NUMERICAL MICROMAGNETICS IN HARD MAGNETIC AND MULTILAYER SYSTEMS

Micromagnetic finite element calculations using a magnetic vector pote ntial to treat long-range dipolar interactions describe the interactiv e magnetization processes which determine the magnetic properties of f ine-grained magnetic materials. Micromagnetic models give a quantitati ve treatment of the correlation between the microstructure and the mag netic properties of melt-spun Nd2Fe14B magnets and of Co/Pt multilayer s, In nanocrystalline permanent magnets, intergrain exchange interacti ons cause nonuniform magnetic states which increase the remanence and act as nucleation sites. Remanence increases with decreasing grain siz e. Remanence enhancement of about 15% with respect to noninteracting p articles can be achieved for an average grain size D less than or equa l to 20 nm. On the other hand, the nucleation field reduces to about 2 0% of the anisotropy field. Once a reversed domain has been nucleated, strong internal stray fields cause the expansion of the domain over s everal grains. The nucleation field of Co/Pt multilayers increases wit h improving texture. Spatial fluctuations of the magnetocrystalline an isotropy energy create barriers for domain wall motion. The pinning fi eld of reversed domains increases with increasing misalignment and wit h increasing grain size. The quality of texture and the grain size sig nificantly influence the jaggedness of domains in Co/Pt multilayers. L arge grains and strong deviations of the easy directions from the film normal deteriorate the smoothness of domains and increase the transit ion width. (C) 1996 American Institute of Physics.