The research in the field of thermoelectric energy conversion was extended by an experimental investigation of a newly emerging field of spin caloritronics, namely spin Seebeck effect (SSE). The SSE layered device, depicted in the Fig.5b, was discovered in 2008 and refers to the conversion of a heat current into a spin current (in a magnetically ordered material) which is further converted into an electrical current by means of the inverse spin Hall effect (ISHE) in the conductive nonmagnetic metal with a large spin Hall angle. The SSE can be thus used as thermoelectric application when the mutually orthogonal orientation of the spin current, the magnetization and the electric field (Fig.5) is the key to maximize energy gain in the composite device. The study of thin films of Y-type hexagonal ferrites Ba2(Zn,Co)2Fe12O22 with a high critical temperature and an easy plane of magnetization parallel to the film surface proved that despite of complicated magnetic structure (limiting the mean free path of spin waves) Y-hexaferrites can be used as highly efficient spin sources down to low temperatures [17]. We succeeded to synthesize thin films of ε-Fe2O3 phase, which is known to exhibit a giant coercive field up to 2 T and may be tentatively used for SSE device without an external magnetic field. The experiment (magnetization, the SSE signal- Fig.6a) confirmed a coercive field ~1.1 T which is the highest value so far reported for ε-Fe2O3 thin films [18].
