Magnetically soft nanocrystalline materials obtained by devitrification of metallic glasses

This paper presents the main features of magnetically soft metallic glasses and nanocrystalline materials obtained by controlled crystallization of metallic glasses, a brief description of the principal methods of nanocrystallization as well as the recent developments in nanocrystalline materials for high-temperature applications. Two groups of alloys were investigated: (Fe, Co)-Si-Nb-Cu-B (FINEMET-type) and (Fe, Co)-(Zr, Nb, Hf)-Cu-B (HITPERM-type). For FINEMET-type alloys it was found that the optimum combination of magnetic properties (coercivity, Curie temperature, magnetostriction) is obtained when Fe:Co ratio is about 1: 1. For HITPERM-type alloys, the best performance and stability are observed when alloys contain Hf, and the worst in the case of Nb. Optimum Hf content is 7 at.%, and 6 at.% B. The HITPERM-type alloys exhibit good stability of properties at 500 degrees C for at least 700 hours.