Two-dimensional surface ordered Mn-Co alloys on Co(001) - art. no. 064421

The spin polarization of various surface alloys of manganese and cobalt on cobalt (001) is determined by the tight-binding linear muffin-tin-orbitals method. An ordered surface alloy restricted to the surface plane i.e., Mn0. 5Co0.5/Co(001), is shown to be moro stable as compared to large islands of Mn or Coin the surface plane. The coupling between Mn and Co is found to be antiferromagnetic in the ground stare with a metastable ferromagnetic conf iguration a few mRy higher in energy. This ferromagnetic coupling between M n and Co is in agreement with the recent magneto-optical Kerr effect and x- ray magnetic-circular dichroism results. The two-dimensional (and two-layer thick) surface-ordered alloy (Mn0.5Co0.5)(2)/Co(001) is more stable as com pared to the perfect Mn monolayer on Co(001) and only solutions with antife rromagnetic couplings between Mn atoms are obtained. A ferromagnetic coupli ng between the Mn atoms at the surface and the Co atoms in the substrate is the ground state. A buried monolayer of Mn, i.e,, Co/Mn/Co(001), is also f ound more stable as compared to Mn/Co(001) so that a complete exchange betw een the surface Mn monolayer and the Co subsurface layer is energetically f avorable.