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## Creator

[Fuyuki Ando](https://orcid.org/0009-0003-7789-8170), [Takamasa Hirai](https://orcid.org/0000-0002-5577-8018), [Abdulkareem Alasli](https://orcid.org/0000-0002-1681-0492), [Hossein Sepehri-Amin](https://orcid.org/0000-0002-7856-7897), [Yutaka Iwasaki](https://orcid.org/0000-0002-7317-4939), Hosei Nagano, [Ken-ichi Uchida](https://orcid.org/0000-0001-7680-3051)

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[Multifunctional composite magnet realizing record-high transverse thermoelectric generation](https://mdr.nims.go.jp/datasets/6501a255-8b01-43a0-ad15-2ea7491f86c8)

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Multifunctional composite magnet realizing record-high transverse thermoelectric generationAs featured in:  Spin Caloritronics Group, Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science, Tsukuba 305-0047, Japan.  Multifunctional composite magnet realizing record-high transverse thermoelectric generation  We have created a novel functional material named “multifunctional composite magnet (MCM)”, which simultaneously exhibits record-high transverse thermoelectric performance and permanent magnet features. Owing to the optimized composite structure and extremely low interfacial electrical and thermal resistivities, the power generation performance of our MCM-based thermopile module is not only record-high among transverse thermoelectric modules but also comparable to that of commercial modules utilizing the Seebeck effect. This multifunctionality will extend application fields of thermoelectrics to everywhere permanent magnets are used. Image reproduced by permission of Ken-ichi Uchida from  Energy Environ .  Sci ., 2025,  18 , 4068  See Fuyuki Ando, Ken-ichi Uchida  et al .,  Energy Environ .  Sci ., 2025,  18 , 4068.Energy &EnvironmentalScience REVIEW ARTICLE  Minghua Chen, Huang Zhang, Stefano Passerini  et al .  Anode-free sodium metal batteries: optimisation of electrolytes and interphases rsc.li/eesISSN 1754-5706Volume 18Number 97 May 2025Pages 3873–4482rsc.li/eesRegistered charity number: 2078904068 |  Energy Environ. Sci., 2025, 18, 4068–4079 This journal is © The Royal Society of Chemistry 2025Cite this: Energy Environ. Sci.,2025, 18, 4068Multifunctional composite magnet realizingrecord-high transverse thermoelectric generation†Fuyuki Ando, *a Takamasa Hirai, a Abdulkareem Alasli, b Hossein Sepehri-Amin,aYutaka Iwasaki,a Hosei Naganob and Ken-ichi Uchida *acPermanent magnets are used in various products and essential for human society. If omnipresentpermanent magnets could directly convert heat into electricity, they would lead to innovative energyharvesting and thermal management technologies. However, achieving such ‘‘multifunctionality’’ hasbeen difficult due to poor thermoelectric performance of conventional magnets. In this work, wedevelop a multifunctional composite magnet (MCM) that enables giant transverse thermoelectricconversion while possessing permanent magnet features. MCM comprising alternately and obliquelystacked SmCo5/Bi0.2Sb1.8Te3 multilayers exhibits an excellent transverse thermoelectric figure of meritzxyT of 0.20 at room temperature owing to the optimized anisotropic structure and extremely lowinterfacial electrical and thermal resistivities between the SmCo5 and Bi0.2Sb1.8Te3 layers. The MCM-based thermopile module generates a maximum of 204 mW at a temperature difference of 152 K,whose power density normalized by the heat transfer area and temperature gradient is not only record-high among transverse thermoelectric modules but also comparable to those of commercialthermoelectric modules utilizing the Seebeck effect. The multifunctionality of our MCM providesunprecedented opportunities for energy harvesting and thermal management everywhere permanentmagnets are currently used.Broader contextFor the realization of a carbon-neutral society, new core technologies for energy harvesting and thermal management are strongly desired in various factoriesand industries including automobile and electronics. We have created a novel functional material named ‘‘multifunctional composite magnet (MCM)’’, whichsimultaneously exhibits practically applicable giant transverse thermoelectric conversion and permanent magnet features. Our developed MCM comprisingalternately and obliquely stacked SmCo5/Bi0.2Sb1.8Te3 multilayers exhibits an excellent transverse thermoelectric figure of merit of 0.20 at room temperatureowing to the optimized anisotropic structure and extremely low interfacial electrical and thermal resistivities between the SmCo5 and Bi0.2Sb1.8Te3 layers. Thepower generation performance of our MCM-based thermopile module is not only record-high among transverse thermoelectric modules but also comparable tothat of commercial modules utilizing the Seebeck effect. This multifunctionality will extend application fields of thermoelectrics to everywhere permanentmagnets are used.1. IntroductionTransverse thermoelectric effects realize the interconversionbetween the charge and heat currents in the orthogonal direc-tion. The orthogonal geometry simplifies the thermoelectricdevice architecture because it can eliminate substrates, electro-des, and their junctions in the thermal circuit. This junction-less structure makes it possible to apply a larger temperaturegradient rT to thermoelectric materials owing to the absenceof substrates, improve the thermoelectric conversion efficiencyowing to the lack of interfacial thermal resistance between thethermoelectric materials and electrodes, and suppress thermaldeterioration at hot-side junctions, all of which are significantissues for conventional longitudinal thermoelectric modulesbased on the Seebeck effect.1–3 To utilize these geometricaladvantages, many recent studies have focused on the develop-ment of physics, materials science, and device architectures fortransverse thermoelectric conversion.a National Institute for Materials Science, Tsukuba 305-0047, Japan.E-mail: ANDO.Fuyuki@nims.go.jp, UCHIDA.Kenichi@nims.go.jpb Department of Mechanical Systems Engineering, Nagoya University, Nagoya 464-8603, Japanc Department of Advanced Materials Science, Graduate School of Frontier Sciences,The University of Tokyo, Kashiwa 277-8561, Japan† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ee04845hReceived 20th October 2024,Accepted 14th February 2025DOI: 10.1039/d4ee04845hrsc.li/eesEnergy &EnvironmentalSciencePAPEROpen Access Article. Published on 18 March 2025. Downloaded on 5/12/2025 2:44:00 AM.  