Giant magneto-impedance effect in nanostructured magnetic wires

The giant magneto-impedance effect (GMI) is studied as a function of the structural modification induced in an Fe73.5Si13.5B9Cu1Nb3 amorphous alloy wire by annealing. The values of GMI are correlated to those structural changes and with the corresponding variation of the magnetic properties and intrinsic resistivity. Excellent soft magnetic properties, associated with low resistivity values, make this nanostructured material as one of the most promising for future applications of the GMI effect. The tailoring of the structure which can be induced by adequate thermal treatments easily allows one to obtain excellent combinations of circumferential permeability μφ and resistivity ρ during different devitrification stages, in order to produce materials for specific aims. Maximum GMI ratios of 200% are found after annealing the wires in the range 550–600 °C, where an optimum compromise between μφ and ρ is found. A simple model is developed correlating the fundamental physical properties of the soft magnetic wires with the measured values of both components of the impedance, allowing the prediction of experimental GMI ratios and an easy visualization of the phenomenon.