Spin Seebeck effect in insulating SrFeO_3-δ films

In SrFeO_3-δ, noncollinear antiferromagnetic spin textures have led to the observation of the topological Hall effect and may give rise to novel magnetic excitations. Here, we measured the spin Seebeck effect in epitaxial, oxygen reduced SrFeO_3-δ films, which are nonferromagnetic and insulating at low temperatures. We detected a spin Seebeck signal below 300 K and the signal is enhanced below ∼100 K, near the ordering temperature of incommensurate antiferromagnetism found in bulk single crystals of SrFeO_3-δ. The spin Seebeck signal increases in magnitude and develops a nonlinear dependence on the magnetic field at lower temperatures. Control experiments were used to verify that the measured signal arises from a spin current and to rule out magnetic proximity effects. Our work shows a detectable spin Seebeck signal in nonferromagnetic insulator SrFeO_3-δ.