Inorg Chem. 2018 Sep 4;57(17):10616-10624. doi: 10.1021/acs.inorgchem.8b01253. Epub 2018 Aug 14.
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.
同时具有磁有序和铁电有序且在室温以上稳定存在的多铁材料很少见。本研究使用第一性原理密度泛函理论计算表明，对于 A 和 A'分别具有+3 和+2 氧化态且具有层状有序的氧空位 AA'FeO 钙钛矿，氟化是获得室温多铁性的有效策略。研究表明，通过控制 A 和 A'阳离子的大小，可以稳定由于混合赝铁电机制引起的非中心对称相，其极化高达 13 μC/cm。氟化还稳定了+3 价的 Fe，从而产生足以在室温以上很好地维持磁有序的超交换相互作用。本研究还表明存在磁电耦合，其中反转自发极化方向的切换模式也会影响磁相互作用的强度。结果表明，具有层状阳离子有序的阴离子空位钙钛矿的低温氟化可能是设计新型多铁材料的有效途径。
