JP2016162881A - Thermoelectric conversion element and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve higher output of a thermoelectric conversion element.SOLUTION: In a thermoelectric conversion element, a magnetic substance layer 502 exhibiting a spin-Seebeck effect and a metal layer 503 exhibiting an inverse spin hole effect are laminated on a substrate 501. The magnetic substance layer 502 has larger spin current rush efficiency in a region on the substrate 501 side in comparison with the region on the metal layer 503 side, and the region on the metal layer 503 side has larger spin current rush efficiency in comparison with the region on the substrate 501 side. In the magnetic substance layer 502, a magnetic material composition continuously changes between the substrate 501 and the metal layer 503.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a thermoelectric conversion element based on a spin Seebeck effect and an inverse spin Hall effect, and a manufacturing method thereof.

  Expectations for thermoelectric conversion elements are increasing as efforts to address environmental and energy issues toward a sustainable society are becoming more active. This is because heat is the most common energy source that can be obtained from any medium such as body temperature, sunlight, engine, industrial waste heat. Therefore, thermoelectric conversion elements are expected to become more important in the future in applications such as increasing the efficiency of energy use in a low-carbon society and supplying power to ubiquitous terminals and sensors.

Recent research has revealed the existence of the “Spin-Seebeck Effect” in magnetic materials. The spin Seebeck effect is a phenomenon in which, when a temperature gradient is applied to a magnetic material, a flow of spin angular momentum of electrons (spin flow) occurs in a direction parallel to the temperature gradient [Patent Document 1]. Patent Document 1 reports the spin Seebeck effect in NiFe films, which are ferromagnetic materials, and Non-Patent Documents 1 and 2 describe magnetic insulators and metal films such as yttrium iron garnet (YIG, Y ₃ Fe ₅ O ₁₂ ). The spin Seebeck effect at the interface is reported.

  The spin current generated by the temperature gradient is converted into a current by the inverse spin-Hall effect. The reverse spin Hall effect is a phenomenon in which a spin current is converted into a current by spin orbit coupling of a substance, and is significant in a substance having a large spin orbit interaction (eg, Pt, Au, etc.). To express.

  In recent years, "spin thermoelectric conversion", which converts the temperature gradient into current via spin by using both the spin Seebeck effect and the inverse spin Hall effect, has attracted attention. A new thermoelectric conversion element, "spin thermoelectric element" Development is expected.

  FIG. 3 is a perspective view showing an outline of the thermoelectric conversion element disclosed in Patent Document 1. As shown in FIG. A thermal spin current converter 102 is formed on the sapphire substrate 101. The thermal spin current conversion unit 102 has a laminated structure of a Ta film 103, a PdPtMn film 104, and a NiFe film 105. Further, a Pt electrode 106 is formed on the NiFe film 105, and both ends of the Pt electrode 106 are connected to terminals 107-1 and 107-2, respectively. In the spin thermoelectric device configured as described above, the NiFe film 105 plays a role of generating a spin current from the temperature gradient by the spin Seebeck effect, and the Pt electrode 106 generates an electromotive force from the spin current by the reverse spin Hall effect. Play a role.

  Specifically, when a temperature gradient is applied in the in-plane direction of the NiFe film 105, a spin current is generated in a direction parallel to the temperature gradient due to the spin Seebeck effect. Then, a spin current flows from the NiFe film 105 to the Pt electrode 106, or a spin current flows from the Pt electrode 106 to the NiFe layer 105. Then, an electromotive force is generated in the Pt electrode 106 in a direction orthogonal to the spin current direction and the magnetization direction of NiFe due to the reverse spin Hall effect. The electromotive force can be taken out from terminals 107-1 and 107-2 provided at both ends of the Pt electrode 106.

Further, as one method for producing a spin thermoelectric element, there is an organometallic decomposition method (MOD (Metal Organic Decomposition) method) as described in Patent Document 2 (International Publication No. 2012/108276). FIG. 4 is a perspective view showing an outline of the thermoelectric conversion element described in Patent Document 2. Gadolinium Gallium Garnet (hereinafter referred to as “GGG”. The composition is Gd ₃ Ga ₅ O ₁₂ ) Substrate 4, Y part of Y site replaced with Bi (Yttrium Iron Garnet, hereinafter referred to as “GGG”) . "Bi _x: YIG" and denoted composition _{Bi x Y 3-x Fe 5} O 12) MOD solution that contains a spin coating a, Bi by sintering _x: create a YIG film 12 can do. Further, a spin thermoelectric element can be formed by forming a Pt electrode 3 on this film by sputtering. By applying a temperature gradient ΔT in the perpendicular direction B of this element and applying a magnetic field in the in-plane direction C, the electromotive force can be taken out from the electrodes 7 and 9.

