Dramatic changes in the magnetic coupling mechanism for La-doped CaMnO3

The exchange interactions in polycrystalline samples of Ca1-xLaxMnO3 (0.00 less than or equal to x less than or equal to 0.05) are studied by means of Raman scattering and electron paramagnetic resonance. Dramatic reductions in the spin-phonon interactions and magnetic correlations are observed for La doping levels as small as similar to2%-3%. These results show that the charge carriers play an important role in the overall exchange coupling in the electron-doped manganites, even at very low doping levels.