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    Inhomogeneous ferromagnetism mimics signatures of the topological Hall effect in SrRuO3 films
    (College Park, MD : APS, 2020) Kim, Gideok; Son, K.; Suyolcu, Y.E.; Miao, L.; Schreiber, N.J.; Nair, H.P.; Putzky, D.; Minola, M.; Christiani, G.; van Aken, P.A.; Shen, K.M.; Schlom, D.G.; Logvenov, G.; Keimer, B.
    Topological transport phenomena in magnetic materials are a major topic of current condensed matter research. One of the most widely studied phenomena is the topological Hall effect (THE), which is generated via spin-orbit interactions between conduction electrons and topological spin textures such as skyrmions. We report a comprehensive set of Hall effect and magnetization measurements on epitaxial films of the prototypical ferromagnetic metal SrRuO3 the magnetic and transport properties of which were systematically modulated by varying the concentration of Ru vacancies. We observe Hall effect anomalies that closely resemble signatures of the THE, but a quantitative analysis demonstrates that they result from inhomogeneities in the ferromagnetic magnetization caused by a nonrandom distribution of Ru vacancies. As such inhomogeneities are difficult to avoid and are rarely characterized independently, our results call into question the identification of topological spin textures in numerous prior transport studies of quantum materials, heterostructures, and devices. Firm conclusions regarding the presence of such textures must meet stringent conditions such as probes that couple directly to the noncollinear magnetization on the atomic scale.
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    Faceting and metal-exchange catalysis in (010) β-Ga2O3 thin films homoepitaxially grown by plasma-assisted molecular beam epitaxy
    (New York : American Institute of Physics, 2018) Mazzolini, P.; Vogt, P.; Schewski, R.; Wouters, C.; Albrecht, M.; Bierwagen, Oliver
    We here present an experimental study on (010)-oriented -Ga2O3 thin films homoepitaxially grown by plasma assisted molecular beam epitaxy. We study the effect of substrate treatments (i.e., O-plasma and Ga-etching) and several deposition parameters (i.e., growth temperature and metal-to-oxygen flux ratio) on the resulting Ga2O3 surface morphology and growth rate. In situ and ex-situ characterizations identified the formation of (110) and (¯110)-facets on the nominally oriented (010) surface induced by the Ga-etching of the substrate and by several growth conditions, suggesting (110) to be a stable (yet unexplored) substrate orientation. Moreover, we demonstrate how metal-exchange catalysis enabled by an additional In-flux significantly increases the growth rate (>threefold increment) of monoclinic Ga2O3 at high growth temperatures, while maintaining a low surface roughness (rms < 0.5 nm) and preventing the incorporation of In into the deposited layer. This study gives important indications for obtaining device-quality thin films and opens up the possibility to enhance the growth rate in -Ga2O3 homoepitaxy on different surfaces [e.g., (100) and (001)] via molecular beam epitaxy.