阅读说明：本技术 热电转换元件及热电转换装置 (Thermoelectric conversion element and thermoelectric conversion device ) 是由 中辻知 酒井明人 于 2018-07-03 设计创作，主要内容包括：热电转换元件(1)由在费米能量E<Sub>F</Sub>附近具有外尔点的能带结构的铁磁性材料构成,并且具有通过反常能斯特效应而产生电动势的热电机制。该铁磁性材料的状态密度表现出能量依赖性,该能量依赖性在费米能量E<Sub>F</Sub>附近取极值。用于决定电动势的热电系数-α<Sub>yx</Sub>具有与-TlogT成比例的温度(T)依赖性。当相对于热电转换元件(1)在+x方向上流过热电流Q(约<Image he="50" wi="74" file="DDA0002316340820000011.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>)时,在+x方向上产生温度差。由此,在热电转换元件(1)中,由于反常能斯特效应而在与热电流Q的方向(+x方向)和磁化M的方向(+z方向)两者均正交的y方向上产生电压V(约<Image he="53" wi="163" file="DDA0002316340820000012.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>)。(The thermoelectric conversion element (1) is formed by converting energy at the Fermi level F A ferromagnetic material having a band structure near the outer point, and a thermoelectric mechanism generating an electromotive force by an abnormal nernst effect. The density of states of the ferromagnetic material exhibits an energy dependence at the fermi energy E F Thermoelectric coefficient- α for determining electromotive force yx Has a temperature (T) dependence proportional to-TlogT. When a thermal current Q (about) flows in the + x direction with respect to the thermoelectric conversion element (1) ) When the temperature difference is generated in the + x direction. Thus, in the thermoelectric conversion element (1), a voltage V (about the order of magnitude of Z) is generated in the y direction orthogonal to both the direction of the thermoelectric current Q (+ x direction) and the direction of the magnetization M (+ z direction) due to the abnormal Nernst effect )。)

1. A thermoelectric conversion element, wherein,

the thermoelectric conversion element is composed of a substance having a band structure with a Verdet point in the vicinity of Fermi energy,

the thermoelectric generator is provided with a thermoelectric generator which generates electromotive force by the abnormal Nerns effect.

2. The thermoelectric conversion element according to claim 1,

the density of states of the substance exhibits an energy dependence which assumes an extreme value near the fermi energy.

3. The thermoelectric conversion element according to claim 1 or 2, wherein,

when the temperature is T, the thermoelectric coefficient that determines the electromotive force exhibits temperature dependence proportional to-TlogT.

4. The thermoelectric conversion element according to any one of claims 1 to 3, wherein,

the substance exhibits ferromagnetism.

5. The thermoelectric conversion element according to any one of claims 1 to 4, wherein,

the substance has a cubic crystal structure.

6. The thermoelectric conversion element according to any one of claims 1 to 5, wherein,

the material has a crystal structure of the full heusler system.

7. The thermoelectric conversion element according to any one of claims 1 to 6, wherein,

the species has a verge point in the range of ± 0.1eV from the fermi energy.

8. The thermoelectric conversion element according to any one of claims 1 to 7, wherein,

the band structure is an energy band structure of the substance obtained by the first principle calculation.

9. The thermoelectric conversion element according to any one of claims 1 to 8, wherein,

the thermoelectric conversion element has a thickness of 0.1 [ mu ] m or more.

10. A thermoelectric conversion device comprising:

a substrate; and

a power generating body that is provided on the substrate and has a plurality of thermoelectric conversion elements,

wherein the plurality of thermoelectric conversion elements each have a shape extending in one direction and are formed of the same substance as the thermoelectric conversion element according to any one of claims 1 to 9,

in the power generator, the plurality of thermoelectric conversion elements are arranged in parallel in a direction perpendicular to the one direction, and are electrically connected in series in a serpentine shape.

11. A thermoelectric conversion device comprising:

the thermoelectric conversion element according to any one of claims 1 to 9; and

the hollow member is a hollow member having a hollow portion,

wherein the thermoelectric conversion element is in a sheet shape and is provided so as to cover an outer surface of the hollow member.

Technical Field

The present invention relates to a thermoelectric conversion element and a thermoelectric conversion device including the thermoelectric conversion element.

