Structure and magnetic properties of Mn Pt (110) - (1×2): A joint x-ray diffraction and theoretical study

The growth of a Mn submonolayer on Pt (110) - (1×2) was studied by surface x-ray diffraction. At room temperature, Mn fills in the empty rows of the clean substrate's missing row structure. At a coverage of 0.5 ML (monolayer), a (1×2) surface alloy is formed, with alternating Pt and Mn dense rows. Upon annealing (or depositing at a substrate temperature of about 570 K), another surface alloy forms with a (2×1) symmetry. It exhibits mixed dense rows where Pt and Mn sites alternate, as in bulk Pt3 Mn. The top layer is corrugated for both the (1×2) and (2×1) surfaces, with Mn lying 0.19±0.03 and 0.16±0.02 Å above the Pt site, respectively. A Pt3 Mn -like slab forms when annealing a 3-ML-thick Mn film. The observed symmetries are at variance with the NiMn and CuMn surfaces where c (2×2) arrangements were found. Theoretical calculations were performed for (1×2), c (2×2), and (2×1) PtMn two-dimensional (2D) alloys on Pt(110). Among them, the latter was found to be the ground state. Both the (1×2) and (2×1) surface alloys form antiferromagnetic (AF) Mn chains running in the [1 1̄ 0] and [001] directions, respectively. The ordering within the surface layer switches to ferromagnetic (F) for a 5-ML-thick Pt3 Mn (110) film albeit with a surface structure quite identical to the (2×1) 2D case. The magnetic moment per Mn atom at the surface is close to 4 μB, in all cases, among the largest values ever found in similar metal-Mn surface alloys: it is directly related to the surface corrugation and to the Mn volume as already observed for other Mn-based surface alloys. The magnetic order, F or AF, is strongly influenced by the local chemical environment of the Mn sites. © 2007 The American Physical Society.