Patent Description:
The Seebeck effect is known as a thermoelectric mechanism that generates an electric voltage when a temperature gradient is applied to a material (see e.g., Patent Literature <NUM>). Unfortunately, in the thermoelectric mechanism using the Seebeck effect, main materials usable at room temperature or more include bismuth, tellurium, lead or the like, and thus are not suitable for practical use due to high toxicity and are not durable due to mechanical fragility and vulnerability to vibration. The Seebeck effect generates the electric voltage in the same direction as the temperature gradient, which requires a complicated three-dimensional structure in which p-type modules and n-type modules are alternately arranged and stand in a direction perpendicular to a surface of a heat source. This leads to a rise in manufacturing cost. In addition, such a three-dimensional structure makes it difficult to achieve a large-area thermoelectric module.

Similarly, the anomalous Nernst effect is known as a thermoelectric mechanism that generates an electric voltage due to a temperature gradient. The anomalous Nernst effect is a phenomenon observed when a heat current flowing through a magnetic material creates a temperature difference, which generates an electric voltage in a direction perpendicular to both a magnetization direction and the temperature gradient. Recent studies have shown that topological electronic structures contribute to increasing a Nernst coefficient much higher than a previously known value (<NUM>µV/K). For example, Non-patent Literature <NUM> discloses a scalable Nernst thermoelectric power generator using a Galfenol (Fe<NUM>Ga<NUM>) wire coiled around a hot cylinder. Non-patent Literature <NUM> investigates the anomalous Nernst effect in a highly ordered γ' -Fe<NUM>N film with anti-perovskite structure, in comparison with disordered Fe-Al crystal films (A2-type Fe<NUM>-xAlx with x=<NUM>-<NUM> at. Patent Literature <NUM> discloses a thermoelectric conversion device including a thermoelectric conversion element composed of an antiferromagnetic material having a non-collinear spin structure.

However, although various magnetic materials exhibiting the anomalous Nernst effect have been developed so far, such metal materials are relatively expensive, which leads to a high cost.

The present invention has been made in view of the foregoing, and an object of the invention is to provide a thermoelectric conversion element made of an inexpensive and non-toxic material, and a thermoelectric conversion device.

A thermoelectric conversion element according to one aspect of the invention is made of: a first material with a stoichiometric composition of Fe<NUM>X where X is a main-group element or a transition element; a second material with an off-stoichiometric composition in which a composition ratio of Fe to X deviates from that of the first material, the second material having a D0<NUM>-type crystal structure or a B2-type crystal structure; a third material obtained by substituting a part of Fe sites in the first material or a part of Fe sites in the second material by a main-group metal element or a transition element other than X; a fourth material with a composition of Fe<NUM>M1<NUM>-xM2x where <NUM><x<<NUM>, and M1 and M2 are main-group elements different from each other; or a fifth material obtained by substituting a part of Fe sites in the first material by a transition element other than X and substituting a part of X sites in the first material by a main-group metal element other than X. The first material, the second material, the third material, the fourth material, and the fifth material exhibit an anomalous Nernst effect.

A thermoelectric conversion device according to one aspect of the invention includes a substrate and a power generator provided on the substrate and including a plurality of thermoelectric conversion elements. Each of the plurality of thermoelectric conversion elements has a shape extending in one direction, and is made of the first material, the second material, the third material, the fourth material, or the fifth material. The plurality of thermoelectric conversion elements are arranged in parallel to one another in a direction perpendicular to the one direction and electrically connected in series to one another.

A thermoelectric conversion device according to another aspect of the invention includes the thermoelectric conversion element described above and a hollow member. The thermoelectric conversion element is a sheet-shaped element or a wire rod covering an outer surface of the hollow member. Advantageous Effects of Invention.

According to the present invention, a thermoelectric conversion element made of an inexpensive and non-toxic material is capable of exhibiting an anomalous Nernst effect.

Exemplary embodiments of the present invention will be described below with reference to the accompanying drawings.

Among materials exhibiting the anomalous Nernst effect, a Nernst coefficient of Co<NUM>MnGa at room temperature reaches a record high value of <NUM>µV/K, reported by inventors of the present application (see <NPL>) and International Publication No. <CIT>).

As described below, the inventors of the present application have been able to demonstrate that a Nernst coefficient of Fe<NUM>Al, which is a binary compound, approaches the record high value. It is known that elements in descending order of Clarke number, which represents the weight ratio of the elements existing near the Earth's surface, are oxygen (O), silicon (Si), aluminum (Al), iron (Fe),. As just described, Fe and Al are relatively large in Clarke number, and thus are very inexpensive and non-toxic materials. Furthermore, Fe<NUM>Al is chemically stable and has a ferromagnetic transition temperature as high as about <NUM>.

<FIG> shows a crystal structure of Fe<NUM>X (where X is a main-group element or a transition element) which is capable of exhibiting the anomalous Nernst effect. As shown in <FIG>, Fe<NUM>X has a D0<NUM>-type structure (a) and an L1<NUM>-type structure (b).

A unit cell of the D0<NUM> structure (a) has eight body-centered cubic (bcc)-type subcells. In each subcell, Fe atoms (Fe(II)) occupy corner points, and each Fe (II) is shared by adjacent eight subcells. Four Fe atoms (Fe(I)) occupy body-centered points of four of the eight subcells, respectively, and four X atoms occupy body-centered points of the remaining four subcells, respectively. For example, a lattice constant "a" of Fe<NUM>Al having the D0<NUM> structure is <NUM>. 64Å (see <NPL>)).

The L1<NUM> structure (b) is a face-centered cubic (fcc)-type crystal structure in which Fe atoms are located at face-centered points, and X atoms are located at corner points.

For example, single crystals of Fe<NUM>Al are prepared by arc-melting Fe and Al with an appropriate ratio, performing crystal growth by a Czochralski drawing method, annealing the crystals at low temperature (e.g., <NUM>), and performing slow cooling to room temperature for several minutes to several tens of minutes. Electron diffraction indicates that the prepared Fe<NUM>Al single crystals are in an ordered phase (D0<NUM> phase (Fm-<NUM>)).

Polycrystals of Fe<NUM>Al are prepared by making polycrystalline samples through arc-melting of Fe and Al with an appropriate ratio, annealing the samples at high temperature (e.g., <NUM>), and performing rapid cooling to room temperature for several seconds. From the phase diagram, the prepared Fe<NUM>Al polycrystals are considered to be in a disordered phase (B2 phase (Pm-<NUM>) or A2 phase (Im-<NUM>)) or mixed crystals in ordered and disordered phases.

