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

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

Research output: Contribution to journalArticle

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Abstract

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
Volume15
Issue number46
DOIs
StatePublished - Nov 26 2003

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Ferroelectricity
Ferromagnetism
ferroelectricity
ferromagnetism
Ions
Strontium
ions
Bismuth
cells
strontium
Ferroelectric materials
bismuth oxides
Electrons
Potential energy
Magnetic moments
Fermi level
stems
Perovskite
bismuth
Electronic structure

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Electronic, Optical and Magnetic Materials

Cite this

Co-existence of ferroelectricity and ferromagnetism in 1.4 nm SrBi2Ta2O11 film. / Tsai, M. H.; Tang, Y. H.; Dey, Sandwip.

In: Journal of Physics Condensed Matter, Vol. 15, No. 46, 26.11.2003, p. 7901-7915.

Research output: Contribution to journalArticle

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abstract = "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.",
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AB - 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.

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