Browsing by Author "Baker, S. H."

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Magnetic and Structural Changes in Cu1-Xalx Alloy Matrix - Embedded Fe Nanoparticle Systems
(Elsevier Science BV, 2019) Kurt, M. S.; Baker, S. H.; Roy, M.; Lees, M. R.
We describe the atomic structure and magnetism in Fe nanoparticles (similar to 2 nm) ebedded in a Cu1-xAlx alloy matrix. Nanocomposite films for these studies were prepared directly from gas phase using a flexible co-deposition technique under Ultra-High Vacuum (UHV) conditions. Fe nanoparticles and the alloy matrix were prepared using a gas aggregation source and MBE sources respectively. Extended x-ray absorption fine structure (EXAFS) experiments indicate that the embedded Fe nanoparticles retain a bcc structure for Al-contents greater than x = 0.13 but, for Al-contents lower than this value, Fe nanoparticles have both fcc and bcc structures. The magnetic moment per Fe atom initially increases with increasing Al-content due to the bcc structure becoming more dominant in the embedded nanoparticles as the Al-content is increased, but then decreases with further increase in Al-content. This decrease is consistent with a modest degree of alloying between Fe and Al atoms at the particle/matrix interfaces.
Magnetism and Structure in Nanocomposite Fe Nanoparticle/Al Matrix Films
(Elsevier Science Sa, 2019) Kurt, M. S.; Baker, S. H.; Roy, M.; Lees, M. R.
We describe magnetometry measurements performed on nanocomposite films formed of Fe nanoparticles embedded in Al matrix. The samples were prepared using a flexible co-deposition technique under Ultra-High Vacuum (UHV) environments. Fe nanoparticles, made by using a gas aggregation source, were co-deposited with an atomic Al beam, made by an MBE source. The Volume Filling Fraction (VFF) of nanoparticles was varied controllably between 4% and 45%, while the mean diameter of Fe nanoparticles produced by the source was similar to 2 nm. Fe K edge extended x-ray absorption fine structure (EXAFS) experiments show that there is a high degree of alloying between Fe nanoparticles and Al atoms. Magnetism in the embedded Fe nanoparticle samples was investigated using a SQUID magnetometer. Atomic moment of Fe in the Fe/Al nanocomposite films increases slightly when the proportion of Fe nanoparticles is increased, but is still significantly lower than the bulk Fe value. In a more detailed analysis, the magnetisation curves were fitted using the Random Anisotropy Model (RAM) which allowed the exchange field and random anisotropy field to be evaluated. The findings and issues raised by this approach are discussed. (C) 2019 Elsevier B.V. All rights reserved.