The anomalous Nernst effect (ANE) is a well-known thermoelectric effect for ferromagnets, namely the generation of an electric voltage perpendicular to both magnetization and an applied temperature gradient. This transverse geometry of ANE leads to various advantages for thermoelectric modules compared to the conventional one based on Seebeck effect, such as simpler structure to efficiently cover a heat source, higher flexibility, lower production cost, and larger conversion efficiency for the same figure of merit [1]. However, the size of ANE is generally very small (on the order of ~0.1 μV/K), which hinders its practical applications. Recent theoretical and experimental investigations on topological materials indicate that the intense Berry curvature of Weyl points near the Fermi energy can enhance the intrinsic ANE, rendering ANE an powerful probe to clarify the topological electronic structure in magnetic Weyl semimetals [2-4]. In other words, a ferromagnet exhibiting a giant ANE may serve as an ideal ground for magnetic Weyl semimetal state.

Fig. 1. Magnetic field dependence of anomalous Nernst coefficient of Co₂MnGa at room temperature.

In this work, we report the giant ANE in a full-Heusler ferromagnet Co₂MnGa, reaching a record high value of S_yx~6 μV/K at room temperature [5] (Fig. 1). The crossover from Mott relation α_yx ~ T to –lnT dependence is observed on warming, where α_yx is the transverse thermoelectric conductivity, indicating the proximity to the quantum Lifshitz transition between type-I and type-II magnetic Weyl fermion states. Out study provides a new guideline for searching new topological magnets which are useful for energy harvesting and spintronics.

References

• [1] M. Mizuguchi and S. Nakatsuji, Sci. Tech. Adv. Mater. 20, 262 (2019).
• [2] D. Xiao et al., Rev. Mod. Phys. 82, 1959 (2010).
• [3] M. Ikhlas et al., Nat. Physics 13, 1085 (2017).
• [4] K. Kuroda et al., Nat. Mater. 16, 1090 (2017).
• [5] A. Sakai et al., Nat. Physics 14, 1110 (2018).

Authors

• A. Sakai, Y. P. Mizuta^b,c, A. A. Nugroho^d, R. Sihombing^d, T. Koretsune^a,c, M.-T. Suzuki^a,c, N. Takemori^c, R. Ishii, D. N.-Hamane, R. Arita^a,c, P. Goswami^e,f, and S. Nakatsuji^a
• ^aCREST, Japan Science and Technology Agency (JST)
• ^bKanazawa University
• ^cCenter for Emergent Matter Science, RIKEN
• ^dBandung Institute of Technology
• ^eUniversity of Maryland
• ^fNorthwestern University