Temperature evolution of BEDT-TTF+1/2 and Dy3+ spin systems in novel organic conductor (BEDT-TTF)2Dy(NO3)4: EPR and SQUID studies

Magnetic properties of novel organic conductor (BEDT-TTF)2Dy(NO3)4 were studied by EPR and SQUID magnetometry methods. Two spin subsystems coexist in this compound: hopping local S = 1/2 (BEDT-TTF+) moments on conducting radical-cation layers with spin contribution to magnetic susceptibility, Iepr(300 K) = 6.3 × 10−4 emu/mol, and strongly localized 4f9-electrons J = 15/2 (Dy3+), χp(300 K) = 4 × 10−2 emu/mol, in the core of individual anions. The phase transition was detected in both EPR at T = 197 K, and transport properties at T = 220 K, but not in static magnetic susceptibility χp(T) measured by SQUID. The transition is attributed to the electronic metal-insulator phase transition induced by a fine rearrangement of Dy(NO3)4− anions. Interlayer (π-f) or intralayer (f-f) exchange interactions have not been found within 2-350 K. However, the local moments of Dy3+ contribute to the magnetic anisotropy of the compound and dipole-dipole spin relaxation on BEDT-TTF layers.