Structure and soft magnetic properties of finemet alloys

Abstract

The soft magnetic properties of Fe_73.5Cu₁Nb₃Si1_3.5B₉ (Finemet) alloys prepared by mechanical alloying were studied using various experimental techniques including MÖssbauer spectroscopy. The study includes the influence of the milling atmosphere. The results are compared with mechanically alloyed Fe-Si alloys as well as with melt-spun Finemet alloys. The coercivity of the mechanically alloyed powder is much larger than that of the melt-spun ribbons, though the saturation magnetisation is the same. This is ascribed to the absence of a grain boundary amorphous ferromagnetic phase resulting in a weakening of the exchange coupling between the nanograins. This study suggests that the interfacial component in Finemet alloys plays a crucial role in achieving good soft magnetic properties. The critical grain size for single domain particle was found to be 10 nm. For very small grain sizes, the existence of superparamagnetism was also studied using Fe-57 Mossbauer spectroscopy.