In-situ magnetic dichroism studies of supported Fe nanoparticles
thesisposted on 2014-12-15, 10:40 authored by Kevin William. Edmonds
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.
Date of award2000-01-01
Awarding institutionUniversity of Leicester