Background

In recent years, a thermoelectric conversion device using an abnormal Nernst effect has been proposed (for example, see patent document 1). The "anomalous nernst effect" is a phenomenon in which, when a temperature difference is generated by flowing a heat flow through a magnetic material, a voltage is generated in a direction orthogonal to both a magnetization direction and a temperature gradient.

The Seebeck effect (Seebeck effect) is widely known as a thermoelectric mechanism that also generates a voltage using a temperature gradient. In the seebeck effect, since a voltage is generated in the same direction as the temperature gradient, the thermoelectric module has a complicated three-dimensional structure, and it is difficult to realize a large area or a thin film. In addition, since a material having high toxicity and scarcity is used, there are problems of weakness, poor vibration resistance, and high manufacturing cost. On the other hand, in the anomalous nernst effect, since a voltage is generated in a direction orthogonal to the temperature gradient, the thermoelectric module can be spread along the heat source, which is advantageous for increasing the area and reducing the film thickness. Furthermore, a material that is inexpensive, has low toxicity, and has high durability can be used.

Disclosure of Invention

Problems to be solved by the invention

As described above, although the abnormal-nerus effect has a certain advantage over the seebeck effect, the current abnormal-nerus effect using a general magnetic material generates a small amount of power, and thus cannot meet the demand of practical use.

Accordingly, an object of the present invention is to provide a thermoelectric conversion element that can generate a larger abnormal-nernst effect than the conventional ones, and a thermoelectric conversion device including the thermoelectric conversion element.

Means for solving the problems

A thermoelectric conversion element according to a first aspect of the present invention is constituted by a substance having a band structure of a peltier point (Weyl point) in the vicinity of Fermi energy (Fermi energy), and has a thermoelectric mechanism that generates an electromotive force by an abnormal nernst effect.

A thermoelectric conversion device according to a second aspect of the present invention includes: a substrate; and a power generating body that is provided over the substrate and has a plurality of thermoelectric conversion elements. The plurality of thermoelectric conversion elements each have a shape extending in one direction, and are formed of a substance having an energy band structure having an outer point in the vicinity of the fermi energy. The plurality of thermoelectric conversion elements of the power generator are arranged in parallel in a direction perpendicular to the one direction, and are electrically connected in series in a serpentine shape.

A thermoelectric conversion device according to a third aspect of the present invention includes: a thermoelectric conversion element is composed of a substance having an energy band structure with a Peltier point in the vicinity of Fermi energy. The thermoelectric conversion element is in a sheet shape and is provided so as to cover an outer surface of the hollow member.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, by using a thermoelectric conversion element composed of a substance having a band structure with a peril point in the vicinity of fermi energy, an abnormal nernst effect larger than that of the prior art can be generated.

Drawings

Fig. 1 is a diagram showing the energy-momentum relationship (band dispersion) of a fermi-crometer (Weyl fermion).

FIG. 2 shows Co ₂Schematic of the crystal structure of MnGa.

Fig. 3 is a schematic diagram showing the structure of a thermoelectric conversion element according to an embodiment of the present invention.

Fig. 4 is a graph showing measurement results of the nernst effect, the hall effect, the magnetic field dependence of magnetization, and the temperature dependence of the thermoelectric conversion element.

Fig. 5 is a graph showing the temperature dependence of the longitudinal resistivity of the thermoelectric conversion element with the seebeck coefficient at zero magnetic field.

Fig. 6A is a graph showing the temperature dependence of the hall conductivity and the peltier coefficient of the thermoelectric conversion element.

Fig. 6B is a graph showing the temperature dependence of the peltier coefficient of fig. 6A by a scaling function near the quantum critical point.

FIG. 7A is a diagram showing Co obtained by the first principle calculation ₂Diagram of band structure of MnGa.

FIG. 7B shows Co ₂Schematic representation of the band dispersion near the fermi energy of MnGa and the symmetry point (inset) of the first brillouin zone and face centered cubic lattice.

FIG. 7C shows the band structure (upper portion) along U-Z-U around the energy E20 meV and the energy distribution _UZSchematic of bery curvature distribution (lower) in the kb plane (U-Z direction) and kc stretch ka ═ kb.

