Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001geoji.144..481d&link_type=abstract
Geophysical Journal International, Volume 144, Issue 2, pp. 481-494.
Astronomy and Astrophysics
Astronomy
13
Haematite, Maghemite, Rock Magnetism, Thermomagnetic Analysis
Scientific paper
The formation of traces of a magnetic phase with a Curie point of 470-475°C is detected during routine thermomagnetic analysis of various haematite types without significant isomorphous substitution. Using heating and cooling rates of 10°min-1, the formation temperature can be as low as 400°C for synthetic haematite samples, whereas higher temperatures, 700-800°C, are required for natural samples. The new phase appears to be persistent to prolonged heating at 1000°C and has a cubic spinel structure with a unit cell length a0=0.8350+/-0.0005nm, similar to pure maghemite. This suggests that the reverse reaction of the γ-Fe2O3->α- Fe2O3 transformation can occur under appropriate conditions. The low Tc of this particular maghemite variety suggests that the vacancy (and/or cation) ordering over the magnetic sublattices is different from usually occurring maghemite. In accordance with Takei & Chiba (1966), who also reported a pure maghemite variety with identical Tc, a cation-deficient spinel structure with part of the vacancies on tetrahedral sites is suggested. Thermally activated release of incorporated hydroxyl groups would trigger the formation of maghemite traces on the surface of well-crystalline haematite planes. Citrate-bicarbonate-dithionite extraction results support the idea that the maghemite is fine-grained and surficial on the haematite because low-field susceptibility values decrease according to the behaviour of fine-grained maghemite particles. The formation of traces of this highly magnetic mineral during routine stepwise thermal demagnetization or during annealing haematite at high temperatures may seriously affect NRM measurements or may be erroneously taken as haematite's defect moment.
de Boer Cor B.
Dekkers Mark J.
No associations
LandOfFree
Unusual thermomagnetic behaviour of haematites: neoformation of a highly magnetic spinel phase on heating in air does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Unusual thermomagnetic behaviour of haematites: neoformation of a highly magnetic spinel phase on heating in air, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Unusual thermomagnetic behaviour of haematites: neoformation of a highly magnetic spinel phase on heating in air will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1211397