Control of the colossal magnetoresistance by strain effect in Nd₀.₅Ca₀.₅MnO₃ thin films

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Thin films of Nd₀.₅Ca₀.₅MnO₃ manganites with colossal magnetoresistance (CMR) properties have been synthesized by the Pulsed Laser Deposition technique on (100)-SrTiO₃. The lattice parameters of these manganites and correlatively their CMR properties can be controlled by the substrate temperature Tₛ. The maximum CMR effect at 75K, calculated as the ratio ρ(H=0T)/ρ(H=7T) is 10⁴ for a deposition temperature of Tₛ=680 degC. Structural studies show that the Nd₀.₅Ca₀.₅MnO₃ film is single phase, [010]-oriented and has a pseudocubic symmetry of the perovskite subcell with a=3.77Å at room temperature. We suggest that correlation between lattice parameters, CMR and substrate temperature Tₛ result mainly from substrate-induced strains which can weaken the charge-ordered state at low temperature.