Thermoelectric conversion element, thermoelectric conversion module, thermoelectric conversion method, and fluctuation detection sensor

Abstract

To provide a thermoelectric conversion element capable of thermoelectric conversion from temperature fluctuations on a microscale, a thermoelectric conversion module, and a thermoelectric conversion method.SOLUTION: A thermoelectric conversion element 200 according to the present invention includes a thermoelectric conversion unit 202 having a nonlinear thermoelectric response characteristic to an input of a heat flow H along a first direction, and electrode units 207a, 207b for extracting a thermoelectric signal JN generated in the thermoelectric conversion unit 202 due to the heat flow H input from the outside to the thermoelectric conversion unit 202 along the first direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a thermoelectric conversion element, a thermoelectric conversion module, a thermoelectric conversion method, and a fluctuation detection sensor. [Background technology]

[0002] Energy harvesting (environmental power generation) technology that collects various forms of energy from the surroundings and converts it into electrical energy has been attracting attention. Thermoelectric conversion elements utilizing the Seebeck effect as described in Patent Document 1 and thermoelectric conversion elements utilizing the spin Seebeck effect as described in Non-Patent Documents 1 and 2 are known as technologies that realize such energy harvesting.

[0003] Also, detectors and sensors are known that detect failure, accident, deterioration, etc. of an object (for example, failure of a device, deterioration of a building, or abnormality in the health of a living organism) by measuring physical quantities such as a specific frequency, temperature, or current value of a substance. For example, Patent Document 2 describes a fire detection device that detects the occurrence of a fire. This fire detection device includes a microphone that collects sounds generated in a monitored area as acoustic data, a frequency analysis unit that calculates a frequency spectrum by frequency analyzing the acoustic data collected by the microphone, and a flame detection unit that determines whether or not the frequency spectrum calculated by the frequency analysis unit contains 1 / f fluctuation characteristics in a frequency band below the standing wave, and detects the occurrence of a flame in the monitored area when it is determined that the 1 / f fluctuation characteristics are contained. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-144212 A [Patent Document 2] Patent No. 7376660 specification [Non-patent literature]

[0005] [Non-Patent Document 1] Kenichi Uchida, Eiji Saito, "Spin Seebeck effect and its application to thermoelectric conversion", Applied Physics, The Applied Physics Society, 2013, Vol. 82, No. 11, pp. 928-931 [Non-Patent Document 2] K. Uchida, et. al., “Observation of the spinSeebeck effect”, Nature, 2008, Vol.455, No. 9, p.778-781 Summary of the Invention [Problem to be solved by the invention]

[0006] Conventionally known thermoelectric conversion elements using the Seebeck effect or spin Seebeck effect convert the temperature gradient generated in an object into electrical energy, but when the temperature gradient is reversed, the polarity of the electric field generated in the element is also reversed. Therefore, the existence of a constant temperature gradient on a macroscale is required for power generation. Therefore, it has been practically impossible to perform thermoelectric conversion from a heat source in which the direction and magnitude of the heat flow change randomly, that is, from temperature fluctuations on a microscale.

[0007] In addition, conventional detectors and sensors for detecting failures, accidents, deterioration, etc., are only able to detect the occurrence of failures, accidents, deterioration, etc., once they have actually occurred in the target object, due to the mechanism of measuring a specific frequency, temperature, current value, etc. of a substance, and therefore cannot detect the signs of such occurrences and prevent them from occurring in advance. It is believed that if it were possible to detect the irregular movement of energy, such as vibrations and electromagnetic noise emitted from the target object, which originally repeats a certain regular movement, it would be possible to capture the signs of failures, accidents, deterioration, etc. of the target object, but in order to do so, it is necessary to detect the fluctuations in such energy, which change randomly on a microscale. However, no sensor capable of detecting microscale energy fluctuations emitted from such targets has been known so far.

[0008] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a thermoelectric conversion element, a thermoelectric conversion module, and a thermoelectric conversion method capable of thermoelectric conversion from micro-scale temperature fluctuations, or to provide a sensor capable of detecting micro-scale energy fluctuations emitted from an object. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the thermoelectric conversion element of the present invention comprises a thermoelectric conversion unit having a nonlinear thermoelectric response characteristic with respect to a heat flow input along a first direction, and an electrode unit for extracting a thermoelectric signal generated in the thermoelectric conversion unit due to a heat flow input from the outside to the thermoelectric conversion unit along the first direction.

[0010] The present inventors have found that, in the thermoelectric conversion element according to the present invention, a thermoelectric signal generated in the thermoelectric conversion unit by an inflowing heat flow is nonlinear with respect to the direction of the heat flow due to the nonlinear thermoelectric response characteristics of the thermoelectric conversion unit, and such a nonlinear thermoelectric signal can be electrically extracted by the electrode unit. Therefore, even from a heat flow whose direction and magnitude change randomly, it is possible to generate a thermoelectric signal in a fixed direction in the thermoelectric conversion unit, making it possible to perform thermoelectric conversion from temperature fluctuations on a microscale.

[0011] In addition, in order to solve the above-mentioned problems, in the thermoelectric conversion element according to the present invention, the thermoelectric conversion section exhibits nonreciprocal conduction based on the breaking of spatial inversion symmetry, and the electrode section can include a pair of electrodes spaced apart from each other on the thermoelectric conversion section for extracting a nonreciprocal thermoelectric signal.

[0012] The inventors of the present application have found that the thermoelectric signal generated in the thermoelectric conversion unit by the incoming heat flow is non-reciprocal with respect to the direction of the heat flow due to the non-reciprocal conduction of the thermoelectric conversion unit, and that such a non-reciprocal thermoelectric signal can be electrically extracted by a pair of electrodes. Therefore, even from a heat flow whose direction and magnitude change randomly, it is possible to generate a thermoelectric signal in a fixed direction in the thermoelectric conversion unit, making it possible to perform thermoelectric conversion from temperature fluctuations on a microscale.

[0013] Furthermore, in the thermoelectric conversion element according to the present invention, it is preferable that the thermoelectric conversion part is a thermoelectric conversion layer including a ferromagnetic metal layer and a paramagnetic metal layer stacked on each other along a second direction perpendicular to the first direction, and the pair of electrodes are provided on the thermoelectric conversion layer along the first direction in the in-plane direction of the thermoelectric conversion layer, spaced apart from each other. This increases the voltage of thermoelectric conversion based on the breaking of spatial inversion symmetry of the thermoelectric conversion layer, thereby particularly increasing the thermoelectric conversion efficiency.

[0014] Furthermore, in the thermoelectric conversion element according to the present invention, the distance between the pair of electrodes can be set to 0.1 μm or more and 1000 μm or less. By setting the distance in this range, the voltage of thermoelectric conversion becomes large, and therefore the thermoelectric conversion efficiency becomes high.

[0015] Furthermore, in the thermoelectric conversion element according to the present invention, it is preferable that the paramagnetic metal layer is composed of a single layer or a plurality of laminated layers, and each of the single layer or the plurality of laminated layers of the paramagnetic metal layer is composed of Pt, Pd, W, AuW alloy, Ta, CuIr alloy, CuBi alloy, BiSb alloy, or BiSe alloy. This makes the nonreciprocity of conduction based on the breaking of the spatial inversion symmetry of the thermoelectric conversion layer particularly large, thereby particularly increasing the thermoelectric conversion efficiency.

[0016] Furthermore, in the thermoelectric conversion element according to the present invention, it is preferable that the ferromagnetic metal layer is composed of a single layer or a plurality of laminated layers, and each of the single layer or the plurality of laminated layers of the ferromagnetic metal layer is composed of a Ni-Fe alloy, Fe, CoNi, Gd, CoFeB alloy, or (Ga,Fe)Sb alloy. These are materials that exhibit ferromagnetism at room temperature, and since non-reciprocity of conduction at room temperature is realized, the thermoelectric conversion efficiency is increased.

[0017] Furthermore, a thermoelectric conversion module according to the present invention includes a plurality of thermoelectric conversion elements according to any one of the above, and the plurality of thermoelectric conversion elements are electrically connected to each other so that the thermoelectric signals from the respective thermoelectric conversion elements can be superimposed with the same polarity, thereby making it possible to extract a large non-reciprocal thermoelectric signal.

[0018] In addition, in order to solve the above-mentioned problems, the thermoelectric conversion method of the present invention includes the steps of: preparing a thermoelectric conversion element including a thermoelectric conversion layer exhibiting nonreciprocal conduction based on the breaking of spatial inversion symmetry; and a pair of electrodes spaced apart from each other and provided on the thermoelectric conversion layer for extracting a nonreciprocal thermoelectric signal, wherein the thermoelectric conversion layer includes a ferromagnetic metal layer and a paramagnetic metal layer stacked on each other, and the pair of electrodes are provided on the paramagnetic metal layer spaced apart from each other in the in-plane direction of the paramagnetic metal layer; and performing thermoelectric conversion while applying a magnetic field of 1 T or less to the ferromagnetic metal layer of the thermoelectric conversion layer.

[0019] According to the thermoelectric conversion method of the present invention, when a magnetic field of 1 T or less is applied and a heat flow flows into a laminate of magnetized ferromagnetic metal layers and paramagnetic metal layers, a spin current is driven in the paramagnetic metal layer, and spin accumulation is formed at the interface between the paramagnetic metal layer and the ferromagnetic metal layer. The polarity of this spin accumulation becomes parallel or antiparallel to the magnetization direction of the ferromagnetic metal layer depending on the direction of the heat flow. The scattering of electrons changes depending on the relative direction between the polarity of this spin accumulation and the magnetization direction, and this causes the thermoelectric signal generated in the thermoelectric conversion layer to be dependent on the direction of the heat flow, that is, nonreciprocity. This is a nonreciprocal thermoelectric signal, and such a nonreciprocal thermoelectric signal can be electrically extracted by a pair of electrodes. Therefore, even if a heat flow whose direction and magnitude change randomly, it is possible to generate a thermoelectric signal in a fixed direction in the paramagnetic metal layer, making it possible to perform thermoelectric conversion from temperature fluctuations on a microscale.

[0020] In addition, in order to solve the above-mentioned problems, the thermoelectric conversion method according to the present invention includes a step of applying a temperature gradient including an AC component to a thermoelectric conversion unit exhibiting nonreciprocal conduction based on the breaking of spatial inversion symmetry, and a step of the thermoelectric conversion unit thermoelectrically converting the temperature gradient including the AC component to generate a nonreciprocal thermoelectric signal.

[0021] According to the thermoelectric conversion method of the present invention, the thermoelectric conversion unit thermoelectrically converts an applied temperature gradient containing an AC component to generate a thermoelectric signal. At this time, the thermoelectric signal becomes a non-reciprocal thermoelectric signal because it is non-linear with respect to the direction of the temperature gradient due to the non-reciprocal conduction characteristics of the thermoelectric conversion unit. As a result, temperature fluctuations on a microscale can be regarded as a temperature gradient containing an AC component, making it possible to perform thermoelectric conversion from temperature fluctuations on a microscale.

[0022] In addition, in order to solve the above-mentioned problems, the fluctuation detection sensor of the present invention comprises a nonlinear response unit having a nonlinear electrical response characteristic to an input of external energy along a first direction, and an electrode unit for extracting an electrical response signal generated in the nonlinear response unit due to energy fluctuations input from the outside to the nonlinear response unit along the first direction.

