Patent Description:
The anomalous Nernst effect in a magnetic body is a phenomenon that generates an electric field in vector product direction (∇T × M) of magnetization M and temperature gradient ∇T. When this is used, since a simple in-plane connection type structure series voltage can be increased, a thermoelectric power generation application and application to a heat flow sensor can be expected (See FIG. <NUM> and Patent Literature <NUM>).

However, the thermopower of the anomalous Nernst effect (anomalous Nernst coefficient) reported so far for various magnetic materials is <NUM>µV/K for Co<NUM>MnGa Heusler's alloy (Non-Patent Literature <NUM>), <NUM>µV/K for FeGa alloy (Non-Patent Literature <NUM>), and <NUM> to <NUM>µV/K for SmCo<NUM> permanent magnet (Non-Patent Literature <NUM>), even if it is large, and when compared with the thermopower of the Seebeck effect (Seebeck coefficient) of the material used for Seebeck thermoelectric power generation being about several <NUM>µV/K, the value remains small by about <NUM> orders of magnitude. The thermoelectric materials are comprehensively described in Non-Patent Literatures <NUM> and <NUM>, for example.

For the above application, development of a magnetic material having high thermopower by the Nernst effect is required, and realization of <NUM>µV/K is required in Non-Patent Literature <NUM>.

<NPL>) describes measurement of the anomalous Nernst effect in a perpendicularly magnetized Ir<NUM>Mn<NUM>/Co<NUM>Fe<NUM>B<NUM>/MgO thin film. The anomalous Nernst coefficient reaches <NUM>µV/K at room temperature.

For thermoelectric power generation applications and heat flow sensor applications, it has been conventionally aimed to realize thermopower due to the high anomalous Nernst effect as an essential characteristic of a magnetic material alone. However, the thermopower achieved at the present time remains at about <NUM>µV/K at the maximum.

The present invention solves the problem, and an object of the present invention is to provide a vertical thermoelectric conversion element having a novel structure capable of enhancing thermopower exhibiting symmetry similar to the anomalous Nernst effect while maintaining thermoelectric conversion characteristics of a magnetic material. Another object of the present invention is to provide a novel device with thermoelectric power generation application or heat flow sensor using the vertical thermoelectric conversion element.

The present inventors propose a structure of a novel vertical thermoelectric conversion element capable of enhancing thermopower exhibiting symmetry similar to the anomalous Nernst effect without essentially improving thermoelectric conversion characteristics of a magnetic material.

According to the vertical thermoelectric conversion element of the present invention, in the magnetic material forming the magnetic body layer, in addition to the anomalous Nernst effect generated by the magnetic material alone, the anomalous Hall effect generated with respect to the Seebeck current is superimposed, and a net anomalous Nernst thermoelectromotive force increasing effect is generated, so that high thermopower can be obtained. In other words, the thermoelectromotive force exhibiting symmetry similar to that of the anomalous Nernst effect is generated by assistance of the Seebeck effect and the anomalous Hall effect, and a vertical thermoelectric conversion element exhibiting high thermopower is obtained.

Hereinafter, the present invention is described with reference to the drawings.

<FIG> is a configuration perspective view of a vertical thermoelectric conversion element showing one embodiment of the present invention. In the figure, the vertical thermoelectric conversion element of the present invention has a three-layer structure of thermoelectric layer <NUM>, magnetic body layer <NUM>, and electrically insulating layer <NUM>, and includes high-temperature-side conductor part <NUM>, low-temperature-side conductor part <NUM>, and output terminals 26a and 26b. EANE indicates the anomalous Nernst effect voltage, ESE indicates the Seebeck effect voltage, M indicates the magnetization direction, ∇T indicates the direction of the temperature gradient from the low temperature side to the high temperature side.