This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.View Article OnlineView Journal  | View Issuehttps://orcid.org/0009-0003-7789-8170https://orcid.org/0000-0002-5577-8018https://orcid.org/0000-0002-1681-0492https://orcid.org/0000-0001-7680-3051http://crossmark.crossref.org/dialog/?doi=10.1039/d4ee04845h&domain=pdf&date_stamp=2025-03-01https://doi.org/10.1039/d4ee04845hhttps://doi.org/10.1039/d4ee04845hhttps://rsc.li/eeshttp://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/https://doi.org/10.1039/d4ee04845hhttps://pubs.rsc.org/en/journals/journal/EEhttps://pubs.rsc.org/en/journals/journal/EE?issueid=EE018009This journal is © The Royal Society of Chemistry 2025 Energy Environ. Sci., 2025, 18, 4068–4079 |  4069The transverse thermoelectric effects are classified intovarious mechanisms.4 Following the classification in ref. 4,the four mechanisms are related to magnetism or spin: theordinary and anomalous Nernst effects,5–21 the spin Seebeckeffect,22 and the Seebeck-effect-driven anomalous Hall effect.23The other mechanisms are unrelated to magnetism or spin: theoff-diagonal Seebeck effects (ODSEs)3,24–40 in natural anisotro-pic crystals and artificial anisotropic composites. The ordinaryNernst effect has been studied for a long period5 to enable largetransverse thermoelectric conversion, but its operation requiresthe application of a large external magnetic field (typicallyabove 2 T). Recently, with the development of topologicalmaterials science and spin caloritronics, the anomalous Nernsteffect (ANE) in magnetic materials has been intensivelystudied.7–10,12–14,17,19 Thermoelectric conversion through ANErequires spatially uniform magnetization, which is typicallyachieved by applying external magnetic fields. From anapplication point of view, ANE for permanent magnets withremanent magnetization Mr has been studied to achievemagnetic-field-free operation of transverse thermoelectricconversion.11,15,20 Although these developments realize multi-functionality enabling transverse thermoelectric conversion,the tiny transverse thermoelectric figure of merit zxyT for ANE(o10�3) hinders future applications of multifunctional mag-nets. By contrast, the studies on ODSEs have independentlyprogressed and predicted a considerably higher zxyT (4 0.1 atroom temperature) compared with that for ANE.28,33,34,37–39ODSE in an artificial composite system is enhanced when twomaterials having opposite Seebeck coefficients, i.e., p- and n-type materials, and large differences in electrical and thermalconductivities are alternately and obliquely stacked (artificiallytilted multilayers, ATMLs).27 However, despite the wide mate-rial selectivity, no attempts have been made to integrate themagnetic functionality into ATMLs, except for a recent study.40Although ATMLs consisting of Nd2Fe14B-type permanent mag-nets and Bi88Sb12 have been developed, their transverse ther-moelectric performance is poor (zxyT o 2.0 � 10�3) because thesign of the Seebeck coefficient of Nd2Fe14B is the same as thatof Bi88Sb12.Here, we have developed MCM that exhibits giant transversethermoelectric conversion in addition to large remanent mag-netization and coercivity (Fig. 1). Our MCM, comprising alter-nately and obliquely stacked SmCo5-type permanent magnets(SmCo5) and thermoelectric Bi0.2Sb1.8Te3 (BST) slabs, experi-mentally exhibits an excellent zxyT of 0.20 at room temperatureowing to the optimized anisotropic composite structure andextremely low interfacial electrical and thermal resistivitiesbetween the SmCo5 and BST layers. Utilizing these high-performance MCM elements, we constructed a lateral thermo-pile module to obtain a higher thermoelectric voltage whilemaintaining the magnetic functionality. The MCM-based mod-ule exhibits an output power P of 204 mW at a temperaturedifference DT of 152 K, which corresponds to the record-highnormalized power density per heat transfer area and rT2 of0.17 mW cm�2 (K mm�1)�2 among those of the transversethermoelectric modules.2. Results and discussion2.1 Magnetic and analytical transverse thermoelectricpropertiesODSE in ATMLs generates an electric field E in the directionperpendicular to rT owing to the anisotropic transport proper-ties in the tilted axes with respect to the rT direction (Fig. 2a).When the thermal conductivity of the two constituent materialsis different, the heat current Jq nonuniformly flows in ATMLs bythe application of rT because Jq is likely to flow in a path witha high thermal conductivity, that is, in the direction parallel tohigh-thermal-conductive layers and perpendicular to low-thermal-conductive layers. Then, through the thermoelectricconversion by the Seebeck effect in the p- and n-type layers, thetransverse component of the charge current Jc (or E) is addi-tively generated (see Note S1 and Fig. S1, ESI,† where thenonuniform charge-to-heat current conversion due to the ori-gin of ODSE was confirmed by the lock-in thermographymethod). Here, the primary characteristic of ODSE is that, evenif the Seebeck coefficient S of the constituent material is nothigh, zxyT can be enhanced by combining p- and n-typematerials whose electrical resistivity r and thermal conduc-tivity k are largely different. Indeed, ATMLs composed of metalsand thermoelectric semiconductors, such as n-type Ni/p-typeBi0.5Sb1.5Te3,28,30,31,34 n-type YbAl3/p-type Bi0.5Sb1.5Te3,33 p-typeFe/n-type Bi2Te2.7Se0.3,37 and n-type Co/p-type Bi0.5Sb1.5Te3,38have been predicted to exhibit zxyT 4 0.1 at room temperatureas well as n-type Bi2Te2.7Se0.3/p-type Bi2�xSbxTe3.39 SmCo5,which is a widely known permanent magnet for its strongmagnetic force and excellent thermal stability,41 also hasmetallic transport properties and negative S.11,15 Thus, weselected p-type BST as a counterpart material for SmCo5, as rand k are one order smaller than those of SmCo5 and the signof S is opposite (Fig. S2, ESI†).We predict the superior transverse thermoelectric perfor-mance in SmCo5/BST-based ATML using analytical matrixcalculations. Based on Goldsmid’s method,27 the thermoelec-tric parameters, i.e., electrical resistivity rij, thermal conductiv-ity kij, and thermopower Sij can be calculated neglectingFig. 1 Schematic of the concept of MCM exhibiting strong magneticforce and superior transverse thermoelectric performance simultaneously.Paper Energy & Environmental ScienceOpen Access Article. Published on 18 March 2025. Downloaded on 5/12/2025 2:44:00 AM.  This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/https://doi.org/10.1039/d4ee04845h4070 |  Energy Environ. Sci., 2025, 18, 4068–4079 This journal is © The Royal Society of Chemistry 2025interfacial contributions. As depicted in Fig. 2a, the off-diagonal Seebeck coefficient Sxy is defined by generated Ein the x-direction and applied rT in the y-direction. r (k) isa proportionality factor between E (Jq) and Jc (rT). Thus, kyyand rxx are used for zxyT because the applied rT and generatedE are in y- and x-directions for the transverse thermoelectricconversion. The thermoelectric parameters of the SmCo5/BST multilayers in the direction parallel (r8, k8, and S8)and perpendicular (r>, k>, and S>) to the stacking planeare analytically calculated using the electrical resistivitiesrSmCo and rBST, thermal conductivities kSmCo and kBST,and Seebeck coefficients SSmCo and SBST for SmCo5 and BST,respectively:27rk ¼rSmCorBSTð1� tÞrSmCo þ trBSTr? ¼ trSmCo þ ð1� tÞrBST(1)kk ¼ tkSmCo þ ð1� tÞkBSTk? ¼kSmCokBSTð1� tÞkSmCo þ tkBST(2)Sk ¼trBSTSSmCo þ ð1� tÞrSmCoSBSTtrBST þ ð1� tÞrSmCoS? ¼tkBSTSSmCo þ ð1� tÞkSmCoSBSTtkBST þ ð1� tÞkSmCo(3)where t = dSmCo/(dSmCo + dBST) denotes the thickness ratio of theSmCo5 layer and dSmCo (dBST) the thickness of the SmCo5 (BST)layer. When the homogeneous SmCo5/BST multilayers arerotated in the xy-plane with the tilt angle y (Fig. 2a), thetransverse thermoelectric properties by ODSE can beexpressed asrxx = r8 cos2 y + r> sin2 y (4)kyy = k8 sin2 y + k> cos2 y (5)Sxy = (S8 � S>)sin y cos y (6)Then, the transverse thermoelectric figure of merit zxyT isgiven byzxyT ¼Sxy2rxxkyyT (7)Fig. 2 Magnetic and analytical transverse thermoelectric properties of MCM. (a) Schematic of MCM composed of SmCo5 and BST with a tiltangle y. An ATML structure induces a nonuniform heat current Jq by the application of a temperature gradient rT in the y-axis, which generates acharge current Jc (or an electric field E) in the transverse direction through thermoelectric conversion by the Seebeck effect. Remanentmagnetization in the SmCo5 layers Mr is oriented along the stacking direction. (b)–(e) Contour plots of the analytical electrical resistivity in the x-axis rxx (b), thermal conductivity in the y-axis kyy (c), off-diagonal Seebeck coefficient Sxy (d), and transverse thermoelectric figure of merit zxyT(e) as a function of the thickness ratio of the SmCo5 layer t and y in SmCo5/BST-based MCM at 300 K. Red points indicate the optimum t and y tomaximize zxyT, i.e., t = 0.5 and y = 251. (f) Photograph of SmCo5/BST-based MCM. (g) Magnetization M of the SmCo5 slab as a function of anexternal magnetic field H in its magnetic easy axis direction. m0 is the vacuum permeability. (h) Temperature T dependences of the calculated zxyTat t = 0.5 and y = 251 and Mr of the SmCo5 slab.Energy & Environmental Science PaperOpen Access Article. Published on 18 March 2025. Downloaded on 5/12/2025 2:44:00 AM.  This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/https://doi.org/10.1039/d4ee04845hThis journal is © The Royal Society of Chemistry 2025 Energy Environ. Sci., 2025, 18, 4068–4079 |  4071Fig. 2b–e show the thickness ratio t and tilt angle y depen-dences of the transverse thermoelectric properties for SmCo5/BST-based ATML, obtained by substituting the measured prop-erties of SmCo5 and BST into eqn (1)–(7) (see also Note S2 andFig. S3, ESI,† where the calculated rij, kij, and Sij were shown).We find that the calculated zxyT in SmCo5/BST-based ATMLreaches 0.26 at the optimum t of 0.5 and y of 251 at T = 300 K(see red points in Fig. 2b–e). Furthermore, we calculated thetemperature T dependence of rxx, kyy, Sxy, and zxyT in the rangeof 300–600 K at t = 0.5 and y = 251 (Fig. 2h and Fig. S4, ESI†).The zxyT value reaches a maximum of 0.32 at 420 K, which ismore than two orders of magnitude higher than that ofNd2Fe14B/BiSb-based ATML.40To experimentally demonstrate the expected performance asMCM, we synthesized SmCo5/BST-based ATML using the calcu-lated optimum y and t values. SmCo5 circular disks and BSTpowders were alternately stacked and bonded using sparkplasma sintering (SPS), followed by cutting the sintered multi-layer into tilted rectangular blocks (see Fig. 2f and the Experi-mental section for details). The accuracies of t and y in theATML block were estimated to be 0.50 � 0.05 and 25 � 11,respectively. The elemental distribution maps of Sm, Co, Bi, Sb,and Te were obtained using scanning electron microscopy withenergy dispersive X-ray spectroscopy (SEM-EDX). The low mag-nification EDX mapping of Sb, Te, and Co and the atomic ratioprofile indicate no complex elemental migrations between theSmCo5 and BST layers (Fig. S5, ESI†). Then, from the highmagnification image around the SmCo5/BST interface shown inFig. 3a, we recognize the growth of interfacial diffusion layerswith a thickness of approximately 10 mm without interfacialvoids. The atomic ratio profile in the stacking direction of theSmCo5 and BST multilayers (Fig. 3b) reveals that the interfacialdiffusion layers of CoTea-based compounds (1.5 o a o 2.0) areformed, which act as adhesive bonds. The magnetic easy axis ofthe SmCo5 disks was out-of-plane. Fig. 2g shows the magnetiza-tion M of the SmCo5 portion cut from the ATML as a function ofthe magnetic field H perpendicular to the stacking plane. TheSmCo5 layers exhibit a large Mr of 0.86 T and a coercivity of0.87 T without deterioration even after sinter-bonding with theBST layers, which confirms that SmCo5/BST-based ATML oper-ates as MCM. Fig. 2h shows the T dependence of Mr, where thepermanent magnet nature is sustained above 600 K owing tothe excellent thermal stability of magnetism of SmCo5.2.2 Interfacial electrical and thermal resistivitiesTo verify the transverse thermoelectric performance of SmCo5/BST-based MCM, it is important to characterize the interfacialelectrical and thermal transport properties at the SmCo5/BSTjunctions because they cause a degradation from the calculatedproperties shown in Fig. 2h as well as the thermoelectricmaterial/electrode junctions in longitudinal thermoelec-tric devices.2,42–44 Despite their importance, the quantitativeFig. 3 Contribution of the interfacial transport properties to the transverse thermoelectric performance of MCM. (a) SEM-EDX images of the crosssection of the SmCo5/BST multilayer. (b) Line profile of the atomic ratios of Sm, Co, Bi, Sb, and Te across the stacking direction. (c) Schematic of the four-terminal resistance measurement setup to investigate the spatial distribution of the electrical resistance by sweeping the probe position. (d) Probeposition dependence of the electrical resistance in the SmCo5/BST multilayer in the stacking direction and (e) its enlarged view indicated by an orangedotted square in (d). Gray dotted line is the approximate position of the SmCo5/BST interface, where a gap indicated by red arrows corresponds to theinterfacial electtical resistance. (f) Schematic of the LIT measurement while applying the square-wave-modulated charge current Jc with the amplitude Jcand frequency f. Lock-in amplitude A (g) and phase j (h) images of the cross section of the SmCo5/BST multilayer at Jc = 1 A and f = 25 Hz. (i) Line profilesof A and j across the SmCo5/BST interface for the white dotted lines with a length of 101 pixels in (g) and (h). Red curves represent the fitting functionsusing the one-dimensional heat equation.Paper Energy & Environmental ScienceOpen Access Article. Published on 18 March 2025. Downloaded on 5/12/2025 2:44:00 AM.  This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/https://doi.org/10.1039/d4ee04845h4072 |  Energy Environ. Sci., 2025, 18, 4068–4079 This journal is © The Royal Society of Chemistry 2025investigation of the interfacial transport properties has notbeen attempted in previous studies.30,33,34,37,38,40 In this study,we experimentally characterized the interfacial electrical andthermal resistivities and their contributions to the volumetricresistances.First, we characterized the interfacial electrical resistancebetween the SmCo5 and BST layers by measuring the spatialdistribution of the electrical resistance. To distinguish theresistances originating from the bulk of SmCo5, bulk of BST,and their interfaces, we prepared a rectangular sample com-prising the SmCo5/BST multilayer in which the cut angle wasperpendicular to the stacking plane (i.e., y = 901). As shown inFig. 