Disorder in Diluted Spin Systems

TL;DR

This paper investigates how substitutional disorder affects the magnetic properties of diluted Heisenberg spin systems, focusing on the stability of ferromagnetism and the Curie temperature across different lattice types and interaction ranges.

Contribution

It introduces a numerical method using magnon Green's functions within Tyablikov approximation to analyze magnetic stability in disordered diluted spin systems for various interactions.

Findings

No magnetic order below critical percolation for short-range interactions.

Linear Curie temperature dependence on spin concentration for long-range interactions.

Method applicable to different lattices and spin magnitudes.

Abstract

The influence of substitutional disorder on the magnetic properties of diluted Heisenberg spin systems is studied with regard to the magnetic stability of ferromagnetic diluted semiconductors (DMS). The equation of motion for the magnon Green's function within Tyablikov approximation is solved numerically for finite systems. The resulting spectral density is then used to estimate the magnetization and Curie temperature of an infinite system. This method is suitable for any form of a ferromagnetic exchange interaction. Besides different lattices and spin magnitude $S$, exchange interactions of different range are examined. The results show that, for short-range interaction, no magnetic order exists below the critical percolation concentration, whereas a linear dependence of the Curie temperature on the concentration of spins is found for ferromagnetic long-range interaction.