Structural and Magnetic Phase Diagrams of Co and Mn Doped Ge (100) Epitaxial Films

We present studies of structural and magnetic properties of epitaxial films of Co$_{x}$Mn$_{y}$Ge$_{1-x-y}$ magnetic semiconductors, grown by combinatorial MBE on Ge (100) substrates. Structural effects were examined \textit{in-situ} by reflection high energy electron diffraction and \textit{ex-situ} by microbeam x-ray diffraction. A ternary epitaxial phase diagram has been determined for doping concentrations (x and y for Co and Mn respectively) up to 30 at {\%}, where regions of coherent epitaxy and associated strain states, and regions of rough disordered growth and the nature of the disorders have been examined and identified. Specifically, within a narrow range of compositions around the atomic ratio between Co and Mn (x/y) of 3, the observed epitaxial strain is low ($<$0.1{\%}) and coherent epitaxial growth is most stable, where the thin film lattice constants obey Vegard's law and they match those of the Ge at x/y =3. Within this region of compositions, high quality epitaxial films of p-type magnetic semiconductors can be stabilized for total doping concentration of transition metal dopants as high as 13 at {\%} and with T$_{C}$ as high as 300 K. A ternary magnetic phase diagram has been measured using magnetooptic Kerr effect. The interplays between structural effects and magnetism have been investigated.