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Crystallographic—magnetic correlations in single-crystal haemo-ilmenite : new evidence for lamellar magnetism

Title data

Robinson, P. ; Heidelbach, Florian ; Hirt, A. M. ; McEnroe, S. A. ; Brown, L. L.:
Crystallographic—magnetic correlations in single-crystal haemo-ilmenite : new evidence for lamellar magnetism.
In: Geophysical Journal International. Vol. 165 (April 2006) Issue 1 . - pp. 17-31.
ISSN 1365-246X
DOI: https://doi.org/10.1111/j.1365-246X.2006.02849.x

Abstract in another language

17 single crystals were identified by electron backscatter diffraction (EBSD) and isolated from coarse massive haemo-ilmenite ore from South Rogaland, Norway. These were studied using the EBSD results, natural remanent magnetization (NRM), and anisotropy of magnetic susceptibility (AMS), to gain a better understanding of angular relationships between crystallographic axes and magnetic properties of haemo-ilmenite in relation to lamellar magnetism. Electron microprobe analyses gave the following average end-member compositions for ilmenite host: 21.1 per cent MgTiO3, 73.7 FeTiO3, 0.5 MnTiO3, 4.3 Fe2O3, 0.2 Cr2O3 and 0.3 V2O3; and for the coarsest (∼3 μm) haematite exsolution lamellae: 3.5 MgTiO3, 22.4 FeTiO3, 71.4 Fe2O3, 1.6 Cr2O3, 1.0 V2O3 and 0.1 Al2O3, making this sample the most Mg- and Cr-rich haemo-ilmenite studied in the province, but with similar element fractionations between the coexisting phases. TEM work on similar material suggests the presence of much thinner exsolution down to 1–2 nm.The EBSD, NRM and AMS results from 12 out of 17 crystals indicate a good agreement between the orientation of crystallographic axes, NRM direction and principal axes of the magnetic susceptibility ellipsoid, with the NRM located in the (0001) basal plane NRM ∧ (0001) < 6.5° and the crystallographic c axis quasi-parallel to the minimum axis of the susceptibility ellipsoid c∧ k3 < 13.5°. In addition, in 10 of these 12 crystals, the remanent magnetization vector is parallel or nearly parallel to the positive direction of a crystallographic a axis NRM ∧a < 20°, hence parallel to a principal magnetic moment direction in haematite as determined by Besser, and not parallel to the spin-canted direction of end-member haematite. This is consistent with a basic property of lamellar magnetism, where the magnetic moment is parallel to the principal moments (sublattice magnetization directions) in haematite. Relationships in three additional crystals with NRM ∧a= 22°–33°, only two with good agreement, can be interpreted as consistent with having a magnetic vector quasi-parallel to the spin-canted direction of haematite.

Further data

Item Type: Article in a journal
Refereed: Yes
Keywords: anisotropy of magnetic susceptibility; electron backscatter diffraction; haematite; haemo-ilmenite; lamellar magnetism; natural remanent magnetization
Institutions of the University: Research Institutions > Research Centres > Bavarian Research Institute of Experimental Geochemistry and Geophysics - BGI
Result of work at the UBT: Yes
DDC Subjects: 500 Science > 550 Earth sciences, geology
Date Deposited: 03 Nov 2020 13:12
Last Modified: 03 Nov 2020 13:12
URI: https://eref.uni-bayreuth.de/id/eprint/58862