The giant magneto-impedance (GMI) effects in amorphous Co70Fe4.5Ni4Nb1Si12.
5B8 alloy ribbon have been observed. It is shown that the GMI effects incre
ase with driving current frequency and an appropriate annealing can enhance
the effect. A large MI ratio of about 120 % in the as-cast sample and a ra
tio of about 400 % in a suitably annealed sample have been measured at 5 MH
z.