Electron spin resonance and magnetization in perovskite and pyrochlore manganites

We have performed electron spin resonance (ESR) and de susceptibility, chi( dc)(T), measurements in La0.7Ca0.3MnO3 perovskite up to 1000 K. This is ade quately described in the paramagnetic regime in the constant coupling appro ximation assuming an effective Heisenberg-like pair interaction. The ESR li newidth is given by Delta H-pp(T) = Delta H-pp(infinity)[C/T chi(T)]. The E SR intensity follows the T dependence of chi(dc)(T) We conclude that the re laxation mechanism is essentially the same for the whole studied paramagnet ic range. The observed behavior reflects the progressive importance of magn etic clustering on approaching T-c. We have found similar T dependence for La0.7Sr0.3MnO3 and La0.7Pb0.3MnO3 perovskites, and also for the pyrochlore In2Mn2O7. (C) 1998 American Institute of Physics.