Abstract
Neutron scattering was used to study the ferromagnetic manganites Nd0.7Sr0.3MnO3 (T-C = 197.9 K) and PT0.63Sr0.37MnO3 (T-C = 300.9 K). The spin dynamical behavior of these two systems is similar at low temperatures but drastically different at temperatures around T-C. While the formation of spin clusters of size (similar to 20 Angstrom) dominates the spin dynamics of the 197.9 K sample close to T-C, the paramagnetic to ferromagnetic transition for the 300.9 K sample is mon conventional. These results, combined with seemingly inconsistent earlier reports, reveal clear systematics in the spin dynamics of the manganites.