Magnetism inRbC60studied by muon-spin rotation

We report an investigation of the magnetic properties of orthorhombic ${\mathrm{RbC}}_{60}$ using muon-spin rotation (μSR). Measurements in zero applied field and high transverse field reveal a transition to a magnetic state below T=60 K. The μSR spectra at low temperatures indicate that the internal magnetic fields are quasistatic on the time scale of a few μs and have a Lorentzian-like distribution. These observations suggest that the magnetic structure is more disordered than a simple spin-density-wave state or an antiferromagnet.