The exchange interactions in polycrystalline samples of ${\mathrm{Ca}}_{1-x}{\mathrm{La}}_x{\mathrm{MnO}}_3$ $\left(0.00\le x\le 0.05\right)$ 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 $\sim 2\%–3\%$. 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.

• Received 27 November 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.5385