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Abstract: Ultrathin epitaxial films of ferromagnetic insulators (FMIs) with Curie temperatures near room temperature are critically needed for use in dissipationless quantum computation and spintronic devices. However, such materials are extremely rare. Here, a room‐temperature FMI is achieved in ultrathin La0.9Ba0.1MnO3 films grown on SrTiO3 substrates via an interface proximity effect. Detailed scanning transmission electron microscopy images clearly demonstrate that MnO6 octahedral rotations in La0.9Ba0.1MnO3 close to the interface are strongly suppressed. As determined from in situ X‐ray photoemission spectroscopy, O K‐edge X‐ray absorption spectroscopy, and density functional theory, the realization of the FMI state arises from a reduction of Mn eg bandwidth caused by the quenched MnO6 octahedral rotations. The emerging FMI state in La0.9Ba0.1MnO3 together with necessary coherent interface achieved with the perovskite substrate gives very high potential for future high performance electronic devices.

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Abstract: Magnetic skyrmions are chiral spin textures that hold great promise as nanoscale information carriers. Since their first observation at room temperature, progress has been made in their current-induced manipulation, with fast motion reported in stray-field-coupled multilayers. However, the complex spin textures with hybrid chiralities and large power dissipation in these multilayers limit their practical implementation and the fundamental understanding of their dynamics. Here, we report on the current-driven motion of Néel skyrmions with diameters in the 100-nm range in an ultrathin Pt / Co / Mg O trilayer. We find that these skyrmions can be driven at a speed of 100 m s − 1 and exhibit a drive-dependent skyrmion Hall effect, which is accounted for by the effect of pinning. Our experiments are well substantiated by an analytical model of the skyrmion dynamics as well as by micromagnetic simulations including material inhomogeneities. This good agreement is enabled by the simple skyrmion spin structure in our system and a thorough characterization of its static and dynamical properties.

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Abstract: Materials suitable for magnonic crystals demand low magnetic damping and long spin-wave propagation distance. In this context Co -based Heusler compounds are ideal candidates for magnonic based applications. In this work, antidot arrays (with different shapes) of epitaxial Co 2 Fe 0.4 Mn 0.6 Si Heusler-alloy thin films are prepared using e-beam lithography and sputtering technique. Magneto-optic Kerr effect (MOKE) and ferromagnetic resonance analysis confirm the presence of dominant cubic and moderate uniaxial magnetic anisotropies in the thin film. Domain imaging via x-ray photoemission electron microscopy on the antidot arrays reveals chainlike switching or correlated bigger domains for different antidot shapes. Time-resolved MOKE microscopy is performed to study the precessional dynamics and magnonic modes of the antidots with different shapes. We show that the optically induced spin-wave spectra in such antidot arrays can be tuned by changing the shape of the holes. The variation in internal-field profiles, pinning energy barrier, and anisotropy modifies the spin-wave spectra dramatically within the antidot arrays with different shapes. We further show that by combining the magnetocrystalline anisotropy with the shape anisotropy, an extra degree of freedom can be achieved to control the magnonic modes in such antidot lattices.

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Abstract: The redox behaviour modification following the addition of zirconia to ceria nanostructures supported on Rh(111) has been investigated using a combination of Low Energy Electron Diffraction (LEED) and X-ray Photoemission Electron Microscopy (XPEEM). Soft X-ray irradiation was employed to reduce ZrO2-x(111) supported on Rh(111) and, by introducing oxygen, the reoxidation process of the thin film was monitored. CeO2(111) was then deposited on zirconia/Rh(111) and, using XPEEM, we determined that the mixed metal oxide formed a phase-separated structure with CeO2(111) nanoparticles on top of the zirconia. Upon exposure of CeO2-x/ZrO2-x/Rh(111) to X-ray illumination, the zirconia no longer undergoes any observable reduction while at the same time the ceria is reduced. Our results indicate a synergy between the zirconia and ceria in the phase-separated system expected in the working catalyst, with oxygen transfer between the metal oxides. This sheds light on the mechanism of the enhancement of catalytic properties seen with the addition of zirconia to ceria and highlights the oxygen storage and release ability of ceria.

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Abstract: Highly spin-polarised materials show great promise in applied spintronics as spin-filters and spin transfer torque magnetic random-access memory devices for data storage. However, controllable magnetisation switching requires materials with a low Gilbert damping parameter and stable magnetic properties at room temperature. Two highly spin-polarised magnetic materials with critical temperatures well above room temperature are characterised using a series of structural and magnetic analysis techniques. Correlation between the magnetic damping and microstructure is observed in both Fe3O4 and Co2FeAl0.5Si0.5 samples and both are seen to improve structurally and show more favourable damping parameters with annealing. Annealing Fe3O4 in CO/CO2 is shown to reduce the antiphase boundary density and decrease the two-magnon scattering-like extrinsic damping effects. The quality of the sample structure and the stoichiometry is also seen to improve considerably after the annealing although the defects are not completely eliminated. An anomalous peak in the damping of the annealed film is observed at 10GHz. Co2FeAl0.5Si0.5 grown on germanium and silicon substrates is seen to also improve with thermal annealing. The Gilbert damping is seen to be lower in the as-grown scheme using the silicon substrate but greater reduction of damping post-annealing is seen on germanium. In both cases the B2 order is observed in the Co2FeAl0.5Si0.5 thin films, and intermixing between the sample and substrate observed above 500oC is sufficient to disrupt the crystal structure and introduce significant extrinsic damping effects which increase the total damping. This prevents the Co2FeAl0.5Si0.5 from reaching the more desirable L21 structure.