[0023] The inventors of the present application have found that, according to the fluctuation detection sensor of the present invention, the electrical response signal generated in the nonlinear response unit by the energy fluctuation input from the outside is nonreciprocal with respect to the direction of the energy flow due to the nonlinear electrical response characteristics of the nonlinear response unit, and such a nonreciprocal electrical response signal can be electrically extracted by the electrode unit. Therefore, even from external energy whose direction and magnitude change randomly, it is possible to generate a nonlinear voltage signal, which is an electrical response signal that is nonreciprocal in a fixed direction, in the nonlinear response unit, and it becomes possible to detect microscale energy fluctuations emitted from the target object.

[0024] Furthermore, in the fluctuation detection sensor according to the present invention, the external energy can be an electric current and / or a heat flow, and the energy fluctuation can be an electric current fluctuation and / or a heat flow fluctuation. In this case, it becomes possible to detect an electric current fluctuation and / or a heat flow fluctuation emitted from an object.

[0025] Furthermore, in the fluctuation detection sensor according to the present invention, the external energy can be a current and the energy fluctuation can be a current fluctuation, in which case it is possible to detect a current fluctuation emitted from an object.

[0026] Furthermore, in the fluctuation detection sensor according to the present invention, the nonlinear response section can have a configuration in which spatial inversion symmetry is broken along a second direction perpendicular to the first direction.

[0027] Furthermore, in the fluctuation detection sensor according to the present invention, the nonlinear response portion can include a ferromagnetic layer and a paramagnetic layer stacked on top of each other along the second direction.

[0028] Furthermore, in the fluctuation detection sensor according to the present invention, the ferromagnetic layer can be configured to have spontaneous magnetization and / or high coercive force.

[0029] Furthermore, in the fluctuation detection sensor according to the present invention, the ferromagnetic layer is a ferromagnetic metal layer and is made of an L10 type ordered alloy made of a magnetic metal and a paramagnetic metal, and the paramagnetic layer can be a paramagnetic metal layer, which can increase the magnitude of the coercive force that the ferromagnetic layer can have. Effect of the Invention

[0030] According to the present invention, a thermoelectric conversion element, a thermoelectric conversion module, and a thermoelectric conversion method capable of thermoelectric conversion from microscale temperature fluctuations are provided, or a sensor capable of detecting microscale energy fluctuations emitted from an object is provided. [Brief description of the drawings]

[0031] [Figure 1] FIG. 1 is a perspective view showing a thermoelectric conversion element according to a first embodiment. [Diagram 2] 1 is a cross-sectional view of a thermoelectric conversion element according to a first embodiment. [Diagram 3] FIG. 2 is a process diagram showing the steps of a thermoelectric conversion method according to the first embodiment. [Figure 4] FIG. 1 is a perspective view showing a configuration of a thermoelectric conversion module using a thermoelectric conversion element. [Diagram 5] FIG. 1 is a schematic diagram showing an experimental method for measuring non-reciprocal thermoelectric signals. [Figure 6] FIG. 1 shows measurement results of an experiment measuring non-reciprocal thermoelectric signals. [Figure 7] FIG. 11 is a perspective view showing a fluctuation detection sensor according to a second embodiment. [Figure 8] FIG. 11 is a cross-sectional view of a fluctuation detection sensor according to a second embodiment. [Figure 9] FIG. 6 is a process diagram showing the steps of an energy conversion method according to a second embodiment. [Figure 10] 1 is a perspective view showing a configuration of a fluctuation detection sensor module using a fluctuation detection sensor. [Figure 11] FIG. 11 is a schematic diagram showing an experimental method for measuring a non-reciprocal voltage signal JN1 in the third embodiment. [Figure 12] FIG. 13 is a diagram showing the measurement results of the experiment in Example 3. [Figure 13] FIG. 11 is a schematic diagram showing an experimental method for measuring a non-reciprocal voltage signal JN1 in the fourth embodiment. [Figure 14] FIG. 13 is a diagram showing the measurement results of the experiment in Example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Hereinafter, the embodiments of the present invention will be described in detail with reference to the accompanying drawings. In each drawing, the same reference numerals are used for the same elements where possible. Furthermore, the dimensional ratios within and between the elements in the drawings are arbitrary for ease of viewing the drawings.

[0033] (First embodiment) FIG. 1 is a perspective view showing a thermoelectric conversion element according to the first embodiment, and FIG. 2 is a cross-sectional view of the thermoelectric conversion element according to the first embodiment.

[0034] As shown in FIGS. 1 and 2, a thermoelectric conversion element 200 according to this embodiment includes a substrate 201, a thermoelectric conversion layer 202 as a thermoelectric conversion section, and a pair of electrodes 207a, 207b as an electrode section.

[0035] The substrate 201 is a plate-like or film-like member as shown in Fig. 1, for example, and has a substantially flat surface 201S. The surface 201S is rectangular when viewed from the Z-axis direction as shown in Fig. 1, for example. The substrate 201 is a member for laminating a thermoelectric conversion layer 202 on the surface 201S. Examples of materials constituting the substrate 201 include metals such as Au, Ag, Cu, and Al, silicon, sapphire, SiC, GaN, yttria-stabilized zirconia (YSZ), and resins such as polyimide, polyethylene terephthalate (PET), and polyethylene naphthalate (PEN).

[0036] 1 and 2 show an orthogonal coordinate system C, in which the Z axis is set in the thickness direction of the substrate 201, and the X axis and the Y axis are set in the long side direction and the short side direction, respectively, of the rectangle of the surface 201S of the substrate 201. The orthogonal coordinate system C is also shown in the subsequent figures as necessary.

[0037] The thermoelectric conversion layer 202 has a single-layer ferromagnetic metal layer 203 and a single-layer paramagnetic metal layer 205 stacked on each other along the Z-axis direction (second direction), and in this embodiment, the ferromagnetic metal layer 203 is stacked on the surface 201S of the substrate 201, and the paramagnetic metal layer 205 is stacked on the ferromagnetic metal layer 203. The ferromagnetic metal layer 203 is made of a metal that exhibits ferromagnetism at a temperature in the usage environment of the thermoelectric conversion element 200. The ferromagnetic metal layer 203 is preferably made of a metal that exhibits ferromagnetism at room temperature (about 300K), and from this viewpoint, it is preferably made of Fe, Co, Ni, Gd, or an alloy containing at least one of them, and is particularly preferably made of a Ni-Fe alloy, Co, or CoFeB.

[0038] The thermoelectric conversion layer 202 is, for example, rectangular in plan view (i.e., when viewed from the Z-axis direction) with a long side along the X-axis direction and a short side along the Y-axis direction. The thickness of the ferromagnetic metal layer 203 is not particularly limited, but can be, for example, 1 nm or more and 100 nm or less.

[0039] The paramagnetic metal layer 205 is made of a metal that exhibits paramagnetism at the temperature of the environment in which the thermoelectric conversion element 200 is used, and is preferably made of a metal that exhibits paramagnetism at room temperature (300K). The paramagnetic metal layer 205 is preferably made of a paramagnetic metal with high spin-orbit interaction in order to enhance the spin-Nernst effect in the paramagnetic metal layer 205 described later, and from this viewpoint, is preferably made of Pt, Pd, W, AuW alloy, Ta, CuIr alloy, CuBi alloy, BiSb alloy, or BiSe alloy, and is particularly preferably made of Pt. The thickness of the paramagnetic metal layer 205 is not particularly limited, but can be, for example, 1 nm or more and 100 nm or less.

[0040] The thermoelectric conversion layer 202 exhibits non-reciprocal conduction based on the breaking of spatial inversion symmetry. Specifically, a paramagnetic metal layer is provided on the surface of the ferromagnetic metal layer 203, but a similar paramagnetic metal layer is not provided on the back surface of the ferromagnetic metal layer 203, and a ferromagnetic metal layer is provided on the back surface of the paramagnetic metal layer 205, but a similar ferromagnetic metal layer is not provided on the surface of the paramagnetic metal layer 205. Therefore, the thermoelectric conversion layer 202 has a structure in which spatial inversion symmetry is broken along the Z-axis direction. The thermoelectric conversion layer 202 has substantial spatial inversion symmetry in the direction along the XY plane. And, due to the breaking of spatial inversion symmetry along the Z-axis direction, the thermoelectric conversion layer 202 exhibits non-reciprocity in terms of electrical conductivity in the in-plane (in the XY plane) direction. As a result, the thermoelectric conversion layer 202 has a non-linear thermoelectric response characteristic with respect to the input of a heat flow H along one of the in-plane (in the XY plane) directions (in this embodiment, the X-axis direction as the first direction) as described later.

[0041] The pair of electrodes 207a, 207b are provided on the thermoelectric conversion layer 202 so as to be spaced apart from each other in an in-plane (XY plane) direction of the thermoelectric conversion layer 202. The pair of electrodes 207a, 207b detects a thermoelectric signal J generated in the thermoelectric conversion layer 202 due to a heat flow H input from the outside to the thermoelectric conversion layer 202 along one of the in-plane (XY plane) directions as described later. NIn this embodiment, the pair of electrodes 207a, 207b are provided on the paramagnetic metal layer 205 so as not to contact the ferromagnetic metal layer 203, and are provided on a surface 205S of the paramagnetic metal layer 205 opposite the ferromagnetic metal layer 203. The pair of electrodes 207a, 207b are spaced apart from each other along the X-axis direction, which is one of the in-plane directions (XY plane) of the paramagnetic metal layer 205. The pair of electrodes 207a, 207b are made of a material having a conductivity capable of extracting a non-reciprocal thermoelectric signal from the thermoelectric conversion layer 202 as described below. Examples of such materials include metal materials such as Cu, Ag, Au, Pt, Ni, Al, constantan, Cr, In, Pd, Fe, Cu alloy, Ti / Au laminate, and Cr / Au laminate, and conductive oxides such as indium tin oxide (ITO) and zinc oxide (ZnO). Cu, Ag, Au, Pt, Ni, Al, constantan, and Cu copper alloy are preferred, and Cu, Au, Ag, Pt, Ni, Ti / Au laminate, and Cr / Au laminate are particularly preferred.

[0042] The thickness of the pair of electrodes 207a, 207b is not particularly limited, but may be, for example, 10 nm or more and 1 μm or less. The separation distance D207 between the pair of electrodes 207a, 207b along the X-axis direction is preferably 0.1 μm or more and 1000 μm or less.

[0043] In addition, the thermoelectric conversion element 200 of this embodiment may include a layer made of an electrically insulating magnetic material that is provided in contact with the ferromagnetic metal layer 203, or may not include such a layer.

[0044] In such a thermoelectric conversion element 200, for example, a substrate 201 is prepared, a material for forming a ferromagnetic metal layer 203 and a material for forming a paramagnetic metal layer 205 are deposited in this order on a surface 201S of the substrate 201 by physical vapor deposition such as DC magnetron sputtering to form a laminate, and the laminate is patterned into a rectangular shape in a plan view by photolithography and lift-off to form a thermoelectric conversion layer 202. Thereafter, a metal material for forming a pair of electrodes 207a, 207b is deposited in an area including the surface 205S of the paramagnetic metal layer 205 by physical vapor deposition such as DC magnetron sputtering to form a metal layer, and the metal layer is patterned into a predetermined shape by photolithography and lift-off to form a pair of electrodes 207a, 207b.

[0045] Next, the thermoelectric conversion method according to the present embodiment will be described. Fig. 3 is a process diagram showing the steps of the thermoelectric conversion method according to the present embodiment. As shown in Fig. 3, the steps of the thermoelectric conversion method according to the present embodiment include step S11 of preparing a thermoelectric conversion element, step S12 of inputting a heat flow, and step S13 of performing thermoelectric conversion while applying an external magnetic field. These steps will be described again with reference to Figs. 1 and 2.

