Jahn-Teller distortions and phase separation in doped manganites

TL;DR

This paper uses a minimal Kondo-lattice model to explore Jahn-Teller distortions and phase separation in doped manganites, revealing complex phase diagrams with magnetic and electronic transitions influenced by temperature and magnetic fields.

Contribution

It introduces a simplified model capturing phase separation and magnetic order transitions in doped manganites, highlighting the impact of Jahn-Teller effects and doping on electronic properties.

Findings

Significant reduction in itinerant charge carriers compared to doping level

Wide range of doping concentrations exhibit phase separation

Temperature and magnetic field variations can induce metal-insulator transitions

Abstract

A "minimal model" of the Kondo-lattice type is used to describe a competition between the localization and metallicity in doped manganites and related magnetic oxides with Jahn-Teller ions. It is shown that the number of itinerant charge carriers can be significantly lower than that implied by the doping level x. A strong tendency to the phase separation is demonstrated for a wide range of intermediate doping concentrations vanishing at low and high doping. The phase diagram of the model in the x-T plane is constructed. At low temperatures, the system is in a state with a long-range magnetic order: antiferromagnetic (AF), ferromagnetic (FM), or AF-FM phase separated (PS) state. At high temperatures, there can exist two types of the paramagnetic (PM) state with zero and nonzero density of the itinerant electrons. In the intermediate temperature range, the phase diagram includes different kinds of the PS states: AF-FM, FM-PM, and PM with different content of itinerant electrons. The applied magnetic field changes the phase diagram favoring the FM ordering. It is shown that the variation of temperature or magnetic field can induce the metal-insulator transition in a certain range of doping levels.