3c, the four-terminal ac resistance was measured while theprobe was scanned along the stacking direction. The measure-ment results shown in Fig. 3d revealed a step-like behaviorreflecting the different electrical resistivities of SmCo5 and BSTlayers, wherein the electrical resistivity of SmCo5 is muchsmaller than that of BST (Fig. S2, ESI†). Significantly, whenwe focus on an interface between the SmCo5 and BST layers(Fig. 3e), the position of which is indicated by a gray dotted line,the resistance profile was observed to be almost continuous.The interfacial electrical resistivity is estimated by linearlyfitting the resistance profiles in the SmCo5 and BST layersand extrapolating the fitting functions to the interface position(red arrows in Fig. 3e). Then, the averaged interfacial electricalresistivity at several interfaces is calculated to be 0.4 � 1.2 mOcm2. This unusually low interfacial resistivity, comparable tolowest-level contact resistivities for thermoelectric devices,42can be attributed to the metallic properties of CoTea-baseddiffusion layers,45–47 whose resistivity is comparable to that ofSmCo5. Meanwhile, the volume resistance–area product ofthe 0.5-mm-thick SmCo5 and BST layers was estimated to be64 � 2 mO cm�2 from the slopes of the fitting functions. Thus,the ratio of the interfacial electrical resistance to the volumetricresistance was 1.2%, which is negligibly small within themargin of the experimental error.The interfacial thermal resistance was also characterizedusing the lock-in thermography (LIT) measurements48–51 forthe same SmCo5/BST multilayer sample with y = 901. Fig. 3fshows a schematic of the LIT measurement setup. A square-wave-modulated Jc with an amplitude Jc of 1 A and a frequency fof 25 Hz, which guarantee the sensitivity of the interfacialthermal resistance in the order of 10�7 m2 K W�1,49 was appliedto the sample in a direction perpendicular to the stackingplane. The thermal images were continuously captured whileapplying Jc to observe the temperature modulation due to thePeltier-effect-induced heat current. When the heat current isdiscontinuous due to the difference in the Peltier coefficient atjunctions, finite heat absorption and release appear in thevicinity of the interfaces.50,51 By extracting the first harmonicresponse of the charge-current-induced temperature modula-tion through Fourier analysis and calculating the lock-inamplitude A and phase j for each pixel of the thermal images,we visualized the pure contribution of the Peltier effect withoutcontamination by Joule heating. Here, the A signals refer to themagnitude of the temperature change in linear response to Jcand j signals to its sign and time delay due to the heatdiffusion. A previous study51 reported that the spatial profilesof the A and j signals can be used to investigate the interfacialthermal resistance because a finite interfacial thermal resis-tance causes discontinuities in A and j. We observed clear Asignals near the SmCo5/BST interfaces (Fig. 3g) and j signalsalternately changing from approximately 01 to 1801 for eachadjacent interface (Fig. 3h), which is consistent with thefeatures of the Peltier-effect-induced temperature modulation.The line profiles of A and j across the SmCo5/BST interfaceare shown in Fig. 3i, where no obvious jumps appear atthe interface position. By fitting the position dependence ofA and j using the one-dimensional heat equation,51 theinterfacial thermal resistance was estimated to be less than1 � 10�6 m2 K W�1. Meanwhile, the thermal conductivities ofSmCo5 and BST layers were 16.3 and 1.0 W m�1 K�1 at 300 K,respectively (Fig. S2, ESI†). Thus, the contribution of the inter-facial thermal resistance to the volumetric thermal resistancewas also negligible (o0.4%).2.3 Characterization of transverse thermoelectricperformanceThe above experiments ensure that the performance degrada-tion due to the presence of multiple interfaces is quite small inour SmCo5/BST-based MCM. To verify the small interfacialcontribution to the transport behavior as depicted in Fig. 2a,we performed a two-dimensional finite element analysis ofthermoelectric conversion in SmCo5/BST-based MCM usingthe thermoelectric module of COMSOL Multiphysics software.A multilayer of SmCo5 (0.5 mm) and BST (0.5 mm) with y = 251and dimensions of 12.4 � 8.3 mm was prepared as shown inFig. 4a. The volumetric transport properties in Fig. S2 (ESI†)and interfacial electrical and thermal resistivities (0.4 mO cm2and 1 � 10�6 m2 K W�1) were used as the material parameters.The boundary condition was fixed so that the upper (lower) sidewas 303 (293) K to input rT in the y-direction and the left andright sides were thermally adiabatic. T and electric potential Vdistributions through the Seebeck effect were simultaneouslycalculated as shown in Fig. 4a and b. Then, we find a gradationof V in the direction perpendicular to the stacking plane,suggesting the generation of finite E in the x-direction throughthe Seebeck effect. By focusing on a central part of the multi-layer and visualizing heat flux (Fig. 4a), we can see a heat-fluxbending with respect to the input rT as depicted in Fig. 2a andT distribution inside the layers owing to the small interfacialthermal resistance. Thus, the generated E (Fig. 4b), localized inthe BST layers due to the large SBSTrT, also directs the obliquedirection to the inputrT, which is the origin of ODSE. Throughthis finite element analysis, we successfully reproduce thetransverse thermoelectric conversion by ODSE26,28 taking theinterfacial resistances into account.To experimentally determine zxyT with negligible contribu-tions from the interfacial electrical and thermal resistances, wedirectly measured Sxy and rxx in SmCo5/BST-based MCM withthe same dimension as that used in the finite element analysisat room temperature. Fig. 4c shows the measurement setup forEnergy & Environmental Science PaperOpen Access Article. Published on 18 March 2025. Downloaded on 5/12/2025 2:44:00 AM.  