Structure and magnetic properties of CoFeZrMBCu soft nanocrystalline alloys

In this article, we report on the effect of substituting Nb, Hf, and Ta for Zr on the crystallization behavior, crystal structure, and magnetic properties of (Co0.95Fe0.05)88Zr7−xMxB4Cu1 (x=0, 1, and 3.5). Samples annealed at temperatures up to 550°C lead to the partial crystallization of very fine bcc-(Co,Fe) and fcc-(Co,Fe) grains, while annealing at 750°C lead to coarser fcc-(Co,Fe) grains and Co–M intermetallic phases. All of the compositions except those with 3.5at.% Nb or Ta show similar low coercive behavior in the as-spun and annealed states. The coercivity of annealed ribbons below 550°C is varied from 0.15to0.46Oe and the magnetization from 128to133emu∕g. High temperature hysteresis loop measurements revealed a nearly constant coercivity for up to 400°C and 20% reduction in magnetic induction, exceeding the performance of Finemet alloys at this temperature.