Structural stability, magnetism, and surface magneto-optic Kerr effect spectra of MnAg(001) surface alloys

The stability of a MnAg surface alloy was investigated employing the total energy and atomic force full-potential linearized augmented plane wave method based on the local density approximation for: (i) a clean Ag(001), (ii) 1 ML Mn overlayer [1 Mn/Ag(001)], (iii) 1 and 2 ML MnAg alloys as overlayers on Ag(001) [1(MnAg)/Ag(001) and 2(MnAg)/Ag(001)], and (iv) 1 ML Mn diffused into Ag(001) substrate [Ag/1 Mn/Ag(001)]. Results obtained show that 2(MnAg)/Ag(001) is much more stable than 1 Mn/Ag(001) (by a large energy difference of 150 meV), whereas 1(MnAg)/Ag(001) is marginally more stable (by a slight energy difference of 8 meV) compared to a separate phase of Ag and Mn atoms. Surface Mn and subsurface Mn atoms in 2(MnAg)/Ag(001) were found to be coupled antiferromagnetically with magnetic moments of 3.96 and -3.55 μ_B, respectively. The surface corrugation (Δz=0.05 a.u.) of 2(MnAg)/Ag(001) was found to be much smaller than that (Δz=0.5 a.u.) of another magnetically stabilized surface alloy system, MnCu/Cu(001). No significant magneto-optical effects for antiferromagnetic Ag/Mn/Ag(001) were found due to the small off-diagonal elements of the optical conductivity.