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)(76.5)B-18 (M = Co, Si) magnetic materials have been investigated. The samples were prepared by splat cooling and subsequent fast annealing treatment between 700 and 800 degrees 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 H-c of 551 kA/m and a remanence mu(0)M(r) of 0.91 T. After optimized annealing the magnetic materials consist of a homogeneous microstructure of Fe3B and (Nd, Tb)(2)Fe14B 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. (C) 1999 American Institute of Physics. [S0021-8979(99)47108-7].