Barium-Based Manganites Ln₁_-<i>_x</i>Ba<i>_x</i>MnO₃ with Ln = {Pr, La}: Phase Transitions and Magnetoresistance Properties

Abstract

Using a “two-steps” synthesis mode, the homogeneity ranges of the perovskites Ln1-xBaxMnO3 were extended up to x = 0.60 for the Pr-based samples and x = 0.50 for the La ones. Two new perovskites, a cubic form and a P-type tetragonal phase (with aC × aC × 2aC parameters) have been isolated. The HREM study shows a nanostructural behavior of the new tetragonal form, only stabilized in small domains. These compounds exhibit a ferromagnetic metallic to paramagnetic insulating transition at increasing temperature, over a large homogeneity range, independent of the nature of the perovskite structure. Consequently, magnetoresistance effects are observed. The Curie temperature reaches values as high as 362 K and goes though a maximum. These properties are discussed considering three factorssize, valence, and mismatch effectswhich are known to govern the CMR properties of the manganites.