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| Titel |
High-field magnetic characterization of natural and synthetic nanostructures in ilmenite-hematite samples |
| VerfasserIn |
Karl Fabian, Christopher I. Thomas, Suzanne A. McEnroe, Peter Robinson, Hiroki Mukai, Joseph Law, Richard Harrison |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250095006
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| Publikation (Nr.) |
 EGU/EGU2014-10444.pdf |
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| Zusammenfassung |
| Natural rocks containing exsolved hemo-ilmenite or ilmeno-hematite, or minerals from the
hematite-ilmenite solid solution series are known to show extreme magnetic properties.
Amongst them are strong exchange bias, high remanence combined with low magnetic
susceptibility, and extremely high coercivity. Experiments within magnetic fields up to 7T
commonly indicate that these materials are not even close to magnetic saturation in this
field range. To obtain a reliable physical understanding of these phenomena, the
magnetization of a series of synthetic quenched and annealed metastable ferri-ilmenite solid
solutions and several naturally exsolved samples, showing lamellar magnetism, were
measured in fields up to 60T in the Dresden High Magnetic Field Laboratory (HLD).
Magnetization change is measured by integrating the voltage induced in a secondary coil
during the primary field pulse lasting 6 ms, and then subtracting a corresponding
background signal from a pulse with an empty holder. The voltage signal is individually
calibrated by comparison to PPMS/MPMS measurements on the same samples. In the
synthetic samples, saturation field and critical exponent of the approach-to-saturation
law depend primarily on the degree of order Q as inferred from Bloch’s law, or a
mean-field model of Ms(T) curves. Details of the approach-to-saturation curves relate to
the nanoscale microstructure of antiphase domains evolved during incremental
ordering. The metamagnetic transition of ilmenite is visible in natural ilmenite
and in a ferri-ilmenite solid solution containing 97% ilmenite. Most remarkably,
it also occurs in natural exsolved titanohematite samples, which show exchange
bias at low temperature. This provides additional evidence for the crucial role of
nanoscale ilmenite lamellae for the unusual magnetic properties of these minerals. |
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