This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/https://doi.org/10.1039/d4ee04845hThis journal is © The Royal Society of Chemistry 2025 Energy Environ. Sci., 2025, 18, 4068–4079 |  4073the transverse thermoelectric voltage V induced by a tempera-ture gradient rT and the four-terminal ac resistance (seeExperimental section for details). Fig. 4d shows that the V valuelinearly increases with rT and quantitatively agrees with thecalculated line obtained from the analytically calculated Sxy(Fig. 2d), indicating that our MCM exhibits the ideally largetransverse thermoelectric conversion. The Sxy value of SmCo5/BST-based MCM was experimentally estimated to be 66.4 �1.1 mV K�1 at room temperature. The ac resistance was mea-sured to be 1.54 � 0.02 mO while the calculated one is 1.17 mO,where the increased resistance can be attributed to cracking inthe SmCo5 disks during the SPS process and to processingerrors, such as y and t.Fig. 4e shows the comparison of zxyT between the valuesestimated from the analytical matrix calculation and directmeasurement of Sxy and rxx for various n-type X/p-type BST-based ATMLs, where X = SmCo5, Bi2Te2.7Se0.3 (BTS), Ni, Co, andYbAl3.33,34,38,39 Note that the analytical kyy values are used forboth calculated and measured zxyT because the direct measure-ment of kyy has never been done due to the difficulty to excludethe contaminated boundary effect. In the previous reports,although the higher zxyT than that of our SmCo5/BST-basedMCM has been predicted based on the analytical calculations,the measured large electrical resistances predominantly causeddegradations in zxyT from the calculated ones. Thus, even if theanalytical calculation suggests the higher zxyT values, the actualzxyT values can be lower due to the interfacial contributions(zxyT o 0.2 when the analytically calculated kyy is used). Incontrast, although the calculated zxyT value of our SmCo5/BST-based MCM is not the best, the extremely low interfacialresistances between the SmCo5 and BST layers successfullysuppress the performance degradation and realize the highzxyT value of 0.20 at room temperature. Thus, the introductionof SmCo5 as the counterpart of BST not only provides themagnetic functionality but also contributes to the record-hightransverse thermoelectric performance.2.4 Giant transverse thermoelectric generation in the MCM-based moduleIn this section, we demonstrate giant transverse thermoelectricgeneration using SmCo5/BST-based MCM. To achieve this, wedeveloped a lateral thermopile module to enhance the thermo-electric voltage for a useful power supply to drive widely usedelectronic devices. Fig. 5a shows a schematic of the modulestructure, where the thin-sliced MCM elements are stackedwith an opposite y between the neighboring elements andintermediated by thin insulator layers. By electrically connect-ing the ends of neighboring MCMs, a long series circuit isformed so that Jc flows in a zigzag manner, as proposed byNorwood1 and Kanno.30 Importantly, the net magnetization ofthe thermopile module Mnet is oriented along the rT directionby the vector sum of M in each MCM element. Thus, the MCM-based thermopile module operates as a permanent magnet.Fig. 5b shows the photograph of the constructed module, whichis composed of 14 elements of magnetized SmCo5/BST-basedMCM (see the Experimental section for details). The fill factorof the MCM elements per heat transfer area exceeds 90% owingto the transverse geometry and very thin (approximately 0.05-mm-thick) insulator layers, ensuring a high thermoelectricoutput density and robustness against mechanical stress.2,3As shown in Fig. 5b, several ferromagnetic metal paper clipscan be hung to the magnetized MCM-based module owing to itslarge Mnet. The internal resistance of the MCM-based moduleRmodule was measured to be 34.8 mO by the four-terminalmeasurement, which deviates from the calculated Rmodule onlyby +11%. Thus, the contribution of the contact resistancebetween the MCM elements to the total resistance is also small.Fig. 5c shows a schematic of the measurement setup fortransverse thermoelectric generation. The MCM-based modulewas sandwiched by the heater and heat bath to apply rT. Thefour-terminal voltage and power measurements were per-formed in the MCM-based module in the demagnetized state.The reason why the magnetic state (M and its stray field) ofFig. 4 (a) and (b) Finite-element analysis of (a) T and (b) electric potentialV distributions through the Seebeck effect in SmCo5/BST-based ATMLtaking the interfacial electrical and thermal resistances into account. Blackarrows indicate a heat flux in (a) and E in (b). (c) Schematic of the setup forthe direct measurement of Sxy and rxx. (d) The temperature gradient rTdependence of the directly measured and analytically calculated thermo-electric voltage V values at room temperature. (e) Comparison of themeasured and calculated zxyT at room temperature for various n-type X/p-type BST-based ATMLs (X = SmCo5, Bi2Te2.7Se0.3, Ni, Co, and YbAl3). Thecalculated kyy values are used for both the measured and calculated zxyT.Paper Energy & Environmental ScienceOpen Access Article. Published on 18 March 2025. Downloaded on 5/12/2025 2:44:00 AM.  This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/https://doi.org/10.1039/d4ee04845h4074 |  Energy Environ. Sci., 2025, 18, 4068–4079 This journal is © The Royal Society of Chemistry 2025SmCo5 does not contribute to the transverse thermoelectricperformance is explained in Note S3 (ESI†).Fig. 5d and e show the results of the transverse thermo-electric generation in the MCM-based module. In the loadcurrent Iload dependence of the thermoelectric voltage V(Fig. 5d), the open-circuit voltage Voc is defined as the V valueat Iload = 0 A and V linearly decreases with increasing Iloadaccording to the internal resistance. P (= IloadV) shows a para-bolic behavior against Iload and has a maximum value (Pmax)when V is the half of Voc. The Voc and Pmax values monotonicallyincreased with increasing DT and reached 219 mV and 204 mW,respectively, at DT = 152 K, which are giant values for thetransverse thermoelectric generation owing to the excellent zxyTwith low interfacial electrical and thermal resistivities. Fig. 5eshows the DT dependence of Pmax and the correspondingmaximum power density omax per heat transfer area, whichwere almost parabolically increased with increasing DT as theyare proportional to the square of Voc, indicating almost nothermal deterioration of the thermoelectric properties at largeDT. Consequently, omax reached 56.7 mW cm�2 at DT = 152 Kowing to the transverse thermoelectric properties of MCM andthe high fill factor of 490%. From the Pmax value and theanalytical transverse thermoelectric properties, we alsoestimated the conversion efficiency for our MCM-based ther-mopile module at DT = 152 K to be 1.6–2.4% (Note S4 andFig. S6, ESI†).We compare the thermoelectric power generation perfor-mance of our MCM-based module with that of various trans-verse and longitudinal thermoelectric modules includingcommercial products. To fairly compare the intrinsic genera-tion performance, we show the rT dependence of omax inFig. 5f because the omax value is proportional to the square ofrT and independent of the mechanism, geometry, and dimen-sion of the thermoelectric modules. Gray dotted guide lines inFig. 