High temperature Mössbauer spectroscopy of titanomagnetite and maghemite in basalts
Mössbauer spectroscopy of basalt lava samples, exhibiting reversible thermal magnetization (J s -T) curves with Curie temperatures of about 840 K, has revealed considerable amounts of maghemite (γ-Fe2O3) in many samples. In view of the expected instability of maghemite at temperatures above 620 K, this reversibility came as a surprise. For further studies of the magnetization-temperature relationship of these minerals, we have constructed an elliptical radiation-heated furnace in which Mössbauer spectra can be acquired at temperatures between 300 and 900 K. Measurements at different temperatures have been obtained for two types of basalts, one in which the magnetic minerals are nearly pure magnetite and the other where the room temperature spectrum indicates a mixture of maghemite and magnetite. The two series show different features of the collapse of the internal magnetic hyperfine field, and the composition of minerals in the samples changes during the treatment, showing maghemite.
KeywordsSpectroscopy Thin Film Furnace Magnetite Curie Temperature
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