Iron-induced magnetic, transport and magnetoresistance behavior in Nd _0.67Sr _0.33MnO ₃ epitaxial films

The effects of Fe doping on Mn site in the colossal magnetoresistive film, Nd0.67Sr0.33MnO3 have been studied by preparing the series Nd0.67Sr0.33Mn1-xFexO3 (x=0, 0.05 and 0.1). Upon doping, no structural changes have been found. However, the Curie temperature, the associated metal-to-insulator transition temperature and the magnetization decrease drastically with Fe doping. The resistivity in the paramagnetic regime for all the samples follows Emin-Holstein's theory of small polaron. The polaron activation energy, W-p and resistivity coefficient, A increase with Fe doping. This effect may be ascribed to the fact that upon Fe doping, the long-range ferromagnetic order is destroyed and, therefore, W-p is enhanced in the system. As compared to the La-based system, Fe doping has a stronger tendency to destabilize the long-range ferromagnetic order in the Nd-based system. Large MR (as high as 90%) observed in the epitaxial NSMFO film may be attributed to the good lattice-matching between the grown film and substrate.