Zero-field μSR in crystalline C60

The C60Mu radical in polycrystalline C60 has been studied in zero magnetic field between 9 K and 200 K, and at room temperature. At low temperatures, we observe three low-frequency oscillations which correspond to the intra-triplet transitions of a completely anisotropic muon-electron hyperfine interaction. These signals exhibit a strongly temperature-dependent T1, attributed to thermally-activated jump rotational diffusion of the Cs0Mu' radical. A fit to an Arhenius law yields an activation energy of 200(20) meV for temperatures below the fcc-sc structural phase transition. At room temperature only the motionally-narrowed 325 MIiz singlet-triplet transition is observed