Spin state of iron in Fe3O4 magnetite and h-Fe3O4
Abstract
The high-pressure behavior of magnetite has been widely debated in the literature. Experimental measurements have found conflicting high-pressure transitions: a charge reordering in magnetite from inverse-spinel to normal-spinel [Pasternak , J. Phys. Chem. Solids0022-369710.1016/j.jpcs.2003.12.013 65, 1531 (2004); Rozenberg , Phys. Rev. B10.1103/PhysRevB.75.020102 75, 020102 (2007)], iron high-spin to intermediate-spin transition in magnetite [Ding , Phys. Rev. Lett.0031-900710.1103/PhysRevLett.100.045508 100, 045508 (2008)], electron delocalization in magnetite [Baudelet , Phys. Rev. B1098-012110.1103/PhysRevB.82.140412 82, 140412 (2010); Glazyrin , Am. Mineral.0003-004X10.2138/am.2011.3862 97, 128 (2012)], and a structural phase transition from magnetite to h-Fe3O4 [Dubrovinsky , J. Phys.: Condens. Matter0953-898410.1088/0953-8984/15/45/009 15, 7697 (2003); Fei , Am. Mineral. 84, 203 (1999); Haavik , Am. Mineral. 85, 514 (2000)]. We present ab initio calculations of iron's spin state in magnetite and h-Fe3O4, which help resolve the high-pressure debate. The results of the calculations find that iron remains high spin in both magnetite and h-Fe3O4; intermediate-spin iron is not stable. In addition, magnetite remains inverse-spinel but undergoes a phase transition to h-Fe3O4 near 10 GPa. Magnetite has a complex magnetic ordering, multiple valence states (Fe2+ and Fe3+), charge ordering, and different local Fe site environments, all of which were accounted for in the calculations. The lack of intermediate-spin iron in magnetite helps resolve the spin state of iron in perovskite, the major mineral in the lower mantle. In both magnetite and perovskite, x-ray emission spectroscopy (XES) measurements in the literature show a drop in satellite peak intensity by approximately half, which is interpreted as intermediate-spin iron. In both minerals, calculations give no indication of intermediate-spin iron and predict high-spin iron to be stable for defect-free crystals. The results question the interpretation of a nonzero drop in XES satellite peak intensities as intermediate-spin iron.
- Publication:
-
Physical Review B
- Pub Date:
- April 2013
- DOI:
- 10.1103/PhysRevB.87.155141
- Bibcode:
- 2013PhRvB..87o5141B
- Keywords:
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- 32.10.Dk;
- 75.30.Kz;
- 75.25.Dk;
- Electric and magnetic moments polarizability;
- Magnetic phase boundaries