Magnetic viscosity and data collapse phenomena in anisotropic magnetic systems are investigated by using the Monte Carlo technique. The definition of the viscosity coefficient, which has been traditionally used to model aftereffect phenomena in scalar magnetic systems, is generalized in order to describe 3-D magnetic systems, where both the direction and the magnitude of the magnetization vector can change in time. Using this generalization of the vector viscosity coefficient, we have analyzed data collapse phenomena in vectorial magnetization processes. It was found that the traditional belled shaped curves of the scalar viscosity coefficient as a function of the applied field can have one or more maxima in the case of vectorial systems. The data collapse phenomena seem to apply to simple magnetization processes (such as first-order rotational reversal curves); however, it cannot be generalized to more complex magnetization processes because of the relatively complicated magnetization dynamics.
A noniterative identification technique is developed for the computation of parameters of the energetic model of hysteresis. Due to the relatively simple form of model equations, we are able to identify the subset of physical parameters (e.g., coercive fields, remnant magnetizations, differential susceptibilities, etc.) that can be described by the model. This allows us to find necessary and sufficient conditions under which the energetic model can be applied to a magnetic material with given physical characteristics, in this way establishing the limits of applicability of the model.
The vectorial properties of thermal relaxation phenomena are modeled by using random fluctuation fields that act as perturbations on the external applied magnetic field. The total magnetic field is used as input in phenomenological vector models of hysteresis, which, in this article, are defined as superposition of scalar models of hysteresis distributed along all possible directions. A Monte Carlo technique is developed to compute the average value of the magnetization vector as a function of time. Whereas in the case of isotropic materials the average value of the magnetization vector usually moves on a straight line oriented towards the direction of the applied field, in the case of anisotropic materials the magnetization vector can switch from one easy axis to another and cross the direction of the applied field. It is shown that, depending on the initial hysteretic state, the trajectory of the magnetization vector can deviate substantially from the straight line, which is a pure three-dimensional relaxation effect.
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