[0046] In step S11 of preparing a thermoelectric conversion element, the above-mentioned thermoelectric conversion element 200 as shown in Figures 1 and 2 is prepared. Next, in step S12 of inputting a heat flow, a heat flow H is applied to a thermoelectric conversion layer 202 that exhibits nonreciprocal conduction based on the breaking of spatial inversion symmetry. Specifically, in step S12 of inputting a heat flow, a heat flow H from the outside that is the target of thermoelectric conversion is input to the thermoelectric conversion layer 202 so as to flow along the X-axis direction, which is one of the in-plane directions (XY plane) of the thermoelectric conversion layer 202.

[0047] The heat flow H of this embodiment corresponds to the above-mentioned "temperature fluctuations on a microscale". The heat flow H is a temperature gradient including a single or multiple AC components. Here, the "AC component" is a component whose heat magnitude periodically fluctuates between positive and negative at a predetermined frequency, and when the heat flow H includes multiple AC components, the frequencies of the AC components are different from each other. As described above, the "temperature fluctuations on a microscale" corresponds to a heat source whose direction and magnitude of the heat flow change randomly, but since a single AC component or multiple AC components with different frequencies included in the temperature fluctuation can be obtained by Fourier transform, the above-mentioned "temperature fluctuations on a microscale" can be regarded as a temperature gradient including a single or multiple AC components.

[0048] Next, step S13 of performing thermoelectric conversion while applying an external magnetic field is performed. In step S13 of performing thermoelectric conversion while applying an external magnetic field, the thermoelectric conversion layer 202 thermoelectrically converts the heat flow H to generate a thermoelectric signal J. N Specifically, in step S13 of performing thermoelectric conversion while applying an external magnetic field, an external magnetic field B generated by a magnetic field generating unit provided outside the thermoelectric conversion element 200 is applied to the ferromagnetic metal layer 203. The direction of application of the external magnetic field B is an in-plane direction (within the XY plane) of the thermoelectric conversion element 200, and is the negative Y-axis direction which is one of the directions perpendicular to the flow direction of the heat flow H. As a result, the ferromagnetic metal layer 203 is magnetized in the direction of the external magnetic field B, and has magnetization 203M oriented in the direction of the external magnetic field B. The application of such an external magnetic field B is maintained while the thermoelectric conversion of the heat flow H is being performed. The magnitude of the external magnetic field B can be, for example, 1 T or less.

[0049] In step S13, when the heat flow H flows into the paramagnetic metal layer 205, a spin current J S is generated along the Z-axis direction and flows into the ferromagnetic metal layer 203. S The polarity of changes to the positive or negative Y-axis direction depending on the direction of the heat flow H. Therefore, when the direction of the heat flow H is reversed, the spin current J S The polarity of the spin current J SThe relative orientation between the polarity of the magnetization 203M of the ferromagnetic metal layer 203 and the direction of the magnetization 203M of the ferromagnetic metal layer 203 is reversed. S It is also possible to reverse the relative orientation between the polarity of and the direction of magnetization 203M.

[0050] Spin current J S When the spin current flows into the ferromagnetic metal layer 203, electron scattering changes depending on the relative direction between the polarity of the spin current and the direction of magnetization 203M of the ferromagnetic metal layer 203. Since the polarity of the spin current near the junction interface between the ferromagnetic metal layer 203 and the paramagnetic metal layer 205 changes depending on the direction of the heat current H, this electron scattering changes depending on the direction of the heat current H. This causes the thermoelectric signal generated in the thermoelectric conversion layer 202 to depend on the direction of the heat current H, i.e., non-reciprocity.

[0051] The thermoelectric signal J thus generated in the thermoelectric conversion layer 202 N becomes non-reciprocal with respect to the direction of the heat flow H due to the non-reciprocal conduction of the thermoelectric conversion layer 202 as described above (i.e., the thermoelectric signal J N changes nonlinearly with respect to the direction of heat flow H), and the thermoelectric signal J N The direction of the non-reciprocal thermoelectric signal J is the positive direction of the X-axis. N The inventors of the present application have found that the thermoelectric conversion element 200 according to this embodiment can extract a non-reciprocal thermoelectric signal J in a fixed direction in the thermoelectric conversion layer 202 even if the direction or magnitude of the heat flow H changes randomly. N Since it is possible to generate thermoelectric power from temperature fluctuations on a microscale,

[0052] In addition, the direction of the external magnetic field B is reversed to the positive direction of the Y axis, and the direction of the magnetization 203M of the ferromagnetic metal layer 203 is reversed to the positive direction of the Y axis, thereby generating a non-reciprocal thermoelectric signal J N The direction of can be inverted to the negative X-axis direction.

[0053] In the thermoelectric conversion layer 202, a non-reciprocal thermoelectric signal J is extracted by a pair of electrodes 207a and 207b. N is the magnitude of the voltage V, the electric field generated in the thermoelectric conversion layer 202 corresponding to V is E, the nonlinear Seebeck coefficient of the thermoelectric conversion layer 202 is S, the distance between the pair of electrodes 207a and 207b is L (D207 in FIG. 2), the temperature gradient in the range of the distance L in the thermoelectric conversion layer 202 is ∇T, and the temperature difference in the range of the distance L in the thermoelectric conversion layer 202 is ΔT, then the electric field E=nonlinear Seebeck coefficient S×(temperature gradient ∇T) 2 By multiplying both sides of this equation by the distance L, we obtain the voltage V = nonlinear Seebeck coefficient S × (temperature difference ΔT) 2 / L, the smaller the distance L between the pair of electrodes 207a, 207b, the larger the voltage V. Therefore, by setting the separation distance D207 between the pair of electrodes 207a, 207b in the X-axis direction to a small value, preferably 1000 μm or less, as described above, the non-reciprocal thermoelectric signal J extracted by the pair of electrodes 207a, 207b can be reduced. N becomes larger.

[0054] The thermoelectric conversion element 200 may also include a heat conductive portion that is provided in contact with or close to the end face on the positive side of the X-axis and / or the end face on the negative side of the X-axis, for facilitating the flow of heat flow H into the thermoelectric conversion layer 202. Such a heat conductive portion may be made of, for example, aluminum, copper, carbon fiber, sapphire, alumina, silicon with a thermal oxide film, or a polymer.

[0055] 4 is a perspective view showing the configuration of a thermoelectric conversion module using the above-mentioned thermoelectric conversion elements. As shown in FIG. 4, a thermoelectric conversion module 300 according to this embodiment includes a plurality of thermoelectric conversion elements 200, and in this embodiment, the thermoelectric conversion module 300 includes four thermoelectric conversion elements 200a, 200b, 200c, and 200d. The four thermoelectric conversion elements 200a, 200b, 200c, and 200d generate non-reciprocal thermoelectric signals J from the respective thermoelectric conversion elements. N are electrically connected to each other so as to be superimposed with the same polarity.

[0056] Specifically, in the thermoelectric conversion module 300, thermoelectric conversion elements 200a and 200c arranged with respect to the orthogonal coordinate system C in the same manner as the thermoelectric conversion element 200 shown in Figures 1 and 2, and thermoelectric conversion elements 200b and 200d arranged with respect to the orthogonal coordinate system C in a manner rotated 180 degrees around the Y axis from the thermoelectric conversion element 200 shown in Figures 1 and 2 are alternately provided along the Y axis direction. Then, the electrode 207a of the thermoelectric conversion element 200a and the electrode 207b of the thermoelectric conversion element 200b are electrically connected, the electrode 207a of the thermoelectric conversion element 200b and the electrode 207b of the thermoelectric conversion element 200c are electrically connected, and the electrode 207a of the thermoelectric conversion element 200c and the electrode 207b of the thermoelectric conversion element 200d are electrically connected. Also, instead of arranging the thermoelectric conversion elements 200b and 200d in a manner rotated 180 degrees around the Y axis, the thermoelectric conversion elements 200b and 200d may be arranged in the same manner as the thermoelectric conversion element 200 shown in Figures 1 and 2 with respect to the orthogonal coordinate system C, similarly to the thermoelectric conversion elements 200a and 200c, and the lamination order of the ferromagnetic metal layer 203 and the paramagnetic metal layer 205 of the thermoelectric conversion layer 202 in the thermoelectric conversion elements 200b and 200d may be reversed. In this case, the electrode 207a of the thermoelectric conversion element 200a and the electrode 207a of the thermoelectric conversion element 200b are electrically connected, the electrode 207b of the thermoelectric conversion element 200b and the electrode 207b of the thermoelectric conversion element 200c are electrically connected, and the electrode 207a of the thermoelectric conversion element 200c and the electrode 207a of the thermoelectric conversion element 200d are electrically connected.

[0057] Moreover, the ferromagnetic metal layers 203 of each of the four thermoelectric conversion elements 200a, 200b, 200c, and 200d are magnetized in the negative Y-axis direction by the external magnetic field B, and have magnetization 203M facing in the negative Y-axis direction.

[0058] The thermoelectric conversion module 300 also includes heat conductive parts 301 and 302 that are provided in contact with or in close proximity to the end faces on the negative side of the X-axis and the end faces on the positive side of the X-axis of the four thermoelectric conversion elements 200a, 200b, 200c, and 200d. This makes it easier for the heat flowing in the X-axis direction to flow into the ferromagnetic metal layers 203 of the four thermoelectric conversion elements 200a, 200b, 200c, and 200d. The thermoelectric conversion module 300 does not necessarily need to include the heat conductive parts 301 and 302.

[0059] When heat flow flows into the ferromagnetic metal layer 203 of each of the four thermoelectric conversion elements 200a, 200b, 200c, and 200d, the nonreciprocal thermoelectric signals generated in each thermoelectric conversion element 200 are superimposed with the same polarity and can then be extracted by electrode 207b of thermoelectric conversion element 200a and electrode 207a of thermoelectric conversion element 200d, making it possible to extract a large nonreciprocal thermoelectric signal.

[0060] (Example) Next, in order to clarify the effect of the invention according to the first embodiment, an example will be described. An element corresponding to the thermoelectric conversion element 200 was fabricated as follows. First, a Si substrate with a thermal oxide film having a thickness of 0.5 mm was prepared as the substrate 201, and a Ni-Fe alloy layer having a thickness of 5 nm as the ferromagnetic metal layer 203 and a Pt layer having a thickness of 5 nm as the paramagnetic metal layer 205 were deposited in this order on the substrate by DC magnetron sputtering to form the thermoelectric conversion layer 202. Then, the thermoelectric conversion layer 202 was patterned into a rectangular shape in plan view with a width of 5 μm in the Y-axis direction and a length of 50 μm in the X-axis direction by photolithography and lift-off. Thereafter, a Ti / Au layer was deposited on the thermoelectric conversion layer 202 by RF magnetron sputtering, and the Ti / Au layer was patterned into a predetermined shape by photolithography and lift-off to form a pair of electrodes corresponding to the pair of electrodes 207a, 207b, thereby producing an element corresponding to the thermoelectric conversion element 200.

