Making ferromagnetic metal MnSi ultrathin films semiconductor

Atomically flat MnSi films were fabricated on Si(1 1 1)-7 × 7 reconstructed surface by molecular beam epitaxy(MBE). Both scanning tunneling microscopy (STM) images and low energy electron diffraction (LEED) patterns demonstrate a well-defined (3×3)R30^o structure reconstruction. A thickness-driven metal–semiconductor transition in MnSi ultrathin films was observed with decreasing the thickness down to 6 ML (monolayers). The temperature dependence of the resistance and the negative magnetoconductivity suggest the MnSi ultrathin films with thickness lower than 6ML exhibit weak anti-localization (WAL) of two-dimensional (2D) electron systems. This finding that not only advances our understanding of the mechanism of thickness-driven metal–semiconductor transition, but also provides a new strategy to use ferromagnetic semiconductor as spin injector in spintronic devices.