High temperature susceptibility in electron doped Ca1-xYxMnO3: Double Exchange vs Superexchange

TL;DR

This study investigates the magnetic susceptibility of electron-doped Ca1-xYxMnO3, revealing how double exchange and superexchange interactions influence magnetic behavior across different doping levels and temperatures.

Contribution

It provides a detailed analysis of magnetic interactions in Ca1-xYxMnO3, combining experimental susceptibility data with Monte Carlo simulations to understand electron delocalization and magnetic polaron formation.

Findings

At low doping, susceptibility follows Curie-Weiss law only above 450 K.

Higher doping levels show Curie-Weiss behavior down to the magnetic ordering temperature.

Electrons are fully delocalized at high temperatures but form magnetic polarons near Tmo.

Abstract

We present a study of the magnetic properties of the electron doped manganites Ca1-xYxMnO3 (for 0<=x<=0.25) in the paramagnetic regime. For the less doped samples (x<=0.1) the magnetic susceptibility, c(T), follows a Curie-Weiss (CW) law only for T > 450 K and, below this temperature, c^-1(T) shows a ferrimagnetic-like curvature. We approached the discussion of these results in terms of a simple mean-field model where double exchange, approximated by a ferromagnetic Heisenberg-like interaction between Mn3+ and Mn4+ ions, competes with classical superexchange. For higher levels of doping (x>=0.15), the CW behaviour is observed down to the magnetic ordering temperature (Tmo) and a better description of c(T) was obtained by assuming full delocalization of the eg electrons. In order to explore the degree of delocalization as a function of T and x, we analyzed the problem through Montecarlo simulations. Within this picture we found that at high T the electrons doped are completely delocalized but, when Tmo is approached, they form magnetic polarons of large spin that cause the observed curvature in c^-1(T) for x<=0.1.