Non-perturbative model and ferromagnetism in dilute magnetsR. Bouzerar1, G. Bouzerar2 and T. Ziman3
1 Université de Picardie Jules Verne (LPMC) - 33 rue Saint-Leu, 80039 Amiens Cedex 01, France
2 Laboratoire Louis Néel - 25 avenue des Martyrs, CNRS, B.P. 166, 38042 Grenoble Cedex 09, France
3 Institut Laue Langevin - B.P. 156, 38042 Grenoble, France
received 19 November 2006; accepted in final form 4 May 2007; published June 2007
published online 25 May 2007
We calculate magnetic couplings in the V-Jpd model for dilute magnets, in order both to identify the relevant parameters which control ferromagnetism and also to bridge the gap between first-principle calculations and model approaches. The magnetic exchange interactions are calculated non-perturbatively and disorder in the configuration of impurities is treated exactly, allowing us to test the validity of effective medium theories. Results differ qualitatively from those of weak coupling. In contrast to mean-field theory, increasing Jpd may not favor high Curie temperatures: TC scales primarily with the bandwidth. High-temperature ferromagnetism at small dilutions is associated with resonant structure in the p-band. Comparison to diluted magnetic semiconductors indicate that Ga(Mn)As has such a resonant structure and thus this material is already close to optimality.
75.10.-b - General theory and models of magnetic ordering.
75.50.Pp - Magnetic semiconductors.
77.80.Bh - Phase transitions and Curie point.
© Europhysics Letters Association 2007