Next, a thermoelectric conversion element according to the embodiments of the present invention and a thermoelectric mechanism thereof will be described with reference to <FIG>.

A thermoelectric conversion element <NUM> according to the embodiments is made of single crystals or polycrystals of Fe<NUM>X which are prepared by the above-described method. As shown in <FIG>, an assumption is made that the thermoelectric conversion element <NUM> has a rectangular parallelepiped shape extending in one direction (direction y), has a predetermined thickness (length in direction z), and is magnetized in a direction +z. When a heat current Q (~-∇T) flows through the thermoelectric conversion element <NUM> in a direction +x, a temperature difference is created in the direction +x. As a result, in the thermoelectric conversion element <NUM>, the anomalous Nernst effect generates electromotive force V (~M×(-VT)) in an outer product direction (direction y) orthogonal to both the direction of the heat current Q (direction +x) and the direction of magnetization M (direction +z).

<FIG> shows comparison results between Nernst coefficients (Syx) of the thermoelectric conversion elements <NUM> made of single crystals of Fe<NUM>Al and Nernst coefficients of thermoelectric conversion elements made of other metal materials, illustrating temperature dependence of the Nernst coefficients. <FIG> is a graph in which the Nernst coefficient of each metal material shown in <FIG> is normalized by the Nernst coefficient at T=<NUM>.

In <FIG> and <FIG>, Fe<NUM>Al#<NUM> represents an observational result of the thermoelectric conversion element <NUM> made of single crystals having an off-stoichiometric composition (Fe-rich, Al-poor) in which a composition ratio of Fe to Al deviates from <NUM>:<NUM>, and Fe<NUM>Al#<NUM> represents an observational result of the thermoelectric conversion element <NUM> made of single crystals having a stoichiometric composition in which the composition ratio of Fe to Al is <NUM>:<NUM>.

In <FIG> and <FIG>, data of L1<NUM>-type MnGa, D0<NUM>-type Mn<NUM>Ga, Co/Ni, FePd, and FePt is based on data disclosed in <NPL>), and data of Fe<NUM>O<NUM> is based on data disclosed in <NPL>). Data of Co<NUM>MnGa is based on the study by the inventors of the present application (see <NPL>); International Publication No. <CIT>).

<FIG> and <FIG> suggest that absolute values |Syx| of the Nernst coefficients of Fe<NUM>Al#<NUM> and Fe<NUM>Al#<NUM> are larger than those of any other metal materials except Co<NUM>MnGa, and in particular, |Syx| of stoichiometric Fe<NUM>Al#<NUM> is larger than that of off-stoichiometric Fe<NUM>Al#<NUM>, reaching about <NUM>µV/K at room temperature (around T=<NUM>) and approaching |Syx| of Co<NUM>MnGa (≈<NUM>µV/K).

Furthermore, <FIG> and <FIG> suggest that Syx of off-stoichiometric Fe<NUM>Al#<NUM> is less affected by temperature change in a temperature range of <NUM> to <NUM> including room temperature, taking an almost constant value.

<FIG> shows magnetic field dependence of the Nernst coefficients (Syx) at T=<NUM> for single crystals (S1 and S2) and a polycrystal (P2) of Fe-Al alloy, and a polycrystal (P1) of Fe-Al-V alloy, and <FIG> shows the temperature dependence of the Nernst coefficients for the single crystals (S1 and S2) and the polycrystal (P2) of the Fe-Al alloy and the polycrystal (P1) of the Fe-Al-V alloy, at a magnetic field B=2T.

In <FIG> and <FIG>, S1 and S2 correspond to Fe<NUM>Al#<NUM> and Fe<NUM>Al#<NUM>, respectively, shown in <FIG>. S1 represents observational results when the magnetic field B parallel to [<NUM>] is applied to the thermoelectric conversion element <NUM>, and the heat current Q parallel to [<NUM>] flows through the thermoelectric conversion element <NUM>. S2 represents observational results when the magnetic field B parallel to [<NUM>] is applied to the thermoelectric conversion element <NUM>, and the heat current Q parallel to [<NUM>] flows through the thermoelectric conversion element <NUM>.

In <FIG> and <FIG>, P1 represents an observational result in the thermoelectric conversion element <NUM> made of the polycrystal of Fe<NUM>V<NUM>Al obtained by substituting a part of Fe sites of Fe<NUM>Al by vanadium (V), and P2 represents an observational result in the thermoelectric conversion element <NUM> made of the polycrystal having a stoichiometric composition in which the composition ratio of Fe to Al is <NUM>:<NUM>.

<FIG> and <FIG> suggest that the single crystals (S1 and S2) have larger absolute values |Syx| of the Nernst coefficients than the polycrystals (P1 and P2). Comparison between the polycrystals P1 and P2 indicates that | Syx | of the stoichiometric binary polycrystal P2 is larger than that of the ternary polycrystal P1.

The Nernst coefficients of the polycrystals (P1 and P2) are less affected by temperature change in a temperature range of <NUM> to <NUM> including room temperature (around T=<NUM>) than those of the single crystals (S1 and S2), taking almost constant values. Although |Syx| of the polycrystals (P1 and P2) is smaller than that of the single crystals (S1 and S2), |Syx| at room temperature is about <NUM> to <NUM>µV/K, reaching a practical level for use in thermoelectric conversion devices such as heat flux sensors. As described above, the polycrystals (P1 and P2) are easier to prepare than the single crystals (S1 and S2).

Next, reference will be made to a thermoelectric conversion device in which the thermoelectric conversion element of the embodiments is modularized.

<FIG> shows an exterior configuration of a thermoelectric conversion device <NUM> according to Example <NUM> of the embodiments. The thermoelectric conversion device <NUM> includes a substrate <NUM> and a power generator <NUM> placed on the substrate <NUM>. In the thermoelectric conversion device <NUM>, when a heat current Q flows from the substrate <NUM> side toward the power generator <NUM>, a temperature difference is created in the power generator <NUM> in the direction of the heat current, and an electric voltage V is generated in the power generator <NUM> by the anomalous Nernst effect.

The substrate <NUM> has a first surface 22a on which the power generator <NUM> is placed, and a second surface 22b opposite to the first surface 22a. Heat from a heat source (not shown) is applied onto the second surface 22b.