[0061] Next, the element is subjected to step S12 of inputting a heat flow at room temperature (300K) and step S13 of performing thermoelectric conversion while applying an external magnetic field, and a non-reciprocal thermoelectric signal J is output from the pair of electrodes 207a and 207b. N Figure 5 shows the non-reciprocal thermoelectric signal J N 5 is a schematic diagram showing an experimental method for measuring the temperature of the thermoelectric conversion element 200. As shown in Fig. 5, a first resistive heater 210 was provided adjacent to an end of the element corresponding to the thermoelectric conversion element 200 in the negative direction of the X-axis, and a second resistive heater 211 was provided adjacent to an end of the element in the positive direction of the X-axis. A first power supply 220 and a second power supply 221 were electrically connected to the first resistive heater 210 and the second resistive heater 211, respectively. A lock-in amplifier 230 was electrically connected between a pair of electrodes 207a and 207b.

[0062] Then, while changing the magnitude of the external magnetic field B applied to the thermoelectric conversion element 200 in the negative direction of the Y axis from 5 mT to −5 mT in 0.1 mT intervals, an AC temperature gradient ΔT that changes sinusoidally with an angular frequency ω in the direction along the X axis is generated by the first resistance heater 210 and the second resistance heater 211 for the thermoelectric conversion element 200. AC Then, the AC temperature gradient ΔT AC ΔV is the y component of the change in the thermoelectric signal corresponding to twice the frequency of 2ω、y was detected by a lock-in amplifier 230.

[0063] AC temperature gradient ΔT AC More specifically, when ω is the angular frequency and t is time, the first power supply 220 supplies V to the first resistance heater 210. dc +V ac Apply an AC voltage of sin(ωt) and V dc -V ac An AC voltage of sin(ωt) was applied to the second resistance heater 211 by the second power supply 221. This caused a change in temperature ΔT AC =(√2)ΔT rms An AC temperature gradient expressed as sin(ωt) is applied (ΔTrms is the effective value of the AC temperature gradient). Therefore, the AC temperature gradient ΔT AC corresponds to a heat flow H containing a single AC component. A voltage source device WF1968 manufactured by NF Corporation was used as the first power supply 220 and the second power supply 221, and a lock-in amplifier LI5640 manufactured by NF Corporation was used as the lock-in amplifier 230. The frequency f (=ω / 2π) of the AC voltage applied by the first power supply 220 and the second power supply 221 was set to 13.723 Hz, and the above ΔT rms The above V ac The lock-in conditions of the lock-in amplifier 230 were set to low dynamic reserve, 500 nV measurement sensitivity, 1 second time constant, and -24 dB slope.

[0064] Figure 6 shows the thermoelectric signal ΔV obtained as a result of the above experiment. 2ω、y 1 is a graph showing the dependence of ΔT on the external magnetic field B applied to the thermoelectric conversion element 200. AC Since varies sinusoidally, no temperature gradient is substantially applied to the thermoelectric conversion element 200 on a macro scale, and ΔT AC corresponds to the temperature fluctuation on a micro scale. If the thermoelectric signal output from the thermoelectric conversion element 200 is an AC temperature gradient ΔT AC If the polarity of the AC temperature gradient ΔT AC The thermoelectric signal ΔV corresponds to twice the frequency of 2ω、y is the AC temperature gradient ΔT AC Since the thermoelectric signals corresponding to the positive and negative phases of the AC temperature gradient ΔT cancel each other out, the result is zero. On the other hand, the thermoelectric signal output from the thermoelectric conversion element 200 is AC When the polarity of the thermoelectric signal is nonlinear (non-reciprocal), the 2ω、y is a finite value.

[0065] In this experiment, as shown in Figure 6, when an external magnetic field B is applied, a finite value of ΔV 2ω、y is detected, and when the polarity of the external magnetic field B is reversed, ΔV 2ω、yThis indicates that the thermoelectric conversion element used in this experiment can generate a thermoelectric signal nonlinearly with respect to the direction of the temperature gradient, and therefore can perform thermoelectric conversion from temperature fluctuations on a microscale where a temperature gradient does not substantially exist on a macroscale.

[0066] The present invention is not limited to the above-described first embodiment, and various modifications are possible.

[0067] For example, in the first embodiment described above, the thermoelectric conversion element 200 includes the substrate 201 (see FIGS. 1 and 2), but the thermoelectric conversion element 200 does not necessarily need to include the substrate 201. In this case, the thermoelectric conversion layer 202 can be formed as a free-standing layer.

[0068] In the above-described first embodiment, the external magnetic field B is applied to the ferromagnetic metal layer 203 in a direction within the plane of the thermoelectric conversion element 200 (within the XY plane) and perpendicular to the direction of the flow of the heat flow H (see FIGS. 1 and 2), but it may be applied in a direction within the plane of the thermoelectric conversion element 200 (within the XY plane) and intersecting the direction of the flow of the heat flow H at an angle other than 90 degrees. However, the external magnetic field B and the heat flow H are set so as not to be parallel or anti-parallel to each other.

[0069] In the above-described first embodiment, thermoelectric conversion is performed while applying an external magnetic field B in step S13 (see FIGS. 1 and 2), but if the ferromagnetic metal layer 203 has magnetization 203M even without application of the external magnetic field B, thermoelectric conversion can be performed in step S13 without applying the external magnetic field B. Methods for achieving this include, for example, forming the ferromagnetic metal layer 203 from a material with a large coercive force so that the ferromagnetic metal layer 203 has magnetization 203M as residual magnetization, or providing the thermoelectric conversion element 200 with a layer or member that applies a static magnetic field or an exchange coupling magnetic field to the ferromagnetic metal layer 203. For example, the thermoelectric conversion element 200 may further include an antiferromagnetic layer such as NiO, IrMn, FeMn, NiMn, PtMn, PdMn, Mn2Au, FeRh, or MnSb laminated on the side of the ferromagnetic metal layer 203 opposite to the paramagnetic metal layer 205 so as to apply an exchange coupling magnetic field to the ferromagnetic metal layer 203. This makes it possible to perform thermoelectric conversion without applying an external magnetic field B.

[0070] In addition, in the above-described first embodiment, the pair of electrodes 207a, 207b are provided on the surface 205S of the paramagnetic metal layer 205 so as not to contact the ferromagnetic metal layer 203 and to be spaced apart from each other along the X-axis direction (see Figures 1 and 2), but they may also be provided on the side surfaces of the paramagnetic metal layer 205 in the positive and negative X-axis directions so as not to contact the ferromagnetic metal layer 203 and to be spaced apart from each other along the X-axis direction.

[0071] In the first embodiment described above, the ferromagnetic metal layer 203 is a single layer (see FIG. 1 and FIG. 2), but the ferromagnetic metal layer 203 may be composed of a plurality of stacked layers of ferromagnetic metals. In this case, each of the plurality of layers is preferably composed of a Ni-Fe alloy, Fe, Co, Ni, Gd, a CoFeB alloy, or a (Ga,Fe)Sb alloy. Such a plurality of stacked layers of ferromagnetic metals may be, for example, a stack in which layers made of a plurality of types of ferromagnetic metals are periodically stacked on one another (for example, a stack in which three types of layers are periodically stacked such as layer A, layer B, layer C, layer A, layer B, layer C, etc., when a layer made of a first ferromagnetic metal is layer A, a layer made of a second ferromagnetic metal is layer B, and a layer made of a third ferromagnetic metal is layer C), or a stack in which layers made of a plurality of types of ferromagnetic metals are randomly stacked on one another (for example, a stack in which three types of layers are randomly stacked such as layer A, layer B, layer C, layer B, layer A, layer C, etc.).

[0072] In the first embodiment described above, the paramagnetic metal layer 205 is a single layer (see FIG. 1 and FIG. 2), but the paramagnetic metal layer 205 may be composed of a plurality of layers of stacked paramagnetic metals. In this case, each of the plurality of layers is preferably composed of Pt, Pd, W, AuW alloy, Ta, CuIr alloy, CuBi alloy, BiSb alloy, or BiSe alloy. Such a plurality of layers of stacked paramagnetic metals may be, for example, a stack in which layers of a plurality of types of paramagnetic metals are periodically stacked on each other (for example, a stack in which three types of layers are periodically stacked such as layer D, layer E, layer F, layer D, layer E, layer F, etc., when a layer of a first paramagnetic metal is layer D, a layer of a second paramagnetic metal is layer E, and a layer of a third paramagnetic metal is layer F), or a stack in which layers of a plurality of types of paramagnetic metals are randomly stacked on each other (for example, a stack in which three types of layers are randomly stacked such as layer D, layer E, layer F, layer E, layer F, etc.). It is preferable that the laminated layers of paramagnetic metal have spin-Nernst angles of the same sign, because this prevents the nonreciprocal thermoelectric signals resulting from the respective layers of paramagnetic metal from cancelling each other out during thermoelectric conversion in the thermoelectric conversion layer 202, thereby increasing the nonreciprocal thermoelectric signal as a whole.

[0073] In the first embodiment described above, the thermoelectric conversion layer 202 includes only one paramagnetic metal layer (paramagnetic metal layer 205) (see FIG. 1 and FIG. 2), but the thermoelectric conversion layer 202 may include a first paramagnetic metal layer and a second paramagnetic metal layer. In this case, the first paramagnetic metal layer, the ferromagnetic metal layer 203, and the second paramagnetic metal layer are laminated in this order along the Z-axis direction so that the ferromagnetic metal layer 203 is interposed between the first paramagnetic metal layer and the second paramagnetic metal layer, thereby forming the thermoelectric conversion layer 202. The preferred materials for the first paramagnetic metal layer and the second paramagnetic metal layer are the same as those for the paramagnetic metal layer 205, but the configurations (materials, film thickness, etc.) of the first paramagnetic metal layer and the second paramagnetic metal layer are selected so that the thermoelectric conversion layer 202 has a structure in which the spatial inversion symmetry is broken along the Z-axis direction.

[0074] In this case, it is preferable that the first paramagnetic metal layer and the second paramagnetic metal layer have spin Nernst angles of opposite signs to each other. (For example, this can be achieved by forming the first paramagnetic metal layer from Pt and the second paramagnetic metal layer from Ta.) This is because, during thermoelectric conversion in the thermoelectric conversion layer 202, spin currents having the same polarity are injected from the first paramagnetic metal layer and the second paramagnetic metal layer to the ferromagnetic metal layer 203, respectively, and the nonreciprocal thermoelectric signal can be increased.

[0075] Furthermore, in this case, each or either of the first and second paramagnetic metal layers may be composed of a plurality of paramagnetic metal layers stacked as described above. In this case, it is preferable that the plurality of paramagnetic metal layers constituting each or either of the first and second paramagnetic metal layers have spin-Nernst angles of the same sign as each other for the reasons described above.

[0076] In addition, in the above-described first embodiment, the pair of electrodes 207a, 207b are provided on the surface 205S of the paramagnetic metal layer 205 (see Figures 1 and 2), but the pair of electrodes 207a, 207b may also be provided on the back surface (the surface on the negative side of the Z-axis) of the ferromagnetic metal layer 203 so as not to be in contact with the paramagnetic metal layer 205 and to be spaced apart from each other along the X-axis direction.

[0077] In the above-described first embodiment, the ferromagnetic metal layer 203 and the paramagnetic metal layer 205 are laminated in this order on the substrate 201 to form the thermoelectric conversion layer 202 (see FIGS. 1 and 2), but the thermoelectric conversion layer 202 may be formed by laminating the paramagnetic metal layer 205 and the ferromagnetic metal layer 203 in this order on the substrate 201. In this case, the pair of electrodes 207a, 207b can be provided on the front surface (the surface on the positive side of the Z-axis) of the ferromagnetic metal layer 203 or the back surface (the surface on the negative side of the Z-axis) of the paramagnetic metal layer 205 so as to be spaced apart from each other along the X-axis direction.

