Spin-Seebeck Effects in Pyrochlore Iridates

The spin-Seebeck effect (SSE) refers to voltage signals induced by the Inverse Spin Hall Effect (ISHE), with thermally driven spin currents through adjacent magnetic systems. It has been studied before mostly in collinear magnetic systems. Here, we present a general theory of the SSE in the case of a non-collinear antiferromagnetic insulator (AFI)/non-magnetic metal heterostructure. In our model, we apply a periodic boundary condition in the transverse plane and an open boundary condition at the interface. If there is a non-equilibrium temperature difference within the two materials, the exchange coupling between the electrons in the metal and magnons of interfacial spins in the AFI can give rise to a longitudinal spin current across the system. We also numerically compute the spin current using a pyrochlore iridate as the AFI where the spin configuration is the all-in-all-out (AIAO) ground state. We compare the results of different crystal interfaces arising from different crystalline orientations to make a connection with experiments and practical devices.