The power generator <NUM> includes a plurality of thermoelectric conversion elements <NUM> and a plurality of thermoelectric conversion elements <NUM>, each having a three-dimensional L shape and being made of a material identical to that of the thermoelectric conversion element <NUM> shown in <FIG>. As shown in <FIG>, the thermoelectric conversion elements <NUM> and the thermoelectric conversion elements <NUM> are alternately arranged in parallel to one another on the substrate <NUM> in a direction (direction y) perpendicular to a longitudinal direction (direction x) of the thermoelectric conversion elements. The number of the thermoelectric conversion elements <NUM> and the thermoelectric conversion elements <NUM> constituting the power generator <NUM> is not limited.

The plurality of thermoelectric conversion elements <NUM> and the plurality of thermoelectric conversion elements <NUM> are arranged such that a direction of magnetization M1 of the thermoelectric conversion elements <NUM> is opposite to a direction of magnetization M2 of the thermoelectric conversion elements <NUM>. The Nernst coefficient of the plurality of thermoelectric conversion elements <NUM> has the same sign as that of the plurality of thermoelectric conversion elements <NUM>.

Each of the thermoelectric conversion elements <NUM> has a first end face 24a and a second end face 24b, both of which are parallel to the longitudinal direction (direction x). Each of the thermoelectric conversion elements <NUM> has a first end face 25a and a second end face 25b, both of which are parallel to the longitudinal direction (direction x). The first end face 25a of the thermoelectric conversion element <NUM> is connected to the second end face 24b of one adjacent thermoelectric conversion element <NUM>, and the second end face 25b of the corresponding thermoelectric conversion element <NUM> is connected to the first end face 24a of another adjacent thermoelectric conversion element <NUM> on the opposite side. With this structure, the thermoelectric conversion elements <NUM> and the thermoelectric conversion elements <NUM> are electrically connected in series to one another. That is, the power generator <NUM> is provided on the first surface 22a of the substrate <NUM> in a serpentine shape.

When heat is applied from the heat source onto the second surface 22b of the substrate <NUM>, the heat current Q flows in the direction +z toward the power generator <NUM>. When the heat current Q creates a temperature difference, the anomalous Nernst effect causes each of the thermoelectric conversion elements <NUM> to generate an electromotive force E1 in the direction (direction -x) orthogonal to both the direction of the magnetization M1 (direction -y) and the direction of the heat current Q (direction +z). The anomalous Nernst effect causes each of the thermoelectric conversion elements <NUM> to generate an electromotive force E2 in the direction (direction +x) orthogonal to both the direction of the magnetization M2 (direction +y) and the direction of the heat current Q (direction +z).

As described above, since the thermoelectric conversion elements <NUM> and the thermoelectric conversion elements <NUM>, which are arranged in parallel to one another, are electrically connected in series to one another, the electromotive force E1 generated in one thermoelectric conversion element <NUM> can be applied to the adjacent thermoelectric conversion element <NUM>. Since the direction of the electromotive force E1 generated in one thermoelectric conversion element <NUM> is opposite to that of the electromotive force E2 generated in the adjacent thermoelectric conversion element <NUM>, the electromotive force in the thermoelectric conversion element <NUM> and the electromotive force in the adjacent thermoelectric conversion element <NUM> are added up, thereby increasing an output voltage V.

As a modification of the thermoelectric conversion device <NUM> in <FIG>, another configuration may be employed in which the plurality of thermoelectric conversion elements <NUM> and the plurality of thermoelectric conversion elements <NUM> are arranged such that the Nernst coefficient of the thermoelectric conversion element <NUM> is opposite in sign to that of the adjacent thermoelectric conversion element <NUM>, and the plurality of thermoelectric conversion elements <NUM> and the plurality of thermoelectric conversion elements <NUM> share the same magnetization direction (that is, the magnetization M1 and the magnetization M2 have the same direction).

<FIG> is a plan view of a thermoelectric conversion device 20A according to Example <NUM> of the embodiments. The thermoelectric conversion device 20A includes, as a power generator 23A, a plurality of rectangular parallelepiped thermoelectric conversion elements 1A having Nernst coefficients with the same sign. Each of the thermoelectric conversion elements 1A is made of a material identical to that of the thermoelectric conversion element <NUM> shown in <FIG>. The thermoelectric conversion elements 1A are arranged in parallel to one another on a substrate 22A in a direction (direction y) perpendicular to the longitudinal direction (direction x) such that they share the same direction of magnetization M (direction y), and the adjacent thermoelectric conversion elements 1A are connected via copper wiring <NUM> so that the thermoelectric conversion elements 1A are electrically connected in series. The heat current flows from the substrate 22A side toward the power generator 23A (in direction z). The thermoelectric conversion device 20A has a configuration in which the adjacent thermoelectric conversion elements 1A are connected via the copper wiring <NUM>, and thus, can be easily manufactured as compared to the thermoelectric conversion device <NUM> of Example <NUM> shown in <FIG>.

The thermoelectric mechanism using the anomalous Nernst effect allows the temperature gradient, the magnetization direction, and the direction of the electric voltage to be orthogonal to one another, which makes it possible to produce a thin sheet-shaped thermoelectric conversion element.

<FIG> shows an exterior configuration of a thermoelectric conversion device <NUM> according to Example <NUM> including a sheet-shaped thermoelectric conversion element <NUM>. Specifically, the thermoelectric conversion device <NUM> includes a hollow member <NUM> and an elongated sheet-shaped (tape-shaped) thermoelectric conversion element <NUM> winding around the hollow member <NUM> to cover an outer surface of the hollow member <NUM>. The thermoelectric conversion element <NUM> is made of a material identical to that of the thermoelectric conversion element <NUM> shown in <FIG>. The magnetization direction of the thermoelectric conversion element <NUM> is parallel to a longitudinal direction (direction x) of the hollow member <NUM>. When the heat current flows in a direction perpendicular to the longitudinal direction (direction x) of the hollow member <NUM> and a temperature gradient is created in a direction from the inside toward the outside of the hollow member <NUM>, the anomalous Nernst effect generates an electric voltage V along a longitudinal direction of the elongated thermoelectric conversion element <NUM> (i.e., a direction perpendicular to both the magnetization direction and the direction of the heat current).

Instead of the elongated sheet-shaped thermoelectric conversion element <NUM> of the thermoelectric conversion device <NUM> of <FIG>, a wire-rod thermoelectric conversion element may be wound around the hollow member <NUM>.

Here, in <FIG>, let the longitudinal length of the thermoelectric conversion element (s) be denoted by L, and the thickness (height) of the thermoelectric conversion element (s) be denoted by H. The electric voltage generated by the anomalous Nernst effect is proportional to L/H. That is, the longer and thinner the thermoelectric conversion element(s), the greater the generated electric voltage. Therefore, the anomalous Nernst effect is expected to be enhanced by employing a power generator having thermoelectric conversion elements which are electrically connected in series, or employing a wire-rod or an elongated sheet-shaped thermoelectric conversion element.

