Zhang Guangbiao, Wang Yuanxu, Cheng Zhenxiang, Yan Yuli, Peng Chengxiao, Wang Chao, Dong Shuai
Institute for Computational Materials Science, School of Physics and Electronics, Henan University, Kaifeng, 475004, People's Republic of China.
Phys Chem Chem Phys. 2015 May 21;17(19):12717-21. doi: 10.1039/c5cp00186b.
We have investigated the structural, electronic, and magnetic properties of A-site-ordered double-perovskite-structured oxides, AA'3B4O12 (A = Na, Ca, and La) with Mn and V at A' and B sites, respectively, using first-principle calculations based on the density functional theory. Our calculation results show that the antiferromagnetic phase is the ground state for all the compounds. By changing the A-site ions from Na(+) to Ca(2+) and then to La(3+), the transfer of charge between Mn and O ions was changed from 1.56 to 1.55 and then to 1.50, and that between the V and O ions changed from 2.01 to 1.95 and then to 1.93, revealing the cause for the unusual site-selective doping effect. Mn 3d electrons dominate the magnetic moment and are localized, with an intense hybridization with O 2p orbitals, which indicates that the magnetic exchange interaction between Mn ions is mediated through O and that the super exchange mechanism will take effect. These materials have a large one-electron bandwidth W, and the ratio of the on-site Coulomb repulsion U to W is less than the critical value (U/W)c, which leads to metallic behavior of AMn3V4O12. This is further evidenced by the large number of free electrons contributed by V at the Fermi surface. These calculations, in combination with the reported experimental data, prove that these double perovskites belong to the rare antiferromagnetic metallic oxides.
我们基于密度泛函理论，通过第一性原理计算，研究了A位有序的双钙钛矿结构氧化物AA'3B4O12（A = Na、Ca和La）在A'和B位分别为Mn和V时的结构、电子和磁性性质。我们的计算结果表明，反铁磁相是所有化合物的基态。通过将A位离子从Na(+)变为Ca(2+)，再变为La(3+)，Mn与O离子之间的电荷转移从1.56变为1.55，再变为1.50，V与O离子之间的电荷转移从2.01变为1.95，再变为1.93，揭示了异常的位点选择性掺杂效应的原因。Mn 3d电子主导磁矩且局域化，与O 2p轨道有强烈杂化，这表明Mn离子之间的磁交换相互作用是通过O介导的，超交换机制将起作用。这些材料具有较大的单电子带宽W，且在位库仑排斥能U与W的比值小于临界值(U/W)c，这导致AMn3V4O12呈现金属行为。费米面上V贡献的大量自由电子进一步证明了这一点。这些计算结果与已报道的实验数据相结合，证明这些双钙钛矿属于罕见的反铁磁金属氧化物。
