Evidences of thermoelectrically driven unidirectional magnetoresistance from a single Weyl ferromagnet Co2MnGa

Abstract

Weyl ferromagnets, with large anomalous Hall (and Nernst) effects, are an ideal playground to study unconventional transport phenomena. Here, we report a sizable unidirectional magnetoresistance with a ratio of up to 7.73 × 10−5 per current density of 1 MA cm−2 in single-layer epitaxial Co2MnGa films. Surprisingly, the nonlinear signal has an isotropic crystallographic axis dependence and scales almost linearly with the film thickness. Both features cannot be explained by the spin transport from an intrinsic band structure, but rather agree with the current induced transverse thermoelectric effect. By employing a 1D heat transfer model to account for the temperature gradient, we derived an analytical expression of this thermoelectrically driven unidirectional magnetoresistance, from which a upper bound of transverse thermopower Sxy = 3.70 ± 1.10 µV K−1 can be obtained. Our work provides direct evidences of thermoelectric voltages in the nonlinear transport signals that may be extended to other material systems as well.