Crystallographic–magnetic correlations in single-crystal haemo-ilmenite: new evidence for lamellar magnetismGeophysical Journal International (2006)
Abstract17 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 ofmagnetic 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 haemoilmenite 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 et al., 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.
- Anisotropy of magnetic susceptibility; electron backscatter diffraction; haematite; haemo-ilmenite; lamellar magnetism; natural remanent magnetization
Publication DateApril, 2006
Citation InformationP. Robinson, F. Heidelbach, A. M. Hirt, S. A. McEnroe, et al.. "Crystallographic–magnetic correlations in single-crystal haemo-ilmenite: new evidence for lamellar magnetism" Geophysical Journal International Vol. 165 Iss. 1 (2006)
Available at: http://works.bepress.com/laurie_brown/6/