Structural, microstructural, and magnetic properties of nanocrystalline-amorphous Fe–Co–Ta–B alloy processed by high-energy mechanical alloying

A nanocrystalline Fe(Co) phase dispersed within an amorphous matrix was achieved after milling of Fe₃₁Co₃₁B₃₀Ta₈ powder mixtures up to 200 h by using a high-energy ball mill. The transformations occurring in the powders during milling were studied with the use of X-ray diffraction and scanning electron microscopy techniques. The transformation of the phase depends upon the milling time. With the increase of milling time, various nanostructured phases such as Fe(Co), Co₂Ta, Co(Ta,B), fcc-Co, Fe-type borides, and amorphous phase were identified. Magnetic properties were also investigated and correlated with microstructural changes. By increasing milling time, irregular variation of saturation magnetization is identified in relation to the change in the composition of the system. Also, the gradual decrease in grain size to a few nanometers resulted in an increase in coercivity while increasing the milling time up to 200 h. The existence of non-magnetic Ta and B atoms in the neighboring Fe and Co atoms and the increase in the volume fraction of the amorphous phase are retained as the major factors of this hard magnetic behavior of the present system.