Hyperfine structure in the ESR spectra of exchange-coupled pairs-copper diethyidithiocarbamate

Abstract

A study of the hyperfine interaction in the ESR of coupled Cu-Cu pairs in single crystals of copper diethyldithiocarbamate as a function of temperature has shown distinct differences in the hyperfine structure in the two fine-structure transitions at 20 K; the spectrum does not have the usual binomial hyperfine pattern for the fine-structure transition of the low field in contrast to that of the high field. The details of the structure of both fine-structure transitions in the 20-K spectrum can be explained by recognizing the fact that the mixing of the nuclear spin states caused by the anisotropic hyperfine interaction affects the electron spin states |+1> and |-1> differently. The anomalous hyperfine structure is found to become symmetric at 77 and 300 K. It is proposed that the reason for this lies in the dynamics of spin-lattice interaction, which limits the lifetime of the spin states in each of the electronic levels |-1>, |0>, and |+1>. The estimate of spin-lattice relaxation time in the temperature range where the changes are observed agrees with those indicated by other studies. The model proposed here for the hyperfine interaction of pairs in the electronic triplet state is of general validity.