FIG. 8A is Co obtained by first principle calculation ₂Graph of spin-resolved state density of MnGa.

Fig. 8B is a graph showing the density of states in the vicinity of the fermi energy in fig. 8A.

FIG. 9 is a graph showing the energy dependence of the number of outliers and the Hall conductance sum- α at the absolute zero point of the thermoelectric conversion element obtained by the first-principle calculation _yxGraph of energy dependence of/T.

Fig. 10A is a schematic diagram showing a relationship between band dispersion and nernst coefficient of TypeI.

Fig. 10B is a diagram showing a relationship between band dispersion and a nernst coefficient of a quantum critical dot.

Fig. 11A is a graph showing the results of measuring the magnetic field dependence of the longitudinal electrical conductivity of the thermoelectric conversion element in each direction of current flow.

Fig. 11B is a graph showing the results of measuring the angular dependence of the magnetic permeability (angle between the magnetic field and the current) of the thermoelectric conversion element in each direction of the current.

FIG. 12 is a graph showing Mn for various ferromagnetic materials and antiferromagnetic materials ₃And a graph showing the comparison result of the magnitudes of the Peltier coefficients of Sn.

Fig. 13 is an external view showing an example of a thermoelectric conversion device including the thermoelectric conversion element according to the present embodiment.

Fig. 14 is an external view showing another example of a thermoelectric conversion device including the thermoelectric conversion element according to the present embodiment.

Detailed Description

Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings.

In recent years, it has been theorized that the topological structure of the electronic structure is related to the thermoelectric mechanism due to the abnormal nernst effect. This theory suggests in particular that by the presence of Fermi energy E _FSince the Berry curvature (Berry curvature) of the neighborhood weil points (Weyl points) may increase the anomalous nernst effect, the search for a substance having a weil fermi (Weyl Fermion) and the synthesis of the substance are expected to promote the development of a thermoelectric conversion device using the anomalous nernst effect.

Exol fermi is a particle without mass described by dirac equation. As shown in fig. 1, the outliers exist at the point where the linear band dispersions intersect and appear as pairs with different chiralities (right and left). A pair of outliers can be considered as positive and negative poles of a virtual magnetic field (bery curvature) in momentum space and are considered to affect the motion of electrons in matter like a magnetic field in real space.

Calculation according to the first principle of recent years shows that the component is Co ₂The metal of TX is the Fermi energy E in momentum space _FThere are candidates for the peril metal of the peril point. Here, T is a transition metal element, and X is any one of Si, Ge, Sn, Al, and Ga. In the present embodiment, the metal is shownFor example, focusing on Co ₂MnGa is a fully Heusler (Full-Heusler) ferromagnetic material.

FIG. 2 schematically shows Co ₂Crystal structure of MnGa. As shown in FIG. 2, Co ₂MnGa has L2 ₁A full heusler structure of type cubic. L2 ₁The unit cell of the structure is composed of four face-centered cubic lattices (fcc), and in the lattice curve, Co atoms are located at (1/4, 1/4, 1/4) and (3/4, 3/4, 3/4), Mn atoms are located at (0, 0, 0), and Ga atoms are located at (1/2, 1/2, 1/2). Co ₂The crystal structure of MnGa can be determined by various diffraction methods such as X-ray diffraction.

Next, a thermoelectric conversion element and a thermoelectric mechanism thereof according to an embodiment of the present invention will be described with reference to fig. 3. The thermoelectric conversion element 1 of the present embodiment is made of Co ₂The MnGa structure is, as shown in fig. 3, a rectangular parallelepiped shape extending in one direction (y direction), has a thickness (length in the z direction) of 0.1 μm or more, and is magnetized in the + z direction. If there is a heat flow in the + x direction in the thermoelectric conversion element 1

When flowing, a temperature difference occurs in the + x direction. Accordingly, according to the abnormal nernst effect, in the thermoelectric conversion element 1, an electromotive force is generated in an outer product direction (y direction) orthogonal to both the direction of the heat flow Q (+ x direction) and the direction of the magnetization M (+ z direction)

Next, an experiment for verifying the abnormal nernst effect of the thermoelectric conversion element 1 will be described.

