Influence of annealing on the magnetic properties and magneto-impedance response in Fe84Zr7B8Cu1 ribbons

X-ray diffraction and magnetic measurements have been used to study the structural and magnetic changes produced by annealing Fe84Zr7B8Cu1 amorphous ribbons at the temperature range 723–923 K for 20 min. Heat treatment causes a devitrification of the amorphous phase giving rise to nucleation and growth of b.c.c. α-Fe phase. Structural and compositional changes result in the amelioration of soft magnetic properties. The giant magneto-impedance (GMI) ratio ΔZ/Z (ΔZ/Z=(Z(H)−Z(Hmax))/Z(Hmax)) is enhanced with the devitrification and reaches the maximal value of about 260% at frequency f=6.5 MHz for the ribbon annealed at 873 K for 20 min. The dependence of strong GMI response on frequency and applied field is related to the superior soft magnetic properties of the annealed samples. The sensitive drop of transverse permeability is the source of MI effect through skin effect.