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

Very large changes are observed in the impedance of a (Co94Fe6)72.5Si1 2.5B15 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 repo rted at axial field values less than 1 Oe in soft nearly zero magnetos trictive Co-based amorphous wires with induced circumferential anisotr opies. In this work the effect of different small saturation magnetost riction constants and induced circumferential anisotropies on the magn eto-impedance for various annealed wires is studied. During current an nealing 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 curr ent amplitude. The impedance as a function of current, frequency and d c axial magnetic field is measured for these wires. All of the wires e xhibit a sharp threshold of the impedance when subjected to axial fiel ds 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 ar e measured in this series. The role of the saturation magnetostriction constant and the induced circumferential anisotropy in the observed m agneto-impedance is discussed.