Ganga B G, Santhosh P N, Nanda B R K
Low Temperature Physics Lab, Department of Physics, IIT Madras, Chennai 600036, India.
J Phys Condens Matter. 2017 Apr 20;29(15):155802. doi: 10.1088/1361-648X/aa58c2. Epub 2017 Jan 11.
Density functional calculations are performed to study the magnetic order of the severely distorted square planar cupric oxide (CuO) and local spin disorder in it in the presence of the transition metal impurities M (=Cr, Mn, Fe, Co and Ni). The distortion in the crystal structure, arisen to reduce the band energy by minimizing the covalent interaction, creates two crisscrossing zigzag spin-1/2 chains. From the spin dimer analysis we find that while the spin chain along [Formula: see text] has strong Heisenberg type antiferromagnetic coupling (J ~ 127 meV), along [Formula: see text] it exhibits weak, but robust, ferromagnetic coupling (J ~ 9 meV) mediated by reminiscent p-d covalent interactions. The impurity effect on the magnetic ordering is independent of M and purely orbital driven. If the given spin-state of M is such that the [Formula: see text] orbital is spin-polarized, then the original long-range ordering is maintained. However, if [Formula: see text] orbital is unoccupied, the absence of corresponding covalent interaction breaks the weak ferromagnetic coupling and a spin-flip takes place at the impurity site leading to breakdown of the long range magnetic ordering.
进行密度泛函计算以研究严重扭曲的方形平面氧化铜（CuO）的磁序以及在存在过渡金属杂质M（= Cr、Mn、Fe、Co和Ni）时其中的局部自旋无序。晶体结构中的畸变是为了通过最小化共价相互作用来降低能带能量，它产生了两条交叉的锯齿形自旋-1/2链。通过自旋二聚体分析我们发现，虽然沿[公式：见原文]的自旋链具有强海森堡型反铁磁耦合（J ~ 127 meV），但沿[公式：见原文]它表现出由类似的p-d共价相互作用介导的弱但稳健的铁磁耦合（J ~ 9 meV）。杂质对磁序的影响与M无关且纯粹由轨道驱动。如果M的给定自旋态使得[公式：见原文]轨道自旋极化，那么原始的长程有序得以维持。然而，如果[公式：见原文]轨道未被占据，相应共价相互作用的缺失会破坏弱铁磁耦合，并且在杂质位点会发生自旋翻转，导致长程磁序的破坏。