The thermoelectric conversion devices illustrated in Example <NUM> to Example <NUM> can be used for various applications. Especially, in a temperature range between room temperature and several hundred degrees Celsius, a self-sustaining power supply for an Internet of Things (IoT) sensor or a heat flux sensor is one possible application.

For example, by applying the thermoelectric conversion device of the embodiments to a heat flux sensor, it is possible to determine whether thermal insulation performance of a building is good or bad. By providing the thermoelectric conversion device in an exhaust device of a motor vehicle, it is possible to convert heat from exhaust gas (waste heat) into electricity, and to effectively use the thermoelectric conversion device as an auxiliary power supply. Further, by arranging heat flux sensors in a mesh-like pattern on a wall surface of a certain space, it is possible to perform space recognition of heat current or heat sources. This technique is expected to be applicable to, for example, a high-precision temperature control of high-density crop cultivation or livestock growth, or to a driver detection system for automatic driving. The heat flux sensors can also be used in room air conditioning management, or core body temperature management in medical treatment. In addition, the thermoelectric conversion element of the embodiments can be formed into powder or paste, thus offering promising applications in a wide range of fields.

The embodiments have focused on the electric voltage generated by the anomalous Nernst effect. In practice, the output voltage can be increased by virtue of synergy among the electric voltage generated by the Seebeck effect resulting from a temperature gradient, the Hall effect that occurs based on the electric voltage generated by the Seebeck effect, and the electric voltage generated by the anomalous Nernst effect.

As described above, according to the thermoelectric conversion element of the embodiments, alloy of Fe and Al which are large in Clarke number and inexpensive and non-toxic materials is capable of exhibiting the anomalous Nernst effect. In particular, by adopting the off-stoichiometric composition in which the composition ratio of Fe to Al is adjusted, or by adopting the polycrystal rather than the single crystal, it is possible to provide the thermoelectric conversion element having a Nernst coefficient insensitive to temperature change in a wide range of <NUM> to <NUM>. This eliminates the need to provide a temperature calibration circuit or a thermometer, which used to be required for heat flux sensors or other such devices made of materials whose Nernst coefficients are very sensitive to temperature change around room temperature. It is therefore possible to manufacture the thermoelectric conversion device at a low cost.

In <FIG>, although the thermoelectric conversion element is made of the Fe-Al alloy, or the Fe-Al-V alloy obtained by substituting a part of Fe sites of the Fe-Al alloy by V, a transition element or a main-group element other than Al, or a transition element other than V can also be employed. That is, the following materials are expected to exhibit the anomalous Nernst effect: a first material with a stoichiometric composition of Fe<NUM>X (where X is a main-group element or a transition element); a second material with an off-stoichiometric composition in which the composition ratio of Fe to X deviates from <NUM>:<NUM>; a third material obtained by substituting a part of Fe sites in the first material or a part of Fe sites in the second material by a main-group metal element or a transition element other than X; a fourth material with a composition of Fe<NUM>M1<NUM>-xM2x (<NUM><x<<NUM>) where M1 and M2 are main-group elements different from each other; or a fifth material obtained by substituting a part of Fe sites in the first material by a transition element other than X and substituting a part of X sites in the first material by a main-group metal element other than X. Candidates for X other than Al include Ga, Ge, Sn, Si, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Sc, Ni, Mn, or Co. Examples of a combination of M1 and M2 constituting the fourth material include a combination of Ga and Al, a combination of Si and Al, and a combination of Ga and B.

For example, the anomalous Nernst effect is also observed in Fe-Ge alloy, Fe-Ga alloy, and Fe-Ga-Al alloy. <FIG> shows magnetic field dependence of the Nernst coefficients (Syx) at T=<NUM> for Fe<NUM>Pt, Fe<NUM>Ge, Fe<NUM>Al, Fe<NUM>Ga<NUM>Al<NUM>, Fe<NUM>Ga, and Co<NUM>MnGa. <FIG> shows the temperature dependence of the Nernst coefficients for Fe<NUM>Pt, Fe<NUM>Ge, Fe<NUM>Al, Fe<NUM>Ga, and Co<NUM>MnGa.

In <FIG> and <FIG>, a data set for Fe<NUM>Ge represents observational results when the magnetic field B parallel to an a axis is applied to the thermoelectric conversion element <NUM> made of hexagonal single crystals of Fe<NUM>Ge, and the heat current Q parallel to a c axis flows through the thermoelectric conversion element <NUM>, a data set for Fe<NUM>Al represents observational results when the magnetic field B parallel to [<NUM>] is applied to the thermoelectric conversion element <NUM> made of cubic single crystals of Fe<NUM>Al, and the heat current Q parallel to [<NUM>] flows through the thermoelectric conversion element <NUM>, and a data set for Fe<NUM>Ga represents observational results when the magnetic field B parallel to [<NUM>] is applied to the thermoelectric conversion element <NUM> made of cubic single crystals of Fe<NUM>Ga, and the heat current Q parallel to [<NUM>-<NUM>] flows through the thermoelectric conversion element <NUM>. In <FIG>, a data set for Fe<NUM>Ga<NUM>Al<NUM> represents observational results when the magnetic field B parallel to [<NUM>] is applied to the thermoelectric conversion element <NUM> made of single crystals of Fe<NUM>Ga<NUM>Al<NUM>, and the heat current Q parallel to [<NUM>-<NUM>] flows through the thermoelectric conversion element <NUM>. In <FIG> and <FIG>, a data set for Fe<NUM>Pt represents observational results when the magnetic field B parallel to [<NUM>] is applied to the thermoelectric conversion element <NUM> made of single crystals of Fe<NUM>Pt, and the heat current Q parallel to [<NUM>-<NUM>] flows through the thermoelectric conversion element <NUM>, and a data set for Co<NUM>MnGa represents observational results when the magnetic field B parallel to [<NUM>] is applied to the thermoelectric conversion element <NUM> made of single crystals of Co<NUM>MnGa, and the heat current Q parallel to [<NUM>] flows through the thermoelectric conversion element <NUM>.

