Dragging of Domains by a Temperature Gradient in Amorphous Ferromagnetic Materials.

A steady, collective, translation of domain walls has been detected through direct wall observations, in metallic ferromagnets subjected to a constant temperature gradient. Two kinds of amorphous materials, Metglas 2826MB and 2705X, are used in these experiments. A 60Hz a.c. external field H(,E)('0) is needed to reduce the effect of pinning forces on the walls. Wall motion cannot be achieved at zero H(,E)('0). The critical temperature gradient required to move walls is of order (TURN)10('2)K/mm, and becomes smaller as the external field is increased. The sense of wall motion reverses itself when the temperature gradient is reversed. This indicates tha the temperature gradient dT/dx is the dominant factor affected wall motion, while the external field H(,E)('0) is not. The region in the (dT/dx, H(,E)('0)) plane corresponding to static walls has a triangular shape. This shape agrees well with a theory which takes into account the finite size of the potential wells representing wall pinning. The shape of the static-wall region also indicates that pinning of walls by the two ends of the sample is dominant over bulk and surface pinning. The dependence of this shape on sample length and thickness indicates that the Nernst -Ettingshausen drive mechanism is dominant over competing drive mechanisms. Wall-speed measurements are also carried out. They show that the speed of walls increases with increasing temperature gradient.