Magnetic phase diagram and structural separation of La0.7(Ca1?ySry)0.3MnO3 thin films

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The structural, magnetic, and transport properties of La0.7(Ca1?ySry)0.3MnO3 films, deposited on a LaAlO3?(001) single crystalline substrate by rf-magnetron sputtering using “soft” (or powder) targets, have been investigated. It was found that at 0.3 ? y ? 0.5 both the rhombohedral (R3c) and the orthorhombic (Pnma) crystal phases in the form of nanoscale clusters are coexistent at room temperature. The observed structural clustering is accompanied by two-stage magnetic and electronic transitions, and governed by a nonuniform distribution of the lattice strain through the film. It was shown that for the films with 0 ? y ? 0.5 the nonlinear (almost parabolic) MR(H) dependence is typical while, for 0.65 ? y ? 1.0, the linear MR(H) behavior is observed at room temperature. The magnetotransport properties of films are explained within the framework of field-dependent activation-energy model. The magnetic phase diagram for La0.7(Ca1?ySry)0.3MnO3 thin-film system is also presented.