ESR study of exchange coupled pairs in copper diethyldithiocarbamate

ESR investigations on exchange coupled pairs of Cu ions in single crystals of Cu(dtc)₂, isomorphously diluted with the corresponding diamagnetic zinc salt, are reported. The spin Hamiltonian parameters for the coupled species (S=1) are:g _{{norm of matrix}}=2.1025, g ₊=2.031, A=75.1×10^-4 cm^-1, B=14.8×10^-4, D=276.0×10^-4 cm^-1 and E=46.7×10^-4 cm^-1. While the g and A tensors show tetragonal symmetry, the zeor-field splitting tensor is rhombic and has principal axes different from those of the g and A tensors. Intensity measurements made down to 4.2 K indicate that the exchange is ferromagnetic with |FFF| ∼ 10 cm^-1. Direct dipole-dipole interaction appears to be the major contribution to the zero-field splitting. A calculation on the distributed point dipole model shows that dipolar interaction is considerably modified by the high covalency of the Cu-S bond and accounts for the rhombic nature of the tensor. The possible exchange mechanisms in Cu(dtc)₂-direct exchange and superexchange through the bridging sulphurs-are discussed.