A magnetization and susceptibility study of the order-disorder transformation in VAu 4; short range order

Abstract

We have studied the kinetics of the order-disorder transformation (ODT) in VAu 4 by measuring the time dependent susceptibility produced by a rapid change in temperature and find a rapid initial increase in χ in which 46 per cent of the final susceptibility is achieved 10 min after the temperature jump. The state thus obtained is interpreted as short range order (SRO) in which a known fraction (46 per cent) of V atoms have only Au nearest neighbors. We find that the average magnetic anisotropy constant K increases with increasing order. For ordered VAu 4, we find K ⋍ 3·0 × 10 7 ergs/cm 3 . The replacement of Au by Ag in VAu 4 allows the existence of SRO but is found to suppress the ODT. Our results confirm the hypothesis that the vanadium moment is localized. We find the temperature independent component of the susceptibility χ B to be approximately 0·7 × 10 −6 cm 3/gm in ordered, disordered, and partially ordered VAu 4. This value of χ B corresponds to a density of states of 22 states/eV-VAu 4, in good agreement with specific heat measurements (SHM) for the ordered phase but not in agreement with SHM for the disordered phase. We find an additional temperature independent component of susceptibility equal to 0·44 × 10 −6 cm 3/gm, which may be due to the orbital paramagnetism of the disordered phase.