[0078] The thermoelectric conversion element, the thermoelectric conversion module, and the thermoelectric conversion method according to the present disclosure have the following configurations. [1] A thermoelectric conversion unit having a nonlinear thermoelectric response characteristic with respect to an input of a heat flow along a first direction; an electrode portion for extracting a thermoelectric signal generated in the thermoelectric conversion portion due to a heat flow input from an outside to the thermoelectric conversion portion along the first direction; A thermoelectric conversion element comprising: [2] The thermoelectric conversion unit exhibits nonreciprocal conduction based on the breaking of spatial inversion symmetry, The thermoelectric conversion element according to [1], comprising, as the electrode portion, a pair of electrodes spaced apart from each other on the thermoelectric conversion portion for extracting a non-reciprocal thermoelectric signal. [3] The thermoelectric conversion section is a thermoelectric conversion layer including a ferromagnetic metal layer and a paramagnetic metal layer stacked on each other along a second direction perpendicular to the first direction, The thermoelectric conversion element according to [2], wherein the pair of electrodes are provided on the thermoelectric conversion layer in an in-plane direction of the thermoelectric conversion layer along the first direction and spaced apart from each other. [4] The thermoelectric conversion element according to [2] or [3], wherein the distance between the pair of electrodes is 0.1 μm or more and 1000 μm or less. [5] The thermoelectric conversion element according to [3] or [4], wherein the paramagnetic metal layer is composed of a single layer or a plurality of laminated layers, and each of the single layer or the plurality of laminated layers of the paramagnetic metal layer is composed of Pt, Pd, W, an AuW alloy, Ta, a CuIr alloy, a CuBi alloy, a BiSb alloy, or a BiSe alloy. [6] A thermoelectric conversion element according to any one of [3] to [5], wherein the ferromagnetic metal layer is composed of a single layer or multiple laminated layers, and each of the single layer or the multiple laminated layers of the ferromagnetic metal layer is composed of a Ni-Fe alloy, Fe, Co, Ni, Gd, a CoFeB alloy, or a (Ga,Fe)Sb alloy. [7] A thermoelectric conversion module comprising a plurality of thermoelectric conversion elements according to any one of [1] to [6], the thermoelectric conversion elements being electrically connected to each other so that thermoelectric signals from each thermoelectric conversion element can be superimposed with the same polarity. [8] A process for preparing a thermoelectric conversion element including a thermoelectric conversion layer exhibiting nonreciprocal conduction based on the breaking of spatial inversion symmetry, and a pair of electrodes spaced apart from each other on the thermoelectric conversion layer for extracting a nonreciprocal thermoelectric signal, the thermoelectric conversion layer including a ferromagnetic metal layer and a paramagnetic metal layer stacked on each other, and the pair of electrodes spaced apart from each other on the thermoelectric conversion layer in an in-plane direction of the thermoelectric conversion layer; performing thermoelectric conversion while applying a magnetic field of 1 T or less to the ferromagnetic metal layer of the thermoelectric conversion layer; The thermoelectric conversion method includes the steps of: [9] A thermoelectric layer that exhibits nonreciprocal conductivity based on the breaking of spatial inversion symmetry. A pair of electrodes for extracting a non-reciprocal thermoelectric signal, the electrodes being spaced apart from each other on the thermoelectric conversion layer; A thermoelectric conversion element comprising: the thermoelectric conversion layer includes a paramagnetic metal layer and a ferromagnetic metal layer stacked on top of each other, A thermoelectric conversion element in which the pair of electrodes are provided on the paramagnetic metal layer at a distance from each other in the in-plane direction of the paramagnetic metal layer (excluding thermoelectric conversion elements having a layer made of an electrically insulating magnetic material provided in contact with a ferromagnetic metal layer).

[10] A step of applying a temperature gradient including an AC component to a thermoelectric conversion unit exhibiting nonreciprocal conduction based on the breaking of spatial inversion symmetry; The thermoelectric conversion unit converts the temperature gradient including the AC component into a thermoelectric signal based on nonreciprocal conduction due to the breaking of spatial inversion symmetry, and generates a nonreciprocal thermoelectric signal. The thermoelectric conversion method includes the steps of:

[11] A thermoelectric conversion method using a thermoelectric conversion unit including a first layer and a second layer, applying a temperature gradient including an AC component to the thermoelectric conversion unit; a step in which the first layer performs thermoelectric conversion on the temperature gradient including the AC component to generate a non-reciprocal thermoelectric signal based on the fact that electron scattering of the spin current flowing in differs depending on the polarity direction of the spin current; The thermoelectric conversion method includes the steps of:

[12] A thermoelectric conversion unit; a first thermal conductive portion provided at one end of the thermoelectric conversion portion in a first direction; a second thermal conductive portion provided at the other end of the thermoelectric conversion portion in the first direction; A pair of electrodes provided on the thermoelectric conversion unit and spaced apart from each other in the first direction; Equipped with A thermoelectric conversion element in which, when a temperature gradient including an AC component is applied between the first thermal conductive portion and the second thermal conductive portion, a DC electrical signal is generated in the thermoelectric conversion portion, and the DC electrical signal can be extracted by the pair of electrodes.

[13] A thermoelectric conversion module including at least a first thermoelectric conversion element and a second thermoelectric conversion element, The first thermoelectric conversion element and the second thermoelectric conversion element each include a thermoelectric conversion unit and a pair of electrodes provided spaced apart from each other on the thermoelectric conversion unit for extracting a non-reciprocal thermoelectric signal; a thermoelectric conversion module, wherein one of the pair of electrodes of the first thermoelectric conversion element and one of the pair of electrodes of the second thermoelectric conversion element are electrically connected to each other such that the non-reciprocal thermoelectric signal from the first thermoelectric conversion element and the non-reciprocal thermoelectric signal from the second thermoelectric conversion element can be superimposed with the same polarity.

[14] A thermoelectric conversion module including at least a first thermoelectric conversion element and a second thermoelectric conversion element, a first thermal conductive portion provided at one end in a first direction of the first thermoelectric conversion element and the second thermoelectric conversion element; a second thermal conductive portion provided at the other end of the first thermoelectric conversion element and the second thermoelectric conversion element in the first direction; A thermoelectric conversion module comprising:

[15] A thermoelectric conversion module according to

[13] or

[14] for converting an applied temperature gradient containing an AC component into a DC electrical signal.

[16] A thermoelectric conversion module including at least a first thermoelectric conversion element and a second thermoelectric conversion element, The first thermoelectric conversion element and the second thermoelectric conversion element each include a thermoelectric conversion unit and a pair of electrodes provided spaced apart from each other on the thermoelectric conversion unit for extracting a non-reciprocal thermoelectric signal; A thermoelectric conversion module in which a surface on which one of the pair of electrodes of the first thermoelectric conversion element is provided and a surface on which one of the pair of electrodes of the second thermoelectric conversion element is provided overlap in an area including the edges of the first thermoelectric conversion element and the second thermoelectric conversion element, thereby electrically connecting the one of the pair of electrodes of the first thermoelectric conversion element and the one of the pair of electrodes of the second thermoelectric conversion element.

[0079] Second embodiment FIG. 7 is a perspective view showing the fluctuation detection sensor according to the second embodiment, and FIG. 8 is a cross-sectional view of the fluctuation detection sensor according to the second embodiment.

[0080] As shown in FIGS. 7 and 8, a fluctuation detection sensor 400 according to this embodiment includes a substrate 401, a nonlinear response layer 402 as a nonlinear response section, and a pair of electrodes 407a, 407b as an electrode section.

[0081] The substrate 401 is a plate-like or film-like member as shown in Fig. 7, for example, and has a substantially flat surface 401S. The surface 401S is rectangular as viewed from the Z-axis direction as shown in Fig. 7, for example. The substrate 401 is a member for laminating a nonlinear response layer 402 on the surface 401S. Examples of materials constituting the substrate 401 include metals such as Au, Ag, Cu, and Al, silicon, sapphire, SiC, GaN, yttria-stabilized zirconia (YSZ), and resins such as polyimide, polyethylene terephthalate (PET), and polyethylene naphthalate (PEN).

[0082] 7 and 8 show an orthogonal coordinate system C, in which the Z axis is set in the thickness direction of substrate 401, and the X axis and Y axis are set in the long side direction and short side direction, respectively, of the rectangle of surface 401S of substrate 401. In the subsequent figures, the orthogonal coordinate system C is also shown as necessary.

[0083] The nonlinear response layer 402 has a nonlinear electric response characteristic to the input of external energy along the X-axis direction, which is the first direction. The external energy is, for example, an electric current and / or a heat flow. In this embodiment, the nonlinear response layer 402 includes a ferromagnetic layer 403 and a paramagnetic layer 405 stacked on each other along the Z-axis direction, which is the second direction, and the ferromagnetic layer 403 is stacked on the substrate 401, and the paramagnetic layer 405 is stacked on the ferromagnetic layer 403. The ferromagnetic layer 403 is made of a material that exhibits ferromagnetism at a temperature in the environment in which the fluctuation detection sensor 400 is used, and is preferably made of a material that exhibits ferromagnetism at room temperature (300K). In this embodiment, the ferromagnetic layer 403 is made of a hard magnetic material and may have spontaneous magnetization 403M. In addition, the ferromagnetic layer 403 preferably has a high coercive force, for example, a coercive force of 50 mT or more.

[0084] Moreover, the ferromagnetic layer 403 is preferably a ferromagnetic metal layer. The ferromagnetic metal layer is preferably made of an L10 ordered alloy consisting of a magnetic metal exhibiting ferromagnetism at room temperature (300K) and a paramagnetic metal exhibiting paramagnetism. The magnetic metal is preferably made of at least one of iron, nickel, cobalt, gadolinium, dysprosium, and terbium, and the paramagnetic metal is preferably made of Pt, Pd, W, an AuW alloy, Ta, a CuIr alloy, a CuBi alloy, a BiSb alloy, or a BiSe alloy. By making the ferromagnetic layer 403 of such an L10 ordered alloy, the ferromagnetic layer 403 can have a particularly large coercive force, and therefore the energy conversion of current fluctuations and / or heat flow fluctuations by the fluctuation detection sensor 400 described later can be efficiently performed at room temperature and in a magnetic field-free environment.

[0085] The nonlinear response layer 402 is, for example, rectangular in plan view (i.e., when viewed from the Z-axis direction) with a long side along the X-axis direction and a short side along the Y-axis direction. The thickness of the ferromagnetic layer 403 is not particularly limited, but can be, for example, 1 nm or more and 100 nm or less.

[0086] The paramagnetic layer 405 is made of a material that exhibits paramagnetism at the temperature in the environment in which the fluctuation detection sensor 400 is used, and is preferably made of a material that exhibits paramagnetism at room temperature (300K). The paramagnetic layer 405 is preferably a paramagnetic metal layer. The paramagnetic metal layer is preferably made of a paramagnetic metal with high spin-orbit interaction in order to increase the spin-Nernst effect and spin-Hall effect inside the paramagnetic metal layer as described below, and from this viewpoint, it is preferably made of Pt, Pd, W, AuW alloy, Ta, CuIr alloy, CuBi alloy, BiSb alloy, or BiSe alloy, and is particularly preferably made of Pt. The thickness of the paramagnetic layer 405 is not particularly limited, but can be, for example, 1 nm or more and 100 nm or less.

