Zero-field Nernst effect in a ferromagnetic kagome-lattice Weyl-semimetal Co3Sn2S2

Abstract: The discovery of magnetic topological semimetals recently attracted significant attention in the field of topology and thermoelectrics. In a thermoelectric device based on the Nernst geometry, an external magnet is required as an integral part. We report a zero-field Nernst effect in a newly discovered hard-ferromagnetic kagome-lattice Weyl-semimetal Co3Sn2S2. A maximum Nernst thermopower of 3 microvolt/K at 80 K in zero field is achieved in this magnetic Weyl-semimetal. Our results demonstrate the possibility of application of topological hard magnetic semimetals for low-power thermoelectric devices based on the Nernst effect and are thus valuable for the comprehensive understanding of transport properties in this class of materials.

• The paper demonstrates that ferromagnetic Co3Sn2S2 exhibits a zero-field Nernst effect of ~3 µV K⁻¹ at 80 K, indicating its promise for low-power thermoelectric applications.
• The study utilizes both experimental measurements and DFT calculations to reveal key band structure effects, including significant Berry curvature contributions.
• The paper highlights the role of strong magnetic anisotropy in generating large coercive fields, which supports the material’s stable thermoelectric performance without an external magnetic field.

Zero-field Nernst Effect in a Ferromagnetic Kagome-Lattice Weyl-Semimetal Co$_3$Sn$_2$S$_2$

This paper is a comprehensive investigation of the zero-field Nernst effect observed in the recently synthesized kagome-lattice Weyl-semimetal, Co$_3$Sn$_2$S$_2$. The authors report an anomalous Nernst thermopower value reaching ~3 µV K$^{-1}$ at 80 K in the absence of an applied magnetic field. The significance of this lies in the inherent magnetism of Co$_3$Sn$_2$S$_2$, which sustains a non-zero Nernst signal even after the external magnetic field is removed. This paper highlights the potential of using topological hard magnetic semimetals in thermoelectric applications, presenting Co$_3$Sn$_2$S$_2$ as a promising candidate.

Key Findings and Results

• Material Properties: Co$_3$Sn$_2$S$_2$ is identified as a type-IA ferromagnet, featuring a crystal structure that supports a unique configuration of Co and Sn atoms leading to strong magnetic anisotropy. It exhibits a Curie temperature of approximately 177 K and a magnetic moment of about 0.89 µ$_B$ per formula unit at peak magnetization.
• Magnetization and Coercivity: The paper presents distinct rectangular hysteresis loops with large coercive fields, observed up to 100 K, which slowly diminish as the temperature nears $T_c$. The strong magnetic anisotropy is advanced as the reason for this large coercive behavior.
• Nernst Thermopower: The study meticulously describes the experimental setup and the results of the Nernst thermopower measurements, explaining the temperature-dependent behavior of $S_{xy}$. The paper effectively demonstrates the attainment of a maximum zero-field Nernst thermopower of ~3 µV K$^{-1}$ in magnetized Co$_3$Sn$_2$S$_2$.
• Theoretical Support: Density-functional-theory (DFT) calculations support the findings, illuminating the intrinsic band structure effects that facilitate the large anomalous Nernst effect. The calculations indicate a significant Berry curvature contribution, associated with the nodal lines and Weyl points inherent to the material's band structure.

Implications and Future Prospects

The significance of this research lies in its potential technological applications in low-power thermoelectric devices. The lack of need for an external magnetic field in the operation of such devices is particularly noteworthy. Co$_3$Sn$_2$S$_2$'s intrinsic properties present a pathway to reduce device complexity and improve durability, necessitating a reevaluation of strategies for optimizing thermoelectric devices.

Furthermore, this paper propels the exploration of magnetic topological materials, paving the way for discovering novel compounds with potentially higher Curie temperatures and larger zero-field Nernst signals. Such advancements could broaden the applications of these materials in quantum computing, sensing, and energy conversion technologies.

Conclusion

This investigation effectively contributes to the fundamental and applied understanding of magnetic topological materials. The demonstration of a zero-field Nernst effect in Co$_3$Sn$_2$S$_2$ marks a notable advancement in thermoelectric research. Continued exploration in this domain could significantly impact the development of next-generation thermoelectric devices and other technologies leveraging the unique properties of magnetic Weyl semimetals. The paper's methodology, combining experimental techniques with first-principle calculations, sets a valuable framework for future studies aimed at harnessing the properties of topological materials for practical applications.