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Band ferromagnetism in systems of variable dimensionality

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

Affiliation

  1. National Institute of Materials Physics, Atomistilor 105b, P.O. Box MG-7, RO-77125 Magurele-Ilfov, Romania

Abstract

The Stoner instability of the paramagnetic state, yielding to the occurence of ferromagnetism, is reviewed for electron density of states reflecting changes in the dimensionality of the system. The situations treated are one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) cases and also a special case where the density of states has a parabolic shape near the Fermi level, and is half-filled at equilibrium. We recover the basic results obtained in the original work of E.C. Stoner [Proc. Roy. Soc. London A 165, 372 (1938)]; also we demonstrate that in 1D and 2D case, whenever the Stoner criterion is satisfied, the system evolves spontaneously towards maximum polarization allowed by Hund's rules. For the 3D case, the situation is that: (i) when the Stoner criterion is satisfied, but the ratio between the Hubbard repulsion energy and the Fermi energy is between 4/3 and 3/2, the system evolves towards a ferromagnetic state with incomplete polarization (the polarization parameter is between 0 and 1); (ii) when , the system evolves towards maximum polarization. This situation was also recognized in the original paper of Stoner, but with no further analysis of the obtained polarizations nor comparison with experimental results. We apply the result of calculation in order to predict the Hubbard interaction energy. Finally, for the case of half-filled parabolic density of states a result quite similar with the case of the free electron 3D DOS is obtained, but here the Hubbard energy has to be compared with the band half-widh, whereas the absolute value of the Fermi energy has no relevance in this model. The Stoner criterion is and for the total energy is minimized for incomplete polarization . We compare the results obtained from the present theoretical study with the newest available experimental data..

Keywords

Band magnetism, Stoner criterion, Low dimensional systems, Variable dimensionality.

Submitted at: Sept. 25, 2008
Accepted at: Nov. 11, 2008

Citation

C. