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Band ferromagnetism in systems of variable dimensionality II: the two-dimensional finite-temperature case

G. A. LUNGU1,* , C. M. TEODORESCU1

Affiliation

  1. National Institute of Materials Physics, P.O. box MG-7, Bucharest-Magurele, Ilfov, 077125, Romania

Abstract

In a previous paper [C.M. Teodorescu and G.A. Lungu, J. Optoelectron. Adv, Mater. 10, 3058 (2008)] we studied the zero temperature problem of the occurence of band ferromagnetism and of the derivation of the Stoner criterion for systems of variable dimensionality: 1D, 2D, 3D. The dimensionality of the system is reflected by a different shape of the density of states. For ideal 2D systems, the density of states is a constant and this seems to be the simplest case to be modelled. In this paper we integrate to this simplest model of constant density of states the influence of temperature, in order to analyse temperature-dependent ferromagnetism in two-dimensional systems, such as magnetic surfaces. Some surprising results are obtained, namely: (i) in contrast to the common belief, in this case the influence of the temperature is to favour, not to inhibit ferromagnetism, i.e. in some conditions ferromagnetism may be obtained at finite temperature, even for systems where the zero temperature Stoner criterion is not satisfied; (ii) for a careful choice of the ratio between the Hubbard energy parameter and the equilibrium zero-temperature Fermi level value , systems nonmagnetic at low temperature which become magnetic at higher temperature may be possible. A short review of the experimental data which may be interpreted within the present formalism is also given..

Keywords

Low-dimensional systems, Ferromagnetism, Stoner criterion, Surfaces.

Submitted at: March 25, 2009
Accepted at: April 28, 2009

Citation

G. A. LUNGU, C. M. TEODORESCU, Band ferromagnetism in systems of variable dimensionality II: the two-dimensional finite-temperature case, Journal of Optoelectronics and Advanced Materials Vol. 11, Iss. 4, pp. 369-379 (2009)