Theoretical search and investigation of magnetic manganese silicide phases on Si (001) surface

Necessity to reduce the mass and dimensions of electronic devices, and at the same time, increasing their perform- ance and energy efficiency, is most pronounced in the field of space device engineering. One possible approach is to develop electronics based on new physical principles, such as manipulating electron spins. The search for materials for such devices requires new strategies within the framework of modern material science, including utilization of methods for theoretical prediction of compounds prospective for their further experimental synthesis and study. One of promising spintronics material families, the Mn-Si system, is a serious challenge for theoretical studies be- cause of its entangled phase diagram with a large number of metastable phases, many of which are found only in cer- tain nanoscale systems such as thin films. The article presents a search and investigation of new manganese silicide phases that can form epitaxial thin films on (001) surface of silicon. This theoretical study was carried out using the evolutionary algorithm for stable structure prediction and is based on the calculations within the framework of the den- sity functional theory. Among the found phases, the tetragonal P4/mmm phase of manganese disilicide has the largest magnetic moment of 0.71 μB per manganese atom. For this phase various configurations of interfaces with crystalline silicon were modeled and their electronic and magnetic properties were determined. High value of spin polarization at the Fermi level (-66 %) indicates the silicide’s great potential for spintronics applications. Additionally, the effect of the finite film thickness on the magnetic moments on manganese atoms, up to the suppression of the spin polarization, is revealed. It is shown that the presence of an in- terface with a silicon substrate significantly affects only the nearest disilicide layer, while the dangling bonds on the disilicide film surface have influence on the electronic structure of 2-3 layers deep into the silicide. This argues for the preservation of the magnetic properties in the disilicide films despite their small thickness starting from several nano- meters.