High-field electron paramagnetic resonance study of the polymerization in Na2Rb1-xCsxC60

We report on the study of the magnetic properties of the low-temperature polymer phases in Na2Rb1-xCsxC60 at 110 GHz microwave frequency with x varying between 0 and 1. The magnetic and structural properties of the polymer phase strongly depend on the Cs content and its electronic structure progressively becomes quasi-one-dimensional as x is increased. While the electronic properties of the polymeric Na2RbC60 appear to be close to three-dimensional metal, Na2Rb0.3Cs0.7C60 shows characteristics of quasi-one-dimensional metal where instability in the electronic structure was found as detected by the sudden disappearance of the ESR intensity due to the opening of the gap at the Fermi surface. The observation of an additional resonance line below 15 K, which could be attributed to antiferromagnetic resonance, suggests that the low-temperature polymeric phase in Na2Rb0.3Cs0.7C60 has a well-defined magnetic ground state.