After preparing a polycrystalline sample by arc melting appropriate proportions of Co, Mn and Ga, Co was prepared by Czochralski method ₂MnGa single crystal. The generated Co was found by X-ray diffraction ₂MnGa exhibits a lattice constant

In the experiment, the dimensions of 7.5X 2.0X 1.3mm were prepared ³Is longThree samples in a square shape were used as the thermoelectric conversion elements 1. The three samples are distinguished by the orientation of the crystal parallel to the direction of the magnetic field B. B | | [100 |)]Sample of (1), B | | [110 | ]]And B | | [111 ]]Are labeled #100, #110, and #111, respectively. In the present embodiment, the transmission phenomenon (nernst effect, seebeck effect, and hall effect) of each sample is measured using a well-known method.

The results of measuring the nernst effect, the seebeck effect, and the hall effect for each sample are shown in fig. 4 to 6A.

Graph a of fig. 4 shows the nernst coefficient-S at room temperature (T300K) _yxShows a magnetic field dependence of [100 ]]Applying a parallel magnetic field B to [110 ]]Applying a parallel magnetic field B to [111 ]]Applying a parallel magnetic field B and causing a parallel heat flow Q to be [001 ]]Or [10-1]Observation at medium flow. Graph B of fig. 4 shows-S when a magnetic field of B-2T is applied to each sample _yxTemperature dependence of (a). From graph b of FIG. 4, it can be clearly seen that-S _yxIncreasing with increasing temperature, it reaches | S at room temperature _yx6 muV/K, reaches S at 400K _yx8 μ V/K, showing an order of magnitude greater value for the anomalous Nernst effect than observed in the prior art.

-S _yxEven if the observed value of (c) is within the seebeck coefficient S shown in the graph b of fig. 5 _xxRatio of (i.e., Nernst angle θ) _N≈tanθ _N＝S _yx/S _xx) Also shown are larger values not seen before. In practice, | S is shown on the right vertical axis of graph a of FIG. 4 _yx/S _xx| takes a value greater than 0.2. In addition, as can be seen from graphs a and b of fig. 4, S _yxThere is almost no anisotropy.

As shown in the graphs c and d of fig. 4, the hall resistivity ρ _yxAt room temperature, 15. mu. omega. cm was reached, and at around 320K, a maximum of 16. mu. omega. cm was reached. Hall angle theta _H≈tanθ _H＝ρ _yx/ρ _xx(right vertical axis of graph c of fig. 4) also takes a larger value exceeding 0.1 at room temperature. Here, ρ _xxIs longitudinal electricityResistivity. Graph a of fig. 5 shows ρ at zero magnetic field _xxTemperature dependence of (a).

The graph e and the graph f of fig. 4 show the magnetic field dependence of the magnetization M at room temperature and the temperature dependence of the magnetization M at a magnetic field B of 2T, respectively. As can be seen from the graphs a, c, and e in fig. 4, both the hall effect and the nernst effect show substantially the same magnetic field dependence as the magnetization curve. This indicates that, at T300K, the contribution of the anomalous term to the hall effect and the nernst effect (. varies.. mu.m) is dominant, while the contribution of the normal term (. varies.. mu.b) is extremely small. As shown in graphs e and f of fig. 4, the saturation magnetization Ms reaches 3.8 μ when T is 300K _BAnd increases with decreasing temperature, reaching about 4 mu at T-5K _BThis is consistent with the values predicted based on the slaite polling law. As can be seen from graphs e and f of fig. 4, the anisotropy of magnetization is almost negligible at T300K, and completely matches the structure of cubic crystals.

Observed Hall resistivity | ρ _yxThe | 15 μ Ω cm is the value of the largest level among the observed values of the abnormal hall effect so far. Similarly, the hall conductivity also shows very large values. Graph a of fig. 6A shows the hall conductivity σ at B ═ 2T _yxTemperature dependence of (a). Here, σ _yx＝-ρ _yx/(ρ _xx ²+ρ _yx ²)。-σ _yxMonotonically increasing with decreasing temperature, -sigma at absolute zero _yxUp to about 2000 omega ^-1cm ^-1. This value is in the same order of magnitude as the value of the known stacked quantum hall effect.

