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Title: In-situ magnetic dichroism studies of supported Fe nanoparticles
Author: Edmonds, Kevin William
Awarding Body: University of Leicester
Current Institution: University of Leicester
Date of Award: 2000
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The magnetic properties of nanoscale Fe particles, size 1-4 nm, have been investigated with magnetic dichroism spectroscopy techniques, using synchrotron radiation. The particles were deposited from a portable high temperature gas-aggregation source, and studied in-situ. X-ray magnetic circular dichroism (XMCD) in x-ray absorption spectroscopy was used to show that isolated nanoscale Fe particles possess an enhanced magnetic moment per atom at 6K, with enhancements as large as 80% observed for the orbital moment morb, and 4% for the spin moment mspin. Non-negligible anisotropic contributions to the magnetic moments were also observed. The magnetic moments decrease both with increasing particle size and with decreasing particle separation. A rapid decrease in the magnetic moments was observed with increasing simple temperature, due to intra-particle disorder of the atomic magnetic moments. At 40K, the total magnetic moment per atom is comparable to the bulk value, although the ratio morb/mspin is enhanced compared to the bulk even at this temperature. The remanent magnetisation of the deposited Fe particles was found to decrease steadily with increasing temperature due to superparamagnetic relaxation. Measured blocking temperatures of 6-9K indicate that the effective magnetic anisotropy constant of 2nm Fe particles is enhanced by around a factor 10 compared to the bulk value. The perturbations introduced by capping deposited Fe particles with a Co overlayer were also investigated using XMCD. The Fe-Co interface was found to result in a 7% increase in mspin per Fe atom, a 20% decrease in morb, and a magnetic anisotropy strongly favouring in-plane magnetisation. X-ray photoemission measurements showed that the deposited Fe particles were largely free from contaminants. Magnetic dichroism effects in XPS provided a corroboration of the XMCD results, and showed that an ultrathin Pd overlayer strong reduces the remanent magnetisation of a 60A Fe cluster-assembled film.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available