Optical Birefringence Measurements in Ferromagnetic and Antiferromagnetic Alternating Heisenberg Chains (CH₃)₂CHNH₃CuCl₃

Abstract

The dependence of optical linear birefringence Δ n on temperature T was measured on a single crystal of (CH₃)₂CHNH₃CuCl₃, which consists of ferromagnetic-antiferromagnetic (F-AF) alternating Heisenberg chains with S=1/2. The curve of dΔ n(T)/d T showed a large peak near 25 K and a small shoulder near 45 K. The presence of these two anomalies is qualitatively similar to the theoretical curve of the magnetic specific heat in ferromagnetic-dominant F-AF chains.