TEMPERATURE-DEPENDENCE OF THE ELECTRONIC SPIN RELAXATION OF DCNQI SALTS

For the elucidation of the charge and spin dynamics of the radical anion salts of DCNQI with metallic counterions we have performed cw- and pulsed ESR experiments (Delta B-pp, T-1e(-1) and T-2e(-1)) between 300 and 4 K at nine salts differing in counterions and sidegroups, respectively. We can explain the relaxation rates by dipolar electron-electron interaction and spin-orbit contribution. In the high temperature range we have a gradual decrease in the number of charge carriers by interband transitions without a slowing down of the mobility. With complete localization of the electron spins (no mobile electrons anymore) exchange interaction governs the spectral density, becoming strongly temperature dependent due to effective spin exchange J(eff)(T), explained by an extended REHAC-model, This effective spin exchange J(eff)(T) includes for the first time a contribution by the metallic counterions. For spin-orbit interaction we developed a model based on F. Adrian [1] not depending on the mixture of Bloch and spin states as given by Elliott [2]. This is achieved by the inclusion of the electronic probability on atoms with higher atomic numbers, modulated by phonons. This model explains the drastic changes in the ESR linewidth of different radical ion salts of DCNQI and allows inductively the prediction of the electronic properties of new radical ion systems of which just the molecular and crystal structure is known.