The spin susceptibility of Rb3C60 probed by Electron Paramagnetic Resonance

Electron Paramagnetic Resonance (EPR) spectra on a powder sample of Rb3C60 were measured between 4.2 and 290 K and they were carefully analysed by using a least-squares fitting procedure. The spin susceptibility derived from the EPR data showed a Pauli paramagnetism in the normal state and a paramagnetism in the superconducting state. The Pauli paramagnetism, together with the behaviour of the linewidth which broadens with increasing temperature, strongly suggests that the observed EPR signal is most likely due to the conduction electron spin resonance. This assignment contradicts with what was reported previously by Janossy et al., where a very broad signal (two orders of magnitude broader than ours) was assigned to the conduction electron spin resonance. From the EPR data, the density of states was estimated to be 20 states eV-1 per C60 molecule which is consistent with the value derived from the 13C NMR data