<FIG> and <FIG> suggest that |Syx| of the Fe<NUM>Ge single crystals is smaller than that of the Fe<NUM>Al single crystals, but is larger than that of the Fe<NUM>Pt single crystals, and |Syx| of the Fe<NUM>Ge single crystals at room temperature exceeds <NUM>µV/K, reaching a practical level for use in thermoelectric conversion devices such as a heat flux sensor. Further, | Syx | of the Fe<NUM>Ga<NUM>Al<NUM> single crystals which are ternary compounds is larger than that of the Fe<NUM>Al single crystals, reaching about <NUM>µV/K at room temperature. Further, | Syx | of the Fe<NUM>Ga single crystals at room temperature is well over <NUM>µV/K, approaching the record high value (<NUM>µV/K) of the Co<NUM>MnGa single crystals. Hexagonal single crystals of Fe<NUM>Ga are also found to exhibit the anomalous Nernst effect.

<FIG> suggests that the Nernst coefficients of the single crystals of Fe<NUM>Ge, Fe<NUM>Al, and Fe<NUM>Ga change slowly with temperature compared to the single crystals of Fe<NUM>Pt and Co<NUM>MnGa, in a temperature range of <NUM> to <NUM>.

The anomalous Nernst effect is also observed in Fe-Sn alloy. <FIG> shows the temperature dependence of the Nernst coefficient of a hexagonal polycrystal of Fe<NUM>Sn which is obtained by melting and synthesizing a polycrystal in an arc furnace, and then performing synthesizing through annealing at <NUM> degrees Celsius for one week. <FIG> shows the temperature dependence of transverse thermoelectric conductivity α[A/Km] at the magnetic field B=2T, which is estimated by the anomalous Nernst effect of Fe<NUM>Sn. This experimental data suggests that the Nernst coefficient |Syx| of the Fe<NUM>Sn polycrystal increases to <NUM>µV/K or more at room temperature or more.

Next, reference will be made to measurement results of the anomalous Nernst effect after preparing mixed crystals between three polycrystals (Fe<NUM>Si, Fe<NUM>Al, and Fe<NUM>Ga).

<FIG> and <FIG> show the Nernst coefficients of polycrystals of Fe<NUM>Si<NUM>-xAlx (<NUM>≤x≤<NUM>) as mixed crystals of Fe<NUM>Si and Fe<NUM>Al, at T=<NUM>. Here, Fe<NUM>Si<NUM>Al<NUM> shown in <FIG> is a soft magnetic material called Sendust. <FIG> and <FIG> suggest that the Nernst coefficient |Syx| increases with an increase in the content of Al except for Fe<NUM>Si<NUM>Al<NUM>.

<FIG> and <FIG> show the Nernst coefficients of polycrystals of Fe<NUM>Al<NUM>-xGax (<NUM>≤x≤<NUM>) as mixed crystals of Fe<NUM>Al and Fe<NUM>Ga, at T=<NUM>. <FIG> also shows the Nernst coefficients of single crystals of Fe<NUM>Al<NUM>-xGax which are prepared at a crystal growth rate of <NUM>/h. <FIG> and <FIG> suggest that the Nernst coefficients |Syx| of the single crystals are larger than those of the polycrystals, and in both the single crystals and the polycrystals, the Nernst coefficient |Syx| increases with an increase in the content of Ga except for the Fe<NUM>Al<NUM>Ga<NUM> polycrystal.

<FIG> shows the Nernst coefficients of single crystals and polycrystals of Fe<NUM>Cu<NUM>-xGax (<NUM><x≤<NUM>) at T=<NUM>, obtained by substituting a part of Ga sites of Fe<NUM>Ga by Cu. The single crystals of Fe<NUM>Cu<NUM>-xGax are also prepared at a crystal growth rate of <NUM>/h. <FIG> suggests that the Nernst coefficient | Syx | of the Fe<NUM>Cu<NUM>-xGax single crystals decreases as the content of Cu increases and the content of Ga decreases, but exceeds <NUM>µV/K at x=<NUM>, reaching a practical level.

Next, experimental results after Fe<NUM>Ga is doped with Nd, Ho, Y, or Tb will be described with reference to <FIG>.

<FIG> shows X-ray diffraction patterns of Nd<NUM>Fe<NUM>Ga and Fe<NUM>Ga, and <FIG> shows magnetic field dependence of magnetization of Nd<NUM>Fe<NUM>Ga at T=<NUM>. <FIG> suggests that Nd<NUM>Fe<NUM>Ga and Fe<NUM>Ga have nearly the same crystal structure. As shown in <FIG>, Nd<NUM>Fe<NUM>Ga has magnetization which reaches a saturation magnetization of <NUM>µB/F. at <NUM> kA/m (<NUM> Oe), and has almost no coercivity.

<FIG> shows magnetic field dependence of the Nernst coefficients at T=<NUM> for a single crystal of Fe<NUM>Ga and a polycrystal of Nd<NUM>Fe<NUM>Ga. <FIG> shows magnetic field dependence of Hall resistivity at T=<NUM> for the single crystal of Fe<NUM>Ga and the polycrystal of Nd<NUM>Fe<NUM>Ga. <FIG> suggests that the Nernst coefficient | Syx | of the Nd<NUM>Fe<NUM>Ga polycrystal is smaller than that of the Fe<NUM>Ga single crystal, but exceeds <NUM>µV/K, reaching a practical level. <FIG> suggests that the magnetic field dependence of the Hall resistivity ρyx of the Fe<NUM>Ga single crystal shows nearly the same behavior as that of the Nd<NUM>Fe<NUM>Ga polycrystal.

<FIG> shows X-ray diffraction patterns of Ho<NUM>Fe<NUM>Ga and Fe<NUM>Ga, and <FIG> shows magnetic field dependence of magnetization of Ho<NUM>Fe<NUM>Ga at T=<NUM>. <FIG> suggests that Ho<NUM>Fe<NUM>Ga and Fe<NUM>Ga have nearly the same crystal structure. As shown in <FIG>, Ho<NUM>Fe<NUM>Ga has magnetization which reaches a saturation magnetization of <NUM>µB/F. at 2T, and has almost no coercivity.

<FIG> shows X-ray diffraction patterns of Y<NUM>Fe<NUM>Ga and Fe<NUM>Ga, and <FIG> shows magnetic field dependence of magnetization of Y<NUM>Fe<NUM>Ga. <FIG> suggests that Y<NUM>Fe<NUM>Ga and Fe<NUM>Ga have nearly the same crystal structure. <FIG> suggests that Y<NUM>Fe<NUM>Ga has magnetization which reaches a saturation magnetization of <NUM>µB/F. at <NUM> kA/m (<NUM> Oe), and has a coercivity of about <NUM> kA/m (<NUM> Oe).

