Orbital-ordering-induced anomalous softening of the ferromagnetic spin   waves in perovskite manganites
  Spin wave excitations were measured in the ferromagnetic phase of Nd$_{1/2}$Sr$_{1/2}$MnO$_{3}$ by neutron scattering. This compound is located in proximity to the A-type antiferromagnetic state, and it shows a clear anisotropy and anomalous softening of the spin wave excitations. The softening in the ferromagnetic phase is induced by the orbital ordering. 
R. Kajimoto, H. Yoshizawa, H. Kawano-Furukawa, H. Kuwahara, Y.   Tomioka, and Y. Tokura