Spin dynamics of Cr-doped La 0.67Ca 0.33MnO 3 in the paramagnetic regime

We report DC magnetization and electron paramagnetic resonance (EPR) measurements in ceramic samples of La _0.67Ca _0.33Mn _{1- y}Cr _yO ₃ (0⩽ y⩽0.1). We have observed a decrease of T_C with doping, which reveals a continuous dilution of the ferromagnetic exchange interaction. On the other hand, although the EPR linewidth (∆ H_pp) depends on the doping level, its high-temperature limit value (∆ H_pp(∞)) remains constant around 0.25 T. This implies that dynamic double exchange (DE) interaction is too slow to contribute to the exchange narrowing process.