We report a series of magnetic and transport measurements on high-quality single crystal samples of colossal magnetoresistive manganites, La0.7Ca0.3MnO3 and Pr0.7Sr0.3MnO3. 1% Fe doping allows a Mössbauer spectroscopy study, which shows i) unusual line broadening within the ferromagnetic phase and ii) a coexistence of ferro- and paramagnetic contributions in a region, T1<T<T2, around the Curie point TC. In the case of Pr0.7Sr0.3Mn O3, the resistivity peak occurs at a considerably higher temperature, TMI > T2. This shows that phase separation into metallic (ferromagnetic) and insulating (paramagnetic) phases cannot be generally responsible for the resistivity peak (and hence for the associated colossal magnetoresistance). Our results can be understood phenomenologically within the two-fluid approach, which also allows for a difference between TC and TMI. Our data indeed imply that while magnetic and transport properties of the manganites are closely inter-related, the two transitions at TC and TMI can be viewed as distinct phenomena.
|Published - 2008