Electronic structure of the muonium center as a shallow donor in ZnO

The electronic structure and the location of muonium centers (Mu) in single-crystalline ZnO were determined for the first time. Two species of Mu centers with extremely small hyperfine parameters have been observed below 40 K. Both Mu centers have an axial-symmetric hyperfine structure along with a [0001] axis, indicating that they are located at the AB_{O,//} and BC_{//} sites. It is inferred from their small ionization energy (~6 meV and 50 meV) and hyperfine parameters (~10^{-4} times the vacuum value) that these centers behave as shallow donors, strongly suggesting that hydrogen is one of the primary origins of n type conductivity in as-grown ZnO.Comment: 4 pages, 4 figures, submitted to PR

Evidence for a ferromagnetic transition in Yb1-xLaxB6 (0≤x≤0.006)

Magnetization and muon spin relaxation (μSR)in Yb1-xLaxB6 have been measured to study whether ferromagnetic moments appear as in La-doped CaB6. Magnetization processes of polycrystalline samples for 0≤x≤0.006 have revealed ferromagnetic hysteresis with a saturation moment of 1 × 10-4μB/f.u. On cooling below 150 K, an increase of the internal field up to 0.6 mT has been observed by zero-field/μSR measurements on both polycrystals and single crystals. These results indicate a ferromagnetic transition at 150 K in this system