Motion of individual domain walls in a nickel-iron ferrite

Samples have been cut from single crystals of the nickel-iron ferrite (NiO) 0.75 (FeO 0.25 Fe 2 O 3 in such a way that they contain one and only one movable ferromagnetic domain wall. The viscous damping coefficient for this wall, which is a measure of the losses associated with domain wall motion in this material, has been measured as a function of temperature. This damping shows a very large increase as the temperature goes down to the region of 77°K. The value of this damping is correlated with the Landau-Lifshitz equation for the rotational motion of magnetization by means of previously available theoretical analysis. In addition, it is suggested that the sharp increase in damping at low temperatures is due to a relaxation associated with a rearrangement of the valence electrons on the divalent and trivalent iron ions in the ferrite. A tentative phenomenological theory of the losses based on this mechanism is presented.

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