@article{discovery1434306,
            note = {{\copyright}2015 American Physical Society},
          volume = {91},
           month = {January},
          number = {3},
         journal = {Physical Review B},
           title = {Magnetic excitation spectrum of LuFe2O4 measured with inelastic neutron scattering},
            year = {2015},
             url = {http://dx.doi.org/10.1103/PhysRevB.91.035103},
            issn = {1098-0121},
        abstract = {We report neutron inelastic-scattering measurements and analysis of the spectrum of magnons propagating within the Fe2O4 bilayers of LuFe2O4. The observed spectrum is consistent with six magnetic modes and a single prominent gap, which is compatible with a single bilayer magnetic unit cell containing six spins. We model the magnon dispersion by linear spin-wave theory and find very good agreement with the domain-averaged spectrum of a spin-charge bilayer superstructure comprising one Fe3+-rich monolayer and one Fe2+-rich monolayer. These findings indicate the existence of polar bilayers in LuFe2O4. We also discuss a model of charge-segregated nonpolar bilayer order which we argue is not consistent with our data but which we cannot exclude definitively. Weak scattering observed below the magnon gap suggests that a fraction of the bilayers contain other combinations of charged monolayers not included in the model. Refined values for the dominant exchange interactions are reported.},
          author = {Gaw, SM and Lewtas, HJ and McMorrow, DF and Kulda, J and Ewings, RA and Perring, TG and McKinnon, RA and Balakrishnan, G and Prabhakaran, D and Boothroyd, AT}
}