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arXiv · 1602.07990

Incommensurate Counterrotating Magnetic Order Stabilized by Kitaev Interactions in the Layered Honeycomb ${\alpha}$-Li$_2$IrO$_3$

S. C. Williams·R. D. Johnson·F. Freund·Sungkyun Choi·A. Jesche·I. Kimchi·S. Manni·A. Bombardi·P. Manuel·P. Gegenwart·R. Coldea
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Abstract

The layered honeycomb magnet $\alpha$-Li$_2$IrO$_3$ has been theoretically proposed as a candidate to display novel magnetic behaviour associated with Kitaev interactions between spin-orbit entangled $j_{\rm eff}=1/2$ magnetic moments on a honeycomb lattice. Here we report single crystal magnetic resonant x-ray diffraction combined with powder magnetic neutron diffraction to reveal an incommensurate magnetic order in the honeycomb layers with Ir magnetic moments counter-rotating on nearest-neighbour sites. This type of magnetic structure has not been reported experimentally before in honeycomb magnets and cannot be explained by a spin Hamiltonian with dominant isotropic (Heisenberg) couplings. The magnetic structure shares many key features with the magnetic order in the structural polytypes $\beta$ and $\gamma$-Li$_2$IrO$_3$, understood theoretically to be stabilized by dominant Kitaev interactions between Ir moments located on the vertices of three-dimensional hyperhoneycomb and stripyhoneycomb lattices, respectively. Based on this analogy and a theoretical soft-spin analysis of magnetic ground states for candidate spin Hamiltonians, we propose that Kitaev interactions also dominate in $\alpha$-Li$_2$IrO$_3$, indicative of universal Kitaev physics across all three members of the harmonic honeycomb family of Li$_2$IrO$_3$ polytypes.

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S. C. Williams, R. D. Johnson, F. Freund, Sungkyun Choi, A. Jesche, I. Kimchi, S. Manni, A. Bombardi, P. Manuel, P. Gegenwart, R. Coldea. 2016-02-25. Incommensurate Counterrotating Magnetic Order Stabilized by Kitaev Interactions in the Layered Honeycomb ${\alpha}$-Li$_2$IrO$_3$. https://doi.org/10.1103/physrevb.93.195158

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