THE FAR-INFRARED MAGNETIC EXCITATION SPECTRUM OF COCL2(NC5H5)2

The quasi-one-dimensional Ising-like system CoCl//2 dipyridine has been studied using a Fourier spectrometer over the range 10-60 cm** minus **1. Spin-cluster excitations from the ground state and spin-cluster resonance between bound states have been observed at fields up to 8 T and temperatures in the range 1. 5 less than T less than 30 K. The excitation energies show the influence of (small) transverse elements in the intra-chain exchange interaction and a transverse magnetic field component. The field and temperature dependence of the intensity have been interpreted on the basis of a pure Ising model, implemented - to finite order - with the effect of transverse elements. The zero-field limit is discussed in detail. The linewidth is only slightly dependent on temperature, in contrast with earlier observations for CoCl//2 multiplied by (times) 2H//2O.