BiMnO_3的铁电铁磁机制,轨道有序和自旋有序的第一原理

First-principles investigation on magnetoelectric mechanism,orbital ordering and spin ordering of BiMnO_3

为了探讨多铁材料铁电畸变的根本机制及其电子结构对于性能的影响,采用基于密度泛函理论的广义梯度近似方法,对多铁材料BiMnO3的高温顺电顺磁相、室温铁电顺磁相和低温铁电铁磁相的电子结构做了第一原理计算.对态密度、电子密度以及Mulliken电荷等计算结果的分析表明:Bi-6p轨道与O-2p轨道间的选择性共价作用增强是铁电畸变的首要引发因素,6s电子的极化也是其导致的效应之一.对与多铁现象共生的轨道有序和自旋有序的研究指出了去中心化的晶格畸变、Jahn-Teller畸变和自旋失措引发的晶格畸变三者之间的相互耦合以及耦合对铁电铁磁性的影响.

To investigate the mechanisms of ferroelectric distortion and the effect of electronic structure on properties of multiferroic material, the electronic properties of muhiferroic BiMnO3 with paraelectric paramagnetic phase at high temperature, ferroelectric paramagnetic phase at room temperature and ferroelectric ferromagnetic phase at low temperature were calculated using density functional theory with spin-polarized generalized-gradient approximation （GGS） method. The analyses on density of states, electron density and Mulliken population show that the reason for off-center displacement is the strong covalent bonding between Bi-6p and O-2p states selectively and orientedly, which also drives the polarization of Bi-6s lone-pair electrons. Furthermore, orbital ordering and spin ordering coexisting with muhiferroic effect were investigated. The coupling among off-center distortion, Jahn-Teller distortion and spin frustration was revealed and its effects on ferroelectric and ferromagnetic was reported.