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Orbital degeneracy as a source of frustration in LiNiO$_2$

F. Vernay·K. Penc·P. Fazekas·F. Mila
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Abstract

Motivated by the absence of cooperative Jahn-Teller effect and of magnetic ordering in LiNiO$_2$, a layered oxide with triangular planes, we study a general spin-orbital model on the triangular lattice. A mean-field approach reveals the presence of several singlet phases between the SU(4) symmetric point and a ferromagnetic phase, a conclusion supported by exact diagonalizations of finite clusters. We argue that one of the phases, characterized by a large number of low-lying singlets associated to dimer coverings of the triangular lattice, could explain the properties of LiNiO$_2$, while a ferro-orbital phase that lies nearby in parameter space leads to a new prediction for the magnetic properties of NaNiO$_2$.

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F. Vernay, K. Penc, P. Fazekas, F. Mila. 2004-01-09. Orbital degeneracy as a source of frustration in LiNiO$_2$. https://doi.org/10.1103/physrevb.70.014428

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