Isotope effect for transport and magnetic properties of La0.35Pr0.35Ca0.3MnO3 thin films

The effect of O-16 --> O-18 isotope substitution on electrical resistivity, magnetoresistance, and ac magnetic susceptibility was studied for La0.35Pr 0.35Ca0.3MnO3 epitaxial thin films deposited onto LaAlO3 and SrTiO3 substra tes. For the films on LaAlO3, the isotope substitution resulted in the reve rsible transition from a metal-like to insulating state. The applied magnet ic field (H greater than or equal to 2 T) transformed the sample with O-18 back to the metallic state. The films on SrTiO3 remained metallic at low te mperatures for both O-16 and O-18, but the shift of the resistivity peak co rresponding to onset of metallic state exceeded 63 K after O-16 --> O-18 su bstitution. The temperature dependence of both resistivity and magnetic sus ceptibility was characterized by hysteresis, especially pronounced in the c ase of the films on LaAlO3. Such a behavior gives certain indications of th e phase separation characteristic of interplay between ferromagnetism and c harge ordering.