Thermoelectric layer <NUM> is composed of a thermoelectric material having a Seebeck effect, one end portion of thermoelectric layer <NUM> is low-temperature-side end portion <NUM>, and the other end portion opposed to low-temperature-side end portion <NUM> is high-temperature-side end portion <NUM>. The thermoelectric material having the Seebeck effect is selected from Bi<NUM>Te<NUM>, PbTe, Si, Ge, an FeSi alloy, a CrSi alloy, an MgSi alloy, a CoSb<NUM> alloy, an Fe<NUM>VAl-based Heusler's alloy, and SrTiO<NUM>. Known thermoelectric materials are exhaustively listed in Non-Patent Literatures <NUM> and <NUM>. For the heating of high-temperature-side end portion <NUM>, for example, electrothermal heating, exhaust heat steam of a boiler device, or high-temperature drainage can be used. For cooling low-temperature-side end portion <NUM>, for example, air cooling or water cooling may be used, and a solid heat dissipation member may be attached.

Magnetic body layer <NUM> is magnetic body layer <NUM> stacked on thermoelectric layer <NUM> and has conductivity and generates a potential in the vector product direction of temperature gradient direction ∇T and magnetization direction M of magnetic layer <NUM> when magnetization or an external magnetic field is applied in the film thickness direction of magnetic body layer <NUM>. Magnetic body layer <NUM> is preferably to include a magnetic material that is a magnetic body having conductivity and having an anomalous Hall angle of <NUM>% or more. In the case of a magnetic body, both the anomalous Nernst effect and the anomalous Hall effect are exhibited, but in order to obtain a large assist effect, it is preferable to select a magnetic material exhibiting a large anomalous Hall effect (anomalous Hall angle).

Here, the anomalous Hall angle is a parameter indicating how much the current is bent in the lateral direction when the current flows through the magnetic body. When the anomalous Hall angle is less than <NUM>%, the potential generated in the vector product direction of temperature gradient direction ∇T and magnetization direction M of magnetic body layer <NUM> is low, which is not preferable for the vertical thermoelectric conversion element. Further, since it is necessary to have spontaneous magnetization at room temperature or higher in practical use, it is preferable to have spontaneous magnetization up to <NUM> or more.

As such the magnetic material having an anomalous Hall angle of <NUM>% or more and spontaneous magnetization up to <NUM> or more, there is at least one kind of magnetic material selected from the group consisting of an L1<NUM>-type ordered alloy, a Heusler's alloy, an iron-based alloy, and a permanent magnet material. That is, for example, the L1<NUM>-type ordered alloy includes FePt, CoPt, FePd, CoPd, FeNi, MnAl, and MnGa. For example, the Heusler's alloy includes Co<NUM>MnGa and Co<NUM>MnAl. For example, the D0<NUM>-type ordered alloy includes Mn<NUM>Ga, Mn<NUM>FeGa, Mn<NUM>CoGa, and Mn<NUM>RuGa. For example, the binary disordered alloy includes FeCr, FeAl, FeGa, FeSi, FeTa, FeIr, FePt, FeSn, FeSm, FeTb, CoFeB, CoTb, and NiPt. For example, the permanent magnet material includes an SmCo<NUM> magnet, an Sm<NUM>Co<NUM> magnet, and an Nd<NUM>Fe<NUM>B magnet. For example, the multilayer film magnetic material includes Co/Pt and Co/Pd. For example, the perovskite-type nitride material includes Mn<NUM>N and Fe<NUM>N. For example, the D0<NUM>-type ordered alloy includes Mn<NUM>Ga, Mn<NUM>Ge, and Mn<NUM>Sn.

Output terminals 26a and 26b are output terminals provided at both end portions in the vector product direction of magnetic body layer <NUM>, which is the vector product direction of temperature gradient direction ∇T of thermoelectric layer <NUM> and magnetization direction M of magnetic body layer <NUM>, for extracting a potential generated in the vector product direction.

Electrically insulating layer <NUM> is an electrically insulating layer having thermal conductivity provided between thermoelectric layer <NUM> and magnetic body layer <NUM> in the stacking direction. As the electrically insulating layer, for example, a layer containing one kind or two or more kinds of oxides such as SiO<NUM> and Al<NUM>O<NUM> or nitrides such as AlN and BN can be used.

High-temperature-side conductor part <NUM> connects high-temperature-side end portion <NUM> of the thermoelectric layer <NUM> and high-temperature-side end portion <NUM> of the magnetic body layer <NUM>, and for example, a conductor wire made of metal having low electric resistance such as a copper wire can be used. Low-temperature-side conductor part <NUM> connects low-temperature-side end portion <NUM> of thermoelectric layer <NUM> and low-temperature-side end portion <NUM> of magnetic body layer <NUM>, and for example, a conductor wire made of metal having low electric resistance such as a copper wire can be used.

