Transport and magnetic properties of Pr_1-xCa_xMnO₃ epitaxial films grown on LaAlO₃ substrates

We have measured physical properties of Pr_1-xCa_xMnO₃ (PCMO) epitaxial thin films with different hole concentrations (x=0.2, 0.3, 0.4, and 0.5) grown on LaAlO₃ (1 0 0) substrates by laser molecular beam epitaxy technique. The temperature dependence of the resistivity shows insulating behavior in all temperature regions and the resistivity itself monotonously decreases as x increases. This insulating nature of PCMO films is similar to that of bulk PCMO crystals. However, we did not find any indication of the resistivity anomaly associated with the onset of charge ordering irrespective of x. These results suggest that the compressive strain strongly suppresses charge-ordered states in PCMO.