10 research outputs found
Competition of Zener and polaron phases in doped CMR manganites
Inspired by the strong experimental evidence for the coexistence of localized
and itinerant charge carriers close to the metal-insulator transition in the
ferromagnetic phase of colossal magnetoresistive manganese perovskites, for a
theoretical description of the CMR transition we propose a two-phase scenario
with percolative characteristics between equal-density polaron and Zener
band-electron states. We find that the subtle balance between these two states
with distinctly different electronic properties can be readily influenced by
varying physical parameters, producing various ``colossal'' effects, such as
the large magnetization and conductivity changes in the vicinity of the
transition temperature.Comment: 8 pages, 5 figure
Mixed-phase description of colossal magnetoresistive manganites
In view of recent experiments, indicating the spatial coexistence of
conducting and insulating regions in the ferromagnetic metallic phase of doped
manganites, we propose a refined mixed-phase description. The model is based on
the competition of a double-exchange driven metallic component and a polaronic
insulating component, whose volume fractions and carrier concentrations are
determined self-consistently by requiring equal pressure and chemical
potential. The resulting phase diagram as well as the order of the phase
transition are in very good agreement with measured data. In addition,
modelling the resistivity of the mixed, percolative phase by a random resistor
network, we obtain a pronounced negative magnetoresistance in the vicinity of
the Curie temperature .Comment: 7 pages, 6 figure