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Large longitudinal and anomalous transverse Magneto-thermoelectric effect in kagome antiferromagnet FeGe

This study reports record-breaking transverse thermoelectric conductivity and a pronounced anomalous Nernst effect in the Kagome antiferromagnet FeGe, attributing these giant effects to large Berry curvature generated by its non-collinear spin texture and highlighting its potential for advanced magneto-thermoelectric applications.

Original authors: Jiajun Ma, Rong Chen, Yazhou Li, Chenfei Shi, Yantao Cao, YuWei Zhang, Jiaxing Liao, Yunfei Han, Guangxi Wen, Jialu Wang, Hanjie Guo, Jianhui Dai, Chenguang Fu, Jin-Ke Bao, Yan Sun, Zhu-An Xu, Yuke Li

Published 2026-08-28

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CC BY 4.0

Original authors: Jiajun Ma, Rong Chen, Yazhou Li, Chenfei Shi, Yantao Cao, YuWei Zhang, Jiaxing Liao, Yunfei Han, Guangxi Wen, Jialu Wang, Hanjie Guo, Jianhui Dai, Chenguang Fu, Jin-Ke Bao, Yan Sun, Zhu-An Xu, Yuke Li

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

For decades, engineers have sought better ways to turn waste heat into electricity, a process that relies on materials capable of generating a voltage when one side is hot and the other is cold. This phenomenon, known as the thermoelectric effect, has traditionally been studied by looking at how electricity flows straight through a material from hot to cold. However, a newer and more promising approach involves looking at what happens when heat and electricity move sideways, perpendicular to the flow of heat, especially when a magnetic field is applied. This sideways movement, called the transverse thermoelectric effect, offers a simpler way to build devices because it does not require complex wiring or multiple materials to function. Recently, scientists have turned their attention to a special class of materials called topological magnets. These are substances where the arrangement of electrons creates unique, protected pathways that can boost these effects, and among them, a specific geometric arrangement of atoms known as a kagome lattice has shown particular promise for generating large electrical responses.

In a recent study, researchers investigated a specific material called FeGe, which is an antiferromagnet, meaning its internal magnetic spins point in opposite directions and cancel each other out, leaving the material with no overall magnetic pull. What makes FeGe unique is that its atoms form a kagome pattern, resembling a woven basket, and it hosts a complex interplay between its magnetic order and a wave-like distortion in its electron density. The team focused on a specific temperature range where the material's magnetic spins tilt slightly, creating a canted structure. By cooling the material and applying a strong magnetic field, they measured how heat and electricity moved through it. They found that when the material entered this tilted magnetic state, its ability to generate a voltage from a temperature difference changed dramatically. In fact, the magnetic field caused the voltage to flip its direction and increase by a factor of over one hundred times compared to its zero-field state, a change that is exceptionally large for this type of material.

The researchers also measured a sideways voltage generated by the temperature difference, known as the Nernst effect, and found it to be surprisingly strong. This effect is driven by the twisting of electron paths in momentum space, a property called Berry curvature, which acts like a hidden force pushing electrons sideways. In FeGe, this effect was so pronounced that the material achieved a record-breaking level of transverse thermoelectric conductivity for an antiferromagnet, reaching a value of 15 amperes per kelvin per meter at low temperatures. This performance rivals that of the best-known ferromagnetic materials, which typically have a net magnetic field, yet FeGe achieves this without any stray magnetic fields. The study explicitly ruled out other common explanations for such large signals, such as the dragging of electrons by magnetic waves or simple changes in how many charge carriers are present, pointing instead to the unique, non-collinear arrangement of spins in the material as the primary cause.

To understand why this happens, the team used computer simulations to model the electronic structure of the material in its tilted magnetic state. These calculations confirmed that the specific way the spins are arranged creates a large amount of the hidden curvature needed to drive the strong sideways electrical current. The results suggest that by tuning the magnetic structure of such materials, scientists can significantly enhance their ability to harvest energy from heat. While the study does not yet describe a finished device, it demonstrates that antiferromagnetic materials with complex spin textures are powerful candidates for future thermoelectric applications, offering a new path to capture energy that is currently lost as heat. The work highlights how the intricate dance of electrons and spins in a crystal lattice can be harnessed to create efficient, solid-state energy converters.

