Dimer formation in half-doped manganites

Abstract Two scenarios are presently under discussion for the description of the CE magnetic structure found in half-doped manganites. One involves a charge ordered phase, with Mn 3+ and Mn 4+ ions present in equal parts. The other, an arrangement of spin dimers along the ferromagnetic Mn zig-zag chains present, with an intermediate valence of 3.5 for all Mn ions. We calculated the spin excitations predicted for these compounds by the two scenarios. We find qualitative differences in the magnon spectra, which should allow to distinguish them by neutron scattering.