Optical Birefringence in CsCuCl 3 : A Quasi One-Dimensional S =1/2 Ferromagnetic Heisenberg System

Short range order effects on the optical birefringence were investigated in an antiferromagnetically coupled linear-chain S =1/2 Heisenberg ferromagnet CsCuCl 3 in a temperature range between 6 K and 450 K. A nearly isomorphic diamagnet CsMgCl 3 was used to extract the magnetic part of birefringence in CsCuCl 3 . The magnetic birefringence was found to have a broad maximum at about 32 K. The effect of the interchain interaction on the birefringence was calculated in terms of a perturbation approach. By comparing the results with the observed temperature dependence of the birefringence, the ratio of inter- to intrachain exchange integrals was obtained as -0.07.