In this letter, a systematic study of the giant magnetoimpedance (GMI) effect in nanostructured Ferich
composite materials reported. The nanostructure of Fe-rich composite materials consisting of ultra-fine
nanoscale Fe(Si) grains embedded in a residual amorphous matrix was attained by annealing their
amorphous precursors at a proper temperature (?550 ?C). The impedance measurements were conducted in
the frequency range of 1-10 MHz for a dc magnetic field varying within ?300 Oe. We demonstrated that the
nanocrystallization of the alloys led to an improved magnetic softness of the material and, hence, to the GMI
effect. It was obvious that, at low frequencies (f ?? 4 MHz), the maximum value of GMI was observed at
near zero field (H dc ?0) and the GMI profiles exhibited a typical single-peak feature. At high frequencies (f
? 5 MHz), however, a two-peak feature was observed. More interestingly, the GMI ratio and its field
sensitivity reached the highest values of 170% and 64%/Oe at a frequency of 2 MHz, respectively. This
result is very beneficial for developing highly sensitive GMI sensor applications. The observed GMI
features in nanostructured Fe-rich composite materials can be interpreted by adapting the skin-effect model
in conjunction with the magnetic-field dependence of the longitudinal permeability.
