Stabilization of half metallicity in Mn-doped silicon upon Ge alloying

We propose SixGe1-x alloys as suitable candidates for spintronic applications. Remarkably, our first-principles investigation explains, within the local spin density approximation, the microscopic mechanism that stabilizes the half metallicity in Si matrices under Ge alloying and shows that it can spontaneously occur: in fact, half metallicity is determined by p-d hybridization in the presence of Ge atoms surrounding Mn impurities, and this particular environment is energetically favored over other possible local composition fluctuations, such as excess of Si atoms around Mn. A detailed discussion of the trends of defect formation energy and of magnetization as a function of alloy composition and configuration completes the present work.