COHERENT WAVES OF MAGNETIC POLARONS PROPAGATING IN LA1-XCAXMNO3 - AN INELASTIC-NEUTRON-SCATTERING STUDY

Inelastic neutron scattering has been performed on semiconducting La1- xCaxMnO3 single crystals, which exhibit a slightly canted magnetic str ucture at a low doping rate (x=0.05,0.08). The dynamic study reveals t he coexistence of two excitation branches with very different characte ristics, and local modes for x=0.05; The first branch is anisotropical ly dispersed and is readily attributed to spin waves; the Mn spins are coupled by exchange forces, indicating a strong decrease of the antif erromagnetic interplane coupling by doping. The second branch is weakl y and isotropically dispersed, which suggests a coupling induced by th e hole hopping. Its unusual q-dependent intensity reveals that this ex citation is associated with a very short ferromagnetic correlation len gth (approximate to 8-10 Angstrom), reminiscent of a picture of mobile ''magnetic polarons.''.