Effects of nanocrystal formation on the soft magnetic properties of Fe-based bulk metallic glasses

We developed several Fe-based bulk metallic glasses with a unique combination of large glass-forming ability and excellent soft magnetic properties by minor doping of Cu in the Fe(76)C(7.0)Si(3.3)B(5.0)P(8.7) alloy. Proper additions of the non-magnetic copper element which has a positive heat of mixing with Fe, coupled with adequate annealing, can stimulate formation of similar to 5 nm alpha Fe ferromagnetic nanocrystals, which results in the increment in the saturation magnetization. Over-annealing which induced coarsening of the alpha-Fe nanocrystals reduces the ferromagnetic exchange interaction between the nanosized alpha-Fe crystals and increases the effective magneto-crystalline anisotropy, thereby deteriorating the soft magnetic properties. (C) 2011 American Institute of Physics. [doi:10.1063/1.3621832]