Observations of Short-Range Order by Optical Birefringence in One-Dimensional Antiferromagnets CsNiCl₃, RbNiCl₃ and CsCoCl₃

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Magnetic short-range order was observed in one-dimensional S=1 Heisenberg (CsNiCl₃, RbNiCl₃) and (Remark: Graphics omitted.) Ising antiferromagnet (CsCoCl₃) up to kT∼10|J| and 3|J|, respectively, by measuring optical birefringences. An isomorphic diamagnet CsMgCl₃ was used, with corresponding states argument, to extract the magnetic contribution Δn_m from the resultant birefringence Δn in these magnetic systems. The temperature T_max, at which the temperature derivative of the magnetic part Δn_m displays a broad maximum, is in agreement with that predicted by the rigorous theory for the specific heat in each linear chain system.