Influence of microstructure on magnetic properties of nanocomposite RE5.5(Fe,Cr,M)76.5B18 (RE=Nd, Tb; Cr⩾3 at %; M=Co,Si) magnetic materials

The microstructure and the magnetic properties of nanocomposite (Nd,Tb)5.5(Fe,Cr,M)76.5B18 (M=Co,Si) magnetic materials have been investigated. The samples were prepared by splat cooling and subsequent fast annealing treatment between 700 and 800 °C in order to develop a nanocrystalline microstructure. Optimum magnetic properties are found in samples with 3 at % Cr. A higher Cr content results in an increase of the coercive field but also in a decrease of both remanence and saturation magnetization. The magnetic properties of splat cooled materials with 3 at % Cr can be improved by the substitution of Co or (Co,Si). Splat cooled flakes with 2.5 at % Co and 0.5 at % Si show a coercive field Hc of 551 kA/m and a remanence μ0Mr of 0.91 T. After optimized annealing the magnetic materials consist of a homogeneous microstructure of Fe3B and (Nd,Tb)2Fe14B grains with a grain size in the range of 10–30 nm. The substitution of Co leads to a slight coarsening of the grain size.