Thin magnetic amorphous wires for GMI sensor

This paper presents a study of the GMI in amorphous conventional wires with nearly zero magnetostriction (Co68.18Fe4.32Si12.5B15) having different diameters obtained by cold drawing processes in multiple steps. The purpose of our work is to find the way in which the sensitivity of GMI effect is affected by the decrease of the wires diameter and also the way in which the stress induced during the cold drawing process influence the configuration of the magnetic domains structure through the modification of the magnetoelastic energy. We have performed a study of the giant magneto-impedance effect (GMI) in nearly zero magnetostrictive conventional amorphous wires with diameters between 150-20 mum. The values of the impedance (Z) and GMI ratio (DeltaZ/Z) were measured in the frequency range 100 kHz - 10 MHz for wires in the as cast state and cold drawn. We obtained a GMI ratio four times higher for cold drawn wires with diameters of 20 - 30 mum subjected to thermomechanical treatments in comparison with the as cast wire of 130 mum diameter. The results are discussed considering the correlation between induced stresses and modifications in circumferential magnetic domains configuration.