JP7570816B2 - Weyl antiferromagnetic powder and thermoelectric conversion element using same - Google Patents

Description

The present invention relates to a Weyl antiferromagnetic powder with high coercivity and a thermoelectric conversion element using the same.

In recent years, research has been conducted into thermoelectric conversion elements that utilize the anomalous Nernst effect. The anomalous Nernst effect is a phenomenon in which, when a heat flow perpendicular to the magnetization is applied to a spontaneously magnetized magnetic material, an electromotive force is generated in a direction perpendicular to both the magnetization and the heat flow. The anomalous Nernst effect allows current to be extracted perpendicular to the heat flow, which is an advantage over the Seebeck effect in that it allows the construction of a thin sheet-like thermoelectric conversion device. For example, Patent Document 1 shows a thermoelectric generation device that uses an FePt film.

Since the anomalous Nernst effect is a phenomenon based on the spontaneous magnetization of a magnetic material, it was commonly believed that the magnetic material required a ferromagnetic material. However, it was discovered that some intermetallic compounds, such as Mn ₃ Sn, produce the anomalous Nernst effect even though they are antiferromagnetic. Patent Document 2 shows an example in which a single crystal of Mn ₃ Sn was produced by the Bridgman method, a heat flow was applied parallel to the [0 1 -1 0] direction of the Mn ₃ Sn crystal, and an external magnetic field was applied parallel to the a-axis [2 -1 -1 0] direction, and the electromotive force per unit temperature was measured. According to this, hysteresis was observed in the electromotive force when the external magnetic field was changed, and the anomalous Nernst effect was confirmed in which a voltage was generated even when the external magnetic field was zero.

JP 2014-72256 A JP 2017-84854 A

The anomalous Nernst effect using a single crystal of Mn ₃ Sn disclosed in Patent Document 2 is due to an "antiferromagnetic material" in which the spins are aligned in opposite directions. Therefore, it is said that the "leakage magnetic field" can be suppressed significantly more than in a thermoelectric conversion device using a "ferromagnetic material" in which the spins are aligned in the same direction. However, since the thermoelectric conversion element obtained by the method shown in Patent Document 2 has a small coercive force, it is desired to improve the coercive force in order to put the thermoelectric conversion device into practical use.

The present invention aims to provide a highly practical technology that is useful for obtaining thermoelectric conversion elements with high coercive force.

A magnetic material that has a band structure with Weyl points created by magnetism is called a "Weyl magnet." A Weyl magnet that is an antiferromagnetic material, such as Mn ₃ Sn, is called a "Weyl antiferromagnet."

In order to achieve the above object, the present invention provides a powder composed of particles mainly composed of a Weyl antiferromagnet, which has a cumulative 50% particle diameter _D50 of 1 to 150 μm and a cumulative 90% particle diameter _D90 of 250 μm or less in a volume-based particle size distribution measured by a laser diffraction/scattering method.

As the Weyl antiferromagnet, one or more intermetallic compounds whose composition formula is _Mn3X (where X is a metal element) and whose crystal structure is a regular lattice of the D019 structure can be applied. The element X can be, for example, one or more elements selected from Sn, Ge, Ga, Pt, Ir, and Rh. More specifically, _Mn3Sn , _Mn3Ge , _Mn3Ga , _Mn3Pt , _Mn3Ir , _Mn3Rh , etc. can be exemplified.

The present invention also provides a thermoelectric conversion element using the above-mentioned Weyl antiferromagnetic powder.

According to the present invention, it is possible to obtain a thermoelectric conversion element with a large coercive force. Since the magnetic material used in the thermoelectric conversion element is in the form of a powder, it is easy to put into industrial use.

