Temperature Dependence of the ESR Line Width in One-Dimensional S=1/2 Antiferromagnet CuCl₂·2NC₅H₅

Abstract

The ESR line width of a typical 1dH S=1/2 AF CuCl₂·2NC₅H₅ has been measured between 1.3 and 300 K. As temperature is lowered the width anomalously decreases down to 5 K with an approximated relation ΔH∝χT and it turns to increase with a relation ΔH∝T^−1.2. It is suggested that the unusual behaviors can be understood by considering the dominant role of the q=0 fluctuations at higher temperatures and also of the q=K₀ fluctuations at lower temperatures in the spin dynamics for S=1/2 AF chains. The critical broadening for 3d ordering will appear at temperatures much nearer T_N.