Dispersive magnetic excitations in the S=1 antiferromagnet Ba3Mn2O8

We present powder inelastic neutron scattering measurements of the S=1 dimerized antiferromagnet Ba(3)Mn(2)O(8). The T=1.4 K magnetic spectrum exhibits a spin gap of Delta approximate to 1.0 meV and a dispersive spectrum with a bandwidth of approximately 1.5 meV. A comparison to coupled dimer models accurately describes the dispersion and scattering intensity and determines the exchange constants in Ba(3)Mn(2)O(8). The wave vector dependent scattering intensity confirms the proposed S=1 dimer bond. Temperature dependent measurements of the magnetic excitations indicate the presence of both singlet-triplet and thermally activated triplet-quintet excitations.