Advances in amorphous and nanocrystalline materials

A new amorphous alloy has been recently introduced which shows a saturation magnetic induction B-s of 1.64 T which is compared with B-s=1.57 T for a currently available Fe-based amorphous alloy and decreased magnetic losses. Such a combination is rare but can be explained in terms of induced magnetic anisotropy being reduced by the alloy's chemistry and its heat treatment. It has been found that the region of magnetization rotation in the new alloy is considerably narrowed, resulting in reduced exciting power in the magnetic devices utilizing the material. Efforts to increase B-s also have been made for nanocrystalline alloys. For example, a nanocrystalline alloy having a composition of Fe80.5Cu1.5Si4B14 shows B-s exceeding 1.8 T. The iron loss at 50 Hz and at 1.6 T induction in a toroidal core of this material is 0.46 W/kg which is 213 that of a grain-oriented silicon steel. At 20 kHz/0.2 T excitation, the iron loss is about 60% of that in an Fe-based amorphous alloy which is widely used in power electronics. Another example is a Fe85Si2B8P4Cu1 nanocrystalline alloy with a B-s of 1.8 T, which is reported to exhibit a magnetic core loss of about 0.2 W/kg at 50 Hz and at 1.5 T induction. This article is a review of these new developments and their impacts on energy efficient magnetic devices. (C) 2012 Elsevier BY. All rights reserved.