Computer simulation of the effect of an ultra soft phase on the magnetic properties of nanocrystalline permanent magnets

Micromagnetic models of assemblies of randomly oriented, exchange coupled, nanocrystals consisting of a magnetically hard uniaxial phase (typified by Nd2Fe14B) together with an ultra-soft phase (typified by a-iron) have been studied numerically. The hard crystallites were located on a three dimensio nal cubic lattice, and cubic crystallites of the soft phase were inserted a t the junctions of every group of eight hard crystallites. Demagnetizing cu rves were obtained as a sequence of static equilibrium states in an increme ntally changing applied field. Values of the coercivity, remanence and ener gy product are reported as functions of the grain size of the hard phase, a nd of (ps, the fractional volume of the soft phase. The dependence on Delta (GH) falls quite rapidly with increasing phi (S). The low anisotropy and h igh saturation magnetization of the a-iron make approximately equal contrib utions to remanence enhancement in the model. Its remanence values are in q uite good agreement with experimental values for Nd2Fe14B containing a-iron . However, its values for the coercivity and energy product, though decided ly lower than those obtained computationally by some other authors, signifi cantly exceed those obtained experimentally, but show a similar variation w ith Delta (GH) and phi (S). (C) 2001 Elsevier Science B.V. All rights reser ved.