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 Nd 2 Fe 14 B) together with an ultra-soft phase (typified by α -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 Δ GH , the grain size of the hard phase, and of ϕ S , the fractional volume of the soft phase. The dependence on Δ GH falls quite rapidly with increasing ϕ S . The low anisotropy and high saturation magnetization of the α -iron make approximately equal contributions to remanence enhancement in the model. Its remanence values are in quite good agreement with experimental values for Nd 2 Fe 14 B containing α -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 Δ GH and ϕ S .