  The magnon dispersion in the charge, orbital and spin ordered phase in
La(0.5)Sr(1.5)MnO(4) has been studied by means of inelastic neutron scattering.
We find an excellent agreement with a magnetic interaction model basing on the
CE-type superstructure. The magnetic excitations are dominated by ferromagnetic
exchange parameters revealing a nearly-one dimensional character at high
energies. The nearest neighbor ferromagnetic interaction in
La(0.5)Sr(1.5)MnO(4) is significantly larger than the one in the metallic
ferromagnetically ordered manganites. The large ferromagnetic interaction in
the charge/orbital ordered phase appears to be essential for the capability of
manganites to switch between metallic and insulating phases.
