Electronic structures of organic conductors, (BEDT-TTF)(2)CsM(SCN)(4) (M=Co, Zn)

H-1-NMR and EPR investigations of new organic conductors, (BEDT-TTF)(2)CsM (SCN)(4)(M=Co, Zn), have been performed. In the Co containing salt, the H-1-NMR spin-lattice relaxation rate, T-1(-1), is governed by the fluctuation of the localized magnetic moments on the Co2+ ions. The evaluated exchange interaction, J/k(B), is 0.09 K A large increase in the H-1-NMR linewidth has been observed below 20 K for the Co salt, which can be explained as the effect of the static magnetization of the paramagnetic Co2+ ions. For the Zn containing salt, which has a closed d-shell, the H-1-NMR T-1(-1) and EPR properties exhibit anomalous behavior below 20 K, indicating a change in the electronic structure of the pi-system around 20 K. The low-temperature electronic structure of the title compounds is discussed in the microscopic view.