论文标题
双双perovskite camncrsbo6中多宣传磁力和超级交流的起源
Origins of multi-sublattice magnetism and superexchange interactions in double-double perovskite CaMnCrSbO6
论文作者
论文摘要
我们已经部署了密度函数理论，Wannier功能分析和平均场计算，以研究双双钙钛矿化合物CAMNCRSBO_ {6}。单位细胞中的晶体非等效的Mn原子具有四面体和平面氧配位（标记为Mn（1）和Mn（2）），而CR原子位于扭曲的氧气氧气八人体的中心。虽然块状磁化和中子衍射表明MN2+和CR3+旋转之间的简单的铁磁顺序（T_C = 49 K），但交换相互作用比两个Sublattice磁系统所期望的更为复杂。电子结构的计算即使没有哈伯德u，也会产生铁磁性绝缘状态。被发现是铁磁。 Mn（2）-O-CR superexchange比Mn（1）-O-CR superexchange弱弱，因此有效地导致了铁磁性。根据简单的3个站点哈伯德模型，我们得出了反铁磁性superexchange强度J_AFM和较弱的铁磁J_FM的表达式。 JAFM对于各种超级交互的相对强度与从DFT获得的相一致。 CR-O-O-CR Super-Superexchange强度（J_SS）的表达（J_SS）是考虑到4个位点哈伯德模型的，它预测了与DFT一致的铁磁交换。最后，我们的平均场计算表明，假设MN2+旋转的四个磁性亚晶状体和CR3+旋转的单个磁性sublattice会产生大大改善的T_C，而简单的两个磁性Sublattice模型会产生更高的T_C。
We have deployed density functional theory, Wannier function analysis and mean-field calculations to investigate the double-double perovskite compound CaMnCrSbO_{6}. The crystallographically non-equivalent Mn atoms in the unit cell have tetrahedral and planar oxygen coordinations (labelled as Mn(1) and Mn(2)), while the Cr atom is in the centre of distorted oxygen octahedron. While the bulk magnetization and neutron diffraction suggest a simpler ferrimagnetic order (T_C=49 K) between Mn2+ and Cr3+ spins, the exchange interactions are more complex than that expected from a two sublattice magnetic system. The electronic structure calculations yield a ferrimagnetic insulating ground state even in absence of Hubbard U which persists for a wide range of U. The Mn(1)-O-Mn(2) (out of plane and in-plane), Mn(1)-O-Cr and Mn(2)-O-Cr superexchange interactions are found to be anti-ferromagnetic, while the Cr-O-O-Cr super-superexchange is found to be ferromagnetic. The Mn(2)-O-Cr superexchange is weaker than the Mn(1)-O-Cr superexchange, thus effectively resulting in ferrimagnetism. From a simple 3-site Hubbard model, we derived expressions for the antiferromagnetic superexchange strength J_AFM and the weaker ferromagnetic J_FM. The relative strengths of JAFM for the various superexchange interactions are in agreement with those obtained from DFT. The expression for Cr-O-O-Cr super-superexchange strength (J_SS), which is derived considering a 4-site Hubbard model, predicts a ferromagnetic exchange in agreement with DFT. Finally, our mean field calculations reveal that assuming a set of four magnetic sub-lattice for Mn2+ spins and a single magnetic sublattice for Cr3+ spins yields a much improved T_C, while a simple two magnetic sublattice model yields a much higher T_C.
