Ground state of a double-exchange system containing impurities: bounds of ferromagnetism

TL;DR

This paper investigates the conditions under which ferromagnetism appears or disappears in a double-exchange system with impurities, using theoretical models and approximations to determine the boundary between magnetic states.

Contribution

It introduces a method to determine the ferromagnetic boundary in a disordered double-exchange system and derives a related $t-J$ model from the Hamiltonian.

Findings

Boundary between ferromagnetic and non-ferromagnetic states identified

Dynamical Mean Field Approximation results agree with energy comparison

Derived a $t-J$ model from the double-exchange Hamiltonian

Abstract

We study the boundary between ferromagnetic and non-ferromagnetic ground state of a double-exchange system with quenched disorder for arbitrary relation between Hund exchange coupling and electron band width. The boundary is found both from the solution of the Dynamical Mean Field Approximation equations and from the comparison of the energies of the saturated ferromagnetic and paramagnetic states. Both methods give very similar results. To explain the disappearance of ferromagnetism in part of the parameter space we derive from the double-exchange Hamiltonian with classical localized spins in the limit of large but finite Hund exchange coupling the $t-J$ model (with classical localized spins).