Composition and magnetic properties of thin films grown by interdiffusion of Mn and Sn-Rich, Ge lattice matched SixGe1-x-ySny layers

We report on the structure and magnetic properties of Mn based ferromagnetic layers on the semiconductor Si_xGe_1-x-ySn_y with Sn content up to y = 0.15 in comparison with layers on Ge and Si_0.75Ge_0.25. The ferromagnetic layers grow by interdiffusion between an evaporated Mn layer and molecular-beam-epitaxy grown semiconductor layers. This approach enables the preparation of Mn based layers, e.g., as a ferromagnetic contact material for Si_xGe_1-x-ySn_y using a self-aligned interdiffusion process, opening up the opportunity for large-scale manufacturing. The samples show a clear phase separation into Si-rich and Ge-rich Mn compounds. All samples are ferromagnetic and exhibit a decrease in saturation magnetization and an increase in coercive field with increasing Si content x. The Curie temperature shows no decisive trend with increasing Si content with values around room temperature. Based on the composition, structure and magnetic properties, we propose a two-layer model to correlate the structure and composition with the observed magnetic properties. We show that the changes in magnetic behavior can be explained solely by considering the Si content of the Si_xGe_1-x-ySn_y substrates with the Sn being largely passive.