Hyungyu Jin

Transverse thermoelectric devices offer a promising alternative to conventional longitudinal architectures due to their simplified, scalable layouts and enhanced mechanical durability. However, their practical deployment has been fundamentally hindered by low output power. Here, we demonstrate a geometric design strategy that increases transverse output power by redistributing the internal temperature field through mirror-symmetry breaking, thereby activating the conventional longitudinal Seebeck response in the transverse direction. We term this phenomenon the geometry-induced transverse Seebeck effect (G-TSE) and develop a topology-optimization framework to systematically design thermoelectric leg architectures that maximize this effect. As a proof of concept, we experimentally validate this strategy using an additively manufactured polycrystalline Fe–50Ni alloy leg, achieving a 998-fold enhancement in transverse output power compared to a standard cuboid geometry under the same applied heat flux. Numerical simulations for conventional Seebeck materials further indicate that this approach can bring transverse devices close to representative longitudinal thermoelectrics in volumetric power density normalized by the square of the applied heat flux. These results establish geometry as a design degree of freedom for transverse thermoelectric energy conversion and provide a systematic route to devices adapted to heat sources of different shapes.

, The anomalous Nernst effect in topological magnets offers a promising route for transverse thermoelectric energy harvesting and heat flux sensing. Maximizing this effect requires strategic band engineering to concentrate topological features near the Fermi level. However, precisely aligning these topological features remains a fundamental challenge in conventional materials design. Here, strategic f-orbital engineering is demonstrated as an effective design principle to significantly amplify the anomalous Nernst effect. By employing the cubic Laves phase CexTb1-xFe2, systematic alignment of active 4f states near the Fermi level is achieved through Ce concentration tuning. This band alignment triggers intense c-f hybridization with the itinerant Fe 3d bands, driving a significant reconstruction of the band structure. Density functional theory calculations corroborate that this strong electronic coupling generates these topological band features, inducing a substantial proliferation of Weyl points concentrated within the immediate vicinity of the Fermi level. Consequently, the pristine CeFe2 achieves a remarkable 13.2-fold enhancement in the anomalous Nernst coefficient (3.3 μV K-1) relative to the unsubstituted TbFe2. Furthermore, its Fe-based ferromagnetic matrix ensures a state-of-the-art anomalous Nernst conductivity of 10 A m-1K-1 across a broad temperature range (50-170 K). While intermediate compositions experience partially suppressed macroscopic transport due to inherent alloy disorder scattering, scaling analysis demonstrates that the giant transverse responses across the entire series are fundamentally driven by the intrinsic Berry curvature. Ultimately, these findings highlight strategic f-orbital engineering as a highly effective design principle for maximizing the anomalous Nernst effect in topological magnets.

As heat flux becomes increasingly localized and time-dependent in high-power electronic systems, conventional steady-state cooling becomes insufficient to suppress rapid temperature rise. Transient supercooling in thermoelectric coolers (TECs), achieved by temporarily applying a current above the optimal steady-state current, enables a transient enhancement of cooling capacity. Although its effectiveness depends strongly on the temporal characteristics of the applied heat flux, previous studies have typically evaluated the transient supercooling using simple square-wave heat loads. In this study, transient supercooling performance is numerically evaluated under realistic and simplified square-wave transient heat flux profiles. A realistic profile is constructed from measured CPU power data, with time-equivalent and peak-equivalent profiles developed for comparison. Performance is quantified by the reduction in maximum temperature (ΔTsup) and temperature controllability (ΔTsup/ΔTfluct), where ΔTfluct is the temperature fluctuation under constant optimal current operation. For a representative CPU operating condition, under the realistic heat flux profile, ΔTsup is 1.20 K and the controllability is 43.8 %. Under the time-equivalent and peak-equivalent heat flux profiles, ΔTsup is 1.80 K and 3.57 K, corresponding to controllability of 67.2 % and 57.9 %, respectively. Both simplified profiles therefore overestimate the transient supercooling performance relative to the realistic profile. This overestimation trend persists across CPU operating conditions, and the experimental results further support these findings. These results indicate that simplified heat flux representations can overestimate the performance of the transient supercooling, and accurate evaluation requires realistic heat flux profiles.

We present a thermoelectric performance enhancement by anion–cation co‐doping in p‐type bismuth tellurides with a cost‐effective and mechanically robust thermoelectric module fabrication process. Polycrystalline (BST) _{1 − x} (NaCl) _x (0 ≤ x ≤ 5.0 mol%) samples were synthesized via melting and hot‐press sintering, and their anisotropic transport properties were investigated. At low NaCl concentrations, Na ⁺ and Cl ⁻ act as effective substitutional dopants, optimizing carrier concentration and mobility while suppressing bipolar thermal conduction via local lattice strain. At higher NaCl contents, nanoscale precipitates form, providing additional phonon scattering without degrading electronic transport. Consequently, a maximum ZT ≈ 1.49 at 350 K and an average ZT _avg ≈ 1.4(300–425 K) were achieved. In parallel, a mechanically robust module architecture using an electrically insulating, low‐thermal‐conductivity PEEK support eliminates wafering and dicing processes. A 31‐pair module fabricated with optimized p‐type (BST) _{1 − x} (NaCl) _x and n‐type (CuI) _0.3 Bi ₂ Te _2.7 Se _0.3 materials exhibit competitive thermoelectric performance to that of commercial Bi ₂ Te ₃ ‐based modules. These results demonstrate a pathway toward economically competitive and mechanically robust next‐generation thermoelectric modules.

