SHORT RANGE ORDER IN Au4V

Abstract

We have made a study of the short range order (SRO) kinetics of the order‐disorder transformation (ODT) in Au4V. In particular, we have measured the time dependent susceptibility produced by a rapid change in temperature. We find a rapid initial increase in X in which approximately 46% of the final susceptibility is achieved 10 min after a temperature jump to a region between 700° and 800°K. XRDF studies indicate no existence of the ordered BCT phase. Thus, this state is believed to be SRO in which a known fraction of V atoms are surrounded by only Au nearest neighbors. Analysis of the kinetic data indicates that the formation of SRO obeys a simple first order rate equation with a single relaxation time τ. The temperature dependence of τ can be described by the equation τ = τo e Em/kT, where Em, the activation energy of vacancy migration, is found to be 0.47 eV. We also find that the average magneto‐crystalline anisotropy constant increases appreciably with the degree of SRO.