Electronic and magnetic structures of the postperovskite-type Fe2O3 and implications for planetary magnetic records and deep interiors.
Recent studies have shown that high pressure (P) induces the metallization of the Fe(2+)-O bonding, the destruction of magnetic ordering in Fe, and the high-spin (HS) to low-spin (LS) transition of Fe in silicate and oxide phases at the deep planetary interiors. Hematite (Fe(2)O(3)) is an important magnetic carrier mineral for deciphering planetary magnetism and a proxy for Fe in the planetary interiors. Here, we present synchrotron Mössbauer spectroscopy and X-ray diffraction combined with ab initio calculations for Fe(2)O(3) revealing the destruction of magnetic ordering at the hematite --> Rh(2)O(3)-II type (RhII) transition at 70 GPa and 300 K, and then the revival of magnetic ordering at the RhII --> postperovskite (PPv) transition after laser heating at 73 GPa. At the latter transition, at least half of Fe(3+) ions transform from LS to HS and Fe(2)O(3) changes from a semiconductor to a metal. This result demonstrates that some magnetic carrier minerals may experience a complex sequence of magnetic ordering changes during impact rather than a monotonic demagnetization. Also local Fe enrichment at Earth's core-mantle boundary will lead to changes in the electronic structure and spin state of Fe in silicate PPv. If the ultra-low-velocity zones are composed of Fe-enriched silicate PPv and/or the basaltic materials are accumulated at the lowermost mantle, high electrical conductivity of these regions will play an important role for the electromagnetic coupling between the mantle and the core.
Shim
Sang-Heon
SH
Department of Earth, Atmospheric, and Planetary Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA. sangshim@mit.edu
Bengtson
Amelia
A
Morgan
Dane
D
Sturhahn
Wolfgang
W
Catalli
Krystle
K
Zhao
Jiyong
J
Lerche
Michael
M
Prakapenka
Vitali
V
D004553:Electric Conductivity; D005290:Ferric Compounds / Q000737:chemistry*; D008280:Magnetics; D008958:Models, Molecular; D016083:Planets; D011312:Pressure; D015204:Spectroscopy, Mossbauer; D014961:X-Ray Diffraction
D005290:Ferric Compounds; C000499:ferric oxide