Browsing by Author "Metaxas, P"

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    Magneto-electronic hydrogen gas sensing
    (Australian Institute of Physics, 2017-01-31) Causer, GL; Leung, C; Callori, SJ; Metaxas, P; Klose, F; Kostylev, M
    Hydrogen (H2) as an energy carrier and associated H2 technologies such as fuel cells are establishing themselves as key players in the current green energy revolution. To address safety issues associated with H2, robust hydrogen gas sensors are required. We report on a superior method of using magneto-electronics to detect the presence of H2. Exploiting the strong affinity of Pd to reversibly absorb and chemically bind H2, resulting in the formation of PdH which expands the Pd lattice by up to 3%, our prototype device is based on the modification of magnetic, structural and electronic properties that occur upon hydrogenation of a Pd layer in a Pd/Co bilayer film. As H2 is absorbed by the Pd lattice, modifications to the perpendicular magnetic anisotropy (PMA) of interfacial Co moments result, leading to a variation of the ferromagnetic resonance (FMR) response of the Co layer. We report on data obtained from the first in-situ FMR polarised neutron reflectometry (PNR) measurement performed on the time-of-flight neutron reflectometer PLATYPUS at ANSTO. Here we simultaneously probed hydrogen depth profiles within Pd as a function of external H2 partial pressure (HPP), and correlated these against hydrogen induced changes to the FMR signal in the ferromagnetic layer. Decreases in the FMR field in excess of 30 Oe were observed upon H2 absorption, as a result of weakening PMA strength due to changes in interfacial electronic properties. In addition, we systematically investigated the relationship between Pd layer thickness and H2 concentration in the Pd layer in the presence of 3.5% HPP, and found that the uptake of hydrogen is severely hindered by post-deposition annealing. Although the annealing process served to remove lattice dislocations which could otherwise be occupied by H2, it led to more repeatable magnetic behaviors of the materials when measured over several H2 absorption/desorption cycles.