Electron Paramagnetic Resonance of Organic Conductors (BEDT-TTF)₂X

Abstract

The electron paramagnetic resonance (EPR) of five different structural classes [β, β′, β″, α′ and κ] of the organic conductors, (BEDT-TTF)₂ X, X = linear anion, is examined. The experimental data show a strong dependence of the peak-to-peak linewidths, spin susceptibilities and microwave conductivities on the crystal structures, and thus, the electronic band structures. The electron spin relaxation times do not obey the Elliott relation in all cases. The g-value shift is very small, and is temperature-independent, except when T<T_SDW for β′-(BEDT-TTF)₂AuCl₂. The spin susceptibility is weakly temperature-dependent for the superconducting β and κ phases, and slightly more for the conducting β″ phase; it increases with increasing temperature. The two insulating phases β′ and α′ show Bonner-Fisher type one-dimensional antiferromagnetic behavior, with transitions to a spin-density wave and a spin-Peierls ground state, respectively. These observations are finally correlated with conductivity and reflectivity measurements, and are discussed in terms of the calculated band structures.