期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 106, 期 14, 页码 5508-5512出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0808549106
关键词
spin ordering; electrical conductivity; high pressure; phase transition
资金
- Consortium for Materials Properties Research in Earth Sciences [EAR 06-49658]
- DOE
- Office of Science
- Office of Basic Energy Sciences [DE-AC02-06CH11357]
Recent studies have shown that high pressure (P) induces the metallization of the Fe2+-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 (Fe2O3) is an important magnetic carrier mineral for deciphering planetary magnetism and a proxy for Fe in the planetary interiors. Here, we present synchrotron Mossbauer spectroscopy and X-ray diffraction combined with ab initio calculations for Fe2O3 revealing the destruction of magnetic ordering at the hematite -> Rh2O3-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 Fe3+ ions transform from LS to HS and Fe2O3 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.
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