Effect of strain and disorder in manganite thin films

We have studied the effect of strain and disorder on the phase separated state in thin films of the manganite (La$_{1-y}$Pr$_{y})_{0.67}$Ca$_{0.33}$MnO$_{3}$(LPCMO, $y$ = 0.4, 0.5, 0.6) grown on (110) NdGaO$_{3}$ substrates using pulsed laser deposition. Due to the competition between the charge-ordered insulating and ferromagnetic metallic phases, thin films of LPCMO display a fluid-like phase separation (FPS) near the insulator-to-metal transition temperature. By applying direct mechanical stress on the LPCMO thin films using a three-point beam bending technique, we observed a colossal piezoresistance in the FPS state of these materials. Our observations show that a small amount of strain ($\sim $10$^{-4})$ can move the phase boundaries in the FPS state. We then modified the extrinsic disorder in the thin films by bombarding them with Ar-ions. Our measurements show a reduction of piezoresistance in the ion-bombarded samples which suggests that such extrinsic disorder can pin the phase boundaries and reduce the fluidity of the FPS state.