Transition of Local Moments Coupled to Itinerant Electrons in the Quasi One-Dimensional Conductor Copper Phthalocyanine Iodide

Copper phthalocyanine iodide is a molecular metal whose conducting stacks incorporate a one-dimensional array of local moments strongly coupled to conduction electrons. Below 20 K the EPR $g$ value of the coupled system increases anomalously and at 8 K the EPR signal broadens abruptly and becomes unobservable. Anomalies in the proton NMR spin-lattice relaxation are observed at the transition temperature. Magnetic susceptibility measurements and NMR linewidth data both indicate that there is little if any static magnetic order below 8 K.