Electron spin resonance and structure of magnetically inequivalent chains in CuCl2·2NC5 H5

Abstract

Interchain exchange coupling $J^{\prime }$ between magnetically inequivalent chains has been studied in the quasi-one-dimensional (1d) salt dichlorobis (pyridine)copper(II) (Cu${\mathrm{Cl}}_2$·2N${\mathrm{C}}_5$ ${\mathrm{H}}_5$, referred to as CPC). Except along symmetry directions, the two types of chains have different $g$ factors, and therefore two separate ESR lines would be seen in the absence of $J^{\prime }$. The coupling $J^{\prime }$ merges the lines, but the width of the single observed line is proportional to the square of the microwave frequency. From the known splitting in the absence of $J^{\prime }$, determined from previous studies of the crystal $g$ tensor, and measurements at 10.9 and at 35 GHz, we deduce $\left|\frac{J^{\prime }}{J}\right|=1.2\mathrm{}\times {10}^{-2\mathrm{}}$, where $J$ is the strong intrachain interaction. Previous theories of ESR in quasi-1d systems were used to relate the linewidth to $J^{\prime }$. In the course of the work a refined determination of the structure has been made and the various possible interchain exchange paths have been elucidated. In regard to the latter, it is noted that since there are in general three different interchain exchange constants which combine differently in their effects on the linewidth and on the ordering temperature $T_N$, direct comparison cannot be made between the effective $J^{\prime }$ reported here and that inferred from $T_N$.