Low-energy magnons in the chiral ferrimagnet Cu 2 OSeO 3 : A coarse-grained approach

• Published in: Physical review. B Vol. 101
• Main Authors: Luo, Yi, Marcus, G G, Trump, B A, Kindervater, J, Stone, M B, Rodriguez-Rivera, J A, Qiu, Yiming, McQueen, T M, Tchernyshyov, O, Broholm, C
• Format: Journal Article
• Language: English
• Published: United States 08.04.2020
• ISSN: 2469-9950
• DOI: 10.1103/PhysRevB.101.144411

We report a comprehensive neutron scattering study of low energy magnetic excitations in the breathing pyrochlore helimagnetic Cu OSeO . Fully documenting the four lowest energy magnetic modes that leave the ferrimagnetic configuration of the "strong tetrahedra" intact ( meV), we find gapless quadratic dispersion at the point for energies above 0.2 meV, two doublets separated by 1.6(2) meV at the point, and a bounded continuum at the point. Our constrained rigid spin cluster model relates these features to Dzyaloshinskii-Moriya (DM) interactions and the incommensurate helical ground state. Combining conventional spin wave theory with a spin cluster form factor accurately reproduces the measured equal time structure factor through multiple Brillouin zones. An effective spin Hamiltonian describing complex anisotropic intercluster interactions is obtained.