Multiferroism in Iron-Based Oxyfluoride Perovskites

Abstract

Multiferroic materials with simultaneous magnetic and ferroelectric ordering that persist above room temperature are rare. Using first-principles density functional theory calculations, we demonstrate fluorination of oxygen-deficient AA'FeO perovskites, where A and A' are cations with +3 and +2 oxidation states, respectively, and have a layered ordering, as an effective strategy to obtain room-temperature multiferroics. We show that by controlling the size of the A and A' cations, it is possible to stabilize a noncentrosymmetric phase arising due to the hybrid improper ferroelectricity mechanism, with polarization as high as 13 μC/cm. The fluorination also stabilizes Fe in +3 oxidation state, which results in superexchange interactions that are strong enough to sustain magnetic order well above room temperature. We also show the presence of a magnetoelectric coupling wherein the switching mode that reverses the direction of the spontaneous polarization also affects the strength of the magnetic interactions. The results show that low-temperature fluorination of anion-deficient perovskites with layered cation ordering can be an effective approach to design new multiferroics.

Multiferroism Induced by Spontaneous Structural Ordering in Antiferromagnetic Iron Perovskites

“…Besides, stabilization of Fe 3+ within the structure can provide strong superexchange interactions to sustain magnetic ordering above room temperature, as for instance in YBaFe 2 O 5 , 21 YFeO 3 , 22 and LaCa 2 Fe 3 O 8 . 23 The combination of these properties of iron can result in multiferroism, as it has been recently suggested for the layered perovskite YCaFe 2 O 5 F. 17 First-principle density functional theory calculations support strong polarization and robust magnetic ordering above room temperature in YCaFe 2 O 5 F; besides, the possibility of preparing this material by a layer-by-layer growth technique capable of imposing Y and Ca ordering has been suggested.…”

“…Despite this, there are ways to combine magnetism and ferroelectricity in perovskites such as BiFeO 3 , in which magnetic ordering is associated with Fe, but the Bi lone-pair is responsible for the ferroelectric behavior . Although ferromagnetism is usually the type of magnetic ordering occurring in magnetoelectric–multiferroic perovskites, the combination of ferroelectricity and antiferromagnetism has been predicted in the orthorhombic BaMnO 3 and in YCaFe 2 O 5 F . Layered-type ordering of different A-cations coupled with particular octahedral tilting systems of the anion sublattice results in non-centrosymmetric polar perovskites. , A more recent approach consisting of the combination of cation ordering with anion-vacancy ordering to generate polar structures has been demonstrated on epitaxially grown SrFeO 2.5 /CaFeO 2.5 thin-film superlattices .…”

Theoretical Investigation of the Role of the Nitride Ion in the Magnetism of Oxynitride MnTaO2N

“…This is probably derived from lower electron density of Mn–O bonds in MnTaO 2 N than that in MnTiO 3 due to higher electronegativity of the O 2– ions as compared to the N 3– ions. Positive correlation between J parameter and covalency has recently been confirmed in oxyfluorides; the superexchange interaction is suppressed by substituting F for O due to the less covalency of metal–F bonds than metal–O bonds. − …”

Perovskite-like K3TiOF5 Exhibits (3 + 1)-Dimensional Commensurate Structure Induced by Octahedrally Coordinated Potassium Ions

“…This observation ultimately led to the conclusion that (NH 4 ) 3 MoO 3 F 3 exhibited a distorted crystal structure, and the oxide and fluoride ions formed a solid solution. Since then, oxyfluoride perovskites have remained of keen interest for their peculiar crystal chemistry and prospect for noncentrosymmetry. − Investigations that followed ultimately revealed that the [MO x F 6– x ] n– heteroleptic units in these perovskites exhibit local anion order. Weak interactions, however, among neighboring anionic groups led to long-range orientational disorder.…”