Neutron scattering study of magnetic excitations in a 5d-based double-perovskite Ba2FeReO6

Motivated by exploring spin-orbit-coupled magnetism in 5d-based transition metal oxides (TMOs) beyond the iridates, we present a powder inelastic neutron scattering study of magnetic excitations in Ba2FeReO6—a member of the double-perovskite family of materials which exhibit half-metallic behavior and high Curie temperatures Tc. We find clear evidence of two well-defined dispersing magnetic modes in its low-temperature ferrimagnetic state. We develop a local moment model, which incorporates the interaction of Fe spins with spin-orbital locked magnetic moments on Re and show that it captures our experimental observations. This allows us to extract moment sizes and exchange couplings, explain the magnitude of Tc, and infer that magnetostructural locking terms are weak. Our study further opens up Re-based compounds as model systems to explore the interplay of strong correlations and spin-orbit coupling in 5d TMOs.