Micromagnetic simulation of structure–property relations in hard and soft magnets

Finite element micromagnetics describes the influence of the microstructure on the magnetic properties of thin film nano-elements and permanent magnets. The particle shape and the grain structure influence both the coercive field and the reversal time of NiFe and Co nano-elements. The performances of a Runge–Kutta method and a semi-implicit backward difference method for the time integration of the Gilbert equation of motion are compared. In an array of closely packed patterned elements, the magnetostatic interactions lead to a spread in the switching field depending on the magnetic state of the neighbors. The effect of the magnetostatic interaction on magnetization reversal can be effectively treated using a hybrid finite element/boundary element method. The very same method is applied to simulate magnetostatic interactions between the particles of a bonded magnet. The magnetostatic interaction field decreases both the remanence and the coercive field of nanocomposite magnets. In hard magnets, domain walls may be pinned at grain boundaries between misoriented grains. The simulation of domain wall motion requires adaptive refinement and coarsening of the mesh, in order to keep the number of degrees of freedom reasonably low.