Stress deformations and structural quenching in charge-ordered Sm_0.5Ca_0.5MnO₃ thin films

Sm_0.5Ca_0.5MnO₃ manganite thin films with charge ordering (CO) and colossal magnetoresistance were synthesized by pulsed laser deposition on (100)-SrTiO₃ and (100)-LaAlO₃ substrates. We first compare the structural modifications as functions of the substrate and film thickness. Secondly, transport properties in magnetic fields up to 24 T were studied and the temperature-field phase diagram describing the stability of the CO state was established. This enables us to compare the thin film to the bulk material. We show that some substrate-induced structural modifications exist as a result of which the CO melting magnetic field is greatly reduced. Moreover, no modification of the lattice parameters is observed with temperature decrease. We then propose an explanation based on the quenching of the thin film’s unit cell which then adopts the in-plane lattice parameters of the substrate and thus prevents the complete setting in of the CO state at low temperatures.