The anomalous Nernst effect in topological magnets offers a promising route for transverse thermoelectric energy harvesting and heat flux sensing. Maximizing this effect requires strategic band engineering to concentrate on topological features near the Fermi level. However, precisely aligning these topological features remains a fundamental challenge in conventional materials design. Here, precise f-orbital localization is demonstrated as an unconventional and highly potent design principle to significantly amplify the anomalous Nernst effect. By employing the cubic Laves phase CexTb1-xFe2, systematic modulation of f-orbital localization near the Fermi level is achieved through Ce concentration tuning. This strategic localization triggers intense c-f hybridization with the itinerant Fe 3d bands, driving a profound reconstruction of the band structure. Density functional theory calculations corroborate that this strong electronic coupling induces a massive proliferation of Weyl points strictly confined within the immediate vicinity of the Fermi level. Consequently, the pristine CeFe2 achieves a remarkable ten-fold enhancement in the anomalous Nernst coefficient (3.3 μV K-1) relative to the unsubstituted TbFe2. Furthermore, its Fe-based ferromagnetic matrix ensures a state-of-the-art anomalous Nernst conductivity of 10 A m-1K-1 across a broad temperature range (50-170 K). While intermediate compositions experience partially suppressed macroscopic transport due to inherent alloy disorder scattering, scaling analysis unequivocally confirms that the giant transverse responses across the entire series are fundamentally driven by the intrinsic Berry curvature. Ultimately, these findings highlight precise f-orbital localization as a highly effective design principle for maximizing the anomalous Nernst effect in topological magnets.

As heat flux becomes increasingly localized and time-dependent in high-power electronic systems, conventional steady-state cooling becomes insufficient to suppress rapid temperature rise. The transient supercooling in thermoelectric coolers (TECs), achieved by temporarily applying a current above the optimal steady-state current, enables a transient enhancement of cooling capacity. However, its effectiveness depends strongly on the temporal characteristics of the applied heat flux. In this study, temperature control using the transient supercooling is evaluated under realistic and simplified transient heat flux conditions. A realistic heat flux profile is constructed from measured CPU power data, and two simplified heat flux profiles, referred to as time-equivalent and peak-equivalent heat flux, are developed for comparison. Numerical simulations using a commercial TEC are performed and validated experimentally. Temperature controllability is defined as the ratio of the reduction in maximum temperature by the transient supercooling (ΔTsup) to the temperature fluctuation under constant optimal current operation (ΔTfluct). Under the realistic heat flux condition, ΔTsup is 0.89 K and the controllability is 32.4%. Under the time-equivalent and peak-equivalent heat flux conditions, ΔTsup is 1.66 K and 2.91 K, corresponding to controllability of 61.9% and 47.2%, respectively. Experimental results agree with the simulations. These results indicate that simplified heat flux representations can overestimate the performance of the transient supercooling, and accurate evaluation requires realistic heat flux conditions.

Spintronic devices based on ferrimagnetic insulators (FMIs) offer promising approaches toward energy‐efficient magnetic memories. A critical challenge in this field is achieving reliable nonvolatile magnetic switching with minimal energy consumption. Temperature‐induced switching, which utilizes temperature modulation instead of electrical currents or magnetic fields, provides a compelling strategy. However, maintaining stable states without continuous energy input has remained problematic. Here, we demonstrate purely temperature‐induced nonvolatile magnetic switching using a bilayer composed of gadolinium iron garnet and holmium iron garnet. Using the longitudinal spin‐Seebeck effect, we probe the Fe sublattice magnetization states and identify significant thermal hysteresis driven by three key factors: (i) a crossover of magnetization from the distinct temperature dependences of the two layers, (ii) strong antiferromagnetic coupling at their interface, and (iii) intrinsic magnetic anisotropies. This hysteresis facilitates stable bistable magnetic states within a finite temperature range. By applying a moderate external magnetic field of 30 Oe, we achieve clear and stable switching with ±25 K temperature modulation. Furthermore, detailed energy analysis reveals that temperature‐induced switching requires up to 66‐fold less energy compared to conventional spin‐orbit torque switching in 100‐nm‐thick FMIs. Our findings indicate that temperature‐induced switching presents a viable, energy‐efficient alternative for magnetic memory applications.

Transverse electron transport in magnetic materials such as the anomalous Hall and Nernst effects holds promise for spintronic and thermoelectric applications. Efforts to enhance transverse transport have focused on finding quantum materials with large Berry curvature, skew scattering, or side jump. Here, we report a distinct approach based on composite formation. Using both theoretical modeling and experiments, we show that disordered composites of two ferromagnetic materials can exhibit significantly stronger transverse transport than constituent materials. This enhancement originates from meandering electron pathways created by the disordered composites. We identify the condition for this enhancement, which can be broadly satisfied across diverse material systems, offering a universal and tunable strategy to engineer large transverse responses.