Structural and magnetic properties of 3d transition metal oxide chains on the (001) surfaces of Ir and Pt

We present a survey of the structural and magnetic properties of submonolayer transition metal dioxides on the (001) surfaces of the heavy face-centered cubic noble metals Ir and Pt performed by spin-averaged scanning tunneling microscopy (STM) and spin-polarized (SP) STM. Our STM results confirm that deposition of Co, Fe, Mn, and Cr on the $(2\ifmmode\times\else\texttimes\fi{}1)$ oxygen-reconstructed Ir(001) surface leads to the formation of quasi-one-dimensional chains with a $(3\ifmmode\times\else\texttimes\fi{}1)$ unit cell. As recently predicted by density functional theory [P. Ferstl et al., Phys. Rev. Lett. 117, 046101 (2016)], our SP-STM images of ${\mathrm{FeO}}_{2}$ and ${\mathrm{MnO}}_{2}$ on Ir(001) show a twofold periodicity along the chains which is characteristic for an antiferromagnetic coupling along the chains. In addition, these two materials also exhibit spontaneous, permanent, and long-range magnetic coupling across the chains. Whereas we find a ferromagnetic interchain coupling for ${\mathrm{FeO}}_{2}$/Ir(001), the magnetic coupling of ${\mathrm{MnO}}_{2}$ on Ir(001) appears to be a noncollinear ${120}^{\ensuremath{\circ}}$ spin spiral, resulting in a $(9\ifmmode\times\else\texttimes\fi{}2)$ magnetic unit cell. On Pt(001), patches of $(3\ifmmode\times\else\texttimes\fi{}1)$-reconstructed oxide chains could only be prepared by transition metal (Co, Fe, and Mn) deposition onto the cold substrate and subsequent annealing in an oxygen atmosphere. Again SP-STM on ${\mathrm{MnO}}_{2}$/Pt(001) reveals a very large, $(15\ifmmode\times\else\texttimes\fi{}2)$ magnetic unit cell which can tentatively be explained by a commensurate ${72}^{\ensuremath{\circ}}$ spin spiral. Large-scale SP-STM images reveal a long-wavelength spin rotation along the ${\mathrm{MnO}}_{2}$ chain.