Development of magnetic softness in high-energy ball milling alloyed Fe50B50

Results are reported about the phase distribution and magnetic properties of high-energy ball milled samples prepared from pure Fe and B powders and having nominal equiatomic composition. After milling the precursor powders for times from 40 to 270 h, the milling product consists of a majority amorphous phase and of milling-time-dependent small percentages of α-Fe, Fe₂B and FeB. The coercivities measured in the as-milled samples were of the order of thousands of A/m and decreased to tens of A/m after a short time; low temperature treatments decreased the coercivity. We propose that this softening process is linked to a combination of stress relaxation and of enhancement of the exchange coupling between the minority crystalline phases and amorphous matrix, this last fact leading to the elimination of hindrances to the domain wall motion.