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 T-c. 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 T-c, 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.112121sciescopu

Incommensurate dynamic correlations in the quasi-two-dimensional spin liquid BiCu2PO6

We report detailed inelastic neutron-scattering measurements on single crystals of the frustrated two-leg ladder BiCu2PO6, whose ground state is described as a spin liquid phase with no long-range order down to 6 K. Two branches of steeply dispersing long-lived spin excitations are observed with excitation gaps of \u3941=1.90(9) meV and \u3942=3.95(8) meV. Significant frustrating next-nearest-neighbor interactions along the ladder leg drive the minimum of each excitation branch to incommensurate wave vectors \u3b61=0.574\u3c0 and \u3b62=0.553\u3c0 for the lower and upper energy branches, respectively. The temperature dependence of the excitation spectrum near the gap energy is consistent with thermal activation into singly and doubly degenerate excited states. The observed magnetic excitation spectrum as well as earlier thermodynamic data could be consistently explained by the presence of strong anisotropic interactions in the ground-state Hamiltonian. \ua9 2013 American Physical Society.Peer reviewed: YesNRC publication: Ye