EPR Line-Widths of a One-Dimensional Heisenberg Antiferromagnet CsMnCl₃2H₂O

Abstract

Temperature and angular variation of EPR line-widths of a one-dimensional Heisenberg antiferromagnet CsMnCl 3 2H 2 O have been measured at K-band frequency above its ordering temperature. A minimum in the angular variation appears at room temperature indicating the dominance of long-time, q ∼0 diffusive modes of torque correlation function. However, the line-shape is Lorentzian because of non-negligible magnitude of interchain interactions. As the temperature is lowered, they broaden and the minimum in their angular variation disappears. These phenomena can be understood when one considers the growth of intrachain spin correlation of wave vector Q 0 and the relative importance of short-time, Gaussian decay modes compared with the q ∼0 modes. Line-widths are calculated within Kubo-Tomita's framework and Fisher's classical treatment. Good, quantitative agreement is attained particularly at low temperatures.