The contribution of extrinsic skew scattering to the anomalous Nernst effect (ANE) provides a potential avenue to enhance transverse thermoelectric response through spin-dependent scattering mechanism. In this study, we show the effect of Cu95Ir5 addition on the enhancement of the anomalous Nernst thermopower (SANE) in a CoFe thin film. A high-throughput screening based on the lock-in-thermography method for thermal responses induced by the anomalous Ettingshausen effect (AEE), the reciprocal of ANE, across a composition-spread thin film of CoFe-Cu95Ir5 identified the optimal composition for ANE. Based on this screening experiment, we fabricated the specific composition (CoFe)63(Cu95Ir5)37 film and measured the electric and thermoelectric transport properties. The SANE value reaches 1.23 & micro;V/K for (CoFe)63(Cu95Ir5)37 at room temperature, which is much higher than that for CoFe as well as composition-matched references (CoFe)64.85(Cu)35.15 and (CoFe)98.15(Ir)1.85, which contain the same amount of only Cu and only Ir, respectively. The scaling analysis on the anomalous Hall effect reveals that the extrinsic skew-scattering contribution is significantly greater for the (CoFe)63(Cu95Ir5)37 film compared to others at 300 K. This enhancement in the extrinsic contribution is attributable to the cooperative role of Cu and Ir; Ir acts as a dominant source of skew scattering due to large spin-orbit interaction, while Cu modifies the scattering potential symmetry and accelerates the skew scattering. These results offer an effective strategy for boosting SANE and provide critical insights into extrinsic mechanisms for ANE.

This letter proposes and demonstrates a flexible architecture for an anomalous-Nernst-effect-based heat flux sensor inspired by kirigami, a traditional Japanese paper-cutting art. A prototype device comprises an amorphous Sm _19 Co _81 film and Ta/Au electrode on a flexible substrate pre-patterned with a periodic-cutting kirigami structure. The estimated heat flux sensitivity of the kirigami-structured sensor was comparable to that of a conventional sensor without a kirigami structure and remained unchanged even when it was stretched by 10%. Our approach opens a pathway toward versatile and mechanically compliant heat flux sensing that is applicable to various surfaces.

Functionally graded materials (FGMs) exhibit continuous property variations that enable unique functionalities and provide efficient platforms for systematic property optimization. Here, we report the fabrication of FGMs with graded structural heterogeneity by annealing an amorphous metal under a one-dimensional temperature gradient. Using lock-in thermography (LIT), we spatially mapped transverse thermoelectric conversion with high spatial and temperature resolution. A pronounced non-monotonic response was observed, with the maximum anomalous Ettingshausen effect, a transverse charge-to-heat conversion in magnetic materials, appearing in the atomic-heterogeneity regime well before crystallization. This enhancement was not captured by conventional structural or longitudinal transport measurements, highlighting the exceptional sensitivity of transverse thermoelectric phenomena to subtle structural variations. Structural analyses using scanning transmission electron microscopy and atom probe tomography revealed Fe-based crystalline alloys and Cu nanoclusters embedded in the amorphous matrix, whose heterogeneity accounts for the enhanced response. These findings establish temperature-gradient-annealed FGMs, combined with LIT, as a powerful methodology for probing structural-heterogeneity-driven transverse electron transport and for designing high-performance flexible materials.

We report a systematic evaluation of the effects of post-deposition annealing temperature and structural ordering on the anomalous Nernst effect (ANE) in Fe2CoSi (FCS) Heusler alloy thin films. The study reveals that amorphous/disordered FCS films exhibit a larger anomalous Nernst coefficient (S-ANE) compared to their crystalline counterparts, in stark contrast to conventional Co-based Heusler alloys, which typically show maximum S-ANE in highly ordered structures. Furthermore, as a strategy for enhancing transverse thermoelectric properties, we explore the (FCS)(100-x)Pt-x composite alloy films by systematically varying the Pt concentration and optimizing the composition. This method effectively enhances the transverse thermoelectric performance of the FCS-based alloys. Our findings offer valuable insights into the design and development of next-generation high-performance ANE materials.

