The effect of substitutions on the hard magnetic properties of Nd-Fe-B based materials

The effect of different substitutions (Co, Ni, Al, Si, Ga) was investigated by studies of the magnetization process and by measurements of the temperature dependence of the anisotropy field Ha and the hysteresis loop (77 K < T < Tc). Additionally 57Fe Mössbauer studies were performed. The Co substitution increases the Curie temperature and reduces the anisotropy. The substitution of nonmagnetic elements such as Al, Si or Ga increases IHc via the microstructure as well as the intrinsic properties. Si and Ga substitution increases IHc and also the Curie temperature; this effect is generally attributed to a preferential substitution of the Fe sites. The rise in HA with substitution of Nd by Dy is in agreement with the increase of IHc. In this case a linear relation between IHc(T) and HA(T) was found and also the magnet parameters are less sensitive to the heat treatment.