Structure and magnetic properties of Mn/Pt(110)-(1x2): A joint x-ray diffraction and theoretical study

摘要

The growth of a Mn submonolayer on Pt(110)-(1x2) 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 (1x2) 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 (2x1) symmetry. It exhibits mixed dense rows where Pt and Mn sites alternate, as in bulk Pt3Mn. The top layer is corrugated for both the (1x2) and (2x1) surfaces, with Mn lying 0.19 +/- 0.03 and 0.16 +/- 0.02 A above the Pt site, respectively. A Pt3Mn-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(2x2) arrangements were found. Theoretical calculations were performed for (1x2), c(2x2), and (2x1) PtMn two-dimensional (2D) alloys on Pt(110). Among them, the latter was found to be the ground state. Both the (1x2) and (2x1) surface alloys form antiferromagnetic (AF) Mn chains running in the [1 (1) over bar0] and [001] directions, respectively. The ordering within the surface layer switches to ferromagnetic (F) for a 5-ML-thick Pt3Mn(110) film albeit with a surface structure quite identical to the (2x1) 2D case. The magnetic moment per Mn atom at the surface is close to 4 mu(B), 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.