双钙钛矿Sr_2CoReO_6的电子结构与磁性

Electronic structures and magnetic properties of Sr_2CoReO_6

基于密度泛函理论(DFT)框架下的第一性原理,采用在广义梯度近似(GGA)下的投影缀加波势,研究了Sr2CoReO6的电子结构和磁性.结果表明:Co和Re原子的磁矩分别为2.425μB和-0.488μB,并通过O原子形成反铁磁耦合;Co2+的s和3个p轨道的占据和未占据态都远离费米能级,并有很小的自旋劈裂;而Re5+的s和3个p轨道的自旋向上和自旋向下态密度均几乎填满;Co/Re原子周围存在的O原子立方对称性的八面体,导致其d轨道劈裂为能量较高的三重简并态t2g(dxy,dyz和dzx)和能量较低的二重简并态eg(d2z和dx2-y2).最近邻的两个Co—Co或Re—Re原子对之间没有直接的相互作用;而沿着任一Co—O—Re—O—Co链或Re—O—Co—O—Re链,Co3d和4s,O 2s和2p以及Re 5p,5d和6s轨道间存在着杂化作用.

The electronic structures and magnetic properties of the double perovskite Sr2 CoReO6 have been studied using the first-principles method based on the density function theory （DFT） with the projector augmented wave （PAW） potentials of the generalized gradient approximation.The calculated results show that the magnetic moments of Co2＋ and Re5＋ are 2.425 μB and -0.488μB respectively,thus antiferromagnetic coupling is constructed via oxygen between them.Both occupied and unoccupied s and three p states of Co2＋ ion are located far from the Fermi level,while all up-spin states and most down-spin states are completely filled for the s and three p states of Re5＋ ion.The presence of the cubic symmetry of the octahedral coordination of the oxygen atoms around Co/Re site results in a splitting of the five-fold degenerate d states of a free Co/Re atom into triply degenerate t2g （dxy,dyz and dzx） states with lower energy and doubly degenerate eg （dz2 and dx2-y2） states with higher energy for either up-spin or down-spin.There are no direct interactions between two nearest Co-Co or Re-Re pairs,whereas along each Co-OReO-Co or Re-O-Co-O-Re chains,the existence of hybridizations between Co 3d and 4s,O 2s and 2p,as well as Re 5p,5d and 6s orbitals are confirmed.