Self-Organized Growth, Structure, and Magnetism of Monatomic Transition-Metal Oxide Chains

We report on the self-organized growth of monatomic transition-metal oxide chains of ($3\ifmmode\times\else\texttimes\fi{}1$) periodicity and unusual $M{\mathrm{O}}_{2}$ stoichiometry ($M=\mathrm{Ni}$, Co, Fe, Mn) on Ir(100). We analyze their structural and magnetic properties by means of quantitative LEED, STM, and density functional theory (DFT) calculations. LEED analyses reveal a fascinating common atomic structure in which the transition-metal atoms sit above a missing-row structure of the surface and are coupled to the substrate only via oxygen atoms. This structure is confirmed by DFT calculations with structural parameters deviating by less than 1.7 pm. The DFT calculations predict that the ${\mathrm{NiO}}_{2}$ chains are nonmagnetic, ${\mathrm{CoO}}_{2}$ chains are ferromagnetic, while ${\mathrm{FeO}}_{2}$ and ${\mathrm{MnO}}_{2}$ are antiferromagnetic. All structures show only weak magnetic interchain coupling. Further, we demonstrate the growth of oxide chains of binary alloys of Co and Ni or Fe on Ir(100), which allows us to produce well-controlled ensembles of ferromagnetic chains of different lengths separated by nonmagnetic or antiferromagnetic segments.