Nernst coefficient S _yxCan be calculated by Peltier coefficient α _yxAnd (4) defining. In general, the current is composed of an electric field ε and a temperature gradient

Is generated and represented as

Here, J, σ, and α are current density tensor and electricity, respectivelyThe conductivity tensor and the thermal conductivity tensor. When the direction of the magnetic field B is parallel to the z-direction, the temperature gradient

Parallel to the x-direction and set J equal to 0, J _y＝σ _yxS _xx+σ _xxS _yx-α _yx0. Here, σ is based on the cubic symmetry _xx＝σ _yy. That is, the peltier coefficient as the transverse (transverse) thermoelectric coefficient is given by equation (1):

peltier coefficient α _yxHall conductivity σ _yxX Seebeck coefficient S _xx+ longitudinal conductivity σ _xxX Nernst coefficient S _yx…(1)

As can be seen from equation (1), the magnitude of the nernst coefficient is determined by the peltier coefficient, and it is effective to evaluate the peltier coefficient on the basis of judging the abnormal nernst effect.

Graph b of fig. 6A shows the calculation of- α using the value obtained by equation (1) and graph a of fig. 4, 5, and 6A _yxAs shown in graph b of fig. 6A, - α _yxIncreasing generally linearly with increasing T before T reaches about 25K, taking a maximum when T reaches about 140K, and then gradually decreasing with increasing T, as can be seen herein, - α _yxThe temperature dependence curve of (a) behaves very similarly to-TlogT, more specifically, when for logT, - α is plotted _yxData of/T (right vertical axis in FIG. 6B) — α at low temperature _yxT Performance and high temperature- α _yxThere is a crossover between the expressions of-TlogT.

- α at Low temperature _yxThe behavior of T is consistent with the Mott equation, which defines the low temperature (k) _BT＜＜E _F) Lower α _yxHall conductivity σ at 0 or T _yxIs determined (α) _yx～-(π ²k _B ²T/3e)

). Here, k _BIs the boltzmann constant, on the other hand, at high temperatures (T between about 30K and 400K) - α _yxThe expression of-TlogT does not follow the Mott equation. The behavior of-TlogT, the thermoelectric coefficient, can be understood by the exol Fermi, as described below.

To show the existence of the outliers, first look at the nearest Co ₂Fermi energy E of MnGa _FThe fermi flour of (1). FIG. 7A shows Co obtained by the first principle calculation ₂Band structure of MnGa. The magnetization M is 4.2 μ _BThe magnetization direction is along [110 ]]In the direction of (a). In FIG. 7A, the pair located near the Brillouin zone boundary and forming the closest Fermi energy E _FThe energy band of the fermi surface (maximum fermi surface) (-0 eV) is represented by a bold line. As shown in fig. 7A to 7C, at the fermi energy E _FNearby E ₀There is a vernal point (+ -) near 20meV, and the fermi surface has a large bery curvature | Ω near the vernal point (+ -) _zL. (fig. 7C).

As shown in FIGS. 7B and 7C, the outer point (+ -) is at the moment of inertia k _UZ(U-Z direction) and kc stretched ka-kb planes, located at + -k along the U-Z-U line at the boundary of the Brillouin zone ₀At ± (2 pi/a) × 0.15. In fig. 7C, the z-component | Ω of the bery curvature in the ka-kb plane is shown in light and dark shading _zDistribution of | in Berry curvature | Ω _zThe relative large position (darker part) of | occurs with a boolean point (+). The outliers in the brillouin zone can be searched by the method of Fukui-Hatsugai-Suzuki (j.phys.soc.jp 74, 1674-.

As shown in fig. 7A and 7B, albeit at fermi energy E _FThe band near the maximum fermi surface intersects the other band to form linear dispersion, but the dispersion of the two bands is substantially flat, so that the density of states (DOS) increases. FIG. 8A shows Co obtained by the first principle calculation ₂Spin-resolved state density of MnGa, FIG. 8B shows _FDensity of states in the vicinity. As shown in fig. 8B, the density of states is at fermi energy E _FAnd 60meV, respectively. That is, it can be seen that Co ₂Density of states of MnGa at Fermi energy E _FNearbyAnd taking a maximum value.

As shown in equation (2), the exol fermi-rons of right (+) and left (-) chirality are described by the low-energy hamilton quantities.

