Department of Physics and Astronomy, West Virginia University , Morgantown, West Virginia 26506-6315, United States.
Physique Théorique des Matériaux, Université de Liège , B-4000 Sart-Tilman, Belgium.
ACS Appl Mater Interfaces. 2016 Feb 3;8(4):2694-703. doi: 10.1021/acsami.5b10814. Epub 2016 Jan 20.
Multiferroic materials have simultaneous magnetic and ferroelectric long-range orders and can be potentially useful for a wide range of applications. Conventional ferroelectricity in oxide perovskites favors nonmagnetic electronic configurations of transition metal ions, thus limiting the number of intrinsic multiferroic materials. On the other hand, this is not necessarily true for multiferroic fluorides. Using molecular beam epitaxy, we demonstrate for the first time that the multiferroic orthorhombic fluoride BaCoF4 can be synthesized in thin film form. Ferroelectric hysteresis measurements and piezoresponse force microscopy show that the films are indeed ferroelectric. From structural information, magnetic measurements, and first-principles calculations, a modified magnetic ground state is identified which can be represented as a combination of bulk collinear antiferromagnetism with two additional canted spin orders oriented along orthogonal axes of the BaCoF4 unit cell. The calculations indicate that an anisotropic epitaxial strain is responsible for this unusual magnetic ground state.
多铁材料具有同时的磁有序和铁电长程有序，可潜在应用于广泛的领域。传统的钙钛矿氧化物中的铁电性有利于过渡金属离子的非磁性电子组态，从而限制了本征多铁材料的数量。另一方面，多铁氟化物则不一定如此。我们首次通过分子束外延证明，多铁正交氟化物 BaCoF4 可以以薄膜形式合成。铁电滞后测量和压电力显微镜表明，这些薄膜确实具有铁电性。从结构信息、磁性测量和第一性原理计算中，确定了一种经过修正的磁性基态，它可以表示为体顺磁反铁磁性与另外两个沿 BaCoF4 单元的正交轴倾斜的自旋有序的组合。计算表明，各向异性外延应变是造成这种异常磁性基态的原因。
