Location and Magnetic Hyperfine Properties of Mn$^{2+}$ in Silicon.

Crystalline Silicon doped with the transition metal ion Mn$^{+2}$ is ferromagnetic at room temperature and thus potentially a useful material for spintronic applications. In attempting to understand from first principles the location of Mn$^{+2}$ and the electronic structure of the ferromagnetic system we have started work first on the dilute system. We have used the Hartree-Fock cluster procedure to determine the binding energies of the three likely locations for Mn$^{2+}$, substitutional (S), tetrahedral interstitial (T$_{i})$ and hexagonal interstitial (H$_{i})$ locations allowing for relaxation of the silicon neighbors. Our calculations show that the H$_{i}$ location is unstable and the S and T$_{i}$ are stable. Our nuclear magnetic hyperfine interactions results for $^{55}$Mn nucleus and $^{29}$Si neighbor will be presented and compared with electron spin resonance [1] experimental data. \newline [1] H.H. Wood bury and G. W. Ludwig Phys. Rev. \underline {117},102(1960)