[ number 1]

Wherein v is ₁、v ₂And v _⊥Are three independent speed parameters and h is the planck constant. According to the above-mentioned Co ₂First principle calculation of MnGa, the exol Fermi is located at E ₀K around 20meV ₀Angle of slope v at 2 pi/a x 0.15 ₂/v ₁＝0.99，v ₁≈10 ⁵m/s. Slope parameter v ₂/v ₁1 corresponds to the quantum critical point, v ₂/v ₁< 1 corresponding to exol fermi type I, v ₂/v ₁> 1 corresponds to type II exol fermi. Exol fermi type I (v) ₂/v ₁< 1) density of states at the exo-site is zero, type II exo-fermi (v) ₂/v ₁> 1) the density of states at the outlier is finite, with electron pockets in contact with hole pockets.

At quantum critical point (v) ₂/v ₁1), energy differential of hall conductivity

Here, using low energy theory, α representing the temperature and chemical potential dependence of Peltier coefficients near quantum critical points can be described using a dimensionless scaling function G over a wide temperature range _yx(T, μ) (see FIG. 6B). Here, μ is a chemical potential. FIG. 6B shows a pass experiment (T) ₀550K) and Density Functional Theory (DFT) calculation (T) ₀6000K) and results obtained from low energy theory (solid line in fig. 6B: (mu-E ₀)/k _BT ₀-0.05) are identical.

I.e. at quantum critical points according to a scaling function of low energy theory

Can be derived α at low temperature _yx～Tlog(|E _F-E ₀|/(hv ₁k ₀2 π)). On the other hand, at k _BT＞|E _F-E ₀At high temperatures, this logarithmic divergence may lead to α _yx～Tlog(k _BT/(hv ₁k ₀2 π)) but does not follow the Mott equation (α) _yxT) therefore, α can be understood by a scaling function of low energy theory around the quantum critical point between type I and type II over a wide temperature range _yxTemperature dependence of (a).

It is worth noting that when the chemical potential μ is tuned to the outlier (μ ═ E) ₀) At an arbitrary low temperature, the scale function does not follow the mott equation (broken line in fig. 6B).

Graph a of FIG. 9 shows for a line 110]Graph b shows- σ when T is 0K _yxGraph c shows- α when T is 0K _yxIn graph a of FIG. 9, +1 and-1 indicate chirality (right-handed or left-handed) at the verge point, and from these graphs a to c, — α _yxT at E ₀It was also found that- α was present even in the vicinity of E-0.1 eV _yxthe/T also assumes an extreme value and the number of outliers increases further. Thus, the outliers may exist at a distance E from the Fermi energy _FIn the range of. + -. 0.1 eV.

Fig. 10A and 10B schematically show the relationship between the band dispersion and the nernst coefficient. As shown in fig. 10A, at the quantum critical point (v) ₁＝v ₂) In isolated type I pheromones, the two bands are in point contact with each other, with zero density of states at the pheromone point. At this time, NernsThe coefficient is about 0.7. mu.V/K. As the quantum critical point is approached, the nernst coefficient increases, and when the quantum critical point is reached (fig. 10B), the dispersion of the two energy bands becomes flat, and the density of states at the outer point increases. At this time, the Nernst coefficient reached a maximum value of about 7 μ V/K. Thus, the flattened dispersion increases the magnitude of the Nernst coefficient by one order of magnitude.

As mentioned above, according to Co ₂First principle calculation of MnGa, shown at E ₀K around 20meV ₀To (2 pi/a) x 0.15 and a slope parameter of v ₂/v ₁The presence of 0.99 of type I exol fermi enables to obtain a nernst coefficient in the vicinity of the quantum critical point.

To further illustrate in Co ₂Evidence of the presence of fermi in MnGa, the longitudinal conductivity σ in each current direction was measured for the thermoelectric conversion element 1 _xxAnd the magnetic permeability σ in each current direction was measured _xx(B)-σ _xx(0) (magnetic-conductivity) angle dependence.