The anomalous Nernst effect (ANE) garners considerable attention owing to its capacity to generate a transverse electric field, which facilitates the development of advanced thermoelectric devices with simplified structures, such as heat flux sensors. Nevertheless, despite the advantages of ANE-based thermoelectric technologies, the need for external magnetic fields in most ANE materials hinders their practical applications. The advancement of permanent magnets showing excellent ANE performance is a crucial solution. In this study, we introduce Pt2CoNi-based thermoelectric permanent magnet thin films that demonstrate substantial in-plane and out-of-plane coercivities (exceeding 1 T) and exhibit impressive ANE performance with a thermopower exceeding 1.8 & micro;VK-1. A comprehensive evaluation of the electrical/thermoelectric transport reveals that these films possess a giant transverse thermoelectric conductivity of 4.1 Am-1K-1 at room temperature, which is among the highest values for permanent magnet films. Furthermore, through systematic and high-throughput investigations, we identify a broad range of compositions for Pt2- q - pCo1+ qNi1+ p films with tunable coercivity and comparable ANE performance, and propose a conceptual design for a single-material-based thermopile utilizing these newly developed materials. This study offers a pathway for the development of efficient and sustainable ANE-based thermoelectric technologies that do not require an external magnetic field.

The global shift towards a carbon-neutral society has accelerated the demand for green energy, driving research into efficient technologies for harvesting energy from low-grade waste heat. Recently, transverse thermoelectrics based on the anomalous Nernst effect (ANE) has gained attention due to their simple device structure, scalability, and manufacturing-friendly nature. While topological single crystals and epitaxial films have been the focus for enhancing the ANE-driven thermoelectric performance, further improvements in material design are necessary for practical applications. Here, we report an easy-to-implement strategy for designing mechanically flexible transverse thermoelectric materials by creating amorphous-crystalline heterogeneous composites. We fabricated and optimized the heterogeneous composites through controlled heat treatment, achieving a significant enhancement of the anomalous Nernst coefficient, while maintaining flexibility. Additionally, the developed materials showed sufficiently large coercivity enabling operation of materials in devices under zero external magnetic field. Using the developed material, we constructed a single-material-based coiled device and demonstrated zero-field operation of the ANE-based energy harvesting from curved heat sources. These results validate the feasibility of using the ANE-based flexible materials for energy harvesting applications.

Current-induced domain-wall motion (CIDWM) in a synthetic antiferromagnet is a key phenomenon for developing potential high-density-packed magnetic domain-wall memory with fast operation. Here, CIDWM is reported in the antiferromagnetically-coupled two Co layers through the Ir interlayer sandwiched by the two Pt layers: Pt/Co/Ir/Co/Pt. The top and bottom Pt layers play a role for generating the spin current coming from the spin Hall effect, which gives rise to the dual spin-orbit torque (SOT) acting on the perpendicular magnetizations of the Co layers. Although a simple argument would predict that SOTs from top and bottom Pt layers cancel each other out, the dual SOT nucleates a reversed magnetic domain and drives the CIDWM effectively at current density of the order of 1011 A m-2. This study also examines the effect of antisymmetric interlayer exchange coupling (AIEC) on CIDWM. A positive correlation between the magnitude of AIEC and the domain wall velocity is found, whereas the current density required for nucleating the reversed domain shows a negative correlation with the magnitude of AIEC. These facts suggest that the existence of AIEC improves the performance of CIDWM. The present results provide a new avenue to design SOT domain wall devices based on a synthetic antiferromagnet.

Transverse thermoelectric effects interconvert charge and heat currents in orthogonal directions due to the breaking of either time-reversal symmetry or structural symmetry, enabling simple and versatile thermal energy harvesting and solid-state cooling/heating within single materials. In comparison to the complex module structures required for the conventional Seebeck and Peltier effects, the transverse thermoelectric effects provide the complete device structures, potentially resolving the fundamental issue of multi-module degradation of thermoelectric conversion performance. This review article provides an overview of all currently known transverse thermoelectric conversion phenomena and principles, as well as their characteristics, and reclassifies them in a unified manner. The performance of the transverse thermoelectric generator, refrigerator, and active cooler is formulated, showing that thermal boundary conditions play an essential role to discuss their behaviors. Examples of recent application research and material development in transverse thermoelectrics are also introduced, followed by a discussion of future prospects.

Thermal conductivity, a fundamental parameter characterizing thermal transport in solids, is typically determined by electron and phonon transport. Although other transport properties including electrical conductivity and thermoelectric conversion coefficients have material-specific values, it is known that thermal conductivity can be modulated artificially via phonon engineering techniques. Here, we demonstrate another way of artificially modulating the heat conduction in solids: magnonic thermal transport engineering. The time-domain thermoreflectance measurements using ferromagnetic metal/insulator junction systems reveal that the thermal conductivity of the ferromagnetic metals and interfacial thermal conductance vary significantly depending on the spatial distribution of nonequilibrium spin currents. Systematic measurements of the thermal transport properties with changing the boundary conditions for spin currents show that the observed thermal transport modulation stems from magnon origin. This observation unveils that magnons significantly contribute to the heat conduction even in ferromagnetic metals at room temperature, upsetting the conventional wisdom that the thermal conductivity mediated by magnons is very small in metals except at low temperatures. The magnonic thermal transport engineering offers a new principle and method for active thermal management.