5f represent functions of omax = brT2 with b = 0.00025,0.005, 0.1, and 2. Transverse thermoelectric modules utilizingthe ordinary Nernst effect and ANE based on BiSb, Co2MnGa,and Nd2Fe14B/SmCo5 exhibit omax less than 0.1 mW cm�2regardless of rT typically due to the low thermopower,16,20,21which has been the barrier towards applications of transversethermoelectrics. Meanwhile, the transverse thermoelectricmodules composed of Bi/Cu- and Ni/BST-based ATMLsreported higher omax of 5.5 and 250 mW cm�2 at rT = 7.8and 42.5 K mm�1, respectively.30,31 However, the problem ofthe conventional ODSE-based module is the performancedegradation due to the interfacial resistances. In this study,Fig. 5 Transverse thermoelectric generation by the MCM-based thermopile module. (a) Schematic of the architecture of the MCM-based thermopilemodule. The MCM elements are alternately stacked with opposite y intermediated by thin insulator layers. By attaching electrodes to connect the ends ofneighboring MCMs in a zigzag manner, a long series circuit is formed to sum up the transverse thermoelectric voltage. Net magnetization of thethermopile module Mnet is oriented along therT direction by the vector sum of M in each MCM element. (b) Photograph of the magnetized MCM-basedmodule hanging many ferromagnetic metal paper clips owing to the large Mnet. Lead wires are connected at the different sides (+)/(�) of the thermopilecircuit. (c) Schematic of the measurement setup for the transverse thermoelectric generation. (d) Load current Iload dependence of the thermoelectricvoltage V and output power P at various values of the temperature difference DT. (e) DT dependence of the maximum output power Pmax and maximumpower density per heat transfer area omax. (f) rT dependence of omax for the MCM-based module used in this study (red stars), transverse (orangetriangles) and longitudinal (green triangles) thermoelectric modules reported in the research papers, and commercial longitudinal thermoelectricmodules (blue triangles). Gray dotted lines represent functions of omax = brT2 with b = 0.00025, 0.005, 0.1, and 2. A high omax/rT2 is positioned to theleft-upper corner as colored with yellow gradation on the background.Energy & Environmental Science PaperOpen Access Article. Published on 18 March 2025. Downloaded on 5/12/2025 2:44:00 AM.  This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/https://doi.org/10.1039/d4ee04845hThis journal is © The Royal Society of Chemistry 2025 Energy Environ. Sci., 2025, 18, 4068–4079 |  4075by synthesizing high-performance MCM with extremely lowinterfacial resistances and constructing a high-density thermo-pile structure, we successfully demonstrated maximum omax of56.7 mW cm�2 at rT of 20.7 K mm�1 (the red stars in Fig. 5f).Here, let us compare the normalized power density omax/rT2in the similar temperature range to exclude the contri-bution of rT. Then, our MCM-based module shows therecord-high power generation performance of omax/rT2 =0.17 mW cm�2 (K mm�1)�2 among all the transverse thermo-electric modules including Bi/Cu- and Ni/BST-based ATMLs(0.09 and 0.14 mW cm�2 (K mm�1)�2, respectively). In Fig. 5f,we also show the omax values of the longitudinal thermoelectricmodules utilizing the Seebeck effect, based on CoSb3, Mg2Si,Mg3Sb2, and Bi2Te3, including commercial products. The omaxvalues are in the range of 15–497 mW cm�2 at DT of 120–200 K,52–58 and the corresponding omax/rT2 values are calcu-lated to be less than 0.07 mW cm�2 (K mm�1)�2. Surprisingly,the potential thermoelectric power density of our MCM-basedmodule is larger than that of the commercial longitudinalthermoelectric modules. Thus, while having versatile transversegeometry and high mechanical durability,1,7 our MCM-basedmodule can generate the practical-level thermoelectricoutput power.2.5 Efficient energy harvesting utilizing multifunctionalityIn this section, we propose a new device concept where themultifunctionality of permanent magnet features and trans-verse thermoelectric conversion improves thermal energy har-vesting performance even if the intrinsic material propertiesare unchanged. Fig. 6a shows a schematic of a cross-sectionalview of the MCM-based module acting as a thermal energyharvester. The magnetic attractive force of the MCM-basedmodule enables not only an easy installation onto a heat sourcemade of a magnetic material but also an efficient heat input byeliminating the vacant space and reducing the contact thermalresistance between MCM and the heat source. In addition, thelateral thermopile geometry allows a surface area on the coolside to increase by changing the height of the neighboringMCM elements, enabling efficient heat release to the air atmo-sphere without attaching a heat bath; such a configuration issuitable for thermal energy harvesting. Hereafter, we refer tothe device structure depicted in Fig. 6a as a built-in heatsink (BHS).For this proof-of-concept demonstration, we prepared theMCM-based modules with and without BHS and comparedtheir thermoelectric power generation performance withoutattaching a heat bath at the cold side. The three thermopilemodules were constructed for the control experiment: (i) ademagnetized module without BHS, (ii) a magnetized modulewithout BHS, and (iii) a magnetized module with BHS (see theExperimental section for details). The internal resistances ofthese modules are 20.4, 21.8, and 21.0 mO, respectively, whichconfirm almost the same volume and electrode contact condi-tions. The photograph in Fig. 6b shows the constructed mod-ules (i) and (iii). Fig. 6c shows the experimental setup for thethermoelectric generation measurement under an air-cooledcondition. A ferromagnetic steel use stainless (SUS) plate withdimensions of 150� 1� 150 mm was coated with a black ink toobserve the surface temperature of the SUS plate (TSUS) using aninfrared camera and heated using a ceramic hot plate. Thethree MCM-based modules (i)–(iii) were put on the SUS plateintermediated by 1-mm-thick insulating polymer sheets(MANION-SC, Sekisui Polymatech Co., Ltd). The copper wiresconnected to the modules were fixed by curing tapes (blue colorparts in the photograph in Fig. 6c) so that the modules did notmove during the measurement. The top surfaces were continu-ously cooled by an air flow using a personal fan to increase theheat transfer coefficient. After setting the temperature of theceramic hot plate and waiting for 10 min, the four-terminalIload–V measurements were performed.Fig. 6d and e show Voc and Pmax as a function of TSUS for thethree MCM-based modules. All the modules show a linearincrease of Voc with the increase of TSUS, which indicates thatrT also linearly increases with TSUS because of the almostconstant Sxy with respect to the temperature (Fig. S4, ESI†).Importantly, the Voc values obviously vary between the threeMCM-based modules even though the intrinsic thermoelectricproperties are almost the same. From the comparison between(i) and (ii), the magnetized module exhibits twice larger Vocthan the demagnetized module, suggesting the enhancementof rT by reducing the thermal contact resistance between theFig. 6 Efficient energy harvesting utilizing multifunctionality. (a) Sche-matic of a cross-sectional view of the MCM-based thermopile moduleused as a thermal energy harvester. (b) Photograph of the MCM-basedmodules comprising 8 elements with (right) and without (left) BHS.