Curie temperature and crystallization behavior of amorphous Fe 80B 15Si 5−xGe x

Abstract

We have utilized a DuPont 1090 Thermal Analysis System to measure the Curie temperature, T C , and crystallization behavior of the system Fe 80B 15Si 5−xGe x, x=0, 1, 2, 3 and 5. T C varies linearly from 662 K for x=0 to 686 K for x=5 in as quenched samples. Annealing above T C has the effect of raising the Curie point 3 K in each sample. Crystallization takes place at each composition in two stages: precipitation of α-Fe followed by crystallization of the remaining amorphous material. The crystallization temperature, T X , as measured by the onset method, decreases linearly with increasing Ge concentration from 780 K for x=0 to 718 K for x=5 (heating rate 20 K/min). The onset method appears to overstimate the temperature at which sufficient precipitation of α-Fe occurs to produce a measurable change in the magnetization. Arrhenius plots are very linear, with very little scatter in the data. The activation energy, E a, for the initiation of crystallization decreases from 3.81 eV for x=0 to 2.65 eV for x=3. There is little change in E a between x=3 and x=5 (2.56 eV). An observable glass transition was absent at each composition, as may be expected from the relatively low value of E a.