When thermoelectric layer <NUM> has substantially the same conductivity as an insulator such as an oxide, electrically insulating layer <NUM> may be omitted. In this case, in the structure in which insulating layer <NUM> is not placed on the high temperature side and the low temperature side, high-temperature-side conductor part <NUM> and low-temperature-side conductor part <NUM> are unnecessary.

The operation of the vertical thermoelectric conversion element configured as described above is described.

Thermoelectric layer <NUM> and magnetic body layer <NUM> are stacked via electrically insulating layer <NUM>, and Seebeck thermoelectromotive force ESE due to thermoelectric material forming thermoelectric layer <NUM> is generated by temperature gradient ∇T of low-temperature-side end portion <NUM> and high-temperature-side end portion <NUM> of thermoelectric layer <NUM>. Since magnetic body layer <NUM> is in thermal contact with thermoelectric layer <NUM> via electrically insulating layer <NUM>, temperature gradient ∇T occurs between low-temperature-side end portion <NUM> and high-temperature-side end portion <NUM> of magnetic body layer <NUM>. Since an external magnetic field is applied to magnetic material layer <NUM> in the film thickness direction, or magnetic material layer <NUM> is magnetized with the film thickness direction as magnetization direction M due to the magnetic anisotropy of magnetic material <NUM> itself, a potential is generated in the vector product direction of temperature gradient direction ∇T and magnetization direction M of magnetic body layer <NUM> by the anomalous Nernst effect.

In thermoelectric layer <NUM> and magnetic body layer <NUM>, high-temperature-side end portion <NUM> of thermoelectric layer <NUM> and high-temperature side end <NUM> of magnetic body layer <NUM> are connected by high-temperature-side conductor part <NUM>, and low-temperature-side end portion <NUM> of thermoelectric layer <NUM> and low-temperature side end <NUM> of magnetic body layer <NUM> are connected by low-temperature-side conductor part <NUM>, so that an electrical closed circuit is formed. Under the temperature gradient, a Seebeck current flows in the magnetic material of magnetic body layer <NUM> due to a large thermoelectromotive force of the Seebeck thermoelectric material. As a result, in magnetic body layer <NUM>, the anomalous Hall effect is driven by the Seebeck current.

In this way, in order to thermally arrange the Seebeck thermoelectric material and the magnetic material that develop a large Seebeck thermoelectromotive force in parallel and to electrically insulate the Seebeck thermoelectric material and the magnetic material from each other, a structure is adopted in which the Seebeck thermoelectric material and the magnetic material are physically separated or an insulator is sandwiched therebetween. From this state, when only the high temperature side and the low temperature side of each of the Seebeck thermoelectric material and the magnetic material are electrically connected to form an electrically closed circuit, in the magnetic material forming the magnetic body layer, in addition to the anomalous Nernst effect generated by the magnetic material alone, the anomalous Hall effect generated with respect to the Seebeck current is superimposed, so that thermoelectromotive force is generated in the same direction as the anomalous Nernst thermoelectromotive force. Therefore, high thermopower can be obtained by the sum of these contributions.

Subsequently, the thermopower by the vertical thermoelectric conversion element of the present invention is calculated.

<FIG> is a model diagram of a Nernst voltage by a Seebeck assist effect. Low-temperature-side end portion <NUM> (TL) and high-temperature-side end portion <NUM> (TH) are located at both ends of thermoelectric layer <NUM>. LxS is a length (width) in the x-axis direction (width direction) of Seebeck thermoelectric material S. LzS is a length in the z-axis direction (longitudinal direction/Seebeck effect voltage direction) of Seebeck thermoelectric material S. LyS is a length (thickness) in the y-axis direction (film thickness direction) of Seebeck thermoelectric material S.

