Observations of Short-Range Order by Optical Birefringence in Quadratic-Layer Antiferromagnets K2NiF4, Rb2NiF4, Ba2NiF6 and K2CoF4

Abstract

By measuring optical birefringences the behaviour of short-range order has been studied on quadratic-layer quasi-Heisenberg antiferromagnets: K2NiF4, Rb2NiF4, Ba2NiF6 and K2COF4. An explicit form of the spin-dependent birefringence for these systems is given, which is proportional to the nearest-neighbouring correlation functions. It is shown that with increasing Ising-like character the high temperature persistence of is reduced. In the case of K2CoF4, where the Ising-like anisotropy is comparable to the isotropic exchange field, a symmetric and logarithmic anomaly in the behaviour of has been observed for |T-TN|/TN<7.5.10-2 around the Néel point. © 1978, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.