(c) Photograph of the measurement setup for thermoelectric powergeneration by (i) a demagnetized module without BHS, (ii) a magnetizedmodule without BHS, and (iii) a magnetized module with BHS. (d) and(e) the SUS plate temperature TSUS dependence of the open-circuit voltageVoc and Pmax for (i)–(iii).Paper Energy & Environmental ScienceOpen Access Article. Published on 18 March 2025. Downloaded on 5/12/2025 2:44:00 AM.  This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/https://doi.org/10.1039/d4ee04845h4076 |  Energy Environ. Sci., 2025, 18, 4068–4079 This journal is © The Royal Society of Chemistry 2025MCM-based module and the SUS plate. In addition, the com-parison between (ii) and (iii) reveals that the introduction of theBHS leads to the enhancement of Voc by B10% owing to theefficient heat release to the air atmosphere. Thus, the installa-tion of magnetic functionality and BHS successfully contributeto increase rT by the efficient heat transfer between the SUSplate, MCM-based module, and air. As a result of the increase ofVoc, Pmax drastically increases (Fig. 6e). As demonstrated here,the multifunctionality of the magnetic attractive force andtransverse thermoelectric conversion will bring about benefitfor versatile thermoelectric applications through easy installa-tion and efficient heat transfer.3. DiscussionHerein, we discuss the possible future developments of MCMsin terms of the power generation performance. While theexperimentally determined zxyT value of 0.20 for our MCMand the estimated conversion efficiency of 1.6–2.4% at DT =152 K for our MCM-based thermopile module are record-highamong those of the transverse thermoelectric modules, thethermoelectric performance can be further improved throughthe following two approaches. One is the direct way to enhanceODSE by exploring permanent magnet materials with higher Sand lower r than those of commercial SmCo5-type magnets andoptimizing interfacial microstructures with low electrical andthermal resistivities, as detailed in this work. Another approachinvolves hybridizing other mechanisms related to magnetismor spin. We have previously demonstrated the hybridization ofthe off-diagonal Peltier effect with the magneto-Peltier, ordin-ary Ettingshausen effects, and ANE in ATMLs,40,59 where thecalculated zxyT varies by 40% depending on an external mag-netic field. In this study, we did not introduce such hybridthermoelectric conversion to prioritize superior multifunction-ality. However, it is possible to improve zxyT by hybridizing ANEand the Seebeck-effect-driven anomalous Hall effect in perma-nent magnets and/or the magneto-Seebeck effect in thermo-electric materials.6,23,60 Thus, exploring magnetic materialswith large anomalous Nernst and Hall effects is essential forfurther development of MCMs. Meanwhile, from the technolo-gical point of view, the magnetic attractive force enables anefficient heat input/output by reducing the contact thermalresistances between MCM and a heat source/bath made of amagnetic material.4. ConclusionsWe developed a novel functional material named MCM anddemonstrated giant transverse thermoelectric generation in theMCM-based thermopile module. Our experiments showed thatMCM consisting of alternately and obliquely stacked SmCo5/BST multilayers exhibited an excellent zxyT of 0.20 at roomtemperature owing to the negligible negative effects of theinterfacial resistances on the thermoelectric properties. Utiliz-ing the high-performance MCM elements, we constructed alateral thermopile module and demonstrated a power genera-tion of 204 mW at DT = 152 K, which corresponds to the highestnormalized power density of 0.17 mW cm�2 (K mm�1)�2 amongthose of the transverse thermoelectric modules. MCM devel-oped in this study paves the way toward new core technologiesfor energy harvesting and thermal management.5. Experimental section5.1 Sample preparation and characterizationSmCo5/BST-based ATMLs were prepared as follows. AnisotropicSmCo5-type magnet disks with a diameter of 20 mm and athickness of 0.5 mm (YX24, Magfine Corporation) and BST alloypowder with 99.9% purity and a particle size of 4200 mm(Toshima Manufacturing Co., Ltd) were employed. The demag-netized SmCo5 disks and BST powder were alternately stackedand bonded using SPS under a pressure of 30 MPa at 450 1C for20–30 min, where the amount of BST powder per unit layer wasapproximately 1.05 g that was transformed to be 0.5-mm-thickafter densification. Finally, the sintered stack was cut into arectangular shape with y of approximately 251. To magnetizethe sintered SmCo5/BST multilayers, a pulse magnetic field of8 T was applied in the direction perpendicular to the stackingplane. The plain BST slab was also prepared using the SPSmethod under the same sintering condition to measure thetransport properties.The temperature dependence of r and S of the SmCo5 andBST slabs was measured using the Seebeck-coefficient/electric-resistance measurement system (ZEM-3, ADVANCE RIKO Inc.).The temperature dependence of k was determined throughthermal diffusivity measured using the laser flush method,specific heat measured using differential scanning calorimetry,and density measured using the Archimedes method. Themagnetization M curve of SmCo5 was measured via super-conducting quantum interference device vibrating sample mag-netometry using a Magnetic Property Measurement System(MPMS3, Quantum Design Inc.).The elemental maps of the cross section of the SmCo5/BSTmultilayer were obtained by SEM-EDX using a Cross-Beam1540ESB (Carl Zeiss AG). To do this, the surface of the samplewas mechanically polished in advance.The interfacial electrical and thermal resistances of theSmCo5/BST multilayer were characterized as described below.The SmCo5/BST multilayer sample with y = 01 and dimensionsof 3.2 � 11.2 � 1.9 mm was prepared. The position dependenceof the four-terminal resistance was measured using the resis-tance distribution measuring instrument (Mottainai EnergyCo., Ltd), where the contact probe was moved in 10-mm incre-ments and alternating current with an amplitude of 100 mAwas applied in the stacking direction. The LIT measurementswere performed using Enhanced Lock-In Thermal Emissionsystem (ELITE, DCG Systems G.K.) at room temperature andatmospheric pressure. The sample was fixed on a plastic platewith low thermal conductivity to reduce heat leakage due tothermal conduction. To enhance the infrared emissivity andEnergy & Environmental Science PaperOpen Access Article. Published on 18 March 2025. Downloaded on 5/12/2025 2:44:00 AM.  