Curie temperature behaviour on annealing of Finemet type amorphous alloys

The time–temperature dependence of Curie temperature (TC) was determined by the DSC method for amorphous Fe73.5Cu1Nb3Si15.5B7 ribbon-shaped alloy on annealing below the crystallization temperature. Relaxation of atomic structure of the amorphous phase on annealing was accompanied by an increase of TC. The σ-shaped time dependence was not characterized, however, by a single value of TC, since long-time annealing of amorphous samples resulted in a slow increase of TC at each temperature. The appearance of two heat capacity maxima observed after short-time annealing at the pre-crystallization temperature was associated with two Curie points (TC1 and TC2). These peaks were related to clustering inside the amorphous phase and to separation into two phases with different chemical compositions. Further annealing resulted in α-Fe nuclei appearance in the amorphous phase and consequently in the disappearance of iron-rich clusters.