REVERSIBLE PERMEABILITY FOR PERPENDICULARLY SUPERPOSED INDUCTION IN METALLIC GLASSES FOR FLUXGATE SENSORS

Co66.5Fe3.5S12B18 metallic glass ribbons with very low magnetostriction have been successfully employed as soft magnetic cores in sensitive sensors for fluxgate magnetometers. Noise levels of 12 pT rms (0.06-10.0 Hz) have been obtained for suitably heat-treated metallic glass. Since the noise is a decisive factor, and in order to correlate it with the irreversible magnetization process of the material, we have studied the behaviour of its reversible permeability in the circumferential direction with a biasing field applied perpendicular to this direction. This method has already been used for studying irreversible processes in the Rayleigh region. Experimental results show completely different behaviours for a core with an as-quenched ribbon and one with a stress-annealed ribbon. In the as-quenched state rotational processes are the dominant sources of noise while for the stress-annealed ribbon core the behaviour is related to domain wall displacement in this range of low excitation fields.