Magnetic and thermal studies of antiferromagnetic linear chains in dichlorobis(pyridine)copper (II)

Abstract

Results of static-susceptibility measurements from 1.5 to 300 K, heat-capacity studies from 0.5 to 10 K, and room-temperature 8.8-GHz EPR measurements are presented for dichlorobis (pyridine)copper(II), a spin-1/2 antiferromagnetic linear-chain crystal. The Bonner-Fisher chains curve gives good agreement with the measured susceptibility values from 2 K to room temperature, for $\frac{J}{k_B}=-13.4\mathrm{}\pm 0.2$ K and $g=2.07\mathrm{}\pm 0.04$. The heat capacity exhibits a sharp anomalous peak 1.130±0.005 K, corresponding to an antiferromagnetic-paramagnetic transition at that temperature. From 4-8 K, the heat capacity is resolved into at $T^3$ lattice contribution with ${\Theta }_D=82.2\mathrm{}\pm 2$ K and a Bonner-Fisher chains curve with $\frac{J}{k_B}=-13.2\mathrm{}\pm 0.3$ K. Principal-axis $g$ values and the orientation of the principal axes with respect to the crystalline axes were determined. The two inequivalent copper ions exhibit only a single resonance line at 8.8 GHz, because of interchain exchange narrowing. The EPR line is found to be Lorentzian out to seven absorption halfwidths. Theoretical line shapes are compared with the experimental data for various estimates of interchain exchange. The Tahir-Kheli decoupling-theory estimate of nearest-interchain-neighbor exchange integral of 0.051 K gives best agreement with the observed line-shape data.