1 is a photograph showing the appearance of a Mn ₃ Sn alloy ingot. 1 shows an X-ray diffraction pattern of a powder specimen prepared from a sample located approximately halfway along the height of an Mn ₃ Sn alloy ingot. Reference X-ray diffraction patterns for pure materials of metallic Mn, Mn oxides and Mn-Sn intermetallic compounds. 3 shows particle size distribution curves of the Mn ₃ Sn crystal powders used in Examples 1 to 3. 4 is a magnetization curve of a sintered body using the powder of Example 1. 4 is a magnetization curve of a sintered body using the powder of Example 2. FIG. 2 is a schematic diagram showing the positions of terminals for power measurement and probes for temperature measurement, as well as the directions of heat flow and magnetic field application, for the Nernst effect measurement samples of Examples 1 to 3. 1 is a graph showing the relationship between the external magnetic field and the magnetic field reversal component ΔS _ANE of the Nernst coefficient S _ANE for a sintered body using the powder of Example 2. FIG. 1 is a schematic diagram showing the configuration of a powder production apparatus using a gas atomization method. 4 is a magnetization curve of a sintered body using the powder of Example 3. 1 is a graph showing the relationship between the external magnetic field and the magnetic field reversal component ΔS _ANE of the Nernst coefficient S _ANE for a sintered body using the powder of Example 3. 4 shows the magnetization curve of a sintered body using the ground sample of Comparative Example 1. 1 is a graph showing the relationship between the external magnetic field and the magnetic field reversal component ΔS _ANE of the Nernst coefficient S _ANE for a polycrystalline body cut from the ingot of Comparative Example 1. Magnetization curve of the single crystal of Comparative Example 2. 1 is a graph showing the relationship between the external magnetic field and the magnetic field reversal component ΔS _ANE of the Nernst coefficient S _ANE for the single crystal of Comparative Example 2.

As a result of research, the inventors have found that a thermoelectric conversion element with high coercivity can be obtained by using powder of a Weyl antiferromagnetic material. It has also been found that a powder with a small average particle size and a particle size distribution with a small proportion of coarse particles is extremely effective in improving the coercivity. In a thermoelectric conversion element formed using a Weyl antiferromagnetic material powder having a cumulative 50% particle size D ₅₀ of 1 to 150 μm and a cumulative 90% particle size D ₉₀ of 250 μm or less in a volume-based particle size distribution measured by a laser diffraction/scattering method, a remarkable improvement in coercivity is observed compared to a thermoelectric conversion element formed using a single crystal of a Weyl antiferromagnetic material. In particular, when a fine Weyl antiferromagnetic material powder having a cumulative 50% particle size D ₅₀ of 1 to 30 μm and a cumulative 90% particle size D ₉₀ of 50 μm or less is used, an even more excellent improvement in coercivity can be obtained.

A relatively simple method for producing the powder is to pulverize an ingot of the Weyl antiferromagnet into fine powder. By classifying the pulverized powder using a mesh filter or the like, it is possible to obtain a Weyl antiferromagnet powder with a particle size distribution adjusted to a cumulative 50% particle size D ₅₀ of 1 to 150 μm and a cumulative 90% particle size D ₉₀ of 250 μm or less. As a method for producing finer powder, for example, a gas atomization method can be applied in which an inert gas is blown in a vacuum onto droplets of molten metal adjusted to the chemical composition of the Weyl antiferromagnet, and the molten metal is directly solidified as fine particles. This method makes it possible to produce a fine Weyl magnet powder with a cumulative 50% particle size D ₅₀ of 1 to 30 μm and a cumulative 90% particle size D ₉₀ of 50 μm or less.

To create a thermoelectric conversion element using powder, it is necessary to form a conductor so that the powder particles maintain contact with each other. Methods for forming a conductor include firing a compressed powder at a temperature lower than the melting point, and applying a conductive paint containing powder to form a conductive film.

As the Weyl antiferromagnet, for example, an intermetallic compound whose composition formula is _Mn3X (where X is a metal element) and whose crystal structure is a regular lattice of the D019 structure can be applied. The molar ratio of Mn to element X is stoichiometrically 3:1, but in reality, there may be some variation from the strict stoichiometric ratio within the range in which the D019 crystal structure can be maintained. In this specification, the compound represented by the composition formula _Mn3X includes those within the above-mentioned range of variation.

