Combined strain and high-pressure oxygen treatment effects and phase separation in La0.67Ca0.33MnO3 thin films

Evidence for phase separation in high-pressure oxygen-treated La_0.67Ca_0.33MnO₃/(100)MgO thin films is presented. This phase-separated state is not observed for the x=0.33 classical doping level either for bulk material or for as-prepared thin films. It originates from the combined influence of two factors: large strains due to the film-substrate lattice mismatch and high-pressure (100 bar) annealing in oxygen. These factors weaken double exchange, drastically enhance low-field magnetoresistance, and lead to hysteresis phenomena. The experimental results are interpreted in terms of phase separation of the film volume into the ferromagnetic conductive matrix with inclusions of spin-glass-like clusters.