[0087] In this embodiment, the nonlinear response layer 402 exhibits nonreciprocal conduction based on the breaking of spatial inversion symmetry. Specifically, a paramagnetic layer is provided on the surface of the ferromagnetic layer 403, but a similar paramagnetic layer is not provided on the back surface of the ferromagnetic layer 403, and a ferromagnetic layer is provided on the back surface of the paramagnetic layer 405, but a similar ferromagnetic layer is not provided on the surface of the paramagnetic layer 405. Therefore, the nonlinear response layer 402 has a structure in which spatial inversion symmetry is broken along the Z-axis direction. The nonlinear response layer 402 has substantial spatial inversion symmetry in the direction along the XY plane. The nonlinear response layer 402 of this embodiment exhibits nonreciprocity in terms of electrical conductivity in the in-plane (XY plane) direction due to the breaking of spatial inversion symmetry along the Z-axis direction.

[0088] The pair of electrodes 407a, 407b are provided on the nonlinear response layer 402 and spaced apart from each other in the in-plane (XY plane) direction of the nonlinear response layer 402. In this embodiment, the pair of electrodes 407a, 407b are provided on the paramagnetic layer 405 so as not to contact the ferromagnetic layer 403, and are provided on a surface 405S of the paramagnetic layer 405 opposite the ferromagnetic layer 403. The pair of electrodes 407a, 407b are spaced apart from each other along the X-axis direction, which is one of the in-plane (XY plane) directions of the paramagnetic layer 405.

[0089] The pair of electrodes 407a, 407b are made of a material having a conductivity capable of extracting a non-reciprocal voltage signal from the nonlinear response layer 402 as described below. Examples of such materials include metal materials such as Cu, Ag, Au, Pt, Ni, Al, constantan, Cr, In, Pd, Fe, Cu alloy, Ti / Au laminate, and Cr / Au laminate, and conductive oxides such as indium tin oxide (ITO) and zinc oxide (ZnO). Cu, Ag, Au, Pt, Ni, Al, constantan, and Cu copper alloy are preferred, and Cu, Au, Ag, Pt, Ni, Ti / Au laminate, and Cr / Au laminate are particularly preferred.

[0090] The thickness of the pair of electrodes 407a, 407b is not particularly limited, but may be, for example, 10 nm or more and 1 μm or less. The separation distance D407 between the pair of electrodes 407a, 407b along the X-axis direction is preferably 0.1 μm or more and 1000 μm or less.

[0091] Furthermore, the fluctuation detection sensor 400 of this embodiment may further include a layer made of an electrically insulating magnetic material provided so as to be in contact with the ferromagnetic layer 403, or may not include such a layer.

[0092] When manufacturing such a fluctuation detection sensor 400, for example, a substrate 401 is prepared, a material for forming the ferromagnetic layer 403 and a material for forming the paramagnetic layer 405 are deposited in this order on the surface 401S of the substrate 401 by physical vapor deposition such as DC magnetron sputtering to form a laminate, and the laminate is patterned into a rectangular shape in a plan view by photolithography and lift-off to form the nonlinear response layer 402. Thereafter, a metal material for forming the pair of electrodes 407a, 407b is deposited in an area including the surface 405S of the paramagnetic layer 405 by physical vapor deposition such as DC magnetron sputtering to form a metal layer, and the metal layer is patterned into a predetermined shape by photolithography and lift-off to form the pair of electrodes 407a, 407b.

[0093] Next, the energy conversion method according to this embodiment will be described. Fig. 9 is a process diagram showing the steps of the energy conversion method according to this embodiment. As shown in Fig. 9, the energy conversion method according to this embodiment includes a step S11 of preparing a fluctuation detection sensor having a nonlinear response layer, a step S12 of inputting a current fluctuation or a heat flow fluctuation to the nonlinear response layer, and a step S13 of performing energy conversion of the current fluctuation or the heat flow fluctuation. These steps will be described again with reference to Figs. 7 and 8.

[0094] In step S11 of preparing a fluctuation detection sensor having a nonlinear response layer, the above-mentioned fluctuation detection sensor 400 is prepared as shown in Figures 7 and 8. Next, in step S12 of inputting current fluctuations or heat flow fluctuations to the nonlinear response layer, current fluctuations Jf or heat flow fluctuations Hf from the outside, which are the subject of energy conversion, are input to the nonlinear response layer 402 in a state in which the ferromagnetic layer 403 has spontaneous magnetization 403M, so as to flow along the X-axis direction, which is one of the in-plane directions (XY plane) of the nonlinear response layer 402.

[0095] In this specification, "current fluctuation" refers to a phenomenon in which current fluctuates over time and space, specifically, a situation in which a current in a certain direction (e.g., the X-axis direction) and a current in the opposite direction (e.g., the -X-axis direction) overlap with each other, causing the direction of the net current to fluctuate over time and space. "Heat flow fluctuation" refers to a phenomenon in which heat flow fluctuates over time and space, specifically, a situation in which a heat flow in a certain direction (e.g., the X-axis direction) and a heat flow in the opposite direction (e.g., the -X-axis direction) overlap with each other, causing the direction of the net heat flow to fluctuate over time and space.

[0096] In step S12, when a current fluctuation Jf is input to the paramagnetic layer 405, a spin current J S1 is generated along the Z-axis direction, and when the heat flow fluctuation Hf is input to the paramagnetic layer 405, the spin current J S1 is generated along the Z axis.

[0097] In step S13, which converts the energy of the current fluctuation or the heat current fluctuation, the spin current J generated as described above is S1 flows into the ferromagnetic layer 403 having the spontaneous magnetization 403M. S1 The polarity of changes to the positive or negative Y-axis direction depending on the direction of the current caused by the current fluctuation Jf (i.e., the net current direction of the current fluctuation Jf at a certain time and place) or the direction of the heat flow caused by the heat flow fluctuation Hf (i.e., the net heat flow direction of the heat flow fluctuation Hf at a certain time and place). Therefore, when the direction of the current or heat flow is reversed, the spin current J S1The polarity of the spin current J S1 The relative orientation between the polarity of the magnetization 403M of the ferromagnetic layer 403 and the direction of the spontaneous magnetization 403M of the ferromagnetic layer 403 is reversed. In addition, by reversing the direction of the spontaneous magnetization 403M of the ferromagnetic layer 403, the spin current J S1 It is also possible to reverse the relative orientation of the polarity of and the direction of the spontaneous magnetization 403M.

[0098] Spin current J S1 flows into the ferromagnetic layer 403, the spin current J S1 The manner of electron scattering changes depending on the relative orientation of the polarity of the ferromagnetic layer 403 and the spontaneous magnetization 403M of the ferromagnetic layer 403. S1 Since the polarity direction of changes depending on the direction of the electric current or heat flow, the mode of the electron scattering changes depending on the direction of the electric current or heat flow. This causes the voltage signal as the electric response signal generated in the nonlinear response layer 402 to depend on the direction of the electric current or heat flow, i.e., nonreciprocity.

[0099] In this way, the voltage conversion signal J as an electrical response signal generated in the nonlinear response layer 402 N1 is non-reciprocal with respect to the direction of the electric current or heat flow due to the non-reciprocal conduction of the non-linear response layer 402 as described above (i.e., the voltage conversion signal J N1 (changes in proportion to the quadratic of the current fluctuation Jf or heat flow fluctuation Hf), and the voltage conversion signal J N1 The direction of the non-reciprocal voltage conversion signal J is the positive direction of the X-axis. N1 The inventors of the present application have found that the non-reciprocal voltage signal J can be electrically extracted via a pair of electrodes 407a, 407b. Therefore, according to the fluctuation detection sensor 400 of this embodiment, even if the direction or magnitude of the current caused by the current fluctuation Jf or the upper heat flow caused by the heat flow fluctuation Hf changes randomly, the non-reciprocal voltage signal J can be generated in a fixed direction in the non-linear response layer 402. N1 Since it is possible to generate a current fluctuation Jf or a heat flow fluctuation Hf on a micro-scale, it becomes possible to detect energy fluctuations from the current fluctuation Jf or the heat flow fluctuation Hf.

[0100] When a current fluctuation Jf is input to the nonlinear response layer 402, a nonreciprocal voltage signal J is extracted by a pair of electrodes 407a and 407b in the nonlinear response layer 402. N1 The magnitude of the voltage is V, the electric field generated in the nonlinear response layer 402 corresponding to V is E, the distance between the pair of electrodes 407a and 407b is L (D407 in FIG. 8), and the current density in the range of the distance L in the nonlinear response layer 402 is j. Then, the electric field E=nonlinear electric transport coefficient γ×electric resistivity ρ×(current density j) 2 By multiplying both sides of this equation by the distance L, the voltage V = L × γ × ρ × j 2 Therefore, the greater the distance L between the pair of electrodes 407a, 407b, the greater the voltage V. Therefore, by setting the separation distance D407 between the pair of electrodes 407a, 407b in the X-axis direction to a large value, preferably 1000 μm or more, as described above, the non-reciprocal voltage signal J taken out by the pair of electrodes 407a, 407b can be reduced. N1 becomes larger.

[0101] Similarly, when a heat flow fluctuation Hf is input to the nonlinear response layer 402, a nonreciprocal voltage signal J is extracted by a pair of electrodes 407a and 407b in the nonlinear response layer 402. N1 is the magnitude of the voltage V, the electric field generated in the nonlinear response layer 402 corresponding to V is E, the nonlinear Seebeck coefficient of the nonlinear response layer 402 is S, the distance between the pair of electrodes 407a and 407b is L (D407 in FIG. 8), the temperature gradient in the range of the distance L in the nonlinear response layer 402 is ∇T, and the temperature difference in the range of the distance L in the nonlinear response layer 402 is ΔT, then, electric field E=nonlinear Seebeck coefficient S×(temperature gradient ∇T) 2 By multiplying both sides of this equation by the distance L, we obtain the voltage V = nonlinear Seebeck coefficient S × (temperature difference ΔT) 2 / L, the smaller the distance L between the pair of electrodes 407a, 407b, the larger the voltage V. Therefore, by setting the separation distance D407 between the pair of electrodes 407a, 407b in the X-axis direction to a small value, preferably 1000 μm or less, as described above, the non-reciprocal voltage signal J extracted by the pair of electrodes 407a, 407b can be reduced.N1 becomes larger.

[0102] The fluctuation detection sensor 400 may also include a heat conductive portion provided in contact with or adjacent to the end face on the positive side of the X-axis and / or the end face on the negative side of the X-axis, for facilitating the flow of the current fluctuation Jf or the heat flow fluctuation Hf into the nonlinear response layer 402. Such a heat conductive portion may be made of, for example, aluminum, copper, carbon fiber, sapphire, alumina, silicon with a thermal oxide film, or a polymer.

[0103] 10 is a perspective view showing the configuration of a fluctuation detection sensor module using the fluctuation detection sensor described above. As shown in FIG. 10, the fluctuation detection sensor module 500 according to this embodiment includes a plurality of fluctuation detection sensors 400, and in this embodiment, the fluctuation detection sensor module 500 includes four fluctuation detection sensors 400a, 400b, 400c, and 400d. The four fluctuation detection sensors 400a, 400b, 400c, and 400d receive non-reciprocal voltage signals J from the respective nonlinear electron transport voltage conversion elements. N1 are electrically connected to each other so as to be superimposed with the same polarity.

