Co-existence of ferroelectricity and ferromagnetism in 1.4 nm SrBi2Ta2O11 film

M. H. Tsai, Y. H. Tang, Sandwip Dey

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7 Scopus citations


In pseudo-tetragonal strontium bismuth tantalate, SrBi2Ta2O9 (SBT), with two formula units per unit cell, bismuth oxide {(Bi2O2)2+} layers alternate with double strontium tantalate perovskite layers {(SrTa2O7)2-}. A unit cell of SBT is truncated to form a sub-cell or film, of composition SrBi2Ta2O11, which is 1.4 nm thick and comprised of a bottom (BiO2)1+ layer, a central (SrTa2O7)2- layer and a top (BiO2)1+ layer. Using spin-polarized first-principles calculations, it is found that this SrBi2Ta2O11 film is multi-ferroic, magnetoelectric, i.e. it simultaneously exhibits ferroelectric and ferromagnetic characteristics. When Ta ions are collectively displaced in the ab plane and in the [110] direction, the calculated double potential energy well, with a depth of -3.1 eV/unit cell at a Ta off-centre displacement of 0.032 nm, reflects the ferroelectric character. The calculated spin-polarized electronic structure reveals that ferromagnetism stems, not from the d electrons of the Ta ions, but predominantly from the unpaired p electrons of the O ions. The O ions in the Sr-O layer have the largest magnetic moment of 1.32 μB. Specifically, the ferromagnetic character is mediated by the unoccupied states of the Sr 5p band above the Fermi level, EF. These states provide a mechanism for the double exchange or hopping of highly localized O 2p (majority) spins between adjacent O ions located on both sides of the Sr ion.

Original languageEnglish (US)
Pages (from-to)7901-7915
Number of pages15
JournalJournal of Physics Condensed Matter
Issue number46
StatePublished - Nov 26 2003

ASJC Scopus subject areas

  • General Materials Science
  • Condensed Matter Physics


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