Examples of _the Weyl antiferromagnet represented by the composition formula _Mn3X include intermetallic compounds such as _Mn3Sn , Mn3Ge, _Mn3Ga , _Mn3Pt , _Mn3Ir , and _Mn3Rh . One of these may be used alone, or two or more may be mixed and used. When two or more intermetallic compounds of Weyl antiferromagnets are mixed and used, a method of preparing powders composed of particles mainly composed of each intermetallic compound and blending the powders is envisaged.

The particles constituting the Weyl antiferromagnet powder of the present invention may contain a different phase in addition to the intermetallic compound phase exhibiting Weyl antiferromagnetism, as long as it is possible to construct a thermoelectric conversion element that exhibits antiferromagnetism in the intended temperature range of the thermoelectric conversion element and that exhibits the anomalous Nernst effect in that temperature range. That is, the present invention targets powders composed of particles mainly composed of Weyl antiferromagnets. The proportion of the main component intermetallic compound phase exhibiting Weyl antiferromagnetism (substance represented by the composition formula _Mn3X ) in the particles is preferably 50 mass% or more. In particular, it is more preferable that the remainder excluding the main component intermetallic compound phase exhibiting Weyl antiferromagnetism is unavoidable impurities.

In general, in Mn-X alloys (where X means a metal element capable of forming the compound Mn ₃ X), the compound Mn ₃ X exists stably in a single phase in a certain composition range close to the Mn ₃ X composition. For example, in the case of Mn-Sn alloys, it has been confirmed that Mn ₃ Sn exists stably as a single phase when the molar ratio of Mn:Sn is in the range of 3.02:0.98 to 3.15:0.85. However, when actually producing an ingot of an Mn-X alloy, even if the alloy is produced with a feed composition within the range in which the compound Mn ₃ X can exist as a single phase, a different phase other than the Mn ₃ X phase may be generated during the solidification process and may be mixed into part of the ingot. Therefore, adjusting the raw material composition (feed composition) depending on the production method so as to obtain powder particles within a composition range in which Mn ₃ X exists stably in a single phase is effective in obtaining a powder consisting mainly of the compound Mn ₃ X with the remainder consisting of unavoidable impurities, i.e., a powder substantially composed of a single phase of Mn ₃ X.

The operating temperature range of the thermoelectric conversion element can be assumed to be, for example, from −270° C. to 680° C. depending on the type of Mn ₃ X. In the case of Mn ₃ Sn, the anomalous Nernst effect is said to be manifested in the range of −223° C. (50 K) to 157° C. (430 K).

Hereinafter, an experimental example will be given in which magnetization and the Nernst effect were examined using Mn ₃ Sn-based Weyl antiferromagnetic powder.

[Example 1]
(Preparation of _Mn3Sn alloy ingot)
The raw materials, metallic Mn and metallic Sn, were weighed out so that the molar ratio was Mn:Sn = 3.07:0.93, and placed in a 50 ml alumina crucible. The total mass of the raw materials was about 120 g. The crucible was placed in an electric furnace, and in an Ar gas atmosphere, the temperature was raised from room temperature to 1200°C over 5 hours, and then the temperature was held at 1200°C for 24 hours, and then the temperature was cooled to around room temperature over 5 hours. The raw materials were melted and solidified using a heat pattern to obtain an ingot of Mn ₃ Sn alloy. Figure 1 shows an example of an external view of the ingot.

Samples were cut from the resulting ingot at four height positions: near the top of the height direction (vertical direction at solidification), near 1/4 position in the height direction from the top, near 1/2 position in the height direction from the top, and near the bottom. In all cases, the sampling position in the horizontal direction of the ingot as viewed in the vertical direction at the time of solidification was the center. Each sample was crushed to obtain a powder sample for X-ray diffraction. The X-ray diffraction pattern of the powder sample at each position was measured using an X-ray diffractometer (Rigaku Corporation; Smartlab) under conditions of Cu-Kα, tube voltage of 40 kV, and tube current of 100 mA.

