, first, iron and gallium are used as starting materials, and a mixture thereof is melted in an inert atmosphere so as not to generate oxides or nitrides to obtain a melt. Since bubbles are mixed in the melt, the melt is depressurized to remove the bubbles in the bubble removing step. By reducing the pressure, bubbles such as air having a specific gravity smaller than that of iron or gallium are degassed from the liquid surface of the melt.

Degassing of bubbles from the melt occurs at around 250 Pa, but in order to degas more efficiently, it is necessary to reduce the pressure of the melt to a pressure of 200 Pa or less. Since the temperature of the melt rises at 500 Pa or less, the seed crystal may melt by maintaining the reduced pressure state at 500 Pa or less for a long time. Therefore, the first decompression that reduces the pressure of the melt to 300 to 500 Pa from the standard atmospheric pressure (101.325 kPa), and 2 to 6 Pa from the pressure due to the first decompression to 200 Pa or less. Depressurize with a second decompression gradient of / min.

(First decompression)
In the first depressurization, the melt is reduced to 300 to 500 Pa, but is preferably reduced to 350 Pa from the viewpoint of preventing sudden boiling of the melt and complete melting of the seed crystal. For example, the first depressurization condition can be appropriately adjusted so that the pressure of the melt reaches 300 to 500 Pa in about 10 to 30 minutes from the standard atmospheric pressure.

(Second decompression)
In the second depressurization, when the depressurization is performed in a short time exceeding 6 Pa / min, the melt tends to boil. On the contrary, when the pressure is reduced for a long time under the condition of less than 2 Pa / min, the seed crystal is easily completely melted. By depressurizing the melt at a gradient of 2-6 Pa / min, these bumps and complete melting of the seed crystals can be avoided.

As an example of the depressurization condition, in order to prevent the swaying of the melt due to the sudden boiling of the melt and to stably avoid the complete melting of the seed crystal, the first decompression condition is reduced from the standard atmospheric pressure to 350 Pa in 10 to 30 minutes. The second depressurization is preferably performed from the pressure due to the first decompression to 200 Pa with a decompression gradient of 2.5 to 5 Pa / min.

Further, when the melt is held under reduced pressure for a long time for more than 2 hours, the seed crystal is easily completely dissolved. Therefore, the retention time of the melt from the start of the first depressurization to the end of the second depressurization is preferably within 2 hours. After the first depressurization, if the depressurizing conditions in the furnace are not stable, it is necessary to maintain the pressure for a certain period of time without further depressurizing treatment so that it becomes stable, and depending on the state in the furnace. The conditions can be appropriately determined in consideration of the decompression rate of the second decompression. For example, the first decompression may be set from standard atmospheric pressure to 350 Pa, the pressure may be maintained for 30 minutes after the first decompression to stabilize the inside of the furnace, and then the second decompression may be performed over 25 to 60 minutes. Good. If there is no problem with the depressurizing conditions in the furnace, it is not necessary to maintain the pressure, and the first depressurization and the second depressurization may be continuously performed.

If growth is started without removing the bubbles in the melt, the bubbles interfere with the growth and polycrystals are likely to occur. Polycrystals are not preferable as members for magnetostrictive vibration power generation and actuators because they may be broken at grain boundaries due to vibration or the like. Further, as in Patent Document 4, it is possible to separate the single crystal portion from the polycrystal, but the production efficiency of the single crystal is lowered. When the reduced pressure time is long and the seed crystal is completely melted, the crystal orientation of the seed crystal is not inherited, and a crystal having an arbitrary growth orientation is grown. According to the present invention, iron in a crystal orientation suitable for a member such as a magnetostrictive vibration power generator or an actuator by removing bubbles in the melt by a bubble removing step and then starting growth, and having no internal defects or the like. Single crystals of gallium alloy can be grown at low cost and in large quantities.

In the present invention, when growing a single crystal of an iron-gallium alloy, iron and gallium can be grown in a container such as a crucible, respectively, but a mixture of granular iron surface coated with gallium is used as a mixture. Can be used. If this mixture is used as a starting material, iron and gallium are in a uniform state, which facilitates alloying and single crystallization, and also suppresses the mixing of air bubbles in the melt. ..