We investigated the effect of composition on the phase and extrinsic magnetic properties of TbCu7-type SmFe-based compounds using a combinatorial sputtering technique. Composition-spread thin films of SmFex (x=6.4-12.7) and SmFexN (x=6.8-12.8) were synthesized using a linear shutter-assisted combinatorial sputtering technique. A high-throughput composition, phase, and magnetic characterization were performed on 18 different locations along the film using X-ray diffraction (XRD), X-ray fluorescence (XRF), and magneto-optical Kerr effect (MOKE) magnetometry. The optimal composition with the highest fraction of the main phase was found to be in SmFe9.8 and SmFe9.5N and beyond this composition, the alpha-Fe secondary ferromagnetic phase emerges. The coercive field and remanence of the SmFe9.5N are estimated to be similar to 0.8 T and similar to 1.2 T, respectively. Further, scanning transmission electron microscopy (STEM) was performed at SmFe9.5N to correlate the microstructure with their extrinsic magnetic properties. Overall, this study demonstrates the impact of composition variation on the phase and extrinsic magnetic properties of TbCu7-type SmFe-based compounds, which can be utilized to tailor magnetic properties for targeted advanced magnet applications.

Hybrid transverse thermoelectric conversion driven by simultaneous action of multiple phenomena offers a promising route for efficient energy conversion. This study demonstrates magnetic‐field‐free hybrid transverse thermoelectric conversion based on the anomalous Nernst and off‐diagonal Seebeck effects in artificially tilted multilayers comprising SmCo 5 /Bi 0.2 Sb 1.8 Te 3 junctions, where the remanent magnetization of SmCo 5 induces the anomalous Nernst effect in the absence of an external magnetic field. The thermoelectric figure of merit is observed to be 0.299 ± 0.005 at room temperature owing to the additive contribution of the anomalous Nernst effect, indicating that the excellent figure of merit due to the off‐diagonal Seebeck effect can further be enhanced by hybridizing the anomalous Nernst effect. These results establish a new approach for high‐performance transverse thermoelectric materials, enabling energy harvesting and cooling applications that leverage magnetically controlled thermoelectric effects without requiring an external magnetic field.

Abstract With the giant magnetoresistance (GMR) effect serving as a vital component in modern spintronic technologies, researchers are dedicating significant efforts to improve the performance of GMR devices through material exploration and design optimization. However, traditional GMR measurement approaches are inefficient for comprehensive material and device optimization. This study proposes a high‐throughput current‐in‐plane GMR measurement technique based on thermal imaging of Joule heating utilizing lock‐in thermography (LIT). This LIT‐based technique is advantageous for efficiently evaluating films with varying compositions and thickness gradients, which is crucial for ongoing material exploration and design optimization to enhance the GMR ratio. First, it is demonstrated that using CoFe/Cu multilayers, the simple Joule heating measurement based on LIT enables quantitative estimation of the GMR ratio. Then, to confirm the usefulness of the proposed method in high‐throughput material screening, a case study is shown to investigate the GMR of CoCu‐based granular films with a composition gradient. These techniques allow to determine the optimum composition with maximum GMR ratio using the single composition‐gradient film and reveal Co22Cu78 as the optimal composition, yielding the largest GMR ratio among the reported polycrystalline CoCu‐based granular films. This demonstration accelerates the material and structural optimization of GMR devices.

The current-induced magnetization switching was investigated for Pt/Co/Ir/Co/Pt films. The measurements based on the conventional four-probe method and the domain structure imaging revealed that the macroscopic switching process for Pt/Co/Ir/Co/Pt is considerably dependent on magnetic structures. The dynamics of spin-orbit torque switching are also shown using the macrospin numerical calculation for both the antiferromagnetically- and ferromagnetically-coupled cases sandwiched by spin Hall layers. The present results provide the macroscopic and microscopic pictures of switching mechanism for the interlayer exchange-coupled systems with dual spin-orbit torque and a guideline to design a spintronic device with high-efficient operation.

Recent research revealed that Sm–Co-based amorphous films prepared by stacking many ultrathin Sm/Co pairs exhibit large in-plane coercivity and realize the zero-field operation of the anomalous Nernst effect (ANE). Here, we investigate the effect of the Sm/Co-pair thickness on the magnetic anisotropy and ANE in Sm–Co-based amorphous films and compare them with a co-sputtered Sm–Co-based amorphous alloy film. We find that the magnetic (magneto-thermoelectric) properties of the co-sputtered film are almost the same as that of the multilayer films with the Sm/Co-pair thickness of ≤1.0 nm (≤3.0 nm). This finding will serve as a guideline for investigating amorphous magneto-thermoelectric materials.

