Critical spin dynamics in Nd1-xSrxMnO3 with x≈0.5

Magnetic ion spin dynamics has been investigated in the perovskite manganite 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 critical slowing down of Mn ion spin fluctuations on approaching the ferromagnetic ordering at similar to 251 K in Nd0.5Sr0.5MnO3. The critical paramagnetic spin fluctuations, measured by the muon spin relaxation rate lambda(1), exhibit a crossover behavior from exchange critical regime to dipolar critical regime. This crossover is explained by considering the suppression of longitudinal and transverse components of spin susceptibility by dipolar interactions 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 muon spin relaxation rates away from Te (nonasymptotic regime), agrees with the experimental and the theoretical results of 3d dipolar ferromagnets. Critical slowing down is not observed in the x = 0.55 crystal at the onset of antiferromagnetic 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 crystal (both above and below TN) is root exponential and indicates nondiffusive relaxation mechanism as is in a magnetic glass. The growth of a glasslike relaxation component concomitant with the magnetic ordering has been observed in both the crystals. We suggest that this glassy component originates from those Mn ions located in local regions containing small and differently sized spin clusters.