Evolution of the Low-Frequency Spin Dynamics in Ferromagnetic Manganites

Neutron scattering was used to study the ferromagnetic manganites Nd0.7Sr0.3MnO₃ ( TC0ex0ex=0ex0ex197.90ex0exK) and Pr0.63Sr0.37MnO₃ ( TC0ex0ex=0ex0ex300.90ex0exK). The spin dynamical behavior of these two systems is similar at low temperatures but drastically different at temperatures around TC. While the formation of spin clusters of size ( ~20) dominates the spin dynamics of the 197.9 K sample close to TC, the paramagnetic to ferromagnetic transition for the 300.9 K sample is more conventional. These results, combined with seemingly inconsistent earlier reports, reveal clear systematics in the spin dynamics of the manganites.