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Nature of magnetism in Ca$_3$Co$_2$O$_6$

Hua Wu·M. W. Haverkort·Z. Hu·D. I. Khomskii·L. H. Tjeng
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Abstract

We find using LSDA+U band structure calculations that the novel one-dimensional cobaltate Ca$_3$Co$_2$O$_6$ is not a ferromagnetic half-metal but a Mott insulator. Both the octahedral and the trigonal Co ions are formally trivalent, with the octahedral being in the low-spin and the trigonal in the high-spin state. The inclusion of the spin-orbit coupling leads to the occupation of the minority-spin $d_{2}$ orbital for the unusually coordinated trigonal Co, producing a giant orbital moment (1.57 $μ_{B}$). It also results in an anomalously large magnetocrystalline anisotropy (of order 70 meV), elucidating why the magnetism is highly Ising-like. The role of the oxygen holes, carrying an induced magnetic moment of 0.13 $μ_{B}$ per oxygen, for the exchange interactions is discussed.

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Hua Wu, M. W. Haverkort, Z. Hu, D. I. Khomskii, L. H. Tjeng. 2005-09-15. Nature of magnetism in Ca$_3$Co$_2$O$_6$. https://doi.org/10.1103/physrevlett.95.186401

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