<FIG> shows magnetic field dependence of magnetization of Tb<NUM>Fe<NUM>Ga prepared by using a mono arc furnace, and <FIG> is a graph illustrating an enlarged view in a low magnetic field region of <FIG> suggest that Tb<NUM>Fe<NUM>Ga has magnetization which reaches a saturation magnetization of <NUM>µB/F. at 2T, and has a coercivity of about <NUM> kA/m (<NUM> Oe).

<FIG> shows an X-ray diffraction pattern of Tb<NUM>Fe<NUM>Ga prepared by using a tetra arc furnace and an X-ray diffraction pattern of Fe<NUM>Ga, and <FIG> shows magnetic field dependence of magnetization of Tb<NUM>Fe<NUM>Ga at T=<NUM>. <FIG> suggests that Tb<NUM>Fe<NUM>Ga and Fe<NUM>Ga have nearly the same crystal structure. As shown in <FIG>, Tb<NUM>Fe<NUM>Ga has magnetization which reaches a saturation magnetization of <NUM>µB/F. at 2T, and has almost no coercivity.

Although <FIG> and <FIG> show the anomalous Nernst effect in the materials (the third materials) obtained by substituting a part of Fe sites of Fe<NUM>Ga by Nd, Ho, or Tb, other third materials obtained through substitution by other lanthanoids (such as Gd) are also expected to exhibit the anomalous Nernst effect.

Next, experimental results after Fe<NUM>Ga is doped with B, Mn, or Pt will be described with reference to <FIG>.

First, reference will be made to the experimental results after Fe<NUM>Ga is doped with B. <FIG> shows X-ray diffraction patterns of Fe<NUM>Ga<NUM>B<NUM>, Fe<NUM>Ga<NUM>B<NUM>, and Fe<NUM>Ga. This indicates that Fe<NUM>Ga<NUM>B<NUM> and Fe<NUM>Ga<NUM>B<NUM> have nearly the same crystal structure as that of Fe<NUM>Ga. Furthermore, energy-dispersive X-ray spectroscopy (EDX) (not shown) suggests that the dopant B appears near the boundary of Fe<NUM>Ga.

<FIG> shows magnetic field dependence of magnetization at T=<NUM> for a needle-like sample and a plate-like sample, both of which are made of Fe<NUM>Ga<NUM>B<NUM>. The needle-like sample (columnar sample) shown in <FIG> is magnetized in a longitudinal direction of the needle-like sample, and a magnetic field is applied in parallel to the longitudinal direction. The plate-like sample shown in <FIG> is magnetized in an in-plane direction of the plate-like sample, and a magnetic field is applied in an out-of-plane direction of the plate-like sample. As just described, in the plate-like sample, since the magnetization direction is perpendicular to the magnetic field direction, it is necessary to apply a strong magnetic field in order to align the magnetization with the magnetic field direction. <FIG> suggests that as for the plate-like sample, the magnetization only slightly linearly changes when the strong magnetic field is applied, whereas as for the needle-like sample having magnetization in the direction parallel to the magnetic field, the magnetization largely changes, and a clear hysteresis loop is observed.

<FIG> shows magnetic field dependence of magnetization of needle-like samples of Fe<NUM>Ga<NUM>B<NUM> and Fe<NUM>Ga. The needle-like samples shown in <FIG> are magnetized in the longitudinal direction, and a magnetic field is applied in parallel to the magnetization direction. Since the magnetization direction is parallel to the magnetic field direction, the magnetization of Fe<NUM>Ga and the magnetization of Fe<NUM>Ga<NUM>B<NUM> are saturated at relatively weak magnetic fields (about <NUM> kA/m (<NUM> Oe) and about <NUM> kA/m (<NUM> Oe), respectively). As shown in <FIG>, a clearer hysteresis loop is observed for Fe<NUM>Ga<NUM>B<NUM> than Fe<NUM>Ga, and a coercivity of Fe<NUM>Ga is about <NUM> A/m (<NUM> Oe), whereas a coercivity of Fe<NUM>Ga<NUM>B<NUM> is about <NUM> kA/m (<NUM> Oe).

<FIG> shows magnetic field dependence of magnetization of plate-like samples of Fe<NUM>Ga<NUM>B<NUM> and Fe<NUM>Ga. The plate-like samples shown in <FIG> are magnetized in the in-plane direction, and a magnetic field is applied in the out-of-plane direction. Since the magnetization direction is perpendicular to the magnetic field direction, a strong magnetic field is required to align the magnetization with the out-of-plane direction. As for both Fe<NUM>Ga and Fe<NUM>Ga<NUM>B<NUM>, the magnetization linearly increases until the magnetic field exceeds <NUM> kA/m (<NUM> kOe), and the hysteresis is weak. In fact, almost no coercivity is observed for Fe<NUM>Ga. In contrast, the enlarged view in a low magnetic field region (inset of <FIG>) suggests that Fe<NUM>Ga<NUM>B<NUM> has a coercivity of about <NUM> kA/m (<NUM> Oe).

<FIG> shows magnetic field dependence of a Nernst coefficient of a plate-like sample of Fe<NUM>Ga<NUM>B<NUM>, and <FIG> shows magnetic field dependence of Hall resistivity of the plate-like sample of Fe<NUM>Ga<NUM>B<NUM>. The plate-like sample shown in <FIG> is magnetized in the in-plane direction, and a magnetic field is applied in the out-of-plane direction, similarly to that in <FIG>. In <FIG>, data points when the magnetic field increases from -<NUM> T to +<NUM> T are indicated by circles, and data points when the magnetic field decreases from +<NUM> T to -<NUM> T are indicated by squares. <FIG> suggests that the Nernst coefficient | Syx | of Fe<NUM>Ga<NUM>B<NUM> reaches 4µV/K, which is about <NUM>% of the Nernst coefficient of the Fe<NUM>Ga polycrystal (<NUM>µV/K : see <FIG> and <FIG>).

As described above, by substituting a part of Ga sites of Fe<NUM>Ga by B, it is possible to increase the coercivity and to secure about <NUM>% of the Nernst coefficient of Fe<NUM>Ga. Thus, it can be said that Fe<NUM>Ga<NUM>B<NUM> is advantageous in manufacturing thermopiles that can work under zero magnetic field.

