Browsing by Author "Granville, S"

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    Ion beam analysis of GdN thin films with a protective GaN capping layer
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2005-11-20) Granville, S; Budde, F; Koo, A; Ruck, BJ; Trodahl, HJ; Bittar, A; Metson, JB; Kennedy, VJ; Prince, KE; Atanacio, AJ
    Rare-earth nitrides represent an interesting class of matrials that exhibit a range of electronic and magnetic properties. Recent LSD+SIC calculations have predicted magnetic properties covering paramagnetic, ferromagnetic, and antiferromagnetic, and elecronic states including metallic, semiconducting, or insulating, and a number exhibit half-metallicity. Due to this wide variety of predicted properties these materials are of considerable interest as potential sources of spin-polarised current for novel devices. Although numerous studies of the rare-earth nitrides are present in the literature, there is still much to be learned about them. The most well studied of these nitrides is GdN, a ferromagnet with the highest Curie temperature of the series. The magnetic properties in particular have been extensively studied, but often the presence of impurities such as O could not be ruled out, and studies have shown that N vacancies or O impurities significantly influence the magnetic quality of GdN. The rare-earth nitrides are sensitive to water vapour and react rapidly upon exposure to atmosphere, so it is an ongoing challenge to produce GdN of a sufficient purity to make characterising its properties an achievable task. In particular the electrical and optical properties of stoichiometric GdN have not both been established reliably, despite their great relevance to the potential usefulness of the material in devices.
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    Nanoscale magnetic arrays through block copolymer templating of polyoxometalates
    (American Chemical Society, 2024-02-08) Clyde, DRM; Cortie, DL; Granville, S; Ware, DC; Brothers, PJ; Malmström, J
    Magnetic nanoarrays promise to enable new energy-efficient computations based on spintronics or magnonics. In this work, we present a block copolymer-assisted strategy for fabricating ordered magnetic nanostructures on silicon and permalloy substrates. Block copolymer micelle-like structures were used as a template in which polyoxometalate (POM) clusters could assemble in an opal-like structure. A combination of microscopy and scattering techniques was used to confirm the structural and organizational features of the fabricated materials. The magnetic properties of these materials were investigated by polarized neutron reflectometry, nuclear magnetic resonance, and magnetometry measurements. The data show that a magnetic structural design was achieved and that a thin layer of patterned POMs strongly influenced an underlying permalloy layer. This work demonstrates that the bottom-up pathway is a potentially viable method for patterning magnetic substrates on a sub-100 nm scale, toward the magnetic nanostructures needed for spintronic or magnonic crystal devices. © 2024 The Authors. Published by American Chemical Society. This publication is licensed under CC-BY-NC-ND 4.0.
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    Unraveling the sign reversal of the anomalous Hall effect in ferromagnet/heavy-metal ultrathin films
    (American Physical Society, 2023-03-01) Zhang, Y; Cortie, DL; LaGrange, T; Lee, W; Butler, T; Ludbrook, B; Granville, S
    The sign reversal in the anomalous Hall effect (AHE) that occurs for material offers great prospects for AHE-based spintronic devices design. However, the mechanisms are still controversial in ultrathin ferromagnetic/heavy metal thin film systems due to the complicatedly interfacial effects. Here, we investigate the AHE sign reversal in ultrathin ferromagnetic Mn2CoAl/Pd films, a system which has shown unusual AHE, significant spin-orbit coupling, and magnetic texturing. Element-sensitive cross-sectional STEM imaging and the depth-resolved magnetization profile from polarized neutron reflectometry identifies the presence of a second ferromagnetic layer from intermixed Co-Pd. To quantitatively explain the sign reversal of the AHE, we build a model based on two contributions, ferromagnetic Mn2CoAl and the intermixed CoPd layer. We also clarify that contributions to the AHE from magnetic proximity and spin Hall effect are negligible. Our work demonstrates that interfacial alloying can be a critical factor and provides insightful methods to determine the origins of the AHE in ferromagnet/heavy-metal thin film systems. © 2024 American Physical Society.