[0104] Specifically, in the fluctuation detection sensor module 500, fluctuation detection sensors 400a and 400c arranged with respect to the Cartesian coordinate system C in the same manner as the fluctuation detection sensor 400 shown in Figures 7 and 8, and fluctuation detection sensors 400b and 400d arranged with respect to the Cartesian coordinate system C in a manner rotated 180 degrees around the Y axis from the fluctuation detection sensor 400 shown in Figures 7 and 8, are alternately provided along the Y axis direction. Then, the electrode 407a of the fluctuation detection sensor 400a and the electrode 407b of the fluctuation detection sensor 400b are electrically connected, the electrode 407a of the fluctuation detection sensor 400b and the electrode 407b of the fluctuation detection sensor 400c are electrically connected, and the electrode 407a of the fluctuation detection sensor 400c and the electrode 407b of the fluctuation detection sensor 400d are electrically connected. Also, instead of arranging the fluctuation detection sensors 400b and 400d in a manner rotated 180 degrees around the Y axis, the fluctuation detection sensors 400b and 400d may be arranged in the same manner as the fluctuation detection sensor 400 shown in Figures 7 and 8 with respect to the Cartesian coordinate system C, similar to the fluctuation detection sensors 400a and 400c, and the stacking order of the ferromagnetic layer 403 and the paramagnetic layer 405 of the nonlinear response layer 402 may be reversed in the fluctuation detection sensors 400b and 400d. In this case, the electrode 407a of the fluctuation detection sensor 400a is electrically connected to the electrode 407a of the fluctuation detection sensor 400b, the electrode 407b of the fluctuation detection sensor 400b is electrically connected to the electrode 407b of the fluctuation detection sensor 400c, and the electrode 407a of the fluctuation detection sensor 400c is electrically connected to the electrode 407a of the fluctuation detection sensor 400d.

[0105] The fluctuation detection sensor module 500 also includes heat conductive parts 501 and 502 provided in contact with or in close proximity to the end faces on the negative side of the X-axis and the end faces on the positive side of the X-axis of the four fluctuation detection sensors 400a, 400b, 400c, and 400d. This makes it easier for the heat flow in the X-axis direction to flow into the ferromagnetic layers 403 of the four fluctuation detection sensors 400a, 400b, 400c, and 400d. The fluctuation detection sensor module 500 does not need to include the heat conductive parts 501 and 502.

[0106] The current fluctuation or heat flow fluctuation flows into the ferromagnetic layer 403 of each of the four fluctuation detection sensors 400a, 400b, 400c, and 400d, and the non-reciprocal voltage signal generated in each fluctuation detection sensor 400 is superimposed with the same polarity and then can be extracted by the electrode 407b of the fluctuation detection sensor 400a and the electrode 407a of the fluctuation detection sensor 400d, so that it is possible to extract a large non-reciprocal voltage signal. The fluctuation detection sensor module 500 can also be provided with more fluctuation detection sensors 400, in which case it is possible to extract a larger non-reciprocal voltage signal.

[0107] (Example 3: Input of current fluctuation) Next, to clarify the effect of the invention according to the second embodiment, examples 3 and 4 will be used for explanation. As example 3, an element corresponding to the fluctuation detection sensor 400 was fabricated as follows, corresponding to step S11 of preparing a fluctuation detection sensor having a nonlinear response layer. First, a magnesium oxide substrate having a thickness of 0.5 mm and a (111) orientation was prepared as the substrate 401, and a ferromagnetic layer 403 was formed on this substrate by co-sputtering at DC 37 W and Pt at RF 109 W and 0.046 nm / s using DC and RF magnetron sputtering methods, forming a CoPt alloy layer, which is an L10 type ordered alloy, having a thickness of 7.5 nm. Furthermore, a Pt layer having a thickness of 7.5 nm was deposited as the paramagnetic layer 405 on this CoPt alloy layer, forming the nonlinear response layer 402. Then, the nonlinear response layer 402 was patterned by photolithography and lift-off into a Hall element shape in plan view, that is, into a shape having a rectangular portion with a width of 10 μm in the Y-axis direction and a length of 40 μm in the X-axis direction in plan view, and two protrusions protruding from both ends of the rectangular portion in the Y-axis direction. Then, a Ti / Au layer was deposited on the nonlinear response layer 402 by RF magnetron sputtering, and the Ti / Au layer was patterned into a predetermined shape by photolithography and lift-off to form a pair of electrodes corresponding to the pair of electrodes 407a and 407b on the protrusions and a pair of electrodes 408a and 408b for an AC power source 418 described later on both ends of the rectangular portion in the X-axis direction, thereby fabricating an element corresponding to the fluctuation detection sensor 400.

[0108] Next, for the element thus created, an experiment was carried out corresponding to step S12 of inputting current fluctuations or heat flow fluctuations to the nonlinear response layer and step S13 of converting the energy of the current fluctuations or heat flow fluctuations. Specifically, a current fluctuation was input to the element at room temperature (300K) in a manner corresponding to step S12, and a non-reciprocal voltage signal J was output from the pair of electrodes 407a and 407b. N1 Figure 11 shows the non-reciprocal voltage signal J N111 is a schematic diagram showing an experimental method for measuring the fluctuation. As shown in Fig. 11, an AC power supply 418 was electrically connected between a pair of electrodes 408a, 408b provided on the fluctuation detection sensor 400. In addition, a lock-in amplifier 430 was electrically connected between the pair of electrodes 407a, 407b.

[0109] Then, while changing the magnitude of the external magnetic field B applied to the fluctuation detection sensor of Example 3 in the negative Y-axis direction from 2T to -2T, an AC current that changes sinusoidally with an angular frequency ω in the direction along the X-axis was applied. Then, ΔV 2ω、y was detected by a lock-in amplifier 430.

[0110] More specifically, when ω is the angular frequency and t is time, the AC power source 418 supplies I AC =(√2)I rms An alternating current expressed as sin(ωt) was applied (I rms (I means the effective value of AC current). rms When the current is 0.01mA, I rms Experiments were performed for each of the cases where the current was 2.77 mA. A 6221-type AC / DC current source manufactured by Tektronix, Inc. in the United States was used as the AC power supply 418, and a lock-in amplifier LI5640 manufactured by NF Corporation was used as the lock-in amplifier 430. The frequency f (=ω / 2π) of the AC voltage applied by the AC power supply 418 was set to 13.423 Hz. The lock-in conditions of the lock-in amplifier 430 were a time constant of 1 second and a slope of -24 dB.

[0111] FIG. 12 shows the voltage signal ΔV obtained as a result of the above experiment of Example 3. 2ω、y FIG. 11 is a graph showing the dependence of the external magnetic field B on I applied to the fluctuation detection sensor of Example 3. AC Since varies sinusoidally, the time average of the current flowing through the fluctuation detection sensor of Example 3 is zero (i.e., AC >=0) and I​AC corresponds to the current fluctuation Jf on a microscale. If the voltage signal output from the fluctuation detection sensor of the third embodiment is an AC current I AC If the polarity of the AC current I AC The voltage signal ΔV corresponding to twice the frequency of 2ω、y is the AC current I AC Since the voltage signals corresponding to the positive and negative phases of the AC current I cancel each other out, the voltage signal output from the fluctuation detection sensor in Example 3 is zero. AC When the polarity of the voltage signal ΔV 2ω、y is a finite value.

[0112] In this experiment, as shown in FIG. rms is 2.77mA, when an external magnetic field B is applied, a finite value of ΔV 2ω、y is detected, and when the polarity of the external magnetic field B is reversed, ΔV 2ω、y The polarity of the voltage signal ΔV was also reversed with respect to the application of the external magnetic field B, as shown by the arrow in FIG. 2ω、y has hysteresis, and the voltage signal ΔV 2ω、y It was revealed that the fluctuation detection sensor of Example 3 can generate a voltage signal non-reciprocally with respect to the direction of the current, and therefore it is possible to convert energy from the current fluctuation Jf to a non-reciprocal voltage signal even when the time average of the current is zero, and even when no external magnetic field is applied.

[0113] (Example 4: Input of heat flow fluctuation) Next, an experiment was carried out for Example 4. As Example 4, an element corresponding to the fluctuation detection sensor 400 was produced as follows, so as to correspond to step S11 of preparing a fluctuation detection sensor having a nonlinear response layer. First, a magnesium oxide substrate having a thickness of 0.5 mm and a (111) orientation was prepared as the substrate 401, and on this substrate, a ferromagnetic layer 403 was co-sputtered by DC 37 W and Pt by RF 109 W at 0.046 nm / s to form a CoPt alloy layer, which is an L10 type ordered alloy, having a thickness of 7.5 nm. Furthermore, a Pt layer having a thickness of 5 nm was deposited as the paramagnetic layer 405 on this CoPt alloy layer to form the nonlinear response layer 402. After that, the nonlinear response layer 402 was patterned by photolithography and lift-off into a rectangular shape in plan view with a width in the Y-axis direction of 7.5 μm and a length in the X-axis direction of 60 μm. Thereafter, a Ti / Au layer was deposited on the nonlinear response layer 402 by RF magnetron sputtering, and the Ti / Au layer was patterned into a predetermined shape by photolithography and lift-off to form a pair of electrodes corresponding to the pair of electrodes 407a, 407b, thereby producing an element corresponding to the fluctuation detection sensor 400.

[0114] Next, for the element thus created, an experiment was carried out corresponding to step S12 of inputting current fluctuations or heat flow fluctuations to the nonlinear response layer and step S13 of converting the energy of the current fluctuations or heat flow fluctuations. Specifically, a heat flow fluctuation Hf was input to the element at room temperature (300K) in step S12, and a non-reciprocal voltage signal J was output from the pair of electrodes 407a and 407b. N1 An experiment was conducted to measure the fluctuation. As shown in Fig. 13, a first resistive heater 410 was provided adjacent to an end of an element corresponding to the fluctuation detection sensor 400 of Example 4 in the negative direction of the X-axis, and a second resistive heater 411 was provided adjacent to an end of the element in the positive direction of the X-axis. A first power supply 420 and a second power supply 421 were electrically connected to the first resistive heater 410 and the second resistive heater 411, respectively. A lock-in amplifier 430 was also electrically connected between a pair of electrodes 407a and 407b.

[0115] Then, while changing the magnitude of the external magnetic field B applied to the fluctuation detection sensor of Example 4 in the negative Y-axis direction from 2 T to -2 T, the first resistance heater 410 and the second resistance heater 411 generate an AC temperature gradient ΔT that changes sinusoidally with an angular frequency ω in the direction along the X-axis for the fluctuation detection sensor of Example 4. AC Then, among the thermoelectric signals generated by the fluctuation detection sensor of Example 4, the AC temperature gradient ΔT AC ΔV is the y component of the change in the thermoelectric signal corresponding to twice the frequency of 2ω、y was detected by a lock-in amplifier 430.

[0116] AC temperature gradient ΔT AC More specifically, when ω is the angular frequency and t is time, the first power supply 420 supplies the first resistive heater 410 with V dc +V ac Apply an AC voltage of sin(ωt) and V dc -V ac An AC voltage of sin(ωt) was applied to the second resistance heater 411 by the second power supply 421. This caused a change in the fluctuation detection sensor 400 in the direction along the X-axis, ΔT AC =(√2)ΔT rms An AC temperature gradient expressed as sin(ωt) was applied (ΔT rms is the effective value of the AC temperature gradient). A voltage source device WF1948 manufactured by NF Corporation was used as the first power supply 420 and the second power supply 421, and a lock-in amplifier LI5640 manufactured by NF Corporation was used as the lock-in amplifier 430. The frequency f (=ω / 2π) of the AC voltages applied by the first power supply 420 and the second power supply 421 was set to 3.723 Hz. The lock-in conditions of the lock-in amplifier 430 were a time constant of 1 second and a slope of -24 dB.

