μSR and SQUID investigation of ammoniated lithium fullerides

The ammoniation of lithium-doped C60 gives rise to (NH3)6LixC60, a system which is chemically expanded while maintaining C60 original cubic symmetry and hence the threefold degeneracy of the C60x- frontier orbitals. Nevertheless, the on-site repulsion U dominates the bandwidth W and, by overcoming the effect of orbital degeneracy, brings to electron localisation. Muon-spin relaxation (μSR) and SQUID magnetometry were used to confirm the presence of a magnetically ordered phase at low temperatures, already reported by Durand and co-workers [Nat. Mater. 2 (2003) 605]. Surprisingly, neither the expected antiferromagnetism nor the even-odd effect on electron band filling were observed down to 2 K.