Spin dynamics of Cr-doped La0.67Ca0.33MnO3 in the paramagnetic regime

We report DC magnetization and electron paramagnetic resonance (EPR) measur ements in ceramic samples of La0.67Ca0.33Mn1-yCryO3 (0 less than or equal t o y less than or equal to 0.1). We have observed a decrease of T-C with dop ing, which reveals a continuous dilution of the ferromagnetic exchange inte raction. On the other hand, although the EPR linewidth (Delta H-pp) depends on the doping level, its high-temperature limit value (Delta H-pp(infinity )) remains constant around 0.25 T. This implies that dynamic double exchang e (DE) interaction is too slow to contribute to the exchange narrowing proc ess. (C) 2000 Elsevier Science B.V. All rights reserved.