Wang W, Yan L-Q, Cong J-Z, Zhao Y-L, Wang F, Shen S-P, Zou T, Zhang D, Wang S-G, Han X-F, Sun Y
State Key Laboratory of Magnetism and Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, P R of China.
Sci Rep. 2013;3:2024. doi: 10.1038/srep02024.
Although the magnetoelectric effects - the mutual control of electric polarization by magnetic fields and magnetism by electric fields, have been intensively studied in a large number of inorganic compounds and heterostructures, they have been rarely observed in organic materials. Here we demonstrate magnetoelectric coupling in a metal-organic framework [(CH3)2NH2]Mn(HCOO)3 which exhibits an order-disorder type of ferroelectricity below 185 K. The magnetic susceptibility starts to deviate from the Curie-Weiss law at the paraelectric-ferroelectric transition temperature, suggesting an enhancement of short-range magnetic correlation in the ferroelectric state. Electron spin resonance study further confirms that the magnetic state indeed changes following the ferroelectric phase transition. Inversely, the ferroelectric polarization can be improved by applying high magnetic fields. We interpret the magnetoelectric coupling in the paramagnetic state in the metal-organic framework as a consequence of the magnetoelastic effect that modifies both the superexchange interaction and the hydrogen bonding.
尽管磁电效应——磁场对电极化以及电场对磁性的相互控制——已在大量无机化合物和异质结构中得到深入研究，但在有机材料中却很少被观察到。在此，我们展示了金属有机框架化合物[(CH3)2NH2]Mn(HCOO)3中的磁电耦合现象，该化合物在185 K以下呈现出有序-无序型铁电性。在顺电-铁电转变温度下，磁化率开始偏离居里-外斯定律，这表明在铁电态下短程磁关联增强。电子自旋共振研究进一步证实，磁态确实随铁电相变而变化。反之，施加高磁场可改善铁电极化。我们将金属有机框架顺磁态中的磁电耦合解释为磁弹性效应的结果，这种效应同时改变了超交换相互作用和氢键。