Next, reference will be made to the experimental results after Fe<NUM>Ga is doped with Mn. <FIG> shows X-ray diffraction patterns of Fe<NUM>Mn<NUM>Ga, Fe<NUM>Mn<NUM>Ga, Fe<NUM>MnGa, and Fe<NUM>Ga, and <FIG> shows magnetic field dependence of magnetization at T=<NUM> for needle-like samples of Fe<NUM>Mn<NUM>Ga and Fe<NUM>Mn<NUM>Ga. The needle-like samples shown in <FIG> are magnetized in the longitudinal direction, and a magnetic field is applied in parallel to the magnetization direction.

<FIG> suggests that Fe<NUM>Mn<NUM>Ga and Fe<NUM>Mn<NUM>Ga have nearly the same crystal structure as that of Fe<NUM>Ga. As shown in <FIG>, Fe<NUM>Mn<NUM>Ga has a large magnetization, but shows almost no hysteresis. In contrast, Fe<NUM>Mn<NUM>Ga shows a small hysteresis and has a coercivity of about <NUM> A/m (<NUM> Oe) (which is the same coercivity as that of the needle-like sample of Fe<NUM>Ga shown in <FIG>), but the magnetization is found to be considerably small as compared to Fe<NUM>Mn<NUM>Ga.

Next, reference will be made to the experimental results after Fe<NUM>Ga is doped with Pt. <FIG> shows X-ray diffraction patterns of Fe<NUM>Pt<NUM>Ga, Fe<NUM>Pt<NUM>Ga<NUM>Ge<NUM>, and Fe<NUM>Ga, and <FIG> shows magnetic field dependence of magnetization at T=<NUM> for needle-like samples of Fe<NUM>Pt<NUM>Ga and Fe<NUM>Pt<NUM>Ga<NUM>Ge<NUM>. The needle-like samples shown in <FIG> are magnetized in the longitudinal direction, and a magnetic field is applied in parallel to the magnetization direction.

<FIG> suggests that Fe<NUM>Pt<NUM>Ga and Fe<NUM>Pt<NUM>Ga<NUM>Ge<NUM> have nearly the same crystal structure as that of Fe<NUM>Ga. As shown in <FIG>, Fe<NUM>Pt<NUM>Ga shows almost no hysteresis. In contrast, Fe<NUM>Pt<NUM>Ga<NUM>Ge<NUM> shows a small hysteresis and has a coercivity of about <NUM> A/m (<NUM> Oe). This indicates that a coercivity is increased by substituting a part of Ga sites of Fe<NUM>Pt<NUM>Ga by Ge.

As described above, since the increase in coercivity can also be found when a part of Ga sites of Fe<NUM>Ga is substituted by B (see <FIG>), the substitution of Ga sites is believed to affect magnetic properties.

The thermoelectric conversion element <NUM> can be implemented as a thin film. Such embodiments will be described next with reference to <FIG>. In the following embodiments, the thermoelectric conversion element <NUM> is made of a first material with a composition of Fe<NUM>X or a second material with an off-stoichiometric composition in which the composition ratio of Fe to X deviates from the first material, but is not limited thereto.

First, a method of producing a thin film will be described. In the example below, the thin film is produced by a sputtering method, but the method of producing the thin film is not limited. For example, a molecular beam epitaxy (MBE) method, a chemical vapor deposition (CVD), a pulsed laser deposition (PLD), a plating method, or other such methods may be adopted.

For example, the method of producing a Fe<NUM>Ga thin film includes, first, using a DC magnetron sputtering apparatus to discharge a target with a composition ratio of Fe to Ga being <NUM>:<NUM> at room temperature, and preparing a thin film of Ga-doped Fe on a [<NUM>]-oriented magnesium oxide (MgO) substrate. The Fe<NUM>Ga sample grown at room temperature is a polycrystalline thin film, but a [<NUM>]-oriented epitaxial thin film can be produced by performing annealing for <NUM> minutes at <NUM> without breaking vacuum after the film growth. As just described, the Fe<NUM>Ga thin film is a [<NUM>]-oriented epitaxial thin film on the [<NUM>]-oriented MgO substrate.

An oxidation resistant layer made of MgO is provided on an outermost surface of the thin film. In addition to MgO, a typical cap layer made of Al, Al<NUM>O<NUM>, SiO<NUM> or the like may be employed as the oxidation resistant layer in order to prevent oxidation. A buffer layer between the thin film and the substrate, or the cap layer on the outermost surface of the thin film is not always necessary.

In the above-described production method using the sputtering apparatus, a T/S distance (which is a distance between the target and the substrate) is preferably in a range of <NUM> to <NUM>. Considering various production methods, the T/S distance may fall within a range of <NUM> to <NUM>.

A ferromagnetic material is difficult to align its magnetization in a direction perpendicular to a temperature difference due to a demagnetizing field, which makes it difficult to generate an electric voltage at zero magnetic field. However, by producing the thin film as described above, the contribution of the demagnetizing field increases in the out-of-plane direction of the thin film, whereas the effect of the demagnetizing field decreases to almost zero in the in-plane direction. This stabilizes the magnetization in the in-plane direction.

Next, a method of measuring the anomalous Nernst effect when a temperature gradient is applied in the in-plane direction to a thin film sample as the thermoelectric conversion element <NUM> will be described with reference to <FIG>. In order to measure such an anomalous Nernst effect, for example, a rectangular parallelepiped structure is used as shown in <FIG>. In the structure of <FIG>, a thin film (Fe<NUM>X thin film) sample with a thickness of <NUM> is stacked on an MgO substrate with a thickness of <NUM>, and an MgO cap layer with a thickness of <NUM> is stacked on the thin film sample. The structure has a longitudinal length of <NUM> and a lateral width of <NUM>. The thin film sample is provided with thermocouples in the longitudinal direction, and the distance between the thermocouples is <NUM>.

As described above, the thin film sample is magnetized in the in-plane direction. As shown in <FIG>, when a magnetic field is applied to the thin film sample in the out-of-plane direction, the magnetization is aligned with the out-of-plane direction. When a heat current Q flows through the thin film sample in the longitudinal direction, a temperature difference ΔT (=T<NUM>-T<NUM>) occurs. As a result, in the same manner as in <FIG>, the anomalous Nernst effect generates an electromotive force Vyx in a direction orthogonal to both the direction of the heat current Q and the magnetization direction (out-of-plane direction).

<FIG> shows the measurement results of the anomalous Nernst effect (magnetic field dependence of a Nernst coefficient at T=<NUM>) when the thin film sample shown in <FIG> is made of Fe<NUM>Ga. <FIG> suggests that the Nernst coefficient |Syx| of Fe<NUM>Ga reaches <NUM>µV/K.

