Controlling the Curie temperature in amorphous glass coated microwires by heat treatment

Abstract

In amorphous ferromagnetic alloys the Curie temperature (Tc) can be changed by modifying the short-range ordering between 3d-atoms, and the kinetics of this change depends on the details of structural relaxation. In the present work, isothermal annealing was used to control Tc in amorphous Fe3.9Co64.82B10.2Si12Cr9Mo0.08 and Fe5Co27.4B12.26Si12.26Ni43.08 microwires with a relatively low Curie point in as-quenched state of 61.5 °C and 48 °C , respectively. The kinetics of structural relaxation in the first alloy appears to result in stronger antiferromagnetic coupling of Cr–Fe and Cr–Co, which lowers Tc down to 53.5 °C on annealing with a temperature of 350 °C during 10 min. Annealing the Ni-based alloys produces a continuous increase in Tc with time and annealing temperatures up to high annealing temperatures near the onset of crystallization. Partial crystallization at higher annealing temperature may also contribute to Tc- change. We demonstrated the controllable change in the Curie temperature in these wires in the range of 53.5–68°C for Cr-containing alloy and 48–72°C for Ni-containing alloys. Fine tuning of the critical temperature can be used in a variety of sensing applications in the important industrial temperature range.