Effects of correlated disorder on the magnetism of double exchange systems

TL;DR

This paper investigates how short-range correlated disorder influences ferromagnetism in double exchange systems, revealing inhomogeneities, altered Curie temperatures, and providing a microscopic model for Griffiths phases.

Contribution

It introduces a model incorporating correlated disorder effects on magnetism in double exchange systems, validated by Monte Carlo simulations, and explains variations in magnetic properties.

Findings

Large inhomogeneities in charge and spin densities

Increased Curie temperatures due to disorder

Small spin stiffnesses and variable D/T_C ratios

Abstract

We study the effects of short-range correlated disorder arising from chemical dopants or local lattice distortions, on the ferromagnetism of 3d double exchange systems. For this, we integrate out the carriers and treat the resulting disordered spin Hamiltonian within local random phase approximation, whose reliability is shown by direct comparison with Monte Carlo simulations. We find large scale inhomogeneities in the charge, couplings and spin densities. Compared with the homogeneous case, we obtain larger Curie temperatures ($T_{C}$) and very small spin stiffnesses ($D$). As a result, large variations of $\frac{D}{T_{C}}$ measured in manganites may be explained by correlated disorder. This work also provides a microscopic model for Griffiths phases in double exchange systems.