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Title: Magnetic properties of nano-scale hematite, α-Fe{sub 2}O{sub 3}, studied by time-of-flight inelastic neutron spectroscopy

Samples of nanoscale hematite, α-Fe{sub 2}O{sub 3}, with different surface geometries and properties have been studied with inelastic time-of-flight neutron scattering. The 15 nm diameter nanoparticles previously shown to have two collective magnetic excitation modes in separate triple-axis neutron scattering studies have been studied in further detail using the advantage of a large detector area, high resolution, and large energy transfer range of the IN5 TOF spectrometer. A mesoporous hematite sample has also been studied, showing similarities to that of the nanoparticle sample and bulk α-Fe{sub 2}O{sub 3}. Analysis of these modes provides temperature dependence of the magnetic anisotropy coefficient along the c-axis, κ{sub 1}. This is shown to remain negative throughout the temperature range studied in both samples, providing an explanation for the previously observed suppression of the Morin transition in the mesoporous material. The values of this anisotropy coefficient are found to lie between those of bulk and nano-particulate samples, showing the hybrid nature of the mesoporous 3-dimensional structure.
Authors:
 [1] ; ; ;  [2] ;  [3] ;  [4] ;  [5] ; ;  [6] ;  [6] ;  [7]
  1. The European Synchrotron Radiation Facility, 6 rue Jules Horowitz, BP220, 38043 Grenoble Cedex 9 (France)
  2. Nanoscience Centre, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen (Denmark)
  3. Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot OX11 OQX (United Kingdom)
  4. Department of Chemical Engineering, University of Delaware, Center for Catalytic Science and Technology, 150 Academy Street, Newark, Delaware 19716-3110 (United States)
  5. Department of Energy Conversion and Storage, Technical University of Denmark, Frederiksborgvej 399, DK-4000 Roskilde (Denmark)
  6. The Institute Laue-Langevin, 6 rue Jules Horowitz, BP156, 38042 Grenoble Cedex 9 (France)
  7. (United Kingdom)
Publication Date:
OSTI Identifier:
22255209
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 140; Journal Issue: 4; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ANISOTROPY; ENERGY TRANSFER; EXCITATION; FERRITES; HEMATITE; IRON OXIDES; MAGNETIC PROPERTIES; NANOSTRUCTURES; NEUTRON DIFFRACTION; NEUTRON SPECTROSCOPY; PARTICLES; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE