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

摘要

The growth of a Mn submonolayer on Pt(110)-(1 X 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 X 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 X 1) symmetry. It exhibits mixed dense rows where Pt and Mn sites alternate, as in bulk Pt_3Mn. The top layer is corrugated for both the (1 X 2) and (2 X 1) surfaces, with Mn lying 0.19 ± 0.03 and 0.16 ± 0.02 A above the Pt site, respectively. A Pt_3Mn-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 X 2) arrangements were found. Theoretical calculations were performed for (1 X 2), c(2 X 2), and (2 X 1) PtMn two-dimensional (2D) alloys on Pt(110). Among them, the latter was found to be the ground state. Both the (1 X 2) and (2 X 1) surface alloys form antiferromagnetic (AF) Mn chains running in the [110] and [001] directions, respectively. The ordering within the surface layer switches to ferromagnetic (F) for a 5-ML-thick Pt_3Mn(110) film albeit with a surface structure quite identical to the (2 X 1) 2D case. The magnetic moment per Mn atom at the surface is close to 4 μ_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.