Orbital degeneracy removed by charge order in triangular antiferromagnet AgNiO2.

Journal article

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 sqrt[3]xsqrt[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.

Authors: Wawrzyńska, E; Coldea, R; Wheeler, E; Mazin, I; Johannes, MD

• Publication status: Published
• Journal: Physical Review Letters
• Volume: 99
• Issue: 15
• Pages: 157204
• Publication date: 2007-10-01
• DOI: 10.1103/physrevlett.99.157204
• EISSN: 1079-7114
• ISSN: 0031-9007
• Language: English
• Keywords: cond-mat.str-el