Date of this Version
The structure of micromagnetic energy barriers responsible for slow magnetization processes is investigated. Thermally activated slow magnetization processes proceed over energy barriers whose structure is determined by the micromagnetic free energy. This restricts the range of physically meaningful energy barriers. An analysis of the underlying micromagnetic free energy yields power-law dependences with exponents of 3/2 or 2 for physically reasonable models. This must be contrasted to other power laws, such as linear laws, and to 1/H-type dependences. In the limit of small energy barriers, corrections to the Arrhenius law become important. In this regime, there is no simple expression for the relaxation behavior, but two requirements help to judge models and approximations. First, at low temperatures, the Arrhenius-type power laws must be reproduced. Second, as in the Arrhenius limit, the approaches must correspond to well-defined energy landscapes.