Giant magneto-impedance in stress-annealed finemet/copper/finemet-based trilayer structures

The resistive and reactive components of magneto-impedance (MI) for finemet/copper/finemet sandwiched structures based on stress-annealed nanocrystalline Fe75Si15B6Cu1Nb3 ribbons as functions of different fields (longitudinal and perpendicular) and frequencies have been measured and analyzed. Maximum changes of 700% and 450% in the resistive and inductive components of MI, respectively, have been obtained in 30–600 kHz frequency range. These large changes in MI are a direct consequence of the large effective relative permeability due to the closed magnetic flux path in the trilayer structure. The influence of perpendicular bias fields (Hper) in the longitudinal MI (LMI) configuration greatly improves the MI ratios and sensitivities. The maximum MI ratio for the resistive component increases to as large as 2500% for Hper∼1 Oe. The sensitivity of the field dependence of resistive component of MI increases from 48%/Oe to 288%/Oe at 600 kHz frequency with the application of Hper∼30 Oe. Such high increase in MI ratios and sensitivities with perpendicular bias fields are due to the formation the favorable (transverse) domain structures.