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| Titel |
Grain Size and Field Dependence of the Morin Transition and Mössbauer Spectroscopy of Synthetic Hematite |
| VerfasserIn |
M. W. R. Volk, R. Egli, S. Gilder |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063733
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| Zusammenfassung |
| Hematite is a common magnetic mineral occurring in sediments, both in detrital and
authigenic form. The dependence of its magnetic properties on grain size and particle surface
are not yet fully understood. Here we present a systematic investigation of magnetic
properties of synthetic hematite particles (14 nm, 22 nm, 34 nm, 147 nm, 11 μm) across the
so-called Morin transition, focusing on the transition temperature and amplitude, transition
hysteresis, and defect moment remaining in the antiferromagnetic phase below the transition
temperature.
While hysteresis parameters above and below the Morin transition did not show
well-defined systematic grain size trends, we found a clear relation between grain
size, applied field, and transition temperature along with results shown by previous
studies. The field dependence of the transition was found to be stronger in smaller
particles.
We measured Mössbauer spectra at room and low temperatures, finding a clear grain size
dependence of Mössbauer parameters. We also found a second sextet in the smallest
particles, whose relative contribution is inversely proportional to the size of the
sample.
The hyperfine field - the magnetic field at the Fe3+ atom in the lattice - decreases with
decreasing grain size. We also found a linear correlation between the transition temperature
and the magnetic hypefine field. |
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