Spin waves in Mn-doped Si: exchange interactions from first-principles calculations G. Rao and J. E. Raynolds College of Nanoscale Science and Engineering, University at Albany, State University of New York

There has been considerable interest in magnetic semiconductors in recent years for potential applications in the field of spintronics.The present work was motivated by recent experimental achievement of above-room- temperature magnetism in Mn doped silicon (Phys.Rev.B \textbf{71}, 033302 (2005)).We present the results of Density Functional calculations that have been carried out to determine the strength of the distance-dependant exchange interaction in Mn-doped Si.The exchange interaction determines the energy difference between ferro-magnetic and anti-ferromagnetic spin configurations and as such it provides for a prediction of spin-wave velocities.Such spin waves, if they exist, are of interest in that they may provide means for transmitting spin-based information. Comparison of the relative energy differences between ferromagnetic and anti-ferromagnetic configurations for a series of Mn locations yielded the distance dependant exchange interaction J(R).Interestingly we find that the exchange interaction is negative (anti-ferromagnetic) for short and long distances and is positive (ferromagnetic) for intermediate distances.This talk will present these findings along with estimates of spin-wave velocities,densities of states,band structure and spin-density distributions.