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Author: Macià, Ferran ×

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    On the Promotion of Catalytic Reactions by Surface Acoustic Waves
    (Weinheim : Wiley-VCH, 2020) von Boehn, Bernhard; Foerster, Michael; von Boehn, Moritz; Prat, Jordi; Macià, Ferran; Casals, Blai; Khaliq, Muhammad Waqas; Hernández-Mínguez, Alberto; Aballe, Lucia; Imbihl, Ronald
    Surface acoustic waves (SAW) allow to manipulate surfaces with potential applications in catalysis, sensor and nanotechnology. SAWs were shown to cause a strong increase in catalytic activity and selectivity in many oxidation and decomposition reactions on metallic and oxidic catalysts. However, the promotion mechanism has not been unambiguously identified. Using stroboscopic X-ray photoelectron spectro-microscopy, we were able to evidence a sub-nanosecond work function change during propagation of 500 MHz SAWs on a 9 nm thick platinum film. We quantify the work function change to 455 μeV. Such a small variation rules out that electronic effects due to elastic deformation (strain) play a major role in the SAW-induced promotion of catalysis. In a second set of experiments, SAW-induced intermixing of a five monolayers thick Rh film on top of polycrystalline platinum was demonstrated to be due to enhanced thermal diffusion caused by an increase of the surface temperature by about 75 K when SAWs were excited. Reversible surface structural changes are suggested to be a major cause for catalytic promotion. © 2020 The Authors. Published by Wiley-VCH GmbH
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    Direct imaging of delayed magneto-dynamic modes induced by surface acoustic waves
    (London : Nature Publishing Group, 2017) Foerster, Michael; Macià, Ferran; Statuto, Nahuel; Finizio, Simone; Hernández-Mínguez, Alberto; Lendínez, Sergi; Santos, Paulo V.; Fontcuberta, Josep; Hernàndez, Joan Manel; Kläui, Mathias; Aballe, Lucia
    The magnetoelastic effect—the change of magnetic properties caused by the elastic deformation of a magnetic material—has been proposed as an alternative approach to magnetic fields for the low-power control of magnetization states of nanoelements since it avoids charge currents, which entail ohmic losses. Here, we have studied the effect of dynamic strain accompanying a surface acoustic wave on magnetic nanostructures in thermal equilibrium. We have developed an experimental technique based on stroboscopic X-ray microscopy that provides a pathway to the quantitative study of strain waves and magnetization at the nanoscale. We have simultaneously imaged the evolution of both strain and magnetization dynamics of nanostructures at the picosecond time scale and found that magnetization modes have a delayed response to the strain modes, adjustable by the magnetic domain configuration. Our results provide fundamental insight into magnetoelastic coupling in nanostructures and have implications for the design of strain-controlled magnetostrictive nano-devices.
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    Twinned-domain-induced magnonic modes in epitaxial LSMO/STO films
    ([London] : IOP, 2017) Wahlström, Erik; Macià, Ferran; Boschker, Jos E; Monsen, Åsmund; Nordblad, Per; Mathieu, Roland; Kent, Andrew D; Tybell, Thomas
    The use of periodic magnetic structures to control the magneto-dynamic properties of materials-Magnonics-is a rapidly developing field. In the last decade, a number of studies have shown that metallic films can be patterned or combined in patterns that give rise to well-defined magnetization modes, which are formed due to band folding or band gap effects. To explore and utilize these effects in a wide frequency range, it is necessary to pattern samples at the sub-micrometer scale. However, it is still a major challenge to produce low-loss magnonic structures with periodicities at such length scales. Here, we show that for a prototypical perovskite, La0.7 Sr0.3MnO3, the twinned structural order can be used to induce a magnetic modulation with a period smaller than 100 nm, demonstrating a bottomup approach for magnonic crystal growth. © 2017 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.