ESR study of the ordering transformation in kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br

Ordering transformation and its effect on the electronic structure of the k appa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br organic superconductor was studied by meas uring annealing induced changes in low temperature ESR spectra and spin sus ceptibility temperature dependence. The transformation is shown to proceed through coexistence of two phases. Besides resistivity decrease, ordering w as shown to increase ESR spin susceptibility (below about 160 K) with a ten dency for restoration of the temperature independent Pauli term. Gaplike sp in susceptibility behavior below 60 K is shown to develop only at some stag e of ordering. These effects point to a relationship between temperature de pendent spin susceptibility in the salt and incomplete ordering.