2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/29408Based on the combined model of the double exchange and the polaron, we have studied the small-to-large polaron crossover transition and explored its effects on the magnetic and transport properties in colossal magnetoresistance (CMR) manganites. We have used the variational Lang-Firsov canonical transformation, and shown that the magnetic and transport properties of both high and low $T_C$ manganites are well described in terms of a single formalism. We have reproduced the rapid resistivity drop below $T_C$, a realistic CMR ratio, and the {\it first-order-like} sharp magnetic phase transition, which are observed in low $T_C$ manganites.5 pages, 3 figures (ps)Strongly Correlated Electronstext