Low-temperature-side end portion <NUM> (TL) and high-temperature-side end portion <NUM> (TH) are located at both ends of the member of magnetic body layer <NUM> in the direction parallel to thermoelectric layer <NUM>. lxN is the length (width) in the x-axis direction (width direction) of the member of magnetic material N in the direction parallel to thermoelectric layer <NUM>. LzN is the length in the z-axis direction (longitudinal direction) of the member of magnetic material N in the direction parallel to thermoelectric layer <NUM>. LyN is the length (thickness) in the y-axis direction (film thickness direction/magnetization direction) of magnetic material N.

Voltage output terminals 26a and 26b are located at both ends of the member of magnetic body layer <NUM> in the direction orthogonal to thermoelectric layer <NUM>. LxN is the length (width) in the x-axis direction (width direction/anomalous Nernst effect voltage direction) of the member of magnetic material N in the direction orthogonal to thermoelectric layer <NUM>. lzN is the length in the z-axis direction (longitudinal direction) of the member of magnetic material N in the direction orthogonal to thermoelectric layer <NUM>.

In order to quantitatively estimate the thermopower by the vertical thermoelectric conversion element of the present invention, the following formula can be formulated corresponding to the model illustrated in <FIG>.

Here, the anomalous Hall effect means that the Hall resistivity increases in proportion to the external magnetic field in the normal Hall effect, but a huge Hall resistivity appears in the ferromagnetic metal in response to a change in magnetization. Empirically, Hall resistivity ρ is expressed by the following equation with respect to external magnetic field H and magnetization M.

Here, RH is a normal Hall coefficient, and RAHE is an anomalous Hall coefficient. Anomalous Hall coefficient RAHE is about <NUM> to <NUM> times larger than normal Hall coefficient RH.

Here, SS is the Seebeck coefficient of Seebeck thermoelectric material S, SN is the Seebeck coefficient of magnetic material N, SANE is the anomalous Nernst coefficient, ρAHE is the anomalous Hall effect coefficient, ρs is the electrical resistivity of Seebeck thermoelectric material S, and ρN is the electrical resistivity of magnetic material N. ExN is electric field E in the x-axis direction (film thickness direction/magnetization direction) of magnetic material N.

The second term on the right side of the above equation is a Nernst (Hall) voltage by Seebeck assist, and the larger the absolute value of the second term on the right side is, the larger the assist effect is. Anomalous Hall resistivity ρAHE in the second term on the right side indicates that the assist effect is large when anomalous Hall resistivity ρARE is large. In denominator of the second term on right side <MAT> indicates that when the electrical resistivity of Seebeck thermoelectric material S is small and the film thickness ratio with respect to magnetic material N is large, the assist effect is large. In a case where the sign of Seebeck coefficient SS of Seebeck thermoelectric material S and the sign of Seebeck coefficient SN of magnetic material N are different signs, SS in the second term on the right side indicates that the assist effect is large when the absolute value of SS is large. In addition, in a case where SS and SN are the same sign, when the absolute value of SS is larger than twice the absolute value of SN, it indicates that the assist effect is large when the absolute value of SS is large.

That is, it can be seen that the conditions under which the assist effect by Seebeck thermoelectric material S increases are a case where the film thickness ratio of the thermoelectric material to the magnetic material is small, the Seebeck electromotive force of the thermoelectric material is large and the electrical resistivity is low, and the anomalous Hall angle of the magnetic material is large. <FIG> illustrates a calculation result obtained by substituting each physical property parameter in this model when Co<NUM>MnGa is used as the magnetic material and an n-type Si substrate is used as the thermoelectric material. As the film thickness ratio of Co<NUM>MnGa to Si decreases, the assist effect increases, and a Nernst electromotive force of <NUM>µV/K at the maximum is realized, as shown by the phenological calculation.

As an example for demonstrating the present invention, a Heusler's alloy magnetic thin film Co<NUM>MnGa was formed on three substrates of n-type doped, p-type doped, and non-doped, and a verification experiment was conducted.

In the first manufacturing process, as shown in <FIG>, a thermally oxidized SiO insulating film having a thickness of <NUM> was formed on the surfaces of all the substrates. Usually, the Co<NUM>MnGa thin film and the Si substrate are electrically insulated.

In the next manufacturing process, as shown in <FIG>, insulating films near both left and right ends of the Co<NUM>MnGa thin film were removed by a laser, metal electrodes were attached to the portions, and the Co<NUM>MnGa thin film and the Si substrate were electrically connected at both ends to form a closed circuit.

