  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 magneto-resistance and magneto-inductance ratios of 700% and
450% have been obtained in 30-600 kHz frequency range respectively. These large
magneto-resistance and magneto-inductive ratios 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 Magneto-impedance (LMI) configuration greatly improves the MI
ratios and sensitivities. The maximum MI ratio for the resistive part increases
to as large as 2500% for Hper ~ 1 Oe. The sensitivity of the magneto-resistance
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 favourable (transverse)
domain structures.
