Evidence for strong effect of quenched correlated disorder on phase separation and magnetism in (La₁₋yPry)₀.₇Ca₀.₃MnO₃

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High resolution neutron diffraction shows that the mesoscopic separation into ferromagnetic (FM) and antiferromagnetic (AFM) phases and the FM transition temperature TC in the perovskite manganite (La₁₋yPry)₀.₇Ca₀.₃MnO₃ strongly depend on the quenched correlated disorder. The different disorder strengths are achieved by different procedures of the sample synthesis and quantitatively characterized by the micro-strain-type diffraction peak broadening. The system shifts to predominantly one phase state with smaller TC as the correlated disorder strength is decreased supporting the viewpoint that the origin of phase separation in the indicated manganite system is the correlated quenched disorder. The ground state of an ultimately chemically homogeneous sample is FM-like containing about 20% of the AFM minority phase. This FM-like state can be readily transformed to the AFM-like one having <20% of FM-phase by the decreasing of the effective charge carrier bandwidth via oxygen isotope substitution.