Further, as the mixture, a mixture of granular iron and granular gallium, a mixture of granular iron and liquid gallium, and an iron-gallium alloy previously prepared by arc melting or the like can be used. Further, it is also possible to grow a single crystal of the iron-gallium alloy by putting a part or the whole amount of the polycrystalline iron-gallium alloy in a container. Since the gaps in the container cause air bubbles, it is possible to suppress the mixing of air bubbles into the melt by putting the raw material into the container as closely as possible.

[Mixture forming step]
The mixture in which the surface of particulate iron is coated with gallium, which was introduced as an example of the mixture, can be obtained, for example, by a mixture forming step. That is, the mixture can be obtained by immersing particulate iron in a gallium melt and stirring it, and then cooling the iron-soaked gallium melt below the freezing point of gallium. Specifically, a solid gallium raw material is placed in a container having low wettability to a gallium melt such as Teflon (registered trademark), and the temperature is raised to 30 ° C. or higher, which is the melting point of gallium, by boiling water or the like, and solid gallium. To melt. Next, the particulate iron raw material is put into the gallium melt, stirred, and then cooled to 30 ° C. or lower. Since the gallium melt has a very high wettability with respect to iron, the surface of iron can be coated with gallium by stirring.

The median diameter (D50) of the particulate iron used as the raw material of the mixture is preferably 40 μm to 3 mm. When the median diameter of iron is less than 40 μm, the specific surface area becomes large, so that the proportion of the oxide film on the iron surface increases, and the proportion of oxides incorporated into the raw material increases, which hinders the growth of single crystals. May be done. In addition, there is a risk of dust explosion, which can be very time-consuming to handle. On the other hand, when the median diameter of iron exceeds 3 mm, the specific surface area becomes too small, which may make it difficult to uniformly coat the iron surface with gallium. When the median diameter (D50) of iron is 40 μm to 3 mm, there is no danger of dust explosion, it is easy to uniformly coat the surface of iron with gallium, and the proportion of oxide film is low, so that the iron gallium alloy It becomes easier to grow a single crystal of.

The grown iron-gallium alloy single crystal may contain 18 to 23% of gallium in terms of atomic weight. If gallium is contained in this range, the iron-gallium alloy can obtain high magnetostrictive characteristics.

In order to grow an iron-gallium alloy having such high magnetostrictive characteristics, the gallium content of the mixture is 18.0% to 23 in atomic weight%, considering the effects of evaporation and segregation of gallium from the raw material melt. It is preferably 0.0%. The balance of the mixture excluding gallium is iron, except for unavoidable impurities such as oxides.

[Other processes]
The method for growing a single crystal of an iron-gallium alloy of the present invention can include other steps in addition to the bubble removing step and the mixture forming step. For example, a growing step of growing a single crystal from a melt based on a seed crystal after the bubble removing step, a melting step of melting a mixture of iron and gallium to obtain a melt before the bubble removing step, and the like can be included.

Hereinafter, the method for growing a single crystal of an iron-gallium alloy according to an embodiment of the present invention will be described more specifically with reference to the single crystal growing apparatus shown in FIG. 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 growing device]
FIG. 1 is a schematic cross-sectional view of a single crystal growing device for growing a single crystal of an iron-gallium alloy. FIG. 1 schematically shows the positional relationship between the single crystal growing crucible 10 in the single crystal growing apparatus 100, the FeGa alloy seed crystal 16, and the mixture 17 of iron and gallium as a raw material.

The single crystal growing device 100 includes a heat insulating material 11, an upper heater 12a, a middle heater 12b, a lower heater 12c, a movable rod 13, a crucible receiver 14, a thermocouple 15, a vacuum pump 18, and a chamber 19. The structure is such that the upper part of the chamber 19 has a high temperature and the lower part has a low temperature, and a melt 17 of a mixture of iron and gallium is obtained by a unidirectional solidification crystal growth method such as the VB method or the VGF method. By solidifying in the crucible 10, a single crystal of FeGa alloy can be grown.

As shown in FIG. 1, in the single crystal growing apparatus 100, a carbon resistance heating heater 12 is arranged inside the heat insulating material 11. During the growth of a single crystal of FeGa alloy, a hot zone is formed by the resistance heating heater 12. The resistance heating heater 12 is composed of an upper heater 12a, a middle heater 12b, and a lower heater 12c, and the temperature gradient in the hot zone can be controlled by adjusting the input power to these heaters 12a to 12c. It has become.

