Mostovoy M V, Khomskii D I
Materials Science Center Rijksuniversiteit Groningen, Nijenborgh 4, The Netherlands.
Phys Rev Lett. 2002 Nov 25;89(22):227203. doi: 10.1103/PhysRevLett.89.227203. Epub 2002 Nov 12.
We show that superexchange interactions in frustrated Jahn-Teller systems with transition metal ions connected by the 90 degrees metal-oxygen-metal bonds (e.g., NaNiO2, LiNiO2, and ZnMn2O4) are much different from those in materials with the 180 degrees bonds. In the 90 degrees -exchange systems spins and orbitals are decoupled: the spin exchange is much weaker than the orbital one and it is ferromagnetic for all orbital states. Though the mean-field orbital ground state is strongly degenerate, quantum orbital fluctuations select particular ferro-orbital states. We explain the orbital and magnetic ordering observed in NaNiO2 and show that LiNiO2 is not a spin-orbital liquid.
我们表明，在具有通过90度金属-氧-金属键相连的过渡金属离子的受挫 Jahn-Teller 体系（例如 NaNiO₂、LiNiO₂ 和 ZnMn₂O₄）中，超交换相互作用与具有180度键的材料中的超交换相互作用有很大不同。在90度交换体系中，自旋和轨道解耦：自旋交换比轨道交换弱得多，并且对于所有轨道状态都是铁磁性的。尽管平均场轨道基态高度简并，但量子轨道涨落会选择特定的铁轨道状态。我们解释了在NaNiO₂ 中观察到的轨道和磁有序，并表明LiNiO₂ 不是自旋-轨道液体。
