Controlling adsorption and spin configurations of Co atoms on Si(111)-(7 x 7)

Combining scanning tunneling microscopy and first-principles calculations, we have shown that single Co atoms adsorbed on a Si(111)-(7 x 7) surface have eight different configurations that possess different spin magnetic moments. Despite the large adsorption energy, we have demonstrated that both the position and the spin state of single adsorbed Co atoms can be well controlled through the vertical atomic manipulation and the "tip-touch" operation that converts Co atoms among various adsorption configurations. Our approach to construct atomic-scale magnetic structures on a semiconductor surface can provide a new pathway to realize spin-based devices, including a scalable solid-state quantum computer.