Fig. 11A is a graph showing the results of measuring the magnetic field dependence of the longitudinal conductivity σ xx at 0.1K and 5K with the magnetic field B parallel to the current I (I | B) and the magnetic field B perpendicular to the current I (I ⊥ B), respectively, fig. 11B is a graph showing the results of I | [100 ] with T | [ 5K and | B | | | 9T, respectively]、I||[110]And I | | [111]Graph of the results of measuring the angle dependence of the permeability (angle θ between magnetic field B and current I.) 0 °, 180 ° and 360 ° correspond to I | B, and 90 ° and 270 ° correspond to I ⊥ B, as can be seen from fig. 11B, the permeability shows cos ²And (3) expression of theta. Further, as is apparent from fig. 11A and 11B, when the magnetic field B and the current I are parallel in a strong magnetic field (e.g., | B | -6T or more), the current I easily flows. This means that chiral anomalies (chiral anomalls) seen in materials containing exol fermi are produced.

FIG. 12 shows Mn for various ferromagnetic and antiferromagnetic materials ₃Sn, magnitude of Perch coefficient | α _yxThe result of the comparison. As is apparent from FIG. 12, Co ₂Large Peltier coefficient of MnGaMn is far larger than other ferromagnetic materials and antiferromagnetic materials ₃Sn。

Next, a thermoelectric conversion device in which the thermoelectric conversion element of the present embodiment is modularized will be described.

Fig. 13 shows an external appearance structure of the thermoelectric conversion device 20 according to the present embodiment. The thermoelectric conversion device 20 includes a substrate 22 and a power generator 23 mounted on the substrate 22. In the thermoelectric conversion device 20, when a heat flow Q flows from the substrate 22 side to the power generating element 23, a temperature difference in the heat flow direction occurs in the power generating element 23, and a voltage V is generated in the power generating element 23 due to the abnormal nernst effect.

The substrate 22 has a first surface 22a on which the power generating body 23 is mounted and a second surface 22b opposite to the first surface 22 a. Heat from a heat source (not shown) is applied to the second surface 22 b.

The power generating body 23 has a plurality of thermoelectric conversion elements 24 and a plurality of thermoelectric conversion elements 25, each having an L-shaped three-dimensional shape, and is composed of the same substance as the thermoelectric conversion element 1 shown in fig. 3. As shown in fig. 13, the plurality of thermoelectric conversion elements 24 and the plurality of thermoelectric conversion elements 25 are alternately arranged in parallel on the substrate 22 in a direction (y direction) perpendicular to each longitudinal direction (x direction). The number of the thermoelectric conversion elements 24 and the thermoelectric conversion elements 25 constituting the power generator 23 is not limited.

Further, the plurality of thermoelectric conversion elements 24 and the plurality of thermoelectric conversion elements 25 are arranged such that the direction of magnetization M1 of the thermoelectric conversion element 24 is opposite to the direction of magnetization M2 of the thermoelectric conversion element 25. Further, the plurality of thermoelectric conversion elements 24 and the plurality of thermoelectric conversion elements 25 have nernst coefficients of the same sign.

The thermoelectric conversion element 24 has a first end face 24a and a second end face 24b parallel to the longitudinal direction (x direction). The thermoelectric conversion element 25 has a first end face 25a and a second end face 25b parallel to the longitudinal direction (x direction). The first end face 25a of the thermoelectric conversion element 25 is connected to the second end face 24b of the adjacent thermoelectric conversion element 24, and the second end face 25b of the thermoelectric conversion element 25 is connected to the first end face 24a of the opposite-side adjacent thermoelectric conversion element 24. Thereby, the plurality of thermoelectric conversion elements 24 and the plurality of thermoelectric conversion elements 25 are electrically connected in series. That is, the power generating body 23 is provided on the first surface 22a of the substrate 22 in a snake shape.

When heat is released from the heat source to the second surface 22b of the substrate 22, the heat flow Q in the + z direction flows to the power generating body 23. When a temperature difference is generated by the heat flow Q, an electromotive force E1 is generated in the thermoelectric conversion element 24 in a direction (x direction) orthogonal to both the direction (y direction) of the magnetization M1 and the direction (+ z direction) of the heat flow Q due to the abnormal-nernst effect. Due to the abnormal-gauss effect, an electromotive force E2 is generated in the thermoelectric conversion element 25 in a direction (+ x direction) orthogonal to both the direction (+ y direction) of the magnetization M2 and the direction (+ z direction) of the heat flow Q.