  However, since the current output of the spin thermoelectric element is small and about several uV / K, it has not been put into practical use. For this reason, increasing the output of the spin thermoelectric element is a major issue. In order to increase the output of the spin thermoelectric device, the generation efficiency of the spin current generated in the magnetic film (spin current generation efficiency) is large, and the rush efficiency when the spin current generated in the magnetic film enters the metal film ( Development of magnetic materials with high spin current entry efficiency is required. However, there is a trade-off between spin current generation efficiency and spin current entry efficiency, and it is difficult to develop a magnetic material having both high spin current generation efficiency and spin current entry efficiency.

  Patent Document 3 describes a thermoelectric conversion element in which an insulating ferromagnetic layer, a metal ferromagnetic layer, and a nonmagnetic metal layer whose magnetization is fixed in one direction are formed in this order on a substrate. Since the interface between the nonmagnetic metal layer and the metal ferromagnetic layer has a higher interface mixing effect than the interface between the nonmagnetic metal layer and the insulating ferromagnetic layer, the spin current from the insulating ferromagnetic layer toward the nonmagnetic metal layer Is described as increasing. As a result, high power generation efficiency can be realized.

  Patent Document 4 describes a thermoelectric conversion in which a spin injection layer is provided between a magnetic layer such as NiFe or YIG having a magnetization component in an in-plane direction and an electromotive layer such as Au, Pt, Pd, or Ir. An element is described. The spin injection layer is made of, for example, iron oxide or nickel oxide, and is provided as an interface for improving the spin injection efficiency from the magnetic layer to the electromotive layer.

JP 2009-130070 International Publication No.2012 / 108276 JP 2014-216333 A Japanese Unexamined Patent Publication No. 2014-072250

Uchida et al. “Spin Seebeck insulator”, Nature Materials, 2010 vol.9 p.894 Uchida et al. “Observation of longitudinal spin-seebeck effect in magnetic insulator”, applied Physics Letters, 2010, vol.97, p172505

  Patent Document 3 has an interface between the insulating ferromagnetic layer and the metal ferromagnetic layer, and Patent Document 4 has an interface between the magnetic layer and the spin current injection layer, where the spin current is scattered. Therefore, the spin current injected into the nonmagnetic metal layer or the electromotive layer is reduced, which hinders improvement of thermoelectric characteristics (thermoelectromotive force).

  An object of the present invention is to solve the above-described problems and provide a spin thermoelectric element with higher output and a method for manufacturing the same.

  The thermoelectric conversion element of the present invention is a thermoelectric conversion element in which a magnetic layer that exhibits a spin Seebeck effect and a metal layer that exhibits an inverse spin Hall effect are stacked on a substrate, wherein the magnetic layer is on the substrate side. This region has a larger spin current efficiency than the region on the metal layer side, the region on the metal layer side has a higher spin current entry efficiency than the region on the substrate side, and the magnetic layer has a composition of a magnetic material. Is continuously changing between the substrate and the metal layer.

  The method for manufacturing a thermoelectric conversion element of the present invention is a method for manufacturing a thermoelectric conversion element in which a magnetic layer that exhibits a spin Seebeck effect and a metal layer that exhibits an inverse spin Hall effect are laminated on a substrate. Then, a solution containing a magnetic material having a high spin current efficiency is applied on the substrate and dried, and a solution containing a magnetic material having a high spin current entry efficiency is applied thereon, dried, and baked. The magnetic layer is characterized in that the composition of the magnetic material continuously changes between the substrate and the metal layer, and then the metal layer is formed.

  According to the present invention, it is possible to further increase the output of the spin thermoelectric element.

It is a perspective view which shows the outline of the spin thermoelectric element as described in 1st embodiment of this invention. Pt / Bi _x Yb _y embodiment of the present invention: is a perspective view showing an outline of a YIG / GGG spin thermoelectric elements. 1 is a perspective view showing an outline of a thermoelectric conversion element disclosed in Patent Document 1. FIG. 6 is a perspective view showing an outline of a thermoelectric conversion element described in Patent Document 2. FIG.

(First embodiment)
A first embodiment of the present invention will be described below in detail with reference to the drawings.
[Description of structure]
FIG. 1 is a perspective view schematically showing the spin thermoelectric element of the first embodiment of the present invention. In this structure, a substrate 501, a magnetic layer 502 and a metal layer 503 are provided. The magnetic layer 502 has a material composition change in the z-axis direction, that is, the stacking direction of the elements. Further, a terminal 504 and a terminal 505 are provided on the metal layer 503.

  The substrate 501 side of the magnetic layer 502 is made of a material having a higher spin current generation efficiency than the metal layer 503 side of the magnetic layer 502. On the other hand, the metal layer 503 side of the magnetic layer 502 is made of a material having a higher spin current entry efficiency than that of the magnetic layer 502 on the substrate 501 side. The composition of the magnetic layer 502 changes continuously between the substrate 501 and the metal layer 503.

