Anomalous insulator-metal transition and weak ferromagnetism in Nd0.37Sr0.63MnO3 thin films

We report thickness-dependent magnetic and transport properties at the boundary separating A- and C-type antiferromagnetic phases in films of the overdoped manganite Nd0.37Sr0.63MnO3. The thin films are prepared by DC magnetron sputtering on single-crystal LaAlO3 substrates. All films, 5-120 nm in thickness, show a paramagnetic-ferromagnetic (PM-FM) transition. The small value of magnetization (<= 0.45 mu(B)/Mn) is suggestive of the weak nature of the FM correlations that is different from the prototype PM-FM transition due to double exchange ( DE). At lower film thicknesses, such as 5 and 25 nm, zero-field resistivity shows an insulator-like behavior. An insulator-metal (IM) transition is observed at higher film thicknesses (>= 60 nm). The magnetic-field independence of the observed IM transition (T-IM similar to 125 K) distinguishes it from the same observed in prototype manganites ( x similar to 0.2-0.4) and explained by DE. For the thinnest films, a CMR effect as large as MR similar to 85% is observed in the low-temperature regime. The observed phenomena can be explained in terms of orbital-fluctuation-induced phase separation. Copyright (c) EPLA, 2008