Carrier induced ferromagnetism in concentrated and diluted local-moment systems

TL;DR

This paper models the magnetic properties of both concentrated and diluted magnetic semiconductors using the Kondo-lattice model, highlighting how low band occupations and carrier compensation influence ferromagnetic ordering.

Contribution

It introduces a theoretical approach combining the Kondo-lattice model with CPA to analyze ferromagnetism in magnetic semiconductors, considering disorder and carrier effects.

Findings

Low band occupations favor ferromagnetism due to indirect coupling.

Ferromagnetism occurs at carrier concentrations smaller than magnetic moment concentration.

Charge carrier compensation is crucial for carrier-induced ferromagnetism in real materials.

Abstract

For modeling the magnetic properties of concentrated and diluted magnetic semiconductors, we use the Kondo-lattice model. The magnetic phase diagram is derived by inspecting the static susceptibility of itinerant band electrons, which are exchange coupled to localized magnetic moments. It turns out that rather low band occupations favour a ferromagnetic ordering of the local moment systems due to an indirect coupling mediated by a spin polarization of the itinerant charge carriers. The disorder in diluted systems is treated by adding a CPA-type concept to the theory. For almost all moment concentrations x, ferromagnetism is possible, however, only for carrier concentrations n distinctly smaller than x. The charge carrier compensation in real magnetic semiconductors (in Ga_{1-x}Mn_{x}As by e.g. antisites) seems to be a necessary condition for getting carrier induced ferromagnetism.