Longitudinal spin Seebeck effect in paramagnetic insulator VO₂thin film

The spin Seebeck effect (SSE) involves the generation of spin current in the presence of a temperature gradient across a magnetically active material. Although much work has been done in ferrimagnetic and antiferromagnetic materials, SSE in paramagnets is considerably less studied, and the mechanism of paramagnetic SSE is still unclear. Here we present a systematic study of the longitudinal SSE (LSSE) in paramagnetic insulating thin film VO₂ at low temperatures. The LSSE grows with increasing field and saturates at high field. With the increasing temperature, the magnitude of LSSE voltage at fixed heater power decreases, and varies as T^-2 relationship between 15 K and 50 K. The LSSE shows the expected angular dependence with the in-plane field orientation and is linear in the heating power. The sign of the LSSE response is not consistent with mobile triplet excitations as the carriers of spin. We will place these results in the context of theoretical discussions of paramagnetic SSE response.