THE FIELD-ANNEALING EFFECT ON MAGNETOIMPEDANCE OF A ZERO MAGNETOSTRICTIVE METALLIC-GLASS

A commercially made metallic glass, VAC6030, was used for the magnetoi mpedance (MI) measurement. Some samples were annealed at a temperature (T-a=340 degrees C) slightly below its Curie point, and cooled in a t ransverse or longitudinal field. The frequency of the probe current wa s from 10 kHz to 10 MHz. MI is defined as Delta R/R=[R(0)/R(H-s)]-1 an d Delta X/X=[X(0)/X(H-s)]-1, where H-s is the saturating field along s ample length, R is the resistance, and X is the reactance. At relative ly low frequencies MI is mostly inductive, at relatively high frequenc ies it is resistive, and a crossover could be defined at a characteris tic frequency f(0). When the sample is in the as-cast state, f(0)=890 kHz. If samples have been field annealed, f(0) could be shifted either downward or upward; f(0) becomes 30 kHz after a transverse anneal, an d 8 MHz after a longitudinal anneal. The field annealing would also ch ange the magnitudes of MI. In theory, if f<f(0), Delta R proportional to f(2) and Delta X proportional to f; however, if f>f(0), both Delta R and Delta X are dominated by the skin-depth effect, and therefore pr oportional to f(1/2) instead. (C) 1996 American Institute of Physics.