Although <FIG> show an example in which the temperature gradient is applied to the thin film sample in the in-plane direction, the anomalous Nernst effect can also occur when a temperature gradient is applied to the thin film sample in the out-of-plane direction as shown in <FIG>. That is, the thin film sample as the thermoelectric conversion element <NUM> is magnetized in the in-plane direction (direction x), and when a heat current Q flows through the thin film sample in the out-of-plane direction (direction z), an electromotive force V is generated in a direction (direction y) orthogonal to both the direction of the heat current Q and the direction of the magnetization M.

In order to measure such an anomalous Nernst effect, for example, a structure shown in <FIG> is used. In the structure of <FIG>, a silicone pad with a thickness of <NUM> is provided on a heat sink made of Cu, an MgO substrate with a thickness of <NUM> is stacked on the silicone pad, a thin film sample with a thickness of <NUM> is stacked on the MgO substrate, and an MgO cap layer with a thickness of <NUM> is stacked on the thin film sample. Voltage terminals are provided at both ends of the MgO cap layer in the longitudinal direction, and these voltage terminals are connected to both end portions of the thin film sample in the longitudinal direction. With this structure, as shown in <FIG>, it is possible to measure an electromotive force Vyx generated in the longitudinal direction of the thin film sample due to the anomalous Nernst effect.

A silicone pad with a thickness of <NUM> is stacked on the MgO cap layer, a copper plate with a thickness of <NUM> is stacked on the silicone pad, and a resistance heater (ceramic heater) is provided on the copper plate. Thermocouples are provided on an upper end of the MgO cap layer and a lower end of the MgO substrate. A heat current from the ceramic heater flows through the thin film sample from the upper end of the MgO cap layer to the lower end of the MgO substrate, and creates a temperature gradient ΔTall. Using the thermocouples, it is possible to measure the temperature gradient ΔTall in the out-of-plane direction [<NUM>-<NUM>]. In <FIG> and <FIG>, the magnetization direction of the thin film sample is parallel to the direction [<NUM>] of the applied magnetic field.

<FIG> shows the measurement results of the anomalous Nernst effect (magnetic field dependence of an electromotive force) at <NUM> when the thin film sample shown in <FIG> and <FIG> is made of Fe<NUM>Ga. <FIG> suggests that unlike in a bulk sample, in the thin film sample of Fe<NUM>Ga, an electromotive force of <NUM>µV is obtained even at zero magnetic field, which is almost the same as a value at a saturation magnetic field. The coercivity of the thin film sample of Fe<NUM>Ga is about <NUM> kA/m (<NUM> Oe).

In this measurement, the temperature difference in the out-of-plane direction obtained by the thermocouples is ΔTall=<NUM>. Here, it is difficult to accurately estimate a temperature gradient ∇Tfilm of the thin film sample itself. Hence, the measurement results shown in <FIG> are used, which are obtained when the temperature gradient is applied in the in-plane direction of the thin film sample and the magnetic field is applied in the out-of-plane direction. Assuming that the Nernst coefficient (<NUM>µV/K) of Fe<NUM>Ga shown in <FIG> is used to calculate ∇Tfilm in the out-of-plane direction, the temperature gradient applied in the out-of-plane direction of the <NUM>-thin film sample of Fe<NUM>Ga can be estimated to be <NUM>/mm.

In the method of producing the thin film described above, annealing is performed after the film growth at room temperature. As described below, polycrystalline or amorphous thin films obtained after the film growth at room temperature without annealing can also exhibit the anomalous Nernst effect as much as the annealed thin film sample.

The non-annealed thin film can be produced easily, and can be used for a flexible film. The [<NUM>]-oriented MgO substrate is required for producing the epitaxial film described above. In contrast, any substrate can be used for producing the polycrystalline films or the amorphous films.

In addition to MgO, examples of substrate materials include, but are not limited to, Si, Al<NUM>O<NUM>, PET, and polyimide.

<FIG> shows measurement results of the anomalous Nernst effect (magnetic field dependence of an electromotive force) at T=<NUM> when as shown in <FIG>, a temperature gradient is applied, in the out-of-plane direction, to the Fe<NUM>Ga thin film sample grown on the MgO substrate without annealing after film growth at room temperature. <FIG> is a graph illustrating an enlarged view in a low magnetic field region of <FIG>. As is the case with <FIG> and <FIG>, in <FIG>, the thickness of the Fe<NUM>Ga thin film sample is <NUM>, and the temperature gradient in the out-of-plane direction obtained by the thermocouples is ΔTall=<NUM> (<NUM>/mm).

<FIG> shows the measurement results of the anomalous Nernst effect (magnetic field dependence of an electromotive force) when a temperature gradient is applied in the out-of-plane direction, to a Fe<NUM>Ga epitaxial film obtained through annealing after the film growth at room temperature, and to a Fe<NUM>Ga amorphous film obtained without annealing after the film growth at room temperature. The measurement result of the amorphous film in <FIG> corresponds to the measurement result shown in <FIG>, and the measurement result of the epitaxial film in <FIG> corresponds to the measurement result of Fe<NUM>Ga shown in <FIG>.

<FIG> and <FIG> suggest that the electromotive force of the amorphous film is almost the same as that of the epitaxial film under a high magnetic field, and is about half of the electromotive force of the epitaxial film at zero magnetic field. That is, a Nernst coefficient of the amorphous thin film sample of Fe<NUM>Ga produced by film growth at room temperature is about <NUM>µV/K at zero magnetic field.

In the embodiments described above (<FIG>), the thickness of the thin film is <NUM>, but the thickness of the thin film is not limited, and may be <NUM> or less, more preferably <NUM> or less.

Claim 1:
A thermoelectric conversion element (<NUM>; 1A; <NUM>; <NUM>; <NUM>) made of one of:
a first material with a stoichiometric composition of Fe<NUM>X where X is a main-group element or a transition element;
a second material with an off-stoichiometric composition in which a composition ratio of Fe to X deviates from that of the first material, the second material having a D0<NUM>-type crystal structure or a B2-type crystal structure;
a third material obtained by substituting a part of Fe sites in the first material or a part of Fe sites in the second material by a main-group metal element or a transition element other than X;
a fourth material with a composition of Fe<NUM>M1<NUM>-xM2x where <NUM><x<<NUM>, and M1 and M2 are main-group elements different from each other; and
a fifth material obtained by substituting a part of Fe sites in the first material by a transition element other than X and substituting a part of X sites in the first material by a main-group metal element other than X, wherein
the first material, the second material, the third material, the fourth material, and the fifth material exhibit an anomalous Nernst effect.