Critical spin dynamics in Nd1-xSrxMnO3 with x approximate to 0.5

Magnetic ion spin dynamics has been investigated in the perovskite manganit e Nd1-xSrxMnO3 single crystals at the hole concentrations x of 0.5 and 0.55 by muon spin relaxation (mu(+)SR) spectroscopy. We have observed the criti cal slowing down of Mn ion spin fluctuations on approaching the ferromagnet ic ordering at similar to 251 K in Nd0.5Sr0.5MnO3. The critical paramagneti c spin fluctuations, measured by the muon spin relaxation rate lambda(1), e xhibit a crossover behavior from exchange critical regime to dipolar critic al regime. This crossover is explained by considering the suppression of lo ngitudinal and transverse components of spin susceptibility by dipolar inte ractions closer to T-C and the dipolar vector q(D) is found to be 0.020(2) Angstrom (-1). The dynamic critical exponent z = 2.00(12), deduced from muo n spin relaxation rates away from Te (nonasymptotic regime), agrees with th e experimental and the theoretical results of 3d dipolar ferromagnets. Crit ical slowing down is not observed in the x = 0.55 crystal at the onset of a ntiferromagnetic ordering at similar to 220 K. Muon spin relaxation in the x = 0.5 crystal (above T-N approximate to 5 160 K) and in the x = 0.55 crys tal (both above and below TN) is root exponential and indicates nondiffusiv e relaxation mechanism as is in a magnetic glass. The growth of a glasslike relaxation component concomitant with the magnetic ordering has been obser ved in both the crystals. We suggest that this glassy component originates from those Mn ions located in local regions containing small and differentl y sized spin clusters.