Technical Summary: Large Longitudinal and Anomalous Transverse Magneto-Thermoelectric Effect in Kagome Antiferromagnet FeGe

Problem and Context
Traditional thermoelectric (TE) research has predominantly focused on optimizing the longitudinal Seebeck effect through band tuning and phonon engineering. However, the investigation of novel electronic structures, particularly in topological materials featuring Dirac cones, flat bands, and van Hove singularities, offers new avenues for enhancing TE performance. While transverse magneto-thermoelectric effects, such as the anomalous Nernst effect (ANE), present advantages like simplified junction design and scalability, high-performance magneto-TE materials remain scarce. Specifically, the interplay between spatially varying spin textures, charge orders, and topology in strongly correlated electronic systems is not well understood. The Kagome antiferromagnet FeGe, which exhibits a complex phase diagram involving a charge density wave (CDW) and canted antiferromagnetic (CAFM) ordering, serves as a candidate platform to explore these interactions.

Methodology
The study utilized high-quality FeGe single crystals grown via the chemical vapor transport (CVT) method and subsequently annealed to ensure long-range CDW ordering. Comprehensive transport measurements were conducted using a six-terminal method for resistivity and Hall effects, and a one-heater–two-thermometer technique for thermopower, thermal conductivity, and the Nernst effect. Measurements were performed in a 14 T cryogenic refrigerator with magnetic fields applied parallel to the ab-plane ( $H \parallel ab$ ) while current and heat flow were along the c-axis ( $I, Q \parallel c$ ). Longitudinal and transverse signals were symmetrized and antisymmetrized, respectively, to eliminate contact misalignment errors.

Complementing the experiments, first-principles calculations were performed using the Vienna ab initio simulation package (VASP). These calculations modeled the electronic band structure under various magnetic configurations, including A-type antiferromagnetism and canted spin structures, incorporating spin-orbit coupling (SOC). The anomalous Nernst conductivity (ANC) was derived using the linear response Kubo formula based on Wannier functions projected from the Bloch wavefunctions.

Key Results

Phase Transitions and Transport Anomalies: The FeGe samples exhibited two distinct phase transitions: a CDW transition at $T_{CDW} \approx 108$ K and a canted-AFM (CAFM) transition at $T_{cant} \approx 56$ K. At $T_{cant}$ , the longitudinal thermopower ( $S_{zz}$ ) and Nernst signal ( $S_{zx}$ ) underwent a sign change from positive to negative, indicating a shift in the majority charge carriers from holes to electrons and a modification of the chemical potential.
Giant Magneto-Thermopower: A magnetic field of 14 T induced a massive change in thermopower. Around $T_{cant}$ , the relative change in thermopower ( $\Delta S_{zz}/S_{zz}$ ) reached $10^2$ – $10^4\%$ . This magnitude is significantly larger than that reported for conventional thermoelectric materials (e.g., Ag $_{2-\delta}$ Te) and other topological semimetals.
Anomalous Nernst Effect (ANE): Below $T_{cant}$ , a pronounced ANE was observed. The anomalous Nernst signal ( $S^A_{zx}$ ) peaked at approximately $1.2~\mu$ V/K at 20 K, exceeding values found in other Kagome canted antiferromagnets like Mn $_3$ Sn/Ge.
Record Transverse Conductivity: The study calculated the anomalous transverse thermoelectric conductivity ( $\alpha^A_{zx}$ ) using the relation $\alpha_{zx} = \sigma_{zz}S_{zx} + \sigma_{zx}S_{zz}$ . The extracted $\alpha^A_{zx}$ reached a maximum of 15 A K $^{-1}$ m $^{-1}$ at 20 K. This value represents the highest record among known antiferromagnetic materials and is comparable to that of the ferromagnetic metal UCo $_{0.8}$ Ru $_{0.2}$ Al.
Mechanism: The large $\alpha^A_{zx}$ is primarily driven by the term $\sigma_{zz}S^A_{zx}$ , suggesting that high electrical conductivity combined with a significant anomalous Nernst signal is the dominant factor. The authors attribute the large Berry curvature responsible for these effects to the non-collinear spin texture in the CAFM state and the topological nature of the Kagome lattice, rather than magnon drag or phonon drag, which were ruled out by temperature and field dependence analysis.

Significance and Claims
The paper claims that FeGe demonstrates that nontrivial spin structures, when coupled with charge order and topological bands, can generate exceptionally large Berry curvature contributions to thermoelectric transport. The observation of a record-breaking transverse thermoelectric conductivity in an antiferromagnet highlights the potential of Kagome antiferromagnets for magneto-thermoelectric applications. Unlike conventional ferromagnets where the ANE scales linearly with magnetization, the large ANE in FeGe arises from topological spin textures, offering a pathway to enhance thermoelectric performance without the complications of stray magnetic fields. The work suggests that tuning the Fermi level in such topological antiferromagnets could further optimize thermoelectric efficiency.

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