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

Abstract

The ESR line width of a typical 1d H S=1/2 AF CuCl 2 ·2NC 5 H 5 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 Δ H ∝χ T and it turns to increase with a relation Δ H ∝ 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 = K 0 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 .