S. Gallego

Magnetic states at the Oxygen surfaces of ZnO and Co-doped ZnO

First principles calculations of the O surfaces of Co-ZnO show that substitutional Co ions develop large magnetic moments which long-range order depends on their mutual distance. The local spin polarization induced at the O atoms is 3 times larger at the surface than in the bulk, and the surface stability is considerably reinforced by Co. Moreover, a robust ferromagnetic state is predicted at the O (0001) surface even in the absence of magnetic atoms, correlated with the number of p holes in the valence band of the oxide, and with a highly anisotropic distribution of the magnetic charge even in the absence of spin-orbit coupling.

Tuning surface metallicity and ferromagnetism by hydrogen adsorption at the polar ZnO(0001) surface

Total energy calculations for the adsorption of hydrogen on the polar Zn-ended ZnO(0001) surface predict that a metal-insulator transition and the reversible switch of surface magnetism can be achieved by varying the hydrogen density on the surface. An on top

Imaging spin-reorientation transitions in consecutive atomic Co layers on Ru(0001)

\text{H}(1\ifmmode\times\else\texttimes\fi{}1)

Noble metal capping effects on the spin-reorientation transitions of Co/Ru(0001)

ordered overlayer with genuine H-Zn chemical bonds is shown to be energetically favorable. The

Oxygen vacancies at Ni/c-ZrO2 interfaces

\text{H}(1\ifmmode\times\else\texttimes\fi{}1)

Charge order at magnetite Fe3O4(0?0?1): surface and Verwey phase transitions

covered surface is metallic and spin polarized. Lower hydrogen coverages lead to a nonmagnetic insulating surface, with strengthened H-Zn bonds and corrugation of the topmost layers. Our results explain the experimental observation of formation of an ordered

Unconventional properties of nanometric FeO(111) films on Ru(0001): stoichiometry and surface structure

\text{H}(1\ifmmode\times\else\texttimes\fi{}1)

Electronic phase transitions in ultrathin magnetite films

overlayer on the ZnO(0001) surface and its unexpected evolution toward a disordered layer. Furthermore, we identify a mechanism which can contribute to the room-temperature ferromagnetism measured in ZnO thin films and nanoparticles.

Order-disorder phase transition on the (100) surface of magnetite

By means of spin-polarized low-energy electron microscopy, we show that the magnetic easy axis of one to three atomic-layer thick cobalt films on Ru(0001) changes its orientation twice during deposition: One-monolayer and three-monolayer thick films are magnetized in plane, while two-monolayer films are magnetized out of plane. The Curie temperatures of films thicker than one monolayer are well above room temperature. Fully relativistic calculations based on the screened Korringa-Kohn-Rostoker method demonstrate that only for two-monolayer cobalt films does the interplay between strain, surface, and interface effects lead to perpendicular magnetization.

Hydrogen-induced reversible spin-reorientation transition and magnetic stripe domain phase in bilayer Co on Ru(0001)

Thin films of Co/Ru(0001) are known to exhibit an unusual spin reorientation transition (SRT) coupled to the completion of Co atomic layers for Co thicknesses under four layers. By means of spin-polarized low-energy electron microscopy, we follow in real space the magnetization orientation during the growth of atomically thick capping layers on Co/Ru(0001). Capping with noble metal (Cu, Ag and Au) elements modifies the SRT depending on the Co and overlayer thickness and on the overlayer material, resulting in an expanded range of structures with high perpendicular magnetic anisotropy. The origin of the SRT can be explained in terms of ab initio calculations of the layer-resolved contributions to the magnetic anisotropy energy. Besides the changes in the SRT introduced by the capping, a quantitative enhancement of the magnetic anisotropy is identified. A detailed analysis of the interplay between strain and purely electronic effects allows us to identify the conditions that lead to a high perpendicular magnetic anisotropy in thin hcp Co films.