Two-fluid behaviour at the origin of the resistivity peak in doped manganites

¹  Department of Physics and the Resnick Institute, Bar-Ilan University - Ramat-Gan 52900, Israel
²  Racah Institute of Physics, The Hebrew University - Jerusalem 91904, Israel
³  Moscow State Steel and Alloys Institute - 119049 Moscow, Russia

Corresponding author: golosov@phys.huji.ac.il

Received: 17 June 2008
Accepted: 14 October 2008

Abstract

We report a series of magnetic and transport measurements on high-quality single crystal samples of colossal magnetoresistive manganites, La_0.7Ca_0.3MnO₃ and Pr_0.7Sr_0.3MnO₃. 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, , around the Curie point T_C. In the case of Pr_0.7Sr_0.3MnO₃, the resistivity peak occurs at a considerably higher temperature, . 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 T_C and T_MI. Our data indeed imply that while magnetic and transport properties of the manganites are closely inter-related, the two transitions at T_C and T_MI can be viewed as distinct phenomena.