Abstract
Using the inelastic neutron scattering technique, we measured the spin wave dispersion over the entire Brillouin zone of room temperature multiferroic BiFeO3 single crystals with magnetic excitations extending to as high as 72.5 meV. The full spin waves can be explained by a simple Heisenberg Hamiltonian with a nearest-neighbor exchange interaction (J = 4.38 meV), a next-nearest-neighbor exchange interaction (J' = 0.15 meV), and a Dzyaloshinskii-Moriya-like term (D = 0.107 meV). This simple Hamiltonian determined, for the first time, for BiFeO3 provides a fundamental ingredient for understanding the novel magnetic properties of BiFeO3.