Structure and soft magnetic properties of Finemet alloys

The soft magnetic properties of Fe73.5Cu1Nb3Si13.5B9 (Finemet) alloys prepa red by mechanical alloying were studied using various experimental techniqu es including Mossbauer spectroscopy. The study includes the influence of th e 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 ribbo ns, though the saturation magnetisation is the same. This is ascribed to th e absence of a grain boundary amorphous ferromagnetic phase resulting in a weakening of the exchange coupling between the nanograins. This study sugge sts that the interfacial component in Finemet alloys plays a crucial role i n achieving good soft magnetic properties. The critical grain size for sing le domain particle was found to be 10 nm. For very small grain sizes, the e xistence of superparamagnetism was also studied using Fe-57 Mossbauer spect roscopy. (C) 2000 Published by Elsevier Science S.A. All rights reserved.