Browsing by Author "Kostylev, M"

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    The effect of hydrogen gas on Pd/[Co/Pd]30/Pd multilayer thin films
    (Elsevier, 2022-06-01) Schefer, TA; Cortie, DL; Kostylev, M
    It is known that large perpendicular magnetic anisotropy is found at interfaces of cobalt (Co) with palladium (Pd). We investigated Pd/[Co/Pd]30/Pd multilayer thin films with very thin Co and Pd layers with ferromagnetic resonance (FMR) spectroscopy in air and in hydrogen gas. A number of samples characterised by different Pd thicknesses were studied. A ferromagnetic resonance (FMR) peak shift similar to Co/Pd bilayer thin films was observed in the presence of hydrogen gas in the sample environment for all samples. The FMR peak shift is larger for samples with thicker Pd layers. Additionally, we found a dependence of the linewidth on the Pd layer thickness and explain this with the presence of spin pumping. © 2022 Elsevier B.V.
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    Hydrogen-driven switching of the magnetic surface anisotropy at the Co/Pd interface
    (American Physical Society, 2019-03-05) Causer, GL; Kostylev, M; Cortie, DL; Wang, XL; Klose, F
    Heterostructures exhibiting perpendicular magnetic anisotropy (PMA) have proven to be indispensable within the magnetic recording industry. By exploiting the hydrogen-induced modifications to PMA which occur exclusively at the ferromagnetic/Pd interface, an opportunity exists to expand the potential applications of PMA-based heterostructures into the realm of hydrogen sensing using ferromagnetic resonance (FMR) - an electron-spin based technology. Here, we present an interface-resolved in-operando study of a Co/Pd film which features tailorable PMA in the presence of hydrogen gas. We combine polarized neutron reflectometry with in-situ FMR to explore the nanoscopic interactions of hydrogen at the Co/Pd interface which affects the spin-resonance condition during hydrogen cycling. Key experimental data and theoretical modelling reveal that the interfacial PMA of the Co/Pd film suppresses non-reversibly upon primary exposure to hydrogen gas – highlighting a potential avenue for spintronics-based hydrogen sensing.
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    Iron oxide-palladium core-shell nanospheres for ferromagnetic resonance-based hydrogen gas sensing
    (Elsevier, 2022-02-08) Khan, S; Lawler, NB; Bake, A; Rahman, R; Cortie, DL; Iyer, KS; Martyniuk, M; Kostylev, M
    Interfaces of ferromagnetic transition metals such as Iron, Cobalt, and Nickel with non-magnetic palladium are of interest due to their unique magnetic and spintronic properties. These interfaces enable ferromagnetic resonance (FMR) based sensing of hydrogen gas. In the present work, we synthesized Fe3O4–Pd core-shell nanospheres via a one-pot synthesis method using the thermal decomposition of Fe3+ acetylacetonate in the presence of a reducing agent to produce the Fe3O4 core, followed by the reduction of a Pd2+ precursor to form the pure Pd shell. We found that our in-situ synthesized core-shell nanostructure is magnetically active and shows excellent H2 gas sensing properties. The effect of reversible hydrogen gas absorption on the magnetism of Fe3O4–Pd core-shell nanospheres was investigated. The hydrogen-induced ferromagnetic-resonance (FMR) peak shift amounted to 30% of the peak linewidth for the virgin state of the sample. In addition, in the presence of hydrogen gas, we observed a fully reversible decrease in the FMR peak linewidth by about two times. This was accompanied by a nearly doubling of the FMR peak height. Response and recovery times of about 2 and 50 s, respectively, were extracted from the measurements. All the data was collected using a mix of just 3% hydrogen in a nitrogen carrier gas. © 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd.
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    Magnetic interface phenomena in nano-architectures and their applications
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2018-11-19) Causer, GL; Cortie, DL; Zhu, HL; Kostylev, M; Ionescu, M; Mankey, GJ; Wang, XL; Klose, F
    Interfaces between heterostructure components in nanoscale films play important roles in communicating low-dimensional phenomena and act as anchor points for the direct control and tunability of device performance. In this talk I will give an overview of our group’s recent investigations into the occurrence of magnetic interface phenomena in low-dimensional thin-film systems which have conceivable utility in future condensed-matter technologies. First, the magnetic interface quality of an FePt3 nano-magnet formed via ion-induced chemical disorder will be analysed [1]. Here, neutron and electron measurements used in combination with density functional theory calculations reveal a rather counterintuitive result which could prove beneficial towards the development of ultra-high density magnetic recording devices. In a second study, the layer-averaged static magnetisation and macroscopic magneto-dynamic behaviours of a Co/Pd bilayer during hydrogen-gas cycling are analysed. To perform this characterisation, we first had to develop and commission an original sample environment which innovatively combines polarised neutron reflectometry and microwave spectroscopy [2]. The Co/Pd interface is found to feature tailorable magnetic surface anisotropy in the presence of hydrogen gas – the mechanism of which could act as a safety switch in next-generation vehicles powered by hydrogen.
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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.