In this example, a total of six kinds of samples of [two kinds × three kinds of substrates] with and without laser removal were evaluated. The Seebeck effect and anomalous Nernst effect were measured by flowing a heat flow in the plane of the substrate. The experimental results are shown in Table <NUM>.

When the Seebeck effect was measured, it was confirmed that in the sample electrically connected to Si, the Seebeck voltage of the Co<NUM>MnGa thin film changed due to the influence of the Seebeck effect of the substrate. In the n-type Si substrate, the voltage is about -<NUM>µV/K without removal of the insulating film by laser, but when a closed circuit was formed, a Seebeck effect of -<NUM>µV/K appeared. In addition, it was confirmed that when the anomalous Nernst effect was measured, in the sample using the n-type Si substrate, the thermoelectromotive force was about + <NUM>µV/K in the case of the magnetic film alone, but the thermoelectromotive force was increased <NUM> times or more to + <NUM>µV/K in the case of being electrically connected to the Si substrate. This output increase is smaller than the prediction + <NUM>µV/K by the above model calculation, but is an experimental result demonstrating the effect of the present invention.

<FIG> is a configuration perspective view illustrating an example of an application element to a thermoelectric power generation application or a heat flow sensor using the vertical thermoelectric conversion element of the present invention.

As illustrated in <FIG>, a series voltage can be amplified by a simple in-plane connection type thermopile structure.

In the Examples, a case where a Si substrate was stacked as a thermoelectric layer, a Co<NUM>MnGa thin film was stacked as a magnetic body layer, and a thermally oxidized SiO insulating film was stacked as an insulating layer is described, but the present invention is not limited thereto, and a thermoelectric material having a Seebeck effect can be used for the thermoelectric layer, a conductive ferromagnetic material can be used for the magnetic body layer, and an electrically insulating material having thermal conductivity can be used for the insulating layer. The thermoelectric material having the Seebeck effect is selected from Bi<NUM>Te<NUM>, PbTe, Si, Ge, an FeSi alloy, a CrSi alloy, an MgSi alloy, a CoSb<NUM> alloy, an Fe<NUM>VAl-based Heusler's alloy, and SrTiO<NUM>.

Claim 1:
A vertical thermoelectric conversion element comprising:
a thermoelectric layer (<NUM>) made of a thermoelectric material exhibiting a Seebeck effect, wherein one end portion of the thermoelectric layer (<NUM>) is on a low temperature side, and the other end portion (<NUM>) opposed to the low-temperature-side end portion (<NUM>) is on a high temperature side;
a magnetic body layer (<NUM>) stacked on the thermoelectric layer (<NUM>), wherein the magnetic body layer (<NUM>) has a magnetization component in a film thickness direction of the magnetic body layer (<NUM>), has conductivity, and generates a potential in a vector product direction of a temperature gradient direction and a magnetization direction of the magnetic body layer (<NUM>);
a low-temperature-side conductor part (<NUM>) connecting a low-temperature-side end portion (<NUM>) of the thermoelectric layer (<NUM>) and a low-temperature-side end portion (<NUM>) of the magnetic body layer (<NUM>),
a high-temperature-side conductor part (<NUM>) connecting a high-temperature-side end portion (<NUM>) of the thermoelectric layer (<NUM>) and a high-temperature-side end portion (<NUM>) of the magnetic body layer (<NUM>); and
output terminals (26a, 26b) provided at both end portions of the magnetic body layer (<NUM>) in the vector product direction, which are in the vector product direction of the temperature gradient direction (∇T) of the thermoelectric layer (<NUM>) and the magnetization direction (M) of the magnetic body layer (<NUM>), for extracting a potential generated in the vector product direction;
wherein the thermoelectric layer (<NUM>) includes at least one kind of thermoelectric material selected from the group of thermoelectric materials including Bi<NUM>Te<NUM>, PbTe, Si, Ge, an Fe-Si alloy, a Cr-Si alloy, an Mg-Si alloy, a CoSb<NUM> alloy, an Fe<NUM>VAl-based Heusler's alloy, and SrTiO<NUM>.