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 dimensional cubic lattice, and cubic crystallites of the soft phase were inserted at the junctions of every group of eight hard crystallites. Demagnetizing curves were obtained as a sequence of static equilibrium states in an incrementally changing applied field. Values of the coercivity, remanence and energy product are reported as functions of the grain size of the hard phase, and 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 high saturation magnetization of the a-iron make approximately equal contributions to remanence enhancement in the model. Its remanence values are in quite good agreement with experimental values for Nd2Fe14B containing a-iron. However, its values for the coercivity and energy product, though decidedly lower than those obtained computationally by some other authors, significantly exceed those obtained experimentally, but show a similar variation with Delta (GH) and phi (S). (C) 2001 Elsevier Science B.V. All rights reserved.