Inside the resistance heating heater 12, a single crystal growing crucible 10 is arranged, and is placed on a crucible receiver 14 (support stand) provided with a movable rod 13 that can move in the vertical direction. The lower part of the crucible for growing a single crystal is filled with the FeGa alloy seed crystal 16, and the FeGa alloy seed crystal 16 is filled with the mixture 17 of iron and gallium.

A chamber 19 and a vacuum pump 18 are installed in the growing furnace, and the raw material can be adjusted to a vacuum atmosphere to grow a single crystal. Further, an inert gas such as argon or nitrogen can be introduced into the chamber 19, and the raw material can be adjusted to an inert atmosphere.

The material of the crucible 10 for growing a single crystal is preferably alumina, which has a low chemical reactivity with a single crystal of an iron-gall alloy and is a high melting point material. Further, magnesia and pyrolytic boron nitride may be used.

The single crystal growing crucible 10 whose upper side is open may be covered with a lid material (not shown) for preventing dust from falling. The single crystal growing crucible 10 is placed on a crucible receiver 14 provided with a movable rod 13 in the single crystal growing device 100 as described above, and the movable rod 13 is moved up and down to grow a single crystal. The crucible 10 can be moved up and down in the growing furnace. Further, a thermocouple 15 capable of monitoring the temperature of the crucible is attached to the crucible 10 for growing a single crystal.

[Method for growing FeGa alloy single crystal]
Next, a single crystal growing method of an iron-gallium alloy by the VB method using the single crystal growing device 100 will be described with reference to FIG. First, a FeGa alloy seed crystal 16 having a main surface orientation of <100> is arranged in the lower part of the single crystal growing crucible 10. Then, a required amount of a mixture 17 of iron and gallium as a raw material is arranged on the FeGa alloy seed crystal 16.

Next, an inert gas such as argon or nitrogen is passed through the chamber 19 to adjust the inside of the chamber 19 to an inert atmosphere. When there is a possibility that gallium nitride or the like is generated, it is preferable to introduce argon gas. After the inside of the chamber 19 becomes an inert atmosphere, the upper heater 12a, the middle heater 12b and the lower heater 12c arranged so as to surround the single crystal growing crucible 10 are operated to raise the temperature, and the mixture of iron and gallium is heated. The melting of 17 is started (melting step).

When the iron / gallium mixture 17 is almost melted into a melt, the vacuum pump 18 is operated to depressurize the inside of the chamber 19 and remove air bubbles in the melt by the first depressurization and the second depressurization (1st decompression and 2nd decompression). Bubble removal step).

After the bubble removing step, an inert gas such as argon or nitrogen is allowed to flow in the chamber 19, the inside of the chamber 19 is adjusted to an inert atmosphere again, and then a single crystal of FeGa alloy is grown inside the crucible 10 for growing a single crystal. (Growth process). Specifically, using the resistance heating heater 12, the temperature above the single crystal growing crucible 10 in which the FeGa alloy seed crystal 16 and the melt (mixture 17 of iron and gallium) are stored is high in the height direction. , Heat so that the temperature below is low. In this state, the temperature in the chamber 19 is raised until the FeGa alloy seed crystal 16 is melted to about the upper half in the height direction, and seeding is performed. After that, while maintaining the temperature gradient in the chamber 19 as it is, the output of the resistance heating heater 12 is gradually lowered to solidify all the melts, and then cooled at a predetermined speed to obtain a single crystal of FeGa alloy. obtain.

Next, after confirming that the temperature in the chamber 19 has reached about room temperature, the single crystal growing crucible 10 containing the grown single crystal is removed from the crucible receiver 14, and further grown from the single crystal growing crucible 10. Take out the single crystal.

Further, the seeding for growing a single crystal of the FeGa alloy is performed by melting the upper part of the FeGa alloy seed crystal 16 and the mixture 17 of iron and gallium to form a stable solid-liquid interface. Here, the temperature of the solid-liquid interface and the holding time at that temperature are important factors in seeding. The reason is that the FeGa alloy seed crystal 16 has a crushed layer formed during the processing of the FeGa alloy seed crystal 16 in the vicinity of the surface thereof, and in order to grow a single crystal, this crushed layer is melted. This is because it needs to be kept. Further, the temperature of the solid-liquid interface and the holding time at that temperature are also important in that the solid-liquid interface must be formed before all the FeGa alloy seed crystals 16 are melted.

