Spin Seebeck effect in the uniaxial antiferromagnet and magnetoelectric Cr₂O₃

Recent years have seen a rapid development of spintronics in the area of spin caloritronics. In particular, the spin Seebeck effect (SSE) has been observed in a diverse class of magnetic materials. In this talk, I will focus on our recent work on the investigation of SSE in the antiferromagntic Cr₂O₃. We found that the SSE is sensitive to the orientation of the sublattice magnetization of Cr₂O₃. This was identified by a unique angular dependence of the SSE signal while the sample is rotated relative an external magnetic field. By taking the measurement in the temperature range where the thermal excitation energy is less than the magnetic anisotropy energy, we observed a suppression of the SSE signal. This phenomenon indicates that the SSE signal is mainly contributed by magnons in the bulk Cr₂O₃. We found that the spin-flop transition in our thin-film Cr₂O₃ can be clearly measured as an abrupt jump and non-hysteretic SSE signal in the angular dependence measurement. Because a magnetoelectric coupling is allowed in Cr₂O₃, we further found that the polarization of the magnon spin current in Cr₂O₃ can be controlled by varying only an electric field while maintaining a constant magnetic field. Our results demonstrate that the SSE can be applied to a large class of antiferromagnets, many of which have multiferroic properties allowing for more efficient electric control of magnon spin currents.