FIG. 2 shows an example of an X-ray diffraction pattern for a powder sample prepared from a sample near the 1/2 position in the height direction. FIG. 3 shows a reference X-ray diffraction pattern for pure materials of metal Mn, Mn oxide, and Mn-Sn intermetallic compounds. No impurity peaks were observed except for a small amount of MnO observed near the top of the ingot. In addition, when samples cut from various parts of the ingot were analyzed by an EDX (energy dispersive X-ray analyzer) attached to an SEM (scanning electron microscope), a small amount of Mn ₃ Sn ₂ phase was detected. The average composition of the other parts was Mn:Sn = 3.03: _0.97 in molar ratio. From the above analysis results, it was confirmed that the above-mentioned melting method can produce an ingot consisting of Mn ₃ Sn phase and a small amount of a different phase. It is considered that the amount of the different phase in the ingot is small enough not to inhibit the physical properties brought about by the Weyl antiferromagnetism of the Mn 3 Sn phase. Therefore, the ingot obtained by this method may be referred to hereinafter as an "ingot of Mn ₃ Sn crystals."Furthermore, the powder derived from the ingot may be referred to as an "Mn ₃ Sn crystal powder."

(Preparation of Powder)
The Mn ₃ Sn crystal ingot (mass: about 200 g) produced by the above method was crushed on an anvil placed in a bag to make small pieces of about 5 mm. 197 g of the small pieces were collected from the bag and crushed with a hammer mill (manufactured by Sansho Industry Co., Ltd.; hammer crusher NH-34S, screen opening: 0.7 mm) to obtain 163 g of coarse powder of Mn ₃ Sn crystal. All the operations from the above-mentioned crushing to the crushing were carried out under a nitrogen atmosphere. The oxygen concentration in the nitrogen atmosphere was 0.2% or less as measured by a high-concentration oxygen concentration meter (manufactured by Ichi-Nenjiko Co., Ltd.; Oxy-medi, model number OXY-1-M).

The volumetric particle size distribution of this _Mn3Sn crystal powder was measured by a laser diffraction/scattering method using a dry laser diffraction particle size distribution analyzer HELOS&RODOS (manufactured by Nippon Laser Co., Ltd.) with a lens having a focal length of 200 mm. The particle size distribution curve is shown in Figure 4 (the same applies to Examples 2 and 3 described below). The powder obtained in this example had a cumulative 10% particle size _D10 of 27.3 μm, a cumulative 50% particle size _D50 of 100.7 μm, and a cumulative 90% particle size _D90 of 227.7 μm.

(Preparation of sintered body using powder)
3 g of the above _Mn3Sn crystal powder was placed in a cylinder of a cylindrical graphite cell with an inner diameter of 10 mm, and a load of 4.5 kN was applied by upper and lower pistons, and the powder was heated in a discharge plasma sintering apparatus in a vacuum atmosphere of about 1 Pa to obtain a cylindrical sintered body with a diameter of 10 mm and a height of about 7 mm. The heating temperature was 500°C, the heating holding time was 30 minutes, and the load of 4.5 kN was maintained during the heating holding time.

(Measurement of magnetic properties)
From the sintered body, multiple cubic samples with sides of 2 mm were cut out, and the magnetic properties of the samples were measured at 300 K using a SQUID (Super Quantum Interference Device) magnetometer by the following method. That is, the temperature of the sample was set to 300 K, a maximum magnetic field of 3 T (30,000 Oe) was applied using a superconducting magnet attached to the SQUID magnetometer, and then the magnetic field was fixed at each measurement point during the magnetic field sweep process from 3 T to -3 T and from -3 T to 3 T, and the magnetization (μ _B /fu) was measured. The magnetization curve is shown in Figure 5. The coercive force was approximately 0.25 T (2,500 Oe).

