Pressure-induced coordination crossover in magnetite; the breakdown of the Verwey-Mott localization hypothesis

M. P. Pasternak, W. M. Xu, G. Kh Rozenberg, R. D. Taylor, R. Jeanloz

Research output: Contribution to journalArticlepeer-review

Abstract

Temperature-dependent 57Fe Mössbauer spectroscopy to 40GPa shows that Fe3O4 magnetite undergoes a coordination crossover (CC), whereby charge density is shifted from octahedral to tetrahedral sites and the spinel structure thus changes from inverse to normal with increasing pressure and decreasing temperature. A precursor to the CC is a d-charge decoupling within the octahedral sites at the inverse-spinel phase. The CC transition takes place almost exactly at the Verwey transition temperature (TV=122K) at ambient pressure. While TV decreases with pressure the CC-transition temperature increases with pressure, reaching 300K at 10GPa. The d electron localization mechanism proposed by Verwey and later by Mott for T<TV is shown to be unrelated to the actual mechanism of the metal-insulator transition attributed to the Verwey transition. It is proposed that a first-order phase transition taking place at ∼TV at ambient pressure opens a small gap within the oxygen p-band, resulting in the observed insulating state at T>TV.

Original languageEnglish
Pages (from-to)L107-L112
JournalJournal of Magnetism and Magnetic Materials
Volume265
Issue number2
DOIs
StatePublished - Sep 2003

Keywords

  • High pressure
  • Mössbauer spectroscopy
  • Phase transition

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