Seebeck effect (Fig. a below) is that an electrical current/voltage is induced by a temperature bias applied across two dissimilar (in terms of thermopower) conductors that are connected at both ends.
The spin analog of the Seebeck effect, Spin Seebeck effect (Fig. b above) is that a spin current/voltage is induced by a temperature bias applied across a ferromagnetic material where the two spin channels act as two dissimilar ‘conductors’.
The first demonstration of spin Seebeck effect is done by Uchida et al. [1] In this experiment, a temperature gradient is applied over a ferromagnetic film (Py) of macroscopic scale (several millimeter in length) in x-direction (see below), then a spin current is measured by a Pt probe put on top, which converts the spin current entering the probe into a change current by inverse spin Hall effect, i.e. convert the spin current flowing in z-direction into a charge current flowing in y-direction.
The measured Hall voltage over the Pt probe is proportional to the magnitude of the applied temperature bias, and the position of the probe. The Hall voltage is opposite when the probe is attached at the opposite ends of the Py film (see below). And the spatial dependence is approximately linear in macroscopic scale, which is very surprising in the present understanding of spin transport theory, because this length scale is much much longer than any type of spin related lengths scale, which is typically less than 1 micrometer in the best case.
In this topic, we are trying to explain the experiment using the thermally activated spin pumping current. [2]
- Reference:
[1]. Uchida, K. et al. Observation of the spin Seebeck effect. Nature 455, 778-781 (2008).
[2]. Xiao, J., Bauer, G.E.W., Maekawa, S. & Brataas, A. Charge pumping and the colored thermal voltage noise in spin valves. Phys. Rev. B 79, 174415-9 (2009).