Search

The perovskite SrRuO3 is a prototypical itinerant ferromagnet which allows interface engineering of its electronic and magnetic properties. We report the synthesis and investigation of atomically flat artificial multilayers of SrRuO3 with the spin-orbit semimetal SrIrO3 in combination with band-structure calculations with a Hubbard U term and topological analysis. The latter reveal an electronic reconstruction and emergence of flat Ru-4dxz bands near the interface, ferromagnetic interlayer coupling, and a negative Berry-curvature contribution to the anomalous Hall effect. We analyze the Hall effect and magnetoresistance measurements as a function of the field angle from an out-of-plane towards an in-plane orientation (either parallel or perpendicular to the current direction) by a two-channel model. The magnetic easy direction is tilted by about 20∘ from the sample normal for low magnetic fields, rotating towards the out-of-plane direction by increasing fields. Fully strained epitaxial growth enables a strong anisotropy of magnetoresistance. An additional Hall effect contribution, not accounted for by the two-channel model, is compatible with stable skyrmions only up to a critical angle of roughly 45∘ from the sample normal. Within about 20∘ from the thin film plane an additional peaklike contribution to the Hall effect suggests the formation of a nontrivial spin structure.

In a combined experimental and theoretical study we assess the role of Co incorporation on the OER activity of LaCoxFe1 xO3. Phase pure perovskites were synthesized up to x 0.300 in 0.025 0.050 steps. HAADF STEM and EDX analysis points towards FeO2 terminated 001 facets in LaFeO3, in accordance with the stability diagram obtained from density functional theory calculations with a Hubbard U term DFT U . Linear sweep voltammetry conducted in a rotating disk electrode setup shows a reduction of the OER overpotential and a nonmonotonic trend with x, with double layer capacitance measurements indicating an intrinsic nature of activity. This is supported by DFT U results that show reduced overpotentials for both Fe and Co reaction sites with the latter reaching values of 0.32 0.40 V, 0.3 V lower than for Fe. This correlates with a stronger reduction of the binding energy difference of the O and OH intermediates towards an optimum value of 1.6 eV for x 0.250, the OH deprotonation being the potential limiting step in most cases. Significant variations of the magnetic moments of both surface and subsurface Co and Fe during OER demonstrate that the beneficial effect is a result of a concerted action involving many surrounding ions, which extends the concept of the active site

A pronounced uniform polar distortion extending over several unit cells enables thin LaAlO3 overlayers on SrTiO3(001) to counteract the charge dipole and thereby neutralize the "polarization catastrophe" that is suggested by simple ion-counting. This unanticipated mechanism, obtained from density functional theory calculations, allows several unit cells of the LaAlO3 overlayer to remain insulating (hence, fully ionic). The band gap of the system, defined by occupied O $2p$ states at the surface and unoccupied Ti 3d states at the interface in some cases $\sim$20 \AA distant, decreases with increasing thickness of the LaAlO3-film before an insulator-to-metal transition and a crossover to an electronic reconstruction occurs at around five monolayers of LaAlO3., Comment: 5 pages, 4 figures, submitted for publication

Using ab initio thermodynamics we compile a phase diagram for the surface of Fe3O4(001) as a function of temperature and oxygen pressures. A hitherto ignored polar termination with octahedral iron and oxygen forming a wave-like structure along the [110]-direction is identified as the lowest energy configuration over a broad range of oxygen gas-phase conditions. This novel geometry is confirmed in a x-ray diffraction analysis. The stabilization of the Fe3O4(001)-surface goes together with dramatic changes in the electronic and magnetic properties, e.g., a halfmetal-to-metal transition., 4 pages, 4 figures