EPR studies on κ-(BEDT-TTF)2Cu[N(CN)2]X

An EPR study of the low temperature phases of κ-(BEDT-TTF)2Cu[N(CN)2]X (X =Br (h8-Br), Cl (h8-Cl)), and a deuterated analog, κ-(d8-BEDT-TTF)2Cu[N(CN)2]Br (d8-Br), is presented. The electronic states above 70 K were found to be quite similar in the three salts. Clear differences were observed in the spin susceptibilities, Xspin, and the absorption linewidths, ΔHpp between the hs-Br and hs-Cl salts. The EPR properties of the d8-Br salt resemble those of the h8-Br salt above 40 K, and below 40 K those of the h8-Cl salt; a clear crossover was found at this temperature. The electronic states of these salts are discussed from a microscopic point of view.