In order to satisfy the above requirements, the temperature of the interface between the FeGa alloy seed crystal 16 and the melt is located within the range from the melting point of the FeGa alloy single crystal to a temperature 20 ° C. higher than the melting point. Set the crystal growth crucible 10. From the viewpoint of more stably growing the single crystal of the FeGa alloy, the temperature of the interface is more preferably in the range from the melting point of the single crystal of the FeGa alloy to a temperature 10 ° C. higher than the melting point. The temperature is maintained at these temperatures for a predetermined time (for example, 1 hour or more, preferably 3 to 6 hours), and the upper part of the FeGa alloy seed crystal 16 and the mixture 17 of iron and gallium are melted for seeding. The FeGa alloy seed crystal 16 is the core of single crystal growth, and the FeGa alloy seed crystal 16 is partially melted in order to be integrated with the FeGa mixed raw material 17, but the entire FeGa alloy seed crystal 16 is melted. It must not be melted.

After the seeding is completed, the single crystal growing crucible 10 is gradually lowered to pass through a region having a temperature gradient in the hot zone. In this way, a single crystal of the FeGa alloy is grown by cooling and solidifying the melt according to the crystal orientation of the FeGa alloy seed crystal 16.

In the single crystal growing method according to the present embodiment, as described above, the interface temperature between the FeGa seed crystal 16 and the mixture 17 of iron and gallium is set to a temperature 20 ° C. higher than the melting point of the FeGa single crystal. Since the melting is performed within the range up to, the upper part of the FeGa alloy seed crystal 16 and the mixture 17 of iron and gallium are melted, and the FeGa alloy seed crystal 16 and the mixture 17 of iron and gallium are combined. Can be integrated. If the interface temperature between the FeGa alloy seed crystal 16 and the mixture 17 of iron and gallium is higher than the above melting point by more than 20 ° C., the bottom surface of the FeGa alloy seed crystal 16 may be melted, and the single crystal. There is a risk that problems will occur in the training of.

Further, the holding time for melting the upper part of the FeGa alloy seed crystal 16 and the mixture 17 of iron and gallium is preferably 1 hour or more as described above. By holding for 1 hour or more, the solid-liquid interface between the FeGa alloy seed crystal 16 and the mixture 17 of iron and gallium can be stabilized, so that a high-quality single crystal having no defects inside the single crystal can be grown. can do. Further, it is more preferable that the holding time is 4 to 6 hours. That is, if the reaction is held for 4 hours or more, the reaction related to seeding is generally in progress, and the reaction is almost completed in 6 hours or less. Therefore, by setting the holding time to 4 to 6 hours, it is possible to stably perform seeding without lowering the productivity of the iron-gallium alloy single crystal.

In the above, the method for growing a single crystal of an iron gallium alloy by the VB method using the single crystal growing device 100 has been described, but the same single crystal growing device 100 is used to move the crucible 10 for growing a single crystal up and down during the growing of a single crystal. A single crystal of an iron-gallium alloy can also be grown by the VGF method in which the resistance heating heater 12 is adjusted to control the temperature instead of moving the crystal to.

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, in an environment of room temperature of 20 ° C., the median diameter is about 1 mm so that the ratio of iron to gallium is 80:20 in stoichiometric ratio, that is, the gallium content is 20% in atomic weight%. The granular iron raw material (purity: 99.9%) and the gallium raw material (purity: 99.99%) were weighed. The weighed gallium raw material was placed in a Teflon (registered trademark) container and melted by boiling in hot water. Further, the iron raw material was put into the melted gallium raw material, stirred in the container, and then cooled to room temperature to prepare a mixture 17 of iron and gallium as a mixed raw material.

Then, at the lower part of the crucible 10 for growing a single crystal made of dense alumina having a thickness of 3 mm, an inner diameter of 52 mm, and a height of 200 mm, a FeGa alloy seed crystal 16 (diameter 5 mm, height 30 mm) whose shape and growing direction have been adjusted in advance The FeGa alloy seed crystal 16 was filled with a mixture 17 of iron and gallium. At this time, as the FeGa alloy seed crystal 16, a crystal having a main plane orientation of <100> was used.

