Excitation Amplitude Dependence of Low Frequency Magneto-impedance of Amorphous Fe73.5Nb3Cu1Si13.5B9 Ribbon

Magneto-impedance (MI) of soft ferromagnetic materials is a sensitive function of the amplitude and frequency of exciting a.c magnetic field. MI (Z) of amorphous ferromagnetic ribbon of nominal composition Fe73.5Nb3 Cu1 Si13.5 B9 is measured at different excitation currents with frequency ranging from 30kHz to 120KHz The excitation (a.c) and biasing (d.c) magnetic fields Hdc are parallel to ribbon axis. At zero dc fields, Z exhibits non-linear dependence on excitation amplitude whereas at higher d.c fields (9Oe) Z is nearly independent of excitation amplitude. The impedance is maximum at zero bias field and sharply decreases as Hdc increases and almost zero hysterisis has been observed as Hdc is scanned. The maximum relative change of impedance (Z(H)-Z(H=0))/Z(H=0) is found to increase from nearly 45 to 60 percent when the excitation fields goes up from 14A/m to 140A/m. The large MI is associated with screening of electromagnetic field by magnetization induced by exciting ac field.