Nonmonotonic Crossover In Electronic Phase Separated Manganite Superlattices Driven By The Superlattice Period

Studying manganite superlattices [(LCMO)(2n)/(PCMO)(n)](t) made of La0.625Ca0.375MnO3 (LCMO) and Pr0.625Ca0.375MnO3 (PCMO), we found an unexpected behavior varying the period n. At small n, the ensemble is a three-dimensional ferromagnetic metal due to interfacial charge transfer. At large n, the LCMO layers dominate transport. However, rather than a smooth interpolation between these limits a sharp transport and magnetic anomaly is found at an intermediate critical PCMO thickness n*. Magnetic force microscopy reveals that the phase-separation length scale also maximizes at n* where, unexpectedly, it becomes comparable to that of the (La1-yPry)(0.625)Ca0.375MnO3 (LPCMO) alloy. We conjecture the phenomenon originates in a disorder-related length scale: Large charge-ordered clusters as in LPCMO can only nucleate when Pr-rich regions reach a critical size related to n*.