The effect of annealing conditions on the power loss of amorphous ribbons

The power loss of amorphous ribbon toroids of Fe81B13.5Si3.5C2and Co58Fe5Ni10Si11B16has been measured under sinusoidal flux conditions, using the lock-in amplifier technique, with flux densities up to 95% of saturation over a frequency from 20 Hz to 20 kHz. The toroids have been annealed at temperatures from 325°C to 425°C, under field and non-field conditions and in atmospheres of air, nitrogen and hydrogen. The effect of annealing conditions (temperature, field, atmosphere) on power loss over a wide range of flux density and frequency will be shown and optimum conditions discussed. It has been found that for iron-based ribbons the optimum annealing temperature depends upon the magnetizing frequency of the toroids, but field annealing in nitrogen gives the lowest power loss. It is found for the cobalt-based ribbon that the difference in loss between as-cast and annealed toroids is very small in contrast to the results for the iron-based ribbons. These experimental variations in power loss with annealing conditions and frequency will be explained by considering the observed domain structures and the metallurgical and magnetic properties of the amorphous ribbons.