NUCLEATION FIELDS AND GRAIN-BOUNDARIES IN HARD MAGNETIC-MATERIALS

Numerical micromagnetic calculations of the nucleation field of two-di mensional magnetic microstructures reveal the effects of interparticle interactions on the magnetization reversal mechanism. The results sho w that the magnetic behavior of interacting particles drastically chan ges with the grain size. For an average grain diameter D > 100 nm the particles of magnetic microstructures are strongly coupled by long-ran ge magnetostatic interactions. Therefore the reduced nucleation field of misoriented grains determines the coercive field of large-grained p article ensembles irrespective of the grain boundary type. In smaller grains long-range demagnetizing fields become less effective. Nonmagne tic boundary phases prevent the expansion of a reversed domain nucleus into the neighboring grains. If the average grain diameter approaches the domain wall width short-range exchange interactions between neigh boring grains increase the nucleation field.