Next, as shown in FIG. 1, the single crystal growing crucible 10 filled with the FeGa alloy seed crystal 16 and the mixture 17 of iron and gallium is placed on the crucible receiver 14 made of porous alumina, and the thermoelectric pair is placed. The tip of 15 was brought into contact with the side surface of the single crystal growing crucible 10. The contact point of the thermocouple 15 with the single crystal growing crucible 10 was set at a height of 15 mm from the bottom surface of the FeGa alloy seed crystal 16.

Next, the movable rod 13 was driven to set the crucible receiver 14 at the bottom of the chamber 19. After that, argon gas was introduced into the chamber 19 to adjust the inside of the chamber 19 to an atmosphere of argon at atmospheric pressure. Further, as the upper heater 12a, the middle heater 12b and the lower heater 12c made of a carbon resistance heating heater, those which can be controlled independently and have a length of 200 mm in the height direction are used.

Then, the temperature of the upper heater 12a was set to 1450 ° C., the temperature of the middle heater 12b was set to 1400 ° C., and the temperature of the lower heater 12c was set to a temperature range of 1300 ° C., and the temperature inside the chamber 19 was raised. After the temperature rise was completed and the temperature in the chamber 19 became stable, the moving rod 13 was driven to raise the crucible receiver 14, so that the single crystal growing crucible 10 was raised at a moderate speed. Since a temperature gradient is formed in the chamber 19 in which the temperature of the upper part is high and the temperature of the lower part is low, the temperature in the single crystal growing crucible 10 rises as it moves to the upper part of the chamber 19, and iron and gallium The mixture 17 was melted to form the melt.

When the mixed raw material is almost melted into a melt, the introduction of argon gas into the chamber 19 is suppressed, and the pressure inside the chamber 19 is reduced from standard atmospheric pressure to 350 Pa in 10 minutes using a vacuum pump (first). (Reduced pressure), and kept as it was for about 30 minutes. Next, the pressure was gradually reduced over 60 minutes at a gradient of 2.5 Pa / min from 350 Pa to 200 Pa or less (second pressure reduction) to remove bubbles in the melt (bubble removal step). After the bubble removing step, the introduction of argon gas was restarted, and the inside of the chamber 19 was adjusted to an inert atmosphere at standard atmospheric pressure.

In the vicinity of the position of the single crystal growing crucible 10 on which the melt was formed, the position of the single crystal growing crucible 10 was determined by driving the movable rod 13 while monitoring the temperature at the contact point position of the thermocouple 15. The temperature was stabilized by raising it by several mm. By repeating this step, the single crystal growing crucible 10 was raised so that the temperature of the thermocouple 15 was in the range of 1350 to 1400 ° C. in a stable state. After determining the position to hold the single crystal growing crucible 10, hold it for 3 hours for seeding, and then drive the movable rod 13 to lower the single crystal growing crucible 10 at 5 mm / h to make the FeGa alloy. Started growing single crystals of. After the descent distance of the single crystal growing crucible 10 became 150 mm, the growing was completed.

After the growth of the single crystal was completed, the ingot of the FeGa alloy single crystal grown from the crucible for growing the single crystal was taken out, and a single crystal of the FeGa alloy having a diameter of 52 mm and a straight body length of 100 mm was obtained. Further, the grown single crystal of the FeGa alloy was cut and the inside of the crystal was observed, but no defects such as vacancies that could be visually confirmed were confirmed.

[Example 2]
Regarding the chemical ratio of the mixture of iron and gallium, the mixture of iron and gallium 17 is the same as in Example 1 except that the ratio of iron to gallium is 82:18 (the gallium content is 18% in atomic weight%). Was prepared, and a single crystal was grown. After the growth of the single crystal was completed, the ingot of the FeGa alloy single crystal grown from the crucible for growing the single crystal was taken out, and a single crystal of the FeGa alloy having a diameter of 52 mm and a straight body length of 100 mm was obtained. Further, the grown FeGa alloy single crystal was cut and the inside of the crystal was observed, but no defects such as vacancies that could be visually confirmed were confirmed.