We report current-induced magnetization switching in Pt/Co/Ir/Co/Pt multilayers with different Ir layer thicknesses (tIr), where the perpendicularly magnetized Co layers are coupled ferromagnetically or antiferromagnetically through an interlayer exchange coupling and are sandwiched by the Pt spin Hall layers. The domain structures formed during switching vary depending on the magnetization alignment, i.e., a ferromagnetically coupled or antiferromagnetically coupled configuration. These results clarify the macroscopic picture of switching process for interlayer exchange-coupled systems. The local picture of the switching process is also examined by a numerical calculation based on a macrospin model, which reveals the switching dynamics triggered by dual spin–orbit torques for both antiferromagnetically and ferromagnetically coupled cases. The numerical calculation shows that the dual spin–orbit torques from the two Pt layers effectively act on the two Co layers not only for the antiferromagnetically coupled case but also for the ferromagnetically coupled one. Our findings deepen the understanding of the switching mechanism in a magnetic multilayer and provide an avenue to design spintronic devices with more efficient spin–orbit torque switching.

We report the observation of the anisotropic magneto-Thomson effect (AMTE), which is one of the higher-order thermoelectric effects in a ferromagnet. Using lock-in thermography, we demonstrated that in a ferromagnetic NiPt alloy, the cooling or heating induced by the Thomson effect depends on the angle between the magnetization direction and the temperature gradient or charge current applied to the alloy. AMTE observed here is the missing ferromagnetic analog of the magneto-Thomson effect in a nonmagnetic conductor, providing the basis for nonlinear spin caloritronics and thermoelectrics.

Transverse thermoelectric generation using magnetic materials is essential to develop active thermal engineering technologies, for which the improvements of not only the thermoelectric output but also applicability and versatility are required. In this study, using combinatorial material science and lock-in thermography technique, we have systematically investigated the transverse thermoelectric performance of Sm-Co-based alloy films. The high-throughput material investigation revealed the best Sm-Co-based alloys with the large anomalous Nernst effect (ANE) as well as the anomalous Ettingshausen effect (AEE). In addition to ANE/AEE, we discovered unique and superior material properties in these alloys: the amorphous structure, low thermal conductivity, and large in-plane coercivity and remanent magnetization. These properties make it advantageous over conventional materials to realize heat flux sensing applications based on ANE, as our Sm-Co-based films can generate thermoelectric output without an external magnetic field. Importantly, the amorphous nature enables the fabrication of these films on various substrates including flexible sheets, making the large-scale and low-cost manufacturing easier. Our demonstration will provide a pathway to develop flexible transverse thermoelectric devices for smart thermal management.

We have characterized Co2MnGa (CMG) Heusler alloy films grown on Y3Fe5O12 (YIG) and Gd3Ga5O12 (GGG) substrates at different deposition temperatures and investigated thermo-spin and magneto-thermoelectric conversion properties by means of a lock-in thermography technique. X-ray diffraction, magnetization, and electrical transport measurements show that the deposition at high substrate temperatures induces the crystallized structures of CMG, while the resistivity of the CMG films on YIG (GGG) prepared at and above 500 degrees C (550 degrees C) becomes too high to measure the thermo-spin and magneto-thermoelectric effects due to large roughness, highlighting the difficulty of fabricating highly ordered continuous CMG films on garnet structures. Our lock-in thermography measurements show that the deposition at high substrate temperatures results in an increase in the current-induced temperature change for CMG/GGG and a decrease in that for CMG/YIG. The former indicates the enhancement of the anomalous Ettingshausen effect in CMG through crystallization. The latter can be explained by the superposition of the anomalous Ettingshausen effect and the spin Peltier effect induced by the positive (negative) charge-to-spin conversion for the amorphous (crystallized) CMG films. These results provide a hint to construct spin-caloritronic devices based on Heusler alloys. Published under an exclusive license by AIP Publishing.

We have investigated the anomalous Ettingshausen effect (AEE) in iron-carbon alloys, i.e., cast irons and steel, using the lock-in thermography. All the alloys exhibit the clear AEE-induced temperature modulation, and their anomalous Ettingshausen coefficient is an order of magnitude greater than that of the pure iron at room temperature. The dimensionless figure of merit for AEE in the ductile cast iron is 55 times greater than that in the pure iron owing to the significant increase of the anomalous Ettingshausen coefficient. Our result reveals a potential of iron-carbon alloys as transverse thermoelectric materials, although the composition and microstructures optimizations are necessary.