Enthalpy relaxation and Curie temperature behavior in Fe(Ni,Co)Zr amorphous alloys

Abstract

Annealing-induced changes in enthalpy relaxation and Curie temperature, T c, were examined for amorphous (Fe 0.85Ni 0.15) 90Zr 10 and (Fe 0.9Co 0.1) 90Zr 10 alloys. The compositional dependence of an endothermic reaction was also examined for amorphous (Fe 1− x Co x ) 90Zr 10 ( x = 0–1) alloys. A reversible endothermic reaction occurs above the annealing temperature, T a. The change in the magnitude of the endothermic peak, ΔC pmax , with T a shows a single stage with a peak at about T x − 400 K (i.e., the temperature that is 400 K lower than crystallization temperature). For (Fe 1− x Co x ) 90Zr 10 alloys, the endothermic reaction is the largest at x = 0.5 and disappearsat x = 0 and 1. The change in T c with T a is related to the increase in T c at T a ≌ T x − 400 K , followed by the decrease in T c at temperatures above T x − 400 K. A good correspondence was observed between the reversible endothermic enthalpy relaxation and the increase in T c and between the irreversible exothermic enthalpy relaxation and the decrease in T c. These results are explained as a consequence of the low-temperature endothermic reaction which is due to the local chemical ordering of FeNi and FeCo atoms with shorter relaxation times. The exothermic reaction is mainly due to the long-range topological change leading to the densification of amorphous structure with longer relaxation times.