First principles study of electronic structure, magnetism and ferroelectric properties of rhombohedral AgFeO2

Using first principles calculation in the framework of density functional theory we have investigated the electronic structure, magnetism and ferroelectric polarization in the triangular lattice antiferromagnet AgFeO2, and compared it to the isostructural system CuFeO2. Our calculations reveal that spin-orbit interaction plays an important role in determining the magnetic property of AgFeO2 and is possibly responsible for its different magnetic ground state in comparison to CuFeO2. Calculations of ferroelectric polarization of AgFeO2 suggest that the spontaneous polarization arises from noncollinear spin arrangement via the spin-orbit coupling. Our calculations also indicate that in addition to electronic contribution, the lattice mediated contribution to the polarization is also important for AgFeO2.