Two-Fluid Behaviour at the Origin of the Resistivity Peak in Doped Manganites

TL;DR

This study investigates the origin of the resistivity peak in doped manganites, revealing that it results from two-fluid behavior involving separate magnetic and electronic transitions, challenging the phase separation explanation.

Contribution

It demonstrates that the resistivity peak is due to distinct magnetic and electronic phase transitions, not phase separation, using magnetic, transport, and spectroscopy measurements.

Findings

Resistivity peak occurs at T_{MI} > T_2, not necessarily linked to phase separation.

Magnetic and transport properties are interconnected but involve separate transitions.

Two-fluid model explains the phenomena without phase separation.

Abstract

We report a series of magnetic and transport measurements on high-quality single crystal samples of colossal magnetoresistive manganites, La_{0.7} Ca_{0.3} Mn O_3 and Pr_{0.7} Sr_{0.3} Mn O_3. 1 % Fe doping allows a Moessbauer spectroscopy study, which shows (i) unusual line broadening within the ferromagnetic phase and (ii) a coexistence of ferro- and paramagnetic contributions in a region, T_1<T<T_2, around the Curie point T_C. In the case of Pr_{0.7} Sr_{0.3} Mn O_3, the resistivity peak occurs at a considerably higher temperature, T_{MI}>T_2. 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 interrelated, the two transitions at T_C and T_{MI} can be viewed as distinct phenomena.