Static magnetic order in the one-dimensional conductorRbC60

Muon-spin-relaxation measurements have been performed in the orthorhombic phase of the quasi-one-dimensional conductor ${\mathrm{RbC}}_{60}$. Evidence for static magnetic order was found at T≤70 K, followed by a change of the magnetic moment/structure below T∼20 K, inferred from a substantial increase of the static random local fields. These results are consistent with the formation of the spin-density-wave state, although the possibility of a random spin freezing cannot be ruled out.