Disordered chromite in the Martian meteorite Allan Hills 84001 |
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Authors: | H P Gunnlaugsson C Bender Koch K Bharuth-Ram M Dietrich Ö Helgason M B Madsen R Mantovan D Naidoo S Steinthorsson L Vistisen G Weyer |
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Institution: | 1. Instituto de Física, Universidade de S?o Paulo, S?o Paulo, Brazil 2. Complex Fluids Group, Instituto de Física, Universidade de Brasília, Brasília, Brazil 3. Complex Fluids Group, Instituto de Química, Universidade de Brasília, Brasília, Brazil 4. Laboratoire Liquides Ioniques et Interfaces Chargées, Université Pierre et Marie Curie, Paris, France
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Abstract: | The magnetic structure of NiFe2O4 nanoparticles has been investigated by means of Mössbauer spectra at T?=?4.2 K in applied fields up to 12 T. Four samples were studied, with mean particle diameters ranging from 4.3 to 8.9 nm. All spectra could be decomposed into three sextets, two corresponding to the ferrimagnetic sublattices of Fe ions in the spinel structure (core) and the third one to randomly frozen spins near the particle surface (shell). The shell thickness, calculated from the fraction of disordered spins, was found to be about one-third of the particle radius at H app?=?0 and to decrease with the applied field toward a common limit of ~0.4 nm. The mean canting angle relative to the field was also found to decrease for increasing fields, at a rate inversely correlated to the particle size. |
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