Hiroshi Shinaoka, Yukitoshi Motome, Takashi Miyake, Shoji Ishibashi
Electronic and magnetic properties of molybdenum pyrochlores $A_2$Mo$_2$O$_7$ are studied by the fully relativistic density-functional theory plus on-site repulsion ($U$) method, with focusing on the insulating material Y$_2$Mo$_2$O$_7$. As $U$ increases, the ground state turns from a ferromagnetic metal into an antiferromagnetic insulator. In the insulating phase, the system exhibits peculiar magnetic degeneracy, which suggests strong anisotropy in the effective magnetic interactions. Analyzing a three-orbital Hubbard model, we show that the degeneracy is not solely in spin but in the spin-orbital entangled object formed under the cooperation of the trigonal distortion, Coulomb interactions, and spin-orbit interaction. The orbital frustration in the $4d^2$ electronic configuration plays an important role. The results give a new insight into the spin-glass behavior in the insulating materials.
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http://arxiv.org/abs/1305.0660
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