[Example 3]
Regarding the chemical ratio of the mixture of iron and gallium, the mixture of iron and gallium 17 is the same as in Example 1 except that the ratio of iron to gallium is 77:23 (the gallium content is 23% in atomic weight%). Was prepared, and a single crystal was grown. After the growth of the single crystal was completed, the ingot of the FeGa alloy single crystal grown from the crucible for growing the single crystal was taken out, and a single crystal of the FeGa alloy having a diameter of 52 mm and a straight body length of 100 mm was obtained. Further, the grown FeGa alloy single crystal was cut and the inside of the crystal was observed, but no defects such as vacancies that could be visually confirmed were confirmed.

[Example 4]
Regarding the stoichiometric ratio of the mixture of iron and gallium, the ratio of iron to gallium was set to 80:20 (gallium content is 20% in terms of atomic weight%). Then, in the bubble removing step, when the mixed raw material is almost melted to become a melt, the introduction of argon gas into the chamber 19 is suppressed, and a vacuum pump is used to move the inside of the chamber 19 from standard atmospheric pressure to 350 Pa for 10 minutes. The pressure was reduced with (first pressure reduction), and the mixture was kept as it was for about 30 minutes. Next, when the crucible was depressurized over 25 minutes with a gradient of 6 Pa / min from 350 Pa to 200 Pa or less (second decompression), the crucible shook violently around 250 Pa on the way, but the melt did not scatter outside the crucible. At 200 Pa, the shaking of the crucible subsided.

Except for the above, a single crystal was grown in the same manner as in Example 1. After the growth of the single crystal was completed, the ingot of the FeGa alloy single crystal grown from the crucible for growing the single crystal was taken out, and a single crystal of the FeGa alloy having a diameter of 52 mm and a straight body length of 100 mm was obtained. Further, the grown FeGa alloy single crystal was cut and the inside of the crystal was observed, but no defects such as vacancies that could be visually confirmed were confirmed.

[Example 5]
Regarding the stoichiometric ratio of the mixture of iron and gallium, the ratio of iron to gallium was set to 80:20 (gallium content is 20% in terms of atomic weight%). Then, in the bubble removing step, when the mixed raw material is almost melted to become a melt, the introduction of argon gas into the chamber 19 is suppressed, and a vacuum pump is used to move the inside of the chamber 19 from standard atmospheric pressure to 500 Pa for 10 minutes. The pressure was reduced with (first pressure reduction), and the mixture was kept as it was for about 30 minutes. Next, the pressure was reduced over 1 hour and 40 minutes with a gradient of 3 Pa / min from 500 Pa to 200 Pa or less (second pressure reduction).

Except for the above, a single crystal was grown in the same manner as in Example 1. After the growth of the single crystal was completed, the ingot of the FeGa alloy single crystal grown from the crucible for growing the single crystal was taken out, and a single crystal of the FeGa alloy having a diameter of 52 mm and a straight body length of 100 mm was obtained. Further, the grown FeGa alloy single crystal was cut and the inside of the crystal was observed, but no defects such as vacancies that could be visually confirmed were confirmed. However, although only about 10% of the unmelted portion of the seed crystal remained, there was no problem in growing the single crystal.

[Comparative Example 1]
A mixture 17 of iron and gallium was prepared in the same manner as in Example 1 except that the bubble removing step was not carried out during the melting of the mixed raw material, and a single crystal growing operation was carried out. After completing the single crystal growth operation, the ingot of the FeGa alloy crystal grown from the single crystal growth chamber 10 was taken out, and a FeGa alloy crystal having a diameter of 52 mm and a straight body length of 100 mm was obtained, but the crystal grain boundaries were It was recognized and was polycrystal. Further, as a result of cutting the grown polycrystal of FeGa alloy and observing the inside of the crystal, a large number of pores were visually confirmed.

[Comparative Example 2]
Regarding the stoichiometric ratio of the mixture of iron and gallium, the ratio of iron to gallium was set to 80:20 (gallium content is 20% in terms of atomic weight%). Then, in the bubble removing step, when the mixed raw material is almost melted to become a melt, the introduction of argon gas into the chamber 19 is suppressed, and a vacuum pump is used to move the inside of the chamber 19 from standard atmospheric pressure to 350 Pa for 10 minutes. The pressure was reduced with, and the mixture was kept as it was for about 30 minutes. Next, when the pressure was reduced from 350 Pa to 200 Pa or less over 15 minutes at a gradient of 10 Pa / min, the melt suddenly boiled and the melt was scattered outside the crucible, so that the growth was stopped.

