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See detailNoncollinear magnetism and single-ion anisotropy in multiferroic perovskites
Weingart, C.; Spaldin, N.; Bousquet, Eric ULg

in Physical Review. B, Condensed Matter and Materials Physics (2012), 86(9),

The link between the crystal distortions of the perovskite structure and the magnetic exchange interaction, the single-ion anisotropy (SIA), and the Dzyaloshinsky-Moriya (DM) interaction are investigated ... [more ▼]

The link between the crystal distortions of the perovskite structure and the magnetic exchange interaction, the single-ion anisotropy (SIA), and the Dzyaloshinsky-Moriya (DM) interaction are investigated by means of density functional calculations. Using BiFeO 3 and LaFeO 3 as model systems, we quantify the relationship between the oxygen octahedra rotations, the ferroelectricity, and the weak ferromagnetism (wFM). We recover the fact that the wFM is due to the DM interaction induced by the oxygen octahedra rotations. We find a simple relationship between the wFM, the oxygen rotation amplitude, and the ratio between the DM vector and the exchange parameter such that the wFM increases with the oxygen octahedra rotation when the SIA does not compete with the DM forces induced on the spins. Unexpectedly, we also find that in spite of the d5 electronic configuration of Fe3 +, the SIA is very large in some structures and is surprisingly strongly sensitive to the chemistry of the A-site cation of the ABO 3 perovskite. In the ground R3c state phase we show that the SIA shape induced by the ferroelectricity and the oxygen octahedra rotations are in competition such that it is possible to turn the wFM "on" and "off" through the relative size of the two types of distortion. © 2012 American Physical Society. [less ▲]

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See detailStrain-induced ferroelectricity in simple rocksalt binary oxides
Bousquet, Eric ULg; Spaldin, N.; Ghosez, Philippe ULg

in Physical Review Letters (2010), 104

Using first-principles density functional calculations, we show that ferroelectricity can be induced in simple alkaline-earth-metal binary oxides such as barium oxide (BaO) using appropriate epitaxial ... [more ▼]

Using first-principles density functional calculations, we show that ferroelectricity can be induced in simple alkaline-earth-metal binary oxides such as barium oxide (BaO) using appropriate epitaxial strains. Going beyond the fundamental discovery, we highlight that the functional properties (polarization, dielectric constant, and piezoelectric response) of such strained binary oxides are comparable in magnitude to those of typical ferroelectric perovskite oxides, making them of direct interest for applications. Finally, we show that magnetic binary oxides such as EuO, with the same rocksalt structure, behave similarly to the alkaline-earth-metal oxides, suggesting a route to new multiferroics combining ferroelectric and magnetic properties. [less ▲]

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