School of Physics and Electronics, Central South University , Changsha 410083, People's Republic of China.
Inorg Chem. 2013 Nov 4;52(21):12529-34. doi: 10.1021/ic401615r. Epub 2013 Oct 23.
We have studied the electronic structures and magnetism of SrFeO2 under pressure by first-principles calculations in the framework of density functional theory (DFT) with GGA+U and HSE06 hybrid functionals, respectively. The pressure-induced spin transition from S = 2 to S = 1 and the antiferromagnetic-ferromagnetic (AFM-FM) transition observed in experiment are well reproduced by taking the site repulsion U and its pressure dependence into account. The electronic structure and its change with the pressure can be qualitatively understood in an ionic model together with the hybridization effects between the Fe 3d and O 2p states. It is found that the pressure leads to a change in Fe 3d electronic configuration from (d(z(2)))(2)(d(xz)d(yz))(2)(d(xy))(1)(d(x(2)-y(2)))(1) under ambient conditions to (d(z(2)))(2)(d(xz)d(yz))(3)(d(xy))(1)(d(x(2)-y(2)))(0) at high pressure. As a result, the spin state transits from S = 2 to S = 1 and both the antiferromagnetic intralayer Fe-O-Fe superexchange interaction and the interlayer Fe-Fe direction exchange coupling at ambient pressure become ferromagnetic at high pressure according to the Goodenough-Kanamori (G-K) rules. Additionally, our calculations predict another spin transition from S = 1 to S = 0 at pressures of about 220 GPa.
我们分别采用基于密度泛函理论（DFT）的广义梯度近似（GGA）+U 和 HSE06 杂化泛函，对 SrFeO2 在压力下的电子结构和磁性进行了第一性原理计算研究。考虑到局域排斥 U 及其压力依赖性，实验中观察到的自旋从 S=2 到 S=1 的转变以及反铁磁-铁磁（AFM-FM）转变得到了很好的重现。结合 Fe 3d 和 O 2p 态之间的杂化效应，我们可以用离子模型定性地理解电子结构及其随压力的变化。研究发现，压力导致 Fe 3d 电子构型从环境条件下的(d(z(2)))(2)(d(xz)d(yz))(2)(d(xy))(1)(d(x(2)-y(2)))(1)转变为高压下的(d(z(2)))(2)(d(xz)d(yz))(3)(d(xy))(1)(d(x(2)-y(2)))(0)。结果，自旋态从 S=2 转变为 S=1，根据古丁-坎纳姆（Goodenough-Kanamori，G-K）规则，反铁磁层内 Fe-O-Fe 超交换相互作用和环境压力下的层间 Fe-Fe 方向交换耦合都变为铁磁。此外，我们的计算预测在约 220 GPa 的压力下还会发生另一个从 S=1 到 S=0 的自旋转变。
