Effects of surface oxidation on magnetic properties of amorphous alloy for choke core use

In order to develop a non-gap type choke core, effects of annealing in oxygen atmosphere on magnetic properties for FeCrBSiC amorphous alloy were investigated. After annealing for 2 hrs at 480/spl deg/C, optimum magnetic properties for choke core were obtained, where the effective permeability was about 400 and was almost constant up to 1 MHz, and the decrease in permeability upon large bias dc current of 16 A was very little. Furthermore it was shown that the ac magnetic loss was very low as compared to the conventional choke cores. With the increase in annealing temperature the magnetic hysteresis loop was inclined without a substantial increase of coercive force and a microstructural change of amorphous phase up to 480/spl deg/C. It was considered that these choke properties were basically due to the interaction between oxidation-induced stress and magnetostriction which brought about the induced magnetic anisotropy perpendicular to the ribbon surface, and also the good soft magnetic properties of amorphous phase.