The influence of Co substitution on the magnetic properties and the giant magneto-impedance effect of (Fe 1-x Co x ) 84 Zr 3.5 Nb 3.5 B 8 Cu 1

The microstructure, magnetic properties and the giant magneto-impedance (GMI) effect of the nanocrystalline (Fe1-xCox)(84)Zr3.5Nb3.5B8Cu1 ribbons have been studied. With increasing Co concentration, the nanocrystallized grain size and volume fraction of the alpha-Fe(Co) phase decrease under the same annealing condition, while the coercivity H-c increases from 1.92 A/m at x=0.0 to 30.38A/m at x=0.8. The effective permeability drops sharply with increasing Co concentration so that the GMI effect goes down. A value of more than 380 % for the magneto-impedance(MI) ratio was measured at frequency f=2.5 MHz and the sensitivity can reach 0.9% (A/m)(-1) for Fe84Zr3.5Nb3.5B8Cu1 ribbon. When a: is equal to 0.8, the MI ratio drops to about 30 % and the sensitivity only reaches a value of lower than 0.025% (A/m)(-1). The concise analysis in theory is also expounded.