Roles of nonequilibrium magnons in nonlinear spin and charge transport

Nonlinear magnetotransport effects that violate Onsager’s reciprocity are of both fundamental and practical interests. Despite a plethora of experimental studies of such effects in various magnetic systems, ranging from metallic magnetic bilayers to magnetic topological insulators, the roles of nonequilibrium magnons in nonlinear spin and charge transport have remained elusive. We will discuss the solutions of a set of coupled kinetic equations for electrons and magnons up to the second order in the applied electric field, whereby electrons and magnons are treated on an equal footing in spin dependent transport. The results will be applied to a few different magnetic systems of particular interest, and dependencies of the nonlinear transport coefficients on temperature, external magnetic field, and magnetic anisotropy will be discussed, shedding light on effective control of nonlinear spin and charge transport mediated by nonequilibrium magnons.