Intrinsic ferromagnetism versus phase segregation in Mn-doped Ge

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 L-2,L-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 2p(3/2) 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. (c) 2007 American Institute of Physics.