Sign of the hyperfine parameters of anomalous muonium in diamond

Observations with the muon-spin-rotation (μSR) technique of the thermally activated transition from the isotropic muonium state Mu to the anisotropic muonium state Mu* in diamond are used to determine the sign of the Mu* hyperfine constants. It is found that the isotropic part of the Mu* hyperfine interaction is negative, indicating the importance of exchange polarization. The transition rate from Mu to Mu* follows an Arrhenius law over more than four decades. Finally, data are presented on the temperature dependence of the hyperfine interaction of isotropic Mu in diamond.