Damping of antiferromagnetic spin waves by valence fluctuations in the double layer perovskite YBaFe2O5

Inelastic neutron scattering experiments show that spin dynamics in the charge-ordered insulating ground state of the double layer perovskite YBaFe2O5 is well described in terms of e(g) superexchange interactions. Above the Verwey transition at T-V=308 K, t(2g) double exchange-type conduction proceeds within antiferromagnetic FeO2-BaO-FeO2 double layers by an electron hopping process that requires a spin flip of the five-coordinated Fe ions, costing an energy of 5 < J > S-2 approximate to 0.1 eV. The hopping process disrupts near-neighbor spin correlations, leading to massive damping of zone-boundary spin waves.