We report on a detailed study of structural, magnetic, and electronic properties of MnxGe1−x single crystals (0<x<0.1) prepared by the Bridgman’s crystal growth technique. The chemical distribution of Mn in a Ge matrix investigated by means of energy dispersive x-ray spectroscopy indicates a strong phase separation in the Ge/Mn system. Temperature-dependent magnetization [M(T)] measurements performed on the Mn-poor part containing 1%–3% of Mn reveal magnetic properties similar to those of a Mn11Ge8 reference sample as well as to those of the highly inhomogeneous Mn-rich parts of the sample. X-ray absorption spectroscopy (XAS) at the Mn L2,3 absorption edge shows that Mn ions in Mn-rich and Mn-poor parts are in the divalent high-spin state. Resonant valence-band photoelectron spectroscopy (ResPES) was performed at the Mn 2p3∕2 absorption edge for the Mn-poor part. The obtained Mn 3d PDOS shows a feature centered at 4.8 eV which is characteristic for the Mn5Ge3 phase. We identify the formation of ferromagnetic intermetallic compounds as the most possible origin of ferromagnetism in both Mn-rich and Mn-poor regions of the MnxGe1−x samples.

We present a detailed study on the structural, magnetic, and optical properties, as well as the electronic structure of epitaxial Co-doped ZnO films prepared by magnetron sputtering. Different preparation conditions were implemented in order to control the concentration of oxygen vacancies in the ZnO host lattice. Magnetization measurements indicate ferromagnetic behavior at low temperature for samples prepared at oxygen-poor conditions whereas the samples prepared at oxygen-rich conditions show extremely small ferromagnetic signal corroborating that ferromagnetism in Zn 1−x Co x O correlates with the presence of the oxygen-related defects. X-ray absorption spectroscopy ͑XAS͒ at the Co L 2, 3 edge together with optical transmittance measurements show that Co ions are present in the high-spin Co 2+ ͑d 7 ͒ state under tetrahedral symmetry indicating a proper incorporation in the ZnO host lattice. Comparison of the O K edge XAS spectra of the samples prepared at different conditions show substantial changes in the spectral line shape which are attributed to the presence of lattice defects such as oxygen vacancies in the ferromagnetic oxygen-poor Co-doped ZnO samples. Our findings indicate that the ferromagnetic properties of Co-doped ZnO samples are strongly correlated with the presence of oxygen vacancies in the ZnO lattice supporting the spin-split impurity band model.

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High quality epitaxial films of Zn 1 x Co x O solid solutions were obtained by low temperature MOCVD process using water vapor up to x 0.33. Depositions were carried out at 300°C on r sapphire substrates. Films structure and composition were investigated by XRD, XPS and EDX measurements. Magnetic properties were examined using SQUID and Kerr effect measurements. All samples showed ferromagnetic behavior at room temperature. NEXAFS and PES were employed to investigate electronic structure of the films.