Browsing by Author "Livesey, KL"

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    Interplay between thermal and magnetic properties of polymer nanocomposites with superparamagnetic Fe3O4 nanoparticles
    (Elsevier, 2023-08-01) Rezoanur Rahman, M; Bake, A; Jumlat Ahmed, AI; Islam, SMKN; Wu, L; Khakbaz, HS; FitzGerald, S; Chalifour, A; Livesey, KL; Knott, JC; Innis, PC; Beirne, S; Cortie, DL
    Magnetic nanoparticles embedded in polymer matrices have excellent potential for multifunctional applications like magnetic remote heating, controlled drug delivery, hyperthermia, and thermally functionalized biomedical devices. A solvent-based processing method was developed to produce magnetic composites consisting of magnetite (Fe3O4) superparamagnetic nanoparticles embedded in a biomedical-grade polyurethane (ChronoFlex® C). The particles had a log-normal size distribution spanning from 4−16 nm, with a mean-size of 9.5 ± 2 nm. X-ray diffraction, transmission electron microscopy, and scanning electron microscopy with elemental mapping were used to assess the phase purity, surface morphology, particle size, and homogeneity of the resulting nanocomposite. The magnetic properties of composites with 7–13 wt% of Fe3O4 were studied between 5 and 300 K using vibrating sample magnetometry. Room temperature magnetic attraction was observed, with a saturation magnetization of up to 5 emu/g and a low coercive field (Hc < 50 Oe), where the non-zero coercive field was attributed to a small fraction of larger particles that are ferromagnetic at room temperature. Field-cooled and zero-field-cooled magnetometry data were fitted to a numerical model to determine the superparamagnetic mean blocking temperature (TB = 90 K) of the embedded magnetite particles, and an effective magnetic anisotropy of 6×105 erg/cm3. Using an AC magnetic field operating at 85 kHz, we demonstrate that remote heating of the base polyurethane material is greatly enhanced by compositing with Fe3O4 nanoparticles, leading to temperatures up to 45 °C within 18 min for composites submerged in water. This work demonstrates the fundamental principles of a custom-designed thermomagnetic polymer composite that could be used in applications, including medical and heat management. © 2023 Published by Elsevier B.V.
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    Structure and magnetism of ultra-small cobalt particles assembled at titania surfaces by ion beam synthesis
    (Elsevier, 2021-12) Bake, A; Rezoanur Rahman, M; Evans, PJ; Cortie, MB; Nancarrow, M; Abrudan, R; Radu, F; Khaydukov, Y; Causer, GL; Callori, SJ; Livesey, KL; Mitchell, DRG; Pastuovic, Z; Wang, XL; Cortie, DL
    Metallic cobalt nanoparticles offer attractive magnetic properties but are vulnerable to oxidation, which suppresses their magnetization. In this article, we report the use of ion beam synthesis to produce ultra-small, oxidation-resistant, cobalt nanoparticles embedded within substoichiometric TiO2-δ thin films. Using high fluence implantation of cobalt at 20–60 keV, the particles were assembled with an average size of 1.5 ± 1 nm. The geometry and structure of the nanoparticles were studied using scanning transmission electron microscopy. Near-edge X-ray fluorescence spectroscopy on the L2,3 Co edges confirms that the majority of the particles beneath the surface are metallic, unoxidised cobalt. Further evidence of the metallic nature of the small particles is provided via their high magnetization and superparamagnetic response between 3 and 300 K with a low blocking temperature of 4.5 K. The magnetic properties were studied using a combination of vibrating sample magnetometry, element-resolved X-ray magnetic circular dichroism, and depth-resolved polarised neutron reflectometry. These techniques provide a unified picture of the magnetic metallic Co particles. We argue, based on these experimental observations and thermodynamic calculations, that the cobalt is protected against oxidation beneath the surface of titania owing to the enthalpic stability of TiO2 over CoO which inhibits solid state reactions. Crown Copyright © 2021 Published by Elsevier B.V.
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    Ultra-small cobalt particles embedded in titania by ion beam synthesis: additional datasets including electron microscopy, neutron reflectometry, modelling outputs and particle size analysis
    (Elsevier, 2022-02) Bake, A; Rahman, R; Evans, PJ; Cortie, MB; Nancarrow, M; Abrudan, R; Radu, F; Khaydukov, Y; Causer, GL; Livesey, KL; Callori, SJ; Mitchell, DRG; Pastuovic, Z; Wang, XL; Cortie, DL
    This Data-in-brief article includes datasets of electron microscopy, polarised neutron reflectometry and magnetometry for ultra-small cobalt particles formed in titania thin films via ion beam synthesis. Raw data for polarised neutron reflectometry, magnetometry and the particle size distribution are included and made available on a public repository. Additional elemental maps from scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) are also presented. Data were obtained using the following types of equipment: the NREX and PLATYPUS polarised neutron reflectometers; a Quantum Design Physical Property Measurement System (14 T); a JEOL JSM-6490LV SEM, and a JEOL ARM-200F scanning transmission electron microscope (STEM). The data is provided as supporting evidence for the article in Applied Surface Science (A. Bake et al., Appl. Surf. Sci., vol. 570, p. 151068, 2021, DOI 10.1016/j.apsusc.2021.151068), where a full discussion is given. The additional supplementary reflectometry and modelling datasets are intended to assist future scientific software development of advanced fitting algorithms for magnetization gradients in thin films. Crown Copyright © 2021 - Open Access CC BY-NC-ND