从分布矩的角度看分子轨道自旋系统NaV₂O₅中的磁交换相互作用
Magnetic exchange interactions in the molecular orbital spin system NaV2O5 from a distributed moment point of view
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中文总结 AI 辅助
研究NaV₂O₅分子轨道自旋系统的磁交换相互作用，采用分布矩方法，将自旋密度集中到原子磁位点，利用线性响应方法计算交换作用，发现钒氧基和桥氧位点磁矩间交换作用与钒原子间相当甚至更大，对临界温度起关键作用，自旋波谱有异常集体激发。
中文摘要 AI 辅助
NaV₂O₅中的磁性源于V₂O₅窄分裂导带的掺杂，使其半填充，导致自旋分辨能带的莫特绝缘分裂，自旋沿锯齿链反铁磁有序。在Pmmn结构中，S = 1/2系统的自旋在两个钒原子间均分，处于分子轨道型态。低于34K时电荷歧化形成V⁴⁺和V⁵⁺，高于此温度情况不明，是各V占据概率相等的波动矩。传统上被描述为四分之一填充的梯子系统，本文采用分布矩方法，将自旋密度集中到单个原子磁位点，包括氧原子上的小感应矩。利用基于准粒子自洽GW能带结构的线性响应方法计算这些位点间的交换相互作用。令人惊讶的是，发现钒氧基和桥氧位点上诱导的小磁矩间的交换相互作用与钒原子间的交换相互作用量级相同甚至更大，其在临界温度中的作用至关重要。从第一性原理提取的经典海森堡型哈密顿量得到的自旋波谱包含高能的异常光学自旋波型集体激发。
英文摘要
The magnetism in NaV2O5 results from doping of the narrow split-off conduction band of V2O5, which becomes half-filled and leads to a Mott-insulating splitting of spin resolved bands with anti-ferromagnetic order of the spins along the zigzag chains. In the Pmmn structure the spin of this S = 1/2 system is equally shared between two vanadium atoms, residing in a molecular orbital type state. While below 34 K a charge disproportionation occurs into V4+ and V5+, the situation above this temperature is less clear and amounts to a fluctuating moment with equal probability of occupancy of each V. While traditionally described as a quarter-filled ladder system with electron spin localized on the rungs of the ladder, we here take a distributed moment approach in terms of the spin density lumped into individual atomic magnetic sites, including the small induced moments on the oxygen atoms. Exchange interactions are calculated between these sites using a linear response approach based on quasiparticle-self-consistent GW band structures. Surprisingly we find the exchange interactions between the small magnetic moments induced on the vanadyl and bridge oxygen sites to be of the same order of magnitude and even larger than the exchange interactions between vanadium atoms. Their role in the critical temperature is found to be crucial. The spin wave spectra obtained from this classical Heisenberg type Hamiltonian extracted from first-principles contains unusual optic spin wave type collective excitations of high energy.
