Disordered Correlated Kondo-lattice model

TL;DR

This paper develops a self-consistent theoretical approach to study the electronic and magnetic properties of disordered local-moment systems like diluted ferromagnetic semiconductors, incorporating disorder effects and long-range interactions.

Contribution

It introduces a novel self-consistent method combining CPA and modified RKKY theory to analyze disordered Kondo-lattice models with detailed dependency on system parameters.

Findings

Exchange integrals are strongly dependent on magnetic ion concentration.

Disorder induces anomalies in the spin spectrum at low dilution.

The theory predicts key magnetic and electronic properties as functions of system parameters.

Abstract

We propose a self-consistent approximate solution of the disordered Kondo-lattice model (KLM) to get the interconnected electronic and magnetic properties of 'local-moment' systems like diluted ferromagnetic semiconductors. Aiming at $(A_{1-x}M_x)$ compounds, where magnetic (M) and non-magnetic (A) atoms distributed randomly over a crystal lattice, we present a theory which treats the subsystems of itinerant charge carriers and localized magnetic moments in a homologous manner. The coupling between the localized moments due to the itinerant electrons (holes) is treated by a modified RKKY-theory which maps the KLM onto an effective Heisenberg model. The exchange integrals turn out to be functionals of the electronic selfenergy guaranteeing selfconsistency of our theory. The disordered electronic and magnetic moment systems are both treated by CPA-type methods. We discuss in detail the dependencies of the key-terms such as the long range and oscillating effectice exchange integrals, 'the local-moment' magnetization, the electron spin polarization, the Curie temperature as well as the electronic and magnonic quasiparticle densities of states on the concentration $x$ of magnetic ions, the carrier concentration $n$, the exchange coupling $J$, and the temperature. The shape and the effective range of the exchange integrals turn out to be strongly $x$-dependent. The disorder causes anomalies in the spin spectrum especially in the low-dilution regime, which are not observed in the mean field approximation.