Neutron Scattering Studies of the Ferroelectric Distortion and Spin   Dynamics in the Type-1 Multiferroic Perovskite Sr0.56Ba0.44MnO3
  The magnetic order, spin dynamics, and crystal structure of the multiferroic Sr0.56Ba0.44MnO3 have been investigated using neutron and x-ray scattering. Ferroelectricity develops at TC=305 K with a polarization of 4.2 microC/cm2 associated with the displacements of the Mn ions, while the Mn4+ spins order below TN = 200 K into a simple G-type commensurate magnetic structure. Below TN the ferroelectric order decreases dramatically demonstrating that the two order parameters are strongly coupled. The ground state spin dynamics are characterized by a spin gap of 4.6(5) meV and the magnon density of states peaking at 43 meV. Detailed spin wave simulations with a gap and isotropic exchange of J=4.8(2) meV describe the excitation spectrum well. Above TN strong spin correlations coexist with robust ferroelectric order. 
Daniel K. Pratt, Jeffrey W. Lynn, James Mais, Omar Chmaissem, Dennis   E. Brown, Stanislaw Kolesnik, and Bogdan Dabrowski
cond-mat.mtrl-sci