Unusually Large Anomalous Nernst Effects in Partially-Crystallized Ferromagnetic Metallic Glasses

Nernst effect is a well-established thermoelectric effect where electrons traveling along the direction of a temperature gradient are deflected by the Lorentz force into the transverse direction perpendicular to both temperature gradient and applied magnetic field. As a result, a finite electric field develops along the transverse direction. In magnetic or topological materials, such transversal deflection occurs owing to different mechanisms classified into intrinsic and extrinsic origins, and the phenomenon is called the anomalous Nernst effect (ANE). Recent studies reported that a large ANE arises in materials possessing a large Berry curvature near the Fermi level. Since its origin is intrinsic electronic band topology, such a large ANE is observed in specific crystalline orientations which requires the use of single crystalline materials. Contrary to the growing research interest in discovering new materials with large Berry curvatures, much less attention has been paid to extrinsic aspects of ANE.<br/>In this talk, we show that unusually large ANE can be obtained even in amorphous ferromagnetic metals, when the degree of disorder within the materials is properly controlled. By applying varied heat treatment conditions to initially amorphous materials, we were able to prepare samples with different crystallinity. Intriguingly, samples with partial crystallization show the largest ANEs, comparable to those of the single crystalline state-of-the-art materials. The fact that the ANEs of fully-crystallized samples are far smaller suggests a significant role of extrinsic contribution to the observed large ANEs in partially-crystallized samples. Such large extrinsic contribution is further supported by detailed analysis of anomalous Hall effect, which reveals an unprecedented scaling relation between the longitudinal resistivity and Hall resistivity. Our work sheds new light on disordered materials as promising candidates for large ANE with better mechanical robustness than their single crystalline counterparts.<br/> <br/><b>Acknowledgement</b><br/> <br/>This work was supported by Samsung Research Funding & Incubation Center of Samsung Electronics under Project Number SRFC-MA2002-02 and by the National Research Foundation of Korea (NRF) grants funded by the Korea government (MSIT) (NRF-2022M3C1A3091988) and by the Ministry of Education, Science and Technology (RS-2023-00252296).