Other
Scientific paper
Jun 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000geoji.141..809d&link_type=abstract
Geophysical Journal International, Volume 141, Issue 3, pp. 809-819.
Other
25
Alteration, Greigite, Hydrothermal Synthesis, Magnetic Properties
Scientific paper
The magnetic behaviour of hydrothermally synthesized greigite was analysed in the temperature range from 4K to 700°C. Below room temperature, hysteresis parameters were determined as a function of temperature, with emphasis on the temperature range below 50K. Saturation magnetization and initial susceptibility were studied above room temperature, along with X-ray diffraction analysis of material heated to various temperatures. The magnetic behaviour of synthetic greigite on heating is determined by chemical alteration rather than by magnetic unblocking. Heating in air yields more discriminative behaviour than heating in argon. When heated in air, the amount of oxygen available for reaction with greigite determines the products and magnetic behaviour. In systems open to contact with air, haematite is the final reaction product. When the contact with air is restricted, magnetite is the final reaction product. When air is excluded, pyrrhotite and magnetite are the final reaction products; the amount of magnetite formed is determined by the purity of the starting greigite and the degree of its surficial oxidation. The saturation magnetization of synthetic greigite is virtually independent of temperature from room temperature down to 4K. The saturation remanent magnetization increases slowly by 20-30 per cent on cooling from room temperature to 4K. A broad maximum is observed at ~10K which may be diagnostic of greigite. The coercive and remanent coercive force both increase smoothly with decreasing temperature to 4K. The coercive force increases from ~50mT at room temperature to approximately 100-120mT at 4K, and the remanent coercive force increases from approximately 50-80mT at room temperature to approximately 110-180mT at 4K.
Dekkers Mark J.
Passier Hilde F.
Schoonen Martin A. A.
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