ESR STUDY OF DYNAMICS OF THE PHASE-TRANSITION IN WURSTER BLUE PERCHLORATE

Wurster's blue perchlorate (WBP) crystal was prepared by an electrochemical oxidation, and its ESR spectra were measured over the range of 100-350 K. Each spectrum shows a single line with an exchange-narrowed Lorentz shape. The ESR spectra have a maximum in the intensity at 193 K, and a minimum in the linewidth near the temperature, which corresponds to the well-known paramagnetic-antiferromagnetic phase transition. The linewidths show remarkable anisotropy, in particular, in the low-temperature region. The angular dependence of linewidth can be accounted for by a one-dimensional spin array along the a-axis of WBP crystal. The linewidth exhibits the most drastic decrease, when the field is applied along to the a-axis. This is because, at the transition point, the cation radicals would more fluctuate along the a-axis than along other axes, since the rearrangement of the Wurster's blue radical cation occurs at the temperature along the a-axis.