[Comparative Example 3]
Regarding the stoichiometric ratio of the mixture of iron and gallium, the ratio of iron to gallium was set to 80:20 (gallium content is 20% in terms of atomic weight%). Then, in the bubble removing step, when the mixed raw material is almost melted to become a melt, the introduction of argon gas into the chamber 19 is suppressed, and a vacuum pump is used to move the inside of the chamber 19 from standard atmospheric pressure to 600 Pa for 10 minutes. The pressure was reduced with, and the mixture was kept as it was for about 30 minutes. Next, the pressure was reduced over 3 hours and 20 minutes with a gradient of 2 Pa / min from 600 Pa to 200 Pa or less.

Except for the above, a single crystal was grown in the same manner as in Example 1. After the growth of the single crystal was completed, the ingot of the FeGa alloy crystal grown from the single crystal growth chamber 10 was taken out, and a FeGa alloy crystal having a diameter of 52 mm and a straight body length of 100 mm was obtained, but grain boundaries were observed. It was polycrystal. As a result of the appearance observation, it was confirmed that all the seed crystals were melted because the uneven surface derived from the crucible was formed in all the seed crystal parts. The <100> orientation of the growing direction could not be confirmed from the seed crystal portion by the X-ray diffractometer. The grown FeGa alloy was cut and the inside of the crystal was observed, but no defects such as vacancies that could be visually confirmed were confirmed.

[Summary]
Even if the stoichiometric ratio of iron and gallium is changed, the bubbles in the melt are removed by performing the bubble removal step, so that a single crystal with no internal visual defects can be grown. (Examples 1 to 3). On the other hand, when the bubbles in the melt were not removed without performing the bubble removing step, polycrystals were grown (Comparative Example 1). It is considered that this is because the remaining bubbles inhibited the growth of the single crystal.

Further, in the bubble removing step, when the second depressurization was performed in a short time, the melt was suddenly boiled (Comparative Example 2), and when the pressure was reduced over a long time, the seed crystal was melted (Comparative Example 3). .. The sudden boiling of these melts and the melting of the seed crystal can be avoided by depressurizing with a decompression gradient of 2 to 6 Pa / min, but in order to prevent crucible shaking and stably avoid the complete melting of the seed crystal, the first step is to avoid it. It was confirmed that the depressurization of the above was set to 350 Pa and the second depressurization should be performed with a gradient of 2.5 to 5 Pa / min.

From the results of the above examples, it is possible to stably grow a single crystal of an iron-gallium alloy by carrying out the bubble removing step. That is, it is clear that in the present invention, by including the bubble removing step, a single crystal of an iron gallium alloy can be produced in a large amount at a low cost as compared with the conventional method described in Patent Document 4 and the like.

10 Crucible for growing single crystals 11 Insulation material 12 Resistance heating heater 12a Upper heater 12b Middle heater 12c Lower heater 13 Movable rod 14 Crucible receiver 15 Thermocouple 16 Iron-gallium alloy seed crystal 17 Iron and gallium mixture 18 Vacuum pump 19 Chamber 100 Single crystal growing device

Claims (3)

It comprises a bubble removal step of depressurizing a melt of a mixture of iron and gallium placed in an inert atmosphere and removing bubbles in the melt.
The depressurization includes a first depressurization for depressurizing the melt to 300 to 500 Pa and a second depressurization for depressurizing the melt from the pressure of the first decompression to 200 Pa or less with a decompression gradient of 2 to 6 Pa / min. A method for growing a single crystal of an iron-gallium alloy. The method for growing a single crystal of an iron gallium alloy according to claim 1, wherein the gallium content of the mixture is 18.0% to 23.0% in terms of atomic weight. The method for growing a single crystal of an iron gallium alloy according to claim 1 or 2, wherein the growth of a single crystal of an iron gallium alloy is carried out by a vertical Bridgeman method or a vertical temperature gradient solidification method.

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