This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/https://doi.org/10.1039/d4ee04845hThis journal is © The Royal Society of Chemistry 2025 Energy Environ. Sci., 2025, 18, 4068–4079 |  4077ensure uniform emission properties, the top surface of thesample was coated with an insulating black ink having anemissivity higher than 0.94 (JSC-3, JAPANSENSOR Corp.). Theviewing areas of the thermal images in Fig. 3g and h and Fig. S1(ESI†) are 1.54 � 1.74 mm and 7.68 � 3.84 mm, respectively.The SmCo5/BST multilayer sample with y = 251 and dimen-sions of 12.4 � 8.3 � 1.1 mm was prepared for the directmeasurements of Sxy and rxx. The 8.3 � 1.1 mm surfaces werecovered with Cerasolzer #297 (Kuroda Techno Co., Ltd) usingthe ultrasonic soldering technique to form electrodes for apply-ing a uniform current. The copper wires were connected to theelectrodes by Cerasolzer #186 (Kuroda Techno Co., Ltd) usingthe soldering iron. This sample was bridged between twoanodized Al blocks, one of which is connected to chip heatersand the other to a heat bath to generate rT in the 8.3 mmdirection. A central part of the 12.4 � 8.3 mm surface wascovered with a black ink and the temperature distribution wasmeasured with an infrared camera. The two Al–1%Si wires weredirectly connected to the 12.4 � 8.3 mm surface with a distanceof 6.5 mm to measure the ac resistance and dc voltage. Howeverthe side surfaces were fully covered with a solder to have analternating current uniformly input to MCM, and V and the acresistance were measured between the point contacts insideMCM to exclude the boundary effect, which might cause thedecrease in Sxy and rxx compared with the analytical values.26,28The ac resistance was measured using a battery internal resis-tance tester (BT3562A, Hioki E.E. Corp.) applying an alternatingcurrent with an amplitude of 100 mA. The dc voltage under theapplication ofrT was measured using a nanovoltmeter (2182A,Tektronix, Inc.).5.2 Construction of the MCM-based thermopile moduleThe rectangular blocks of SmCo5/BST-based ATML with t = 0.5and y = 251 were sliced into a rectangular shape with dimen-sions of 15.4 � 7.3 � 1.5 mm. To create electrodes to electricallyconnect the MCM elements in series, the 7.3 � 1.5 mm surfaceswere firmly covered with Cerasolzer #297 (Kuroda Techno Co.,Ltd) using the ultrasonic soldering technique. The 14 MCMelements were alternately stacked with the opposite y andintermediated by 0.05-mm-thick insulating paper towels andheat-resistant glue (Duralco NM25, Cotronics Corp.). Aftercuring for more than 4 h, the neighboring MCM elements wereelectrically connected to form a zigzag circuit by Cerasolzer#186 (Kuroda Techno Co., Ltd) using the soldering iron. At theends of the thermopile circuit, enameled copper wires wereconnected using Cerasolzer #186 for power generation mea-surements. Finally, the heat transfer surfaces and the base ofthe copper wires were covered with the same heat-resistant glueto obtain smooth surfaces and fix the wires. The module shownin Fig. 5b was magnetized by a pulse magnetic field of 8 T alongthe direction of the heat current.The three thermopile modules were constructed for thecontrol experiment in Fig. 6: (i) a demagnetized module with-out BHS, (ii) a magnetized module without BHS, and (iii) amagnetized module with BHS. For (i) and (ii), 8 elements ofSmCo5/BST-based ATMLs with t = 0.5 and y = 251 were preparedwith a rectangular shape of 12.2 � 7.3 � 1.5 mm. Meanwhile,for (iii), 4 elements with two different heights (8 elements intotal) were alternately connected. To keep the same volume asthose of (i) and (ii), the size of the smaller (larger) element was12.2 � 6.3 � 1.5 mm (12.2 � 8.3 � 1.5 mm). To magnetize (ii)and (iii) after the construction, a pulse magnetic field of 8 T wasapplied along the direction of the heat current.5.3 Transverse thermoelectric generation measurementsA custom-made sample holder was used to measure the trans-verse thermoelectric power generation. The MCM-based mod-ule was sandwiched between a heater plate and an aluminumheat sink. Ethylene glycol cooled at 273 K was circulated insidethe heat sink during the measurements. To form uniformthermal contacts between the heater, module, and heat sink,2-mm-thick AlN ceramic plates and 1-mm-thick insulatingpolymer sheets (MANION-SC, Sekisui Polymatech Co., Ltd) witha high thermal conductivity of approximately 25 W m�1 K�1were inserted and screwed down, where the module was indirect contact with the polymer sheets (Fig. 5c). The sidesurface of the module was covered with insulating black inkto measure DT using an infrared camera. After the applicationand stabilization of rT for 10 min, the Iload dependence of Vwas measured three times and averaged. To characterize theinternal resistance of the MCM-based module, the Iload–V curvewas measured from �100 to +100 mA. To characterize thepower generation performance, the Iload–V curve was measuredfrom 0 to +6000 mA. The raw data of the Iload–V curves for theMCM-based module included the voltage drop due to thecopper wires. Thus, the Iload–V curves only for two copper wires,whose ends were short-circuited using Cerasolzer #186, weresubtracted from the raw data to evaluate the pure thermo-electric performance of the MCM-based module.Author contributionsF. A. and K. U. conceived the idea, planned and supervised thestudy, designed the experiments, prepared the samples, devel-oped an explanation of the results, and prepared the manu-script. F. A. and T. H. collected the data of the thermoelectricproperties and LIT images. F. A. calculated the transversethermoelectric properties. H. S. A. observed and analyzed themicrostructure. F. A. and Y. I. analyzed the interfacial electricalresistance. A. A. and H. N. analyzed the interfacial thermalresistance. All the authors discussed the results and commen-ted on the manuscript.Data availabilityThe data supporting this article have been included as part ofthe ESI.†Conflicts of interestThe authors declare no conflict of interest.Paper Energy & Environmental ScienceOpen Access Article. Published on 18 March 2025. Downloaded on 5/12/2025 2:44:00 AM.  This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.View Article Onlinehttp://creativecommons.org/licenses/by/3.0/http://creativecommons.org/licenses/by/3.0/https://doi.org/10.1039/d4ee04845h4078 |  Energy Environ. Sci., 2025, 18, 4068–4079 This journal is © The Royal Society of Chemistry 2025AcknowledgementsThe authors thank K. Suzuki, M. Isomura, and W. Zhou fortechnical supports and Y. Oikawa for valuable discussions. Thiswork was supported by ERATO ‘‘Magnetic Thermal Manage-ment Materials’’ (No. JPMJER2201) from Japan Science andTechnology Agency (JST), Grants-in-Aid for Scientific Research(KAKENHI) (No. 24K17610) from Japan Society for the Promo-tion of Science (JSPS), and NEC Corporation.References1 M. H. Norwood, J. Appl. Phys., 1963, 34, 594–599.2 G. Min and D. M. Rowe, J. Power Sources, 1992, 38, 253–259.3 D. M. Rowe, Thermoelectrics Handbook: Macro to Nano, CRCPress, New York, 2006.4 K. Uchida and J. P. Heremans, Joule, 2022, 6, 2240–2245.5 A. Von Ettingshausen and W. Nernst, Ann. Phys., 1886, 265,343–347.6 A. W. Smith, Phys. Rev., 1921, 17, 23–37.7 Y. Sakuraba, Scr. Mater., 2016, 111, 29–32.8 M. Ikhlas, T. Tomita, T. Koretsune, M. T. Suzuki, D. Nishio-Hamane, R. Arita, Y. Otani and S. Nakatsuji, Nat. Phys.,2017, 13, 1085–1090.9 A. Sakai, Y. P. Mizuta, A. A. Nugroho, R. Sihombing, T.Koretsune, M. T. Suzuki, N. Takemori, R. Ishii, D. Nishio-Hamane, R. 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