[0117] FIG. 14 shows the voltage signal ΔV obtained as a result of the above experiment in Example 4. 2ω、y 1 is a graph showing the dependence of the external magnetic field B on ΔT applied to the fluctuation detection sensor of Example 4. ACSince varies sinusoidally, on a macro scale, the fluctuation detection sensor of Example 4 is not substantially subjected to a temperature gradient, and ΔT AC corresponds to the temperature fluctuation on a micro scale. If the voltage signal output from the fluctuation detection sensor of Example 4 is equal to the AC temperature gradient ΔT AC If the polarity of the AC temperature gradient ΔT AC The voltage signal ΔV corresponding to twice the frequency of 2ω、y is the AC temperature gradient ΔT AC Since the thermoelectric signals corresponding to the positive and negative phases of the temperature gradient ΔT cancel each other out, the voltage signal output from the fluctuation detection sensor in Example 4 becomes zero. AC When the polarity of the voltage signal ΔV 2ω、y is a finite value.

[0118] In this experiment, as shown in FIG. 14, when an external magnetic field B is applied, a finite value of ΔV 2ω、y is detected, and when the polarity of the external magnetic field B is reversed, ΔV 2ω、y The polarity of the voltage signal ΔV 2ω、y It was revealed that the fluctuation detection sensor of Example 4 can generate a voltage signal non-reciprocally in the direction of the temperature gradient, and therefore it is possible to convert energy from heat flow fluctuations Hf at a microscale where a temperature gradient does not substantially exist at a macroscale into a non-reciprocal voltage signal.

[0119] The present invention is not limited to the above-described second embodiment, and various modifications are possible.

[0120] For example, in the second embodiment described above, the fluctuation detection sensor 400 includes the substrate 401 (see FIGS. 7 and 8), but the fluctuation detection sensor 400 does not need to include the substrate 401. In this case, the nonlinear response layer 402 can be formed as a free-standing layer.

[0121] In addition, in the above-mentioned second embodiment, in step S12 of inputting current fluctuations or heat flow fluctuations to the nonlinear response layer, either the current fluctuations Jf or the heat flow fluctuations Hf are input to the nonlinear response layer 402 (see Figures 7 and 8), but both the current fluctuations Jf and the heat flow fluctuations Hf may be input to the nonlinear response layer 402 in a superimposed manner.

[0122] In addition, in the above-mentioned second embodiment, step S12 of inputting current fluctuations or heat flow fluctuations to the nonlinear response layer and step S13 of converting the energy of the current fluctuations or heat flow fluctuations are performed in a state in which the ferromagnetic layer 403 has spontaneous magnetization 403M. However, these steps may also be performed while the ferromagnetic layer 403 is made of a soft magnetic material and an external magnetic field is applied to the ferromagnetic layer 403 to magnetize the ferromagnetic layer 403 to an extent equivalent to the spontaneous magnetization 403M.

[0123] In addition, in the above-described second embodiment, the pair of electrodes 407a, 407b are provided on the surface 405S of the paramagnetic layer 405 so as not to contact the ferromagnetic layer 403 and to be spaced apart from each other along the X-axis direction (see FIGS. 7 and 8). However, they may be provided on the side surfaces of the paramagnetic layer 405 in the positive and negative X-axis directions so as not to contact the ferromagnetic layer 403 and to be spaced apart from each other along the X-axis direction.

[0124] In the second embodiment described above, the paramagnetic layer 405 is a single layer (see FIG. 7 and FIG. 8), but the paramagnetic layer 405 may be made of a plurality of layers of stacked paramagnetic metals. In this case, each of the plurality of layers is preferably made of Pt, Pd, W, AuW alloy, Ta, CuIr alloy, CuBi alloy, BiSb alloy, or BiSe alloy. Such a plurality of layers of stacked paramagnetic metals may be, for example, a stack in which layers of a plurality of types of paramagnetic metals are stacked periodically on one another (for example, a stack in which three types of layers are stacked periodically, such as layer D, layer E, layer F, layer D, layer E, layer F, etc., when a layer of a first paramagnetic metal is layer D, a layer of a second paramagnetic metal is layer E, and a layer of a third paramagnetic metal is layer F), or a stack in which layers of a plurality of types of paramagnetic metals are randomly stacked on one another (for example, a stack in which three types of layers are randomly stacked, such as layer D, layer E, layer F, layer E, layer F, etc.). It is preferable that the laminated multiple paramagnetic metal layers have spin Nernst angles of the same sign, because this prevents the non-reciprocal voltage signals resulting from the multiple paramagnetic metal layers from canceling each other out during energy conversion in the nonlinear response layer 402, thereby increasing the non-reciprocal voltage signal as a whole.

[0125] In the second embodiment described above, the nonlinear response layer 402 includes only one paramagnetic layer (paramagnetic layer 405) such as a paramagnetic metal layer (see FIG. 7 and FIG. 8), but the nonlinear response layer 402 may include a first paramagnetic layer such as a paramagnetic metal layer and a second paramagnetic layer such as a paramagnetic metal layer. In this case, the first paramagnetic layer, the ferromagnetic layer 403, and the second paramagnetic layer are laminated in this order along the Z-axis direction so that the ferromagnetic layer 403 is interposed between the first paramagnetic layer and the second paramagnetic layer to form the nonlinear response layer 402. The preferred materials for the first paramagnetic layer and the second paramagnetic layer are the same as those for the paramagnetic layer 405, but it is preferable to select the configurations (constituent materials, film thickness, etc.) of the first paramagnetic layer and the second paramagnetic layer so that the nonlinear response layer 402 has a structure in which spatial inversion symmetry is broken along the Z-axis direction.

[0126] In this case, it is preferable that the first paramagnetic layer and the second paramagnetic layer have spin Nernst angles of opposite signs to each other (for example, this can be achieved by forming the first paramagnetic layer from Pt and the second paramagnetic layer from Ta). This is because, during energy conversion in the nonlinear response layer 402, spin currents having the same polarity are injected from the first paramagnetic layer and the second paramagnetic layer to the ferromagnetic layer 403, respectively, and the nonreciprocal voltage signal can be increased.

[0127] Furthermore, in this case, each or either of the first and second paramagnetic layers may be made of a plurality of paramagnetic metal layers stacked as described above. In this case, it is preferable that the plurality of paramagnetic metal layers constituting each or either of the first and second paramagnetic layers have spin-Nernst angles of the same sign as each other for the reasons described above.

[0128] In addition, in the above-mentioned second embodiment, the pair of electrodes 407a, 407b are provided on the surface 405S of the paramagnetic layer 405 (see Figures 7 and 8), but the pair of electrodes 407a, 407b may be provided on the back surface (the surface on the negative side of the Z-axis) of the ferromagnetic layer 403 so as not to be in contact with the paramagnetic layer 405 and to be spaced apart from each other along the X-axis direction.

[0129] In the second embodiment described above, the ferromagnetic layer 403 and the paramagnetic layer 405 are laminated in this order on the substrate 401 to form the nonlinear response layer 402 (see FIGS. 7 and 8), but the paramagnetic layer 405 and the ferromagnetic layer 403 may be laminated in this order on the substrate 401 to form the nonlinear response layer 402. In this case, the pair of electrodes 407a, 407b can be provided on the front surface (the surface on the Z-axis positive side) of the ferromagnetic layer 403 or the back surface (the surface on the Z-axis negative side) of the ferromagnetic layer 405 so as to be spaced apart from each other along the X-axis direction.

[0130] The fluctuation detection sensor of the present disclosure has the following configuration. [1] A nonlinear response unit having a nonlinear electrical response characteristic in response to an input of external energy along a first direction; an electrode unit for extracting an electrical response signal generated in the nonlinear response unit due to an energy fluctuation input from the outside to the nonlinear response unit along the first direction; A vibration detection sensor. [2] The fluctuation detection sensor described in [1], wherein the external energy is an electric current and / or a heat flow, and the energy fluctuations are electric current fluctuations and / or heat flow fluctuations. [3] The fluctuation detection sensor according to [1] or [2], wherein the external energy is an electric current and the energy fluctuations are current fluctuations. [4] The fluctuation detection sensor according to any one of [1] to [3], wherein the nonlinear response unit has a configuration in which spatial inversion symmetry is broken along a second direction perpendicular to the first direction. [5] The fluctuation detection sensor according to any one of [1] to [4], wherein the nonlinear response section includes a ferromagnetic layer and a paramagnetic layer stacked on top of each other along the second direction. [6] The fluctuation detection sensor according to any one of [1] to [5], wherein the ferromagnetic layer is configured to have spontaneous magnetization. [7] The fluctuation detection sensor according to any one of [1] to [6], wherein the ferromagnetic layer is a ferromagnetic metal layer and is composed of an L10 type ordered alloy consisting of a magnetic metal and a paramagnetic metal, and the paramagnetic layer is a paramagnetic metal layer. [Explanation of symbols]

[0131] 200... thermoelectric conversion element, 202... thermoelectric conversion layer, 203... ferromagnetic metal layer, 205... paramagnetic metal layer, 207a, 207b... pair of electrodes.

Claims

1. a thermoelectric conversion unit having a nonlinear thermoelectric response characteristic with respect to an input of a heat flow along a first direction; an electrode portion for extracting a thermoelectric signal generated in the thermoelectric conversion portion due to a heat flow input from an outside to the thermoelectric conversion portion along the first direction; A thermoelectric conversion element comprising:

2. The thermoelectric conversion unit exhibits nonreciprocal conduction based on breaking of spatial inversion symmetry, The thermoelectric conversion element according to claim 1 , comprising, as the electrode portion, a pair of electrodes provided spaced apart from each other on the thermoelectric conversion portion for extracting a non-reciprocal thermoelectric signal.

3. the thermoelectric conversion section is a thermoelectric conversion layer including a ferromagnetic metal layer and a paramagnetic metal layer stacked on each other along a second direction perpendicular to the first direction, The thermoelectric conversion element according to claim 2 , wherein the pair of electrodes are provided on the thermoelectric conversion layer in the first direction in an in-plane direction of the thermoelectric conversion layer and spaced apart from each other.

4. The thermoelectric conversion element according to claim 3 , wherein the distance between the pair of electrodes is 0.1 μm or more and 1000 μm or less.

5. The thermoelectric conversion element according to claim 3, wherein the paramagnetic metal layer is composed of a single layer or a plurality of laminated layers, and each of the single layer or the plurality of laminated layers of the paramagnetic metal layer is composed of Pt, Pd, W, an AuW alloy, Ta, a CuIr alloy, a CuBi alloy, a BiSb alloy, or a BiSe alloy.

6. The thermoelectric conversion element according to any one of claims 3 to 5, wherein the ferromagnetic metal layer is composed of a single layer or a plurality of laminated layers, and each of the single layer or the plurality of laminated layers of the ferromagnetic metal layer is composed of a Ni-Fe alloy, Fe, Co, Ni, Gd, a CoFeB alloy, or a (Ga,Fe)Sb alloy.

7. A thermoelectric conversion module comprising a plurality of the thermoelectric conversion elements according to claim 1, the plurality of thermoelectric conversion elements being electrically connected to each other such that thermoelectric signals from each of the thermoelectric conversion elements can be superimposed with the same polarity.

8. Applying a temperature gradient including an AC component to a thermoelectric conversion unit exhibiting nonreciprocal conduction based on a broken spatial inversion symmetry; A step in which the thermoelectric conversion unit thermoelectrically converts the temperature gradient including the AC component to generate a non-reciprocal thermoelectric signal; The thermoelectric conversion method includes the steps of:

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