Structure, magnetic and transport properties of MnxGe1−x films

Ge1−xMnx (x=0.05, 0.07, 0.11, 0.15, 0.19, 0.23, 0.26, 0.29) thin films were prepared by magnetron sputtering. All the films had a Ge cubic structure, and no indication of a secondary phase was found in any sample using X-ray diffraction (XRD). The crystal lattice constant increases with the Mn concentration, in accordance with Vegard's law. No films show any clear magnetic domain structure under a magnetic force microscope (MFM). Atom force microscope (AFM) measurements show that all films have a uniform particle size distribution, and a columnar growth pattern. X-ray photoelectron spectroscopy (XPS) measurements indicate that the Mn atoms are not solely in a bivalent state. Electrical transport properties show that the resistance of the films increases with increasing Mn concentration, suggesting that the Mn ions are in deep-level acceptor states, while resistance decreases with increasing temperature, which is a typical semiconductor property. The ferromagnetism is intrinsic and long-ranged, mediated mainly by hole carriers through s, p–d exchange coupling.