First-principles study of the magnetic interactions in honeycomb Na2IrO3
First-principles study of the magnetic interactions in honeycomb Na2IrO3
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蜂窝状 Na2IrO3 中磁相互作用的第一性原理研究
DOI：
10.1103/physrevb.98.094401
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发表时间：
2018-09-04
影响因子：
3.7
通讯作者：
Gong, X. G.
中科院分区：
文献类型：
--
作者：
Hou, Y. S.;Yang, J. H.;Gong, X. G.
蜂窝状铱酸盐Na 2 IrO 3是一种J（eff）= 1/2的磁体，是实现量子自旋液体的潜在平台。许多实验表明，它的磁基态是锯齿形反铁磁序。然而，解释这种有序的理论模型仍然缺乏共识，因为它的第二近邻（NN）和长程第三近邻磁相互作用非常不清楚。通过在第一性原理计算中适当地考虑通过限制它们的方向而获得的轨道矩，我们得到轨道矩和自旋矩之间的相对角度相当小，并且在几度的数量级，从而验证了Na 2 IrO 3中的J（eff）= 1/2状态。令人惊讶的是，我们发现长程第三NN海森堡相互作用是相当大的，而第二NN磁相互作用是可以忽略不计的。此外，我们发现，相当大的长程第三NN海森堡相互作用密切相关的Wannier轨道的J（eff）= 1/2状态在三个NN Ir原子的可观的分布。基于我们的研究，我们提出了一个最小的J（1）-K-1-Gamma（1）-J（3）模型，其中磁激发在5.6 meV处有一个强度峰，与非弹性中子散射实验一致[Phys. Rev. Lett. 108，127204（2012）]。目前的工作再次表明，在第一性原理计算中约束轨道矩是研究J（eff）= 1/2磁体中有趣的磁性的有力方法，它为深入了解蜂窝J（eff）= 1/2磁体中发现的新磁性铺平了道路。
Honeycomb iridate Na2IrO3, a J(eff) = 1/2 magnet, is a potential platform for realizing quantum spin liquid. Many experiments have shown that its magnetic ground state is a zigzag antiferromagnetic order. However, there is still a lack of consensus on the theoretical model explaining such order, since its second-nearest-neighbor (NN) and long-range third-NN magnetic interactions are highly unclear. By properly considering the orbital moments achieved through constraining their directions in first-principles calculations, we obtain that the relative angle between orbital and spin moments is fairly small and in the order of several degrees, which thus validates the J(eff) = 1/2 state in Na2IrO3. Surprisingly, we find that the long-range third-NN Heisenberg interactions are sizable, whereas the second-NN magnetic interactions are negligible. Furthermore, we show that sizable long-range third-NN Heisenberg interactions closely correlate with the appreciable distribution of Wannier orbitals of J(eff) = 1/2 states over the three NN Ir atoms. Based on our study, we propose a minimal J(1)-K-1-Gamma(1)-J(3) model in which the magnetic excitations have an intensity peak at 5.6 meV, consistent with the inelastic neutron-scattering experiment [Phys. Rev. Lett. 108, 127204 (2012)]. The present work demonstrates again that constraining orbital moments in first-principles calculations is a powerful way to investigate the intriguing magnetism in J(eff) = 1/2 magnets, and it paves the way toward gaining a deep insight into the novel magnetism discovered in the honeycomb J(eff) = 1/2 magnets.