[Example 2]
Powder was prepared using an ingot of Mn ₃ Sn alloy prepared in the same manner as in Example 1. In this example, small pieces of about 5 mm crushed in the same manner as in Example 1 were put into a sample mill (SK-M10 type manufactured by Kyoritsu Riko Co., Ltd.) and crushed for 30 seconds in a nitrogen atmosphere to prepare a powder with a smaller average particle size than that of Example 1. All operations from the above-mentioned crushing to crushing were performed in a nitrogen atmosphere. The oxygen concentration in the nitrogen atmosphere was 0.2% or less, as in Example 1. The cumulative 10% particle size D ₁₀ of the powder obtained in this example was 9.6 μm, the cumulative 50% particle size D ₅₀ was 50.1 μm, and the cumulative 90% particle size D ₉₀ was 165.1 μm. The particle size distribution curve is shown in FIG. 4.

Using this powder, a sintered body was produced in the same manner as in Example 1. From the sintered body, several cubic samples with a side length of 2 mm were cut out, and the magnetic properties were measured in the same manner as in Example 1. The magnetization curve is shown in Figure 6.

(Measurement of the Nernst effect)
A rectangular parallelepiped sample of 1.5 mm x 1.5 mm x 7 mm was cut out from the above-mentioned fired body. A terminal for measuring electromotive force and a probe for measuring temperature were attached to this sample, and a magnetic field was applied while a heat flow was generated in the longitudinal direction of the sample in a physical property measurement system PPMS device manufactured by Quantum Design, and the electromotive force as a thermoelectric conversion element was measured. Figure 7 shows the attachment positions of the terminal for measuring electromotive force and the probe for measuring temperature, and the directions of the heat flow and magnetic field. Electromotive force measurement terminals 2a and 2b were attached to the center positions of the opposing sides of sample 1 with conductive epoxy adhesive, respectively, so that the voltage (V) generated between both terminals could be measured with a voltmeter. This voltage is generated by the anomalous Nernst effect, so it is indicated as V _ANE . Two temperature measurement probes were attached to the top surface of sample 1 at two points with a longitudinal interval of 5 mm with conductive epoxy adhesive, so that the temperature difference ΔT between the temperatures T ₁ (K) and T ₂ (K) at the two points could be monitored. One end face of the sample 1 in the longitudinal direction was heated by a resistance heater, and the other end face was connected to a heat bath, so that one end face in the longitudinal direction was heated by a resistance heater, and the other end face was connected to a heat bath and cooled, forming a temperature gradient in the longitudinal direction of the sample. The black arrow (4) in the figure indicates the direction of heat flow in the sample. After the temperatures _T1 and _T2 were stabilized, a magnetic field was applied to the sample, and the voltage V _ANE (V) was measured. The white arrow (5) in the figure indicates the direction of the magnetic field. The magnetic field was swept between 3T and -3T, and between -3T and 3T. The Nernst coefficient S _ANE (μV/K) was calculated using the following formula (1).
S _ANE (μV/K) = V _ANE (V) / 1.5 (mm) / [(T ₁ - T ₂ ) (K) / 5.0 (mm)] ... (1)

The measurement results of the Nernst coefficient ΔS _ANE are shown in Fig. 8. In order to clearly show the reversal magnetic field of the Nernst coefficient S _ANE due to the magnetic field, the value ΔS _ANE obtained by normalizing the magnetic field reversal component of the Nernst coefficient S _ANE by the Nernst coefficient S _ANE at zero magnetic field (about 0.3 µV/K) is used as the value on the vertical axis of the graph (similarly in Figs. 11, 13, and 15 described later).
As can be seen from FIG. 8, the Nernst effect occurs even in zero magnetic field. In other words, the anomalous Nernst effect is manifested, and an electromotive force is generated by temperature difference alone. Although Mn ₃ Sn is an antiferromagnetic material, the anomalous Nernst effect is manifested, which is believed to be due to the creation of a virtual magnetic field caused by the material being a Weyl magnet. The coercive force of the thermoelectric conversion element using the Weyl antiferromagnetic powder of this example is approximately 0.25 T (2500 Oe). This is evaluated as a practical coercive force that can withstand use inside general electronic devices and around automobile engines.

