Magnetization processes in small particles and nanocrystalline materials

Micromagnetic calculations using computational techniques are a pre-requisite to treat complex magnetization processes in ensembles of ferromagnetic grains. Applying the finite element method, the critical fields for the reversal of magnetization are determined as a function of grain size, isotropic and textured distribution of easy axes and different magnetic properties of grain boundaries. Adapting the mesh sizes of finite elements to the gradients of the direction cosines of the spontaneous magnetization, inhomogeneous spin distributions are determined within the grains as well as within grain boundaries. Coercive fields will be determined for nanocrystalline ensembles of grains. taking into account exchange and dipolar coupling between grains and inhomogeneous magnetic material parameters,within the grain boundaries. The results of these investigations will give information on the role of exchange coupling between the grains, dipolar long-range magnetic stray fields and the remanence enhancing by exchange coupling between. the grains. From the model calculations general rules for the development of optimized nanocrystalline materials with large remanences and large coercivities will be derived. (C) 1999 Elsevier Science B.V. All rights reserved.