Detection of paramagnetic to charge-ordered insulator phase transitions in phase separated (La1−yPry

Hole-doped manganese oxides (manganites) exhibit phase separation which allows for the manipulation of phase transitions with the application of external stimuli. The three competing phases of the manganite (La1−yPry)1−xCaxMnO3 (LPCMO) are paramagnetic insulating (PMI), charge-ordered insulating (COI), and ferromagnetic metallic (FMM). In LPCMO thin films, the substrate induced strain often makes it difficult to distinguish between the two insulating phases (PMI and COI) using resistivity and/or magnetization measurements. Here we report a method for determining the PMI-COI transition temperature of LPCMO thin films by fitting resistance vs. temperature (R−T) data to the Arrhenius equation. This method also yields the activation energy in the COI phase which agrees with direct measurements using scanning tunneling microscopy. Analysis of the R−T data suggests that adiabatic polaron hopping is the transport mechanism in both the PMI and COI phases while variable range hopping (VRH) is the dominant mechanism in the mixed FMM/COI state.