[Example 3]
(Preparation of Powder)
In this example, powder was produced directly from the molten Mn ₃ Sn alloy by the gas atomization method. Figure 9 shows a schematic diagram of the configuration of a powder production apparatus using the gas atomization method. The powder was produced as follows. The raw materials, metal Mn and metal Sn, were weighed out so that the molar ratio was Mn:Sn = 3.07:0.93, and placed in a CP crucible (porous alumina) with a hole at the bottom and set in a high-frequency induction heating device. The chamber was evacuated and then filled with Ar gas. The hole at the bottom of the crucible was closed with a stopper rod. The raw materials were melted by high-frequency induction heating and held at 1450°C for 40 minutes, after which the stopper rod was raised and the molten alloy was dropped from the hole at the bottom of the crucible into the lower space in the chamber. Ar gas was sprayed onto the molten metal that had appeared in the lower space to turn the droplets into fine particles and rapidly cool and solidify, obtaining an alloy powder (atomized powder).

The obtained alloy powder was subjected to X-ray diffraction and EDX analysis in the same manner as above, and the powder was found to be composed of particles consisting of almost a single phase of Mn ₃ Sn, with an average composition of Mn:Sn=3.02:0.98 in molar ratio. Therefore, this powder can also be called "Mn ₃ Sn crystal powder" as above. The particle size distribution of this Mn ₃ Sn crystal powder was measured by the method shown in Example 1. The particle size distribution curve is shown in Figure 4. The cumulative 10% particle diameter D ₁₀ of the powder obtained in this example was 4.8 μm, the cumulative 50% particle diameter D ₅₀ was 15.2 μm, and the cumulative 90% particle diameter D ₉₀ was 31.9 μm.

Using this powder, a sintered body was produced in the same manner as in Example 1. A number of cubic samples with a side length of 2 mm were cut out from the sintered body, and the magnetic properties were measured in the same manner as in Example 1. FIG. 10 shows the magnetization curve. In addition, a rectangular parallelepiped sample of 1.5 mm x 1.5 mm x 7 mm was cut out from the above sintered body, and the Nernst effect was measured in the same manner as in Example 2. FIG. 11 shows the measurement results of the Nernst coefficient ΔS _ANE . The coercive force of the thermoelectric conversion element using the Weyl antiferromagnetic powder of this example was about 0.5 T (5000 Oe), which was higher than those of Examples 1 and 2. It was found that the fineness of the Weyl antiferromagnetic powder by the atomization method is extremely effective in improving the coercive force of the thermoelectric conversion element using the powder. The mechanism by which the coercive force is improved by using such a finely-refined Weyl antiferromagnetic material has not been fully elucidated at present, but it is speculated that the contribution of pinning the domain wall increases as the particle diameter approaches the size of a single magnetic domain.

[Comparative Example 1]
Powder was prepared using an ingot of Mn ₃ Sn alloy prepared in the same manner as in Example 1. In this example, small pieces of about 5 mm crushed in the same manner as in Example 1 were manually crushed in an alumina mortar. The crushed material obtained was sieved through a sieve with a mesh size of 200 μm. 68% of the crushed material remained on the sieve in terms of mass percentage. For this crushed material sample, a particle size distribution measurement was attempted using a dry laser diffraction particle size distribution measurement device as in Example 1, but since the particle diameter of the sample was coarse, the measurement range was exceeded by a lens with a focal length of 200 mm, and the particle size distribution could not be measured.

