We report a high-resolution neutron diffraction study on the orbitally degenerate spin-1/2 hexagonal metallic antiferromagnet AgNiO2. A structural transition to a tripled unit cell with expanded and contracted NiO6 octahedra indicates 3×3 charge order on the Ni triangular lattice. This suggests charge order as a possible mechanism of lifting the orbital degeneracy in the presence of charge fluctuations, as an alternative to the more usual Jahn-Teller distortions. A novel magnetic ground state is observed at low temperatures with the electron-rich S=1 Ni sites arranged in alternating ferromagnetic rows on a triangular lattice, surrounded by a honeycomb network of nonmagnetic and metallic Ni ions. We also report first-principles band-structure calculations that explain microscopically the origin of these phenomena. © 2007 The American Physical Society.
CITATION STYLE
Wawrzyńska, E., Coldea, R., Wheeler, E. M., Mazin, I. I., Johannes, M. D., Sörgel, T., … Radaelli, P. G. (2007). Orbital degeneracy removed by charge order in triangular antiferromagnet AgNiO2. Physical Review Letters, 99(15). https://doi.org/10.1103/PhysRevLett.99.157204
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