As described above, since the thermoelectric conversion elements 24 and the thermoelectric conversion elements 25 arranged in parallel are electrically connected in series, the electromotive force E1 generated in one thermoelectric conversion element 24 can be applied to the adjacent thermoelectric conversion element 25. Further, since the electromotive force E1 generated in one thermoelectric conversion element 24 is opposite in direction to the electromotive force E2 generated in the adjacent thermoelectric conversion element 25, the electromotive forces can be accumulated in the adjacent thermoelectric conversion element 24 and thermoelectric conversion element 25, respectively, and the output voltage V can be increased.

As a modification of the thermoelectric conversion device 20 of fig. 13, the following configuration may be adopted: the thermoelectric conversion elements 24 and the thermoelectric conversion elements 25 have nernst coefficients of opposite signs to each other, and are arranged in such a manner that the plurality of thermoelectric conversion elements 24 are the same as the magnetization direction of the plurality of thermoelectric conversion elements 25 (i.e., the direction of the magnetization M1 and the direction of the magnetization M2 are the same).

The thermoelectric conversion device according to the present embodiment is not limited to the embodiment shown in fig. 13. In the abnormal nernst effect, since the temperature gradient, the magnetization direction, and the voltage direction are orthogonal to each other, a sheet-like thermoelectric conversion element can be manufactured.

Fig. 14 shows an external appearance structure of the thermoelectric conversion device 30 including the sheet-like thermoelectric conversion element 32. Specifically, the thermoelectric conversion device 30 includes: a hollow member 31, and a long sheet-like thermoelectric conversion element 32 provided to cover (wrap) the outer surface of the hollow member 31. The thermoelectric conversion element 32 is composed of the same substance as the thermoelectric conversion element 1 shown in fig. 3. The magnetization direction of the thermoelectric conversion element 32 is parallel to the longitudinal direction (x direction) of the hollow member 31. When a heat flow is generated in a direction perpendicular to the longitudinal direction (x direction) of the hollow member 31 and a temperature gradient is generated in a direction from the inside to the outside of the hollow member 31, a voltage V is generated along the longitudinal direction (a direction perpendicular to the magnetization direction and the heat flow direction) of the long-shaped thermoelectric conversion element 32 due to the abnormal gauss effect.

Here, in fig. 13 and 14, when the length in the longitudinal direction of the thermoelectric conversion element is L and the thickness (height) is H, the voltage due to the abnormal nernst effect is proportional to L/H. That is, the longer and thinner the thermoelectric conversion element is, the larger the generated voltage is. Therefore, it is expected that the anomalous nernst effect can be enhanced by using the power generator 23 (fig. 13) in which the plurality of thermoelectric conversion elements 24 and the plurality of thermoelectric conversion elements 25 are electrically connected in series in a serpentine shape or the thermoelectric conversion elements 32 (fig. 14) in a long sheet shape.

The thermoelectric conversion devices 20 and 30 can be applied to various apparatuses. For example, whether the thermal insulation performance of a building is excellent or not can be determined by providing a thermoelectric conversion device in the heat flow sensor. Further, a thermoelectric conversion device can be provided in an exhaust device of a motorcycle or the like to generate electricity using the heat (waste heat) of exhaust gas, and the thermoelectric conversion device can be effectively used as an auxiliary power source.

In the present embodiment, the voltage due to the abnormal nernst effect is focused on, but the output voltage can be increased by the synergistic effect of the voltage due to the seebeck effect caused by the temperature gradient, the hall effect based on the voltage due to the seebeck effect, and the voltage due to the abnormal nernst effect.

In this embodiment, for Co ₂MnGa is a substance that enhances the anomalous nernst effect due to the presence of fermi. Except for Co ₂In addition to MnGa, as a candidate substance which can enhance the anomalous nernst effect due to the presence of pheromone, there can be mentioned: co ₂MnAl、Co ₂MnIn、Mn ₃Ga、Mn ₃Ge、Fe ₂NiGa、CoTiSb、CoVSb、CoCrSb、CoMnSb、TiGa ₂Mn and the like.

Description of the reference numerals

1. 24, 25, 32: thermoelectric conversion element

20. 30: thermoelectric conversion device

22: substrate

23: power generator

31: hollow member