Using the above pulverized sample, a sintered body was produced in the same manner as in Example 1. From the sintered body, a number of cubic samples with a side length of 2 mm were cut out, and the magnetic properties were measured in the same manner as in Example 1. The magnetization curve is shown in FIG. 12. In addition, a rectangular parallelepiped sample (polycrystalline body) of 1.5 mm x 1.5 mm x 7 mm was cut out directly from the above ingot. At that time, the rectangular parallelepiped sample was taken from a portion of the ingot where defects such as shrinkage cavities were not observed, so that the longitudinal direction of the sample coincided with the horizontal direction at the time of solidification of the ingot. The Nernst effect was investigated using this rectangular parallelepiped sample in the same manner as in Example 1. FIG. 13 shows the measurement result of the Nernst coefficient ΔS _ANE . The coercive force of the thermoelectric conversion element using the Weyl antiferromagnet of this example was about 0.05 T (500 Oe), which was significantly lower than that of the example using the powder of the Weyl antiferromagnet. With such a low coercive force, there is a risk that the material will be demagnetized by the magnetic field near the permanent magnet or magnetic components, making it difficult to construct a highly reliable thermoelectric conversion element.

[Comparative Example 2]
An ingot of Mn ₃ Sn alloy prepared by the same method as in Example 1 was melted, and a single crystal of Mn ₃ Sn was prepared by the Bridgman process. The maximum temperature of the Bridgman furnace was 1080°C, and the sample was moved at a speed of 1.5 mm/h. The composition of the obtained single crystal was analyzed by ICP-AES, and the molar ratio was Mn:Sn=3.06:0.94.

From this single crystal, a number of cubic samples with a side length of 2 mm were cut out, and magnetic measurements were performed in the same manner as in Example 1. At that time, the direction of application of the external magnetic field was made to coincide with the [2-1-10] direction of the Mn ₃ Sn crystal. FIG. 14 shows the magnetization curve. Also, from the above single crystal, a rectangular parallelepiped sample of 1.5 mm×1.5 mm×7 mm was cut out, and the Nernst effect was examined in the same manner as in Example 1. At that time, the direction of the heat flow (the longitudinal direction of the rectangular parallelepiped sample) was made to coincide with the [0 1-10] direction of the Mn ₃ Sn crystal, and the direction of application of the external magnetic field was made to coincide with the [2-1-10] direction of the Mn ₃ Sn crystal. FIG. 15 shows the measurement results of the Nernst coefficient ΔS _ANE . The coercive force of the thermoelectric conversion element using the Weyl antiferromagnetic single crystal of this example was less than 0.01 T (100 Oe).
The coercive force was significantly lower than that of the example using the Weyl antiferromagnetic powder.

1 Nernst effect measurement sample 2a, 2b Electromotive force measurement terminals 31, 32 Temperature measurement position 4 Heat flow direction in sample 5 Magnetic field direction

Claims (5)

A powder composed of particles mainly composed of a Weyl antiferromagnetic material, in which, in a volume-based particle size distribution measured by a laser diffraction/scattering method, a cumulative 50% particle diameter D ₅₀ is 1 to 150 μm and a cumulative 90% particle diameter D ₉₀ is 250 μm or less. 2. The Weyl antiferromagnetic powder according to claim 1, wherein the Weyl antiferromagnetic material is an intermetallic compound having a D019 structure represented by a composition formula _Mn3X , where X is a metal element. 2. The Weyl antiferromagnetic powder according to claim 1, wherein the Weyl antiferromagnetic material is a compound represented by the chemical formula _Mn3X , where X is one or more elements selected from the group consisting of Sn, Ge, Ga, Pt, Ir and Rh. 2. The Weyl antiferromagnetic powder according to claim 1, wherein the Weyl antiferromagnetic material is one or more compounds selected from the group consisting of _Mn3Sn , _Mn3Ge , _Mn3Ga , _Mn3Pt , _Mn3Ir , and _Mn3Rh . A thermoelectric conversion element using the Weyl antiferromagnetic powder according to any one of claims 1 to 4.

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