MAGNETIC AND STRUCTURAL-PROPERTIES OF NANOCRYSTALLINE FE77B19CU1NB3 ALLOY

The influence of small additions of Cu and Nb into Fe-B amorphous materials on their crystallization process has been investigated by differential scanning calorimetry, X-ray diffraction and observations of hysteresis loops. The Fe77B19Cu1Nb3 alloy has been selected to analyze the correlation between structural changes during the crystallization process and the evolution of magnetic properties. It is shown that alpha-Fe nanocrystallites, with average grain size in the range 33-25 nm, are grown during the first crystallization step. At the same time, the coercivity increases from 2.4 A m-1 in the as-cast state to 80-120 A m-1 and an increase of the saturation magnetization of about 14% is observed. The appearance of the perpendicular magnetic anisotropy has also been observed. The sample overannealed is fully crystallized, Fe-B precipitates and the coercive field increases up to 2640 A m-1. The annealing process does not lead to a major magnetic softening, in the material investigated, as is the case for the iron-rich nanocrystals containing silicon. This fact is discussed in the present work in terms of the ferromagnetic exchange correlation length.