Abstract
On the basis of first-principles calculations we show that the M-type hexaferrite BaFe12O19 exhibits frustrated antiferroelectricity associated with its trigonal bipyramidal Fe3+ sites. The ferroelectric (FE) state of BaFe12O19, reachable by applying an external electric field to the antiferroelectric (AFE) state, can be made stable at room temperature by appropriate element substitution or strain engineering. Thus M-type hexaferrite, as a new type of multiferoic with coexistence of antiferroelectricity and ferrimagnetism, provide a basis for studying the phenomenon of frustrated antiferroelectricity and realizing multiple state memory devices.
Highlights
On the basis of first-principles calculations, we show that the M-type hexaferrite BaFe12O19 exhibits frustrated antiferroelectricity associated with its trigonal bipyramidal Fe3þ sites
The trigonal bipyramidal (TBP) Fe3þ ion lies on the equatorial plane of
The x-ray-diffraction study at room temperature [12] suggested that the Fe3þ ion is displaced out of the equatorial mirror plane by about 0.16 Å, which was supported by a Mössbauer study [13]
Summary
A comprehensive first-principles study to resolve this controversy and reveal that the M-type hexaferrite. Contrary to the conclusion of the empirical rigid-ion model [15], our calculations show the presence of two unstable modes in the whole Brillouin zone of the phonon dispersion [Fig. 1(b)], providing clear evidence for the structural instability in BaFe12O19. The energies (EDFT) of the five states from the density functional theory (DFT) calculations aPrehi;jcioEmiDjDpIariend with Fig. 2, their total DDI energies EDDI 1⁄4 which reveals that the DFT results are very well described by the DDI model This is probably because the dipoles associated with the displacement of the TBP Fe3þ ions are well separated from each other, so the short-range interactions between the dipoles are not important, unlike the case of traditional FE systems (e.g., BaTiO3) [17].
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