We have investigated magnetic properties of atomic wires of Ga-substituted Mn on the GaAs(110) surface using first-principles calculations based on the spin-density functional theory. Mn atomic wires are assumed to align along the <110>-, <001>-, and <211>-directions. The <110>-oriented wire is most stable energitically, and has the ferromagnetic ground state with the magnetic moment of 4.0 μ
B per Mn atom. The band structure has a large dispersion along the wire and exhibits a half-metallic state. The ferromagnetic character of the Mn wire results from the double exchange interaction through the
p-
d hybridization between the Mn-3
d and the GaAs surface states.
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