Spin–charge–orbital structures and frustration in multiferroicRFe2O4

Abstract

We examine theoretically the spin, charge and orbital states in a frustrated systemRFe2O4. We suggest that the orbital degree of freedom is active in anFe2+ ion. To describe the spin, charge and orbital states, the effective Hamiltonian for theelectronic state is derived. By utilizing the Monte Carlo simulation in a finite-sizecluster, we investigate the charge, spin and orbital structures. It is shown thatthe obtained charge and spin states are consistent with experimental results inRFe2O4. The numerical simulation for the effective orbital model does not show the conventionalorbital order. We discuss possible orbital states at low temperatures.