arXiv subjects

Sang J. Park

Publications and source records attributed to Sang J. Park.

7 recordsLinked to original sources

arXiv2026

Observation of orbital-angular-momentum-driven temperature modulation via the spin Peltier effect

Angular-momentum transport provides a pathway for controlling energy flow in solids beyond conventional charge-based mechanisms. While spin currents are known to mediate spin-caloritronic phenomena such as the spin Peltier effect (SPE), the role of orbital angular momentum in heat transport remains largely unexplored. Here we demonstrate orbital-angular-momentum-driven temperature modulation via the SPE in yttrium iron garnet/Pt/CuOx heterostructures. Using wedge-shaped CuOx layers combined with spatially resolved active thermal measurement techniques, we map the continuous thickness dependence and quantitatively disentangle the spin- and orbital-current-mediated contributions within a single device. The orbital-mediated component exhibits a pronounced maximum at an intermediate thickness, revealing a characteristic length scale for interfacial orbital-angular-momentum generation and propagation at the Cu/CuOx interface. These results provide direct experimental evidence that charge-current-driven orbital angular momentum can drive SPE-induced temperature modulation, establishing interfacial orbital processes as an additional channel for heat transport and providing a pathway toward spin-orbit caloritronics.

cond-mat.mtrl-sci↗

arXiv2026

Trans-scale spin Seebeck effect in nanostructured bulk composites based on magnetic insulator

The spin Seebeck effect (SSE) enables thermoelectric conversion through thermally generated spin currents in magnetic materials, offering a promising transverse geometry for scalable devices. However, conventional SSE devices are confined to nanoscale thin-film architectures, with significantly restricted output power due to the intrinsic constraints of spin and magnon diffusion lengths. Here, we demonstrate a trans-scale SSE using nano-structured bulk composites composed of Pt-coated yttrium iron garnet powders fabricated via dynamic powder sputtering and low-temperature sintering. The resulting three-dimensional composites exhibit continuous Pt channels and robust mechanical integrity. Transverse thermoelectric measurements confirm isotropic SSE signals at the bulk scale. Power analysis indicates that the three-dimensional architecture enables scalable volumetric thermoelectric power generation beyond diffusion-limited thin-film SSE geometries. This work establishes a scalable platform for bulk SSE-based thermoelectrics, bridging nanoscale spin caloritronics with macroscopic device integration.

cond-mat.mtrl-sci↗

arXiv2026

Enhanced transverse electron transport via disordered composite formation

Transverse electron transport in magnetic materials - manifested in effects such as the anomalous Hall and Nernst effects - holds promise for spintronic and thermoelectric applications. While recent advances have focused on enhancing such transport through topological single crystals via intrinsic mechanisms linked to Berry curvature, practical limitations remain due to their mechanical fragility and narrow material scope. Here, we demonstrate a distinct approach for transverse transport enhancement based on composite formation. Using both theoretical modeling and experiments, we show that disordered mixtures of two ferromagnetic materials can exhibit significantly stronger transverse electron deflection than either constituent alone. This enhancement originates from meandering electron pathways created by the disordered mixture of two materials and does not rely on long-range crystalline order. The identified requirements for this mechanism can be broadly satisfied across different material systems, offering a universal and tunable strategy to engineer large transverse responses in structurally robust platforms.

cond-mat.mtrl-sci↗

arXiv2026

Structural heterogeneity-induced enhancement of transverse magneto-thermoelectric conversion revealed by thermoelectric imaging in functionally graded materials

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, 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 heterogeneity. 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 designing high-performance flexible materials.

cond-mat.mtrl-sci↗

arXiv2025

High-throughput development of flexible amorphous materials showing large anomalous Nernst effect via automatic annealing and thermoelectric imaging

This work demonstrates high-throughput screening of flexible magnetic materials for efficient transverse thermoelectric conversion based on the anomalous Nernst effect (ANE). The approach integrates automated annealing and contactless measurement of transport properties using lock-in thermography. We screen 151 Fe-based alloy ribbons with varying compositions and annealing conditions. Seven high-performance candidates with mechanical flexibility are identified, exhibiting anomalous Nernst coefficients of up to 4.8 uV/K, the highest value reported for flexible materials. Structural analysis reveals that ANE enhancement occurs universally near the first crystallization temperature of the Fe-based ribbons, without strong correlation with composition. Notably, the enhancement is also observed in samples without Cu or Fe nanoclusters, indicating that short-range atomic order in the amorphous matrix may play a role in ANE. These findings demonstrate the effectiveness of high-throughput methodologies for discovering advanced ANE materials and provide new insights into thermoelectric conversion in disordered systems where conventional design principles fall short.

cond-mat.mtrl-sci↗

arXiv2024

Designing flexible hard magnetic materials for zero-magnetic-field operation of the anomalous Nernst effect

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 focused 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 and magnetically hard transverse thermoelectric materials by creating amorphous-crystalline heterogeneous composites. We fabricated and optimized the heterogeneous composites through controlled heat treatment, achieving significant enhancements in the coercivity and anomalous Nernst coefficient, while maintaining flexibility. Additionally, using the developed material, we constructed a single-material-based coiled device and demonstrated the 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.

cond-mat.mtrl-sci↗

arXiv2024

Large Transverse Thermopower in Shape-Engineered Tilted Leg Thermopile

We demonstrate that a novel device design, where a shape-engineered tilted-leg thermopile structure is employed, significantly enhances the output voltage in the transverse direction. Owing to the shape engineering of the leg geometry, an additional temperature gradient develops along the long direction of the leg, which is perpendicular to the direction of the applied temperature gradient, thereby generating an additional Seebeck voltage V_SE that adds to the Anomalous Nernst effect (ANE) voltage V_ANE. We further show that a simple adjustment of electrode position within the device can further increase V_SE. The tilted leg device with electrode adjustment demonstrates a 990% enhanced transverse output voltage compared to that of conventional rectangular leg thermopile-structured devices, wherein only the ANE occurs. This combined output voltage from both the Seebeck effect and ANE is equivalent to the value that surpasses the state-of-the-art ANE materials and devices currently available. The numerical analysis shows the tendencies of the electrical and thermal outputs of the tilted-leg device, which guides a way to further improve the output voltage. Our study paves the way to develop highly efficient transverse TE devices that can overcome intrinsic materials challenges by utilizing the degree of freedom of device design.

physics.app-ph↗