INFLUENCE OF MAGNETOSTRICTION ON MAGNETO-IMPEDANCE IN AMORPHOUS SOFT FERROMAGNETIC WIRES

Very large changes are observed in the impedance of a (Co94Fe6)72.5Si12.5B15 soft ferromagnetic wire in the presence of axial fields of the order of 1 Oe. Changes of the impedance of 200% or more have been reported at axial field values less than 1 Oe in soft nearly zero magnetostrictive Co-based amorphous wires with induced circumferential anisotropies. In this work the effect of different small saturation magnetostriction constants and induced circumferential anisotropies on the magneto-impedance for various annealed wires is studied. During current annealing a circumferential anisotropy is induced. Also, the saturation magnetostriction constant changes continuously from a small negative (-7x10(-8)) to a small positive value (+6x10(-8)) depending on the current amplitude. The impedance as a function of current, frequency and dc axial magnetic field is measured for these wires. All of the wires exhibit a sharp threshold of the impedance when subjected to axial fields less than 1 Oe. Changes in the impedance, DELTAV/V=(V(H)-V(0))/V(0), of the order of 200% with maximum slopes reaching up to 1700 %/Oe are measured in this series. The role of the saturation magnetostriction constant and the induced circumferential anisotropy in the observed magneto-impedance is discussed.