  We investigate magnetic excitations in half-doped colossal magnetoresistance
manganites. In particular, we focus on spin excitations in the CE phase
originally proposed by Goodenough (Phys. Rev. 100, 564 (1955)). Using a
localized spin model we calculated magnons for 3D-perovskite compounds such as
La$_{1-x}$M$_x$MnO$_3$, where M=Ca,Sr,Ba, and for their 2D-laminar
counterparts. We compared them with predictions for the spin excitations
corresponding to other phases proposed. For the laminar half-doped manganite
La$_{0.5}$Sr$_{1.5}$MnO$_4$, for which magnon measurements by inelastic neutron
scattering exist, as well as an estimation of the magnetic couplings, our
calculations agree well with the experimental data.
