High-frequency magnetoimpedance in amorphous and nanostructured Fe_73.5Si_13.5B₉Cu₁Nb₃ wires

The evolution from the amorphous to nanocrystalline state in Fe_73.5Si_13.5B₉Cu₁Nb₃ amorphous wires has been studied by means of high-frequency magnetoimpedance (MI) effect, using driving frequencies ranging from 0.1 to 500 MHz. A furnace isothermal annealing has been employed to nanocrystallize the wires (1 h at 565 °C in an argon atmosphere), while other samples were annealed at lower temperatures (300, 400 and 475 °C during 1 h), in order to evaluate the influence of annealing temperature on the MI effect. The MI response is modified by the influence of both the applied bias field and the driving frequency on the current distribution in the samples.