Microstructure, magnetism and magnetotransport of epitaxial Sm0.45Nd0.08Sr0.47MnO3 thin films

Abstract

The growth of low bandwidth manganite thin films having optical magnetic and transport properties has been found to be extremely difficult. In the present study we have prepared thin films of a low bandwidth manganite Sm0.45Nd0.08Sr0.47MnO3 and carried out detailed study of microstructural and magnetotransport properties. Thin films (thickness ∼36 nm and ∼80 nm) of Sm0.45Nd0.08Sr0.47MnO3 were grown by dc magnetron sputtering on (001) oriented LaAlO3 single-crystal substrate and post-annealed in oxygen. The x-ray diffraction (θ–2θ) shows that the as grown films, irrespective of the thickness are under extremely high compressive strain, which is only partially relaxed by post deposition annealing in oxygen. High resolution x-ray diffraction (ω–2θ scans) shows the occurrence of Pendellösung fringes in the ∼36 nm film, which appear to get disordered in the thicker ∼80 nm film. This shows that the films have grown epitaxially at lower thickness and at higher thickness the microstructural degradation destroys its global nature. The epitaxial growth is confirmed by occurrence of step-terrace morphology in the 36 nm film, which, however, appears to be less prominent at higher film thickness of ∼80 nm. The as-grown films do not show any insulator metal transition and only weak paramagnetic-to-ferromagnetic transition is observed. The O2 annealed 36 nm film shows a broad paramagnetic to ferromagnetic transition at ≈100 K but no insulator–metal transition is seen. Magnetic field (H) produces insulator metal transition and colossal decrement in the resistivity (ρ) in the 36 nm film. At T < TC, ρ–H curves show strong hysteresis, which is a signature of a first-order phase transition. In the 80 nm a paramagnetic insulator to ferromagnetic metal transition occurs at TC ≈ 145 K but magnetic field induced colossal decrease in resistivity and the ρ–H hysteresis is reduced considerably. Our results clearly show that the electrical transport is strongly influenced by the phase separation in these films. The differences in the magnetic properties and magnetic field dependent electrical transport behaviours are attributed to the modulation of the phase separated state due to the strain induced variation in the fraction of the competing ferromagnetic metallic and antiferromagnetic-charge ordered insulating phases.