Thermal forces on ferromagnetic domain walls, associated with the wall entropy

Abstract

At any finite temperature, an entropy S* is stored in the thermal spin disorder of a ferromagnetic domain wall. Thus, a domain wall moving across a temperature gradient dT/dx constitutes a thermal engine carrying entropy and heat from a hot to a cold reservoir, and transforming it partly into work. This work is performed through a force Fx applied to the wall. Using the first and second laws, we find Fx=-S*dT/dx. Rough estimates of S* are obtained from the temperature dependence of the wall surface energy. They suggest that this "wall-entropy force" may be comparable in magnitude to the force caused by the Nernst effect, described earlier.