  A material having a large spin current generation efficiency is a material having a large spin relaxation. For example, a c-site of YIG is converted to Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er with orbital angular momentum quantum number L. , Tm, Yb, or any other substituted magnetic material. A material with high spin current entry efficiency is a material with low spin relaxation, for example, the c site of YIG or YIG, La, Gd, Lu, Bi, Ca, Cu, etc. that do not have orbital angular momentum quantum numbers. This corresponds to a magnetic material substituted with one of these elements. The metal layer 503 is preferably composed of an element having a large spin orbit interaction, such as Au, Pt, Ir, or Bi.

  The thickness of the magnetic layer 502 can be changed in accordance with the use of thermoelectric power generation and the temperature range, but it is usually desirable to set it to about several tens of nanometers to several um, which is about the diffusion length of thermal magnon. Further, the thickness of the metal layer 503 is preferably set to several nm to several hundred nm, which is about the spin diffusion length of the electromotive layer.

By applying a magnetic field in the x direction (direction perpendicular to the line connecting the two terminals 504 and 505 in the stacking plane of the element) and a temperature gradient in the z direction (stacking direction of the element) of this spin thermoelectric element, spin Seebeck Due to the effect, a spin current is generated in the z direction in the magnetic layer. When this spin current enters the metal layer 503, the spin current is converted into a current by the reverse spin Hall effect. Thereby, the electromotive force can be taken out from the terminal 504 and the terminal 505.
[Description of effects]
As described above, a material having a high spin current generation efficiency is used near the substrate 501 of the magnetic layer 502, and a material having a high spin current entry efficiency is used near the metal layer 503 of the magnetic layer 502. A large spin current generated in the vicinity of the substrate of the layer 502 can efficiently enter the metal layer 503 through a material having a high spin entry efficiency. As a result, the output of the spin thermoelectric element can be further increased.

On the other hand, Patent Document 3 has an interface between the insulating ferromagnetic layer and the metal ferromagnetic layer, and Patent Document 4 has an interface between the magnetic layer and the spin current injection layer, where the spin current is scattered. Therefore, the spin current injected into the nonmagnetic metal layer or the electromotive layer is reduced, which hinders improvement of thermoelectric characteristics (thermoelectromotive force). However, compared to the case where an interface exists as in Patent Documents 3 and 4, the composition from one region having a high spin current generation efficiency to a region having a high spin current entry efficiency in one magnetic layer 502 as in this embodiment. When is continuously changed, the interface does not exist. Therefore, scattering of the spin current at the interface is eliminated, and as a result, the thermoelectric characteristics are improved.
[Description of manufacturing method]
With reference to FIG. 1, the example of the manufacturing method of the spin thermoelectric element of this embodiment is demonstrated. First, a magnetic layer 502 having a material composition change in the z-axis direction is formed on a GGG substrate 501 by an organometallic decomposition method (MOD method).

  In this procedure, a MOD solution of a magnetic material having a high spin current generation efficiency is applied on the GGG substrate 501 with a spin coater, and then dried to remove the organic solvent. On top of that, a MOD solution of a magnetic material having a high spin flow entry efficiency is applied by a spin coater, and then dried to remove the organic solvent. Next, provisional baking is performed to decompose and volatilize the organic matter, and then main baking is performed to convert to oxide and crystallize.

  By firing together the MOD solution of the material having a high spin current generation efficiency and the MOD solution of the material having a high spin current injection efficiency in this way, the substrate 501 side is a material having a high spin current generation efficiency and the metal layer 503 side is a spin. It is possible to create a magnetic layer 502 that is made of a material having a high flow entry efficiency and in which the composition changes gently. Finally, a metal layer 503 made of an element having a large spin orbit interaction (for example, Au, Pt, Ir, Bi, etc.) is formed on the magnetic layer 502 thus formed. Examples of the method include a sputtering method, a vapor deposition method, a plating method, and a screen printing method.

  By applying a magnetic field in the x direction and a temperature gradient in the z direction of the spin thermoelectric element, an electromotive force can be taken out from the terminal 504 and the terminal 505.

  Compared to the case of forming in two layers as in Patent Documents 3 and 4, the manufacturing method of this embodiment can simplify the process. For example, when creating a magnetic layer and a spin injection layer as separate layers by the MOD method, a total of 8 processes (spin coating of magnetic layer material ⇒ drying ⇒ temporary firing ⇒ firing ⇒ spin coating of spin injection layer material ⇒ drying ⇒ Temporary firing ⇒ Main sintering) However, in this embodiment, as described above, a total of six processes (spin coating of magnetic layer material → drying → spin coating of spin injection layer material → drying → temporary firing → main sintering) are sufficient.

  The method for manufacturing the spin thermoelectric element is merely an example, and the present invention is not limited to this.

2, GGG substrate 601 as the substrate, YIG and Bi part of and replaced with Yb and Bi Y site _x Yb _y as magnetic _{layers: YIG (Bi x Yb y Y} 2 Fe 5 O 12) magnetic layers 602 (hereinafter Bi _x Yb _y: abbreviated as YIG magnetic layer 602), a Pt layer 603 as a metal layer Pt / Bi _x Yb _y: is a perspective view showing an outline of a YIG / GGG spin thermoelectric elements. Since Yb has an orbital angular momentum quantum number L, spin relaxation is large and spin current generation efficiency is large. In addition, since Bi does not have the orbital angular momentum quantum number L, spin relaxation is small and spin current entry efficiency is large.

First, Bi organometallic decomposition (MOD) method on the GGG substrate 601 _x Yb _y: Create a YIG magnetic layer 602. The procedure is as follows. _First , a Yb ₁ : YIG MOD solution is applied onto the GGG substrate 601 with a spin coater, and then dried to remove the organic solvent. On top of this, a Bi ₁ : YIG MOD solution is applied with a spin coater and then dried to remove the organic solvent. Next, pre-baking is performed to decompose and volatilize the organic matter, and then main baking is performed to perform oxidation and crystallization. Next, Bi _x Yb _y created: forming the Pt layer 603 by a sputtering method on YIG magnetic layer 602.

  By applying a magnetic field in the x direction and a temperature gradient in the z direction of the spin thermoelectric element, an electromotive force can be taken out from the terminal 604 and the terminal 605.

The Bi _x Yb _y : YIG magnetic layer 602 of the Pt / B _{i x} Yb _y : YIG / GGG spin thermoelectric element created by the above procedure has a large amount of Yb and a small amount of Bi on the GGG substrate 601 side (x is small and y is large). The Pt layer 603 side is in a state where Yb is small and Bi is large (x is large and y is small). Therefore the _{Pt / Bi x Yb y: YIG} / GGG spin thermoelectric element, the spin current generator efficiency and spin current inrush efficiency are both large, it is possible to generate a larger thermoelectromotive force.

501 board
502 Magnetic layer
503 metal layer
504, 505 terminals
601 GGG board
602 Bi _x Yb _y : YIG magnetic layer
603 Pt layer
604, 605 terminals

Claims (8)

A thermoelectric conversion element in which a magnetic layer expressing a spin Seebeck effect and a metal layer expressing a reverse spin Hall effect are laminated on a substrate,
In the magnetic layer, the region on the substrate side has a higher spin current efficiency than the region on the metal layer side, and the region on the metal layer side has a higher spin current entry efficiency than the region on the substrate side,
The thermoelectric conversion element, wherein the magnetic layer has a composition of a magnetic material that continuously changes between the substrate and the metal layer.   2. The thermoelectric conversion device according to claim 1, wherein the region on the metal layer side of the magnetic layer has a smaller spin relaxation than the region on the substrate side of the magnetic layer. 3. element.   3. The thermoelectric conversion element according to claim 1, wherein the region on the metal layer side of the magnetic layer is YIG or a part of the c-site of YIG is an element Bi not including an orbital angular momentum quantum number. A thermoelectric conversion element using a magnetic material substituted with Cu, Ca, La, Gd or Lu. 4. The thermoelectric conversion element according to claim 1, wherein a region on the substrate side of the magnetic layer includes a part of a c-site of YIG and an element Ce including an orbital angular momentum quantum number. 5. A thermoelectric conversion element using a magnetic material substituted with Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb or Lu.   5. The thermoelectric conversion element according to claim 1, wherein two terminals are provided on the metal layer, a magnetic field is applied in a direction in the lamination plane of the magnetic layer, and a temperature is applied in the lamination direction. A thermoelectric conversion element, wherein an electromotive force is taken out between the two terminals by applying a gradient.   6. The thermoelectric conversion element according to claim 1, wherein the thickness of the magnetic layer is about the diffusion length of thermal magnon. A method of manufacturing a thermoelectric conversion element in which a magnetic layer that expresses a spin Seebeck effect and a metal layer that expresses a reverse spin Hall effect are laminated on a substrate,
By applying and drying a solution containing a magnetic material having a large spin current efficiency on the substrate, applying and drying a solution containing a magnetic material having a large spin current efficiency on the substrate, and baking it. The magnetic layer is configured so that the composition of the magnetic material continuously changes between the substrate and the metal layer;
Thereafter, the metal layer is formed. A method for manufacturing a thermoelectric conversion element.   8. The method of manufacturing a thermoelectric conversion element according to claim 7, wherein the solution containing a magnetic material having a high spin current efficiency is a solution containing Yb: YIG, and includes the magnetic material having a high spin current entry efficiency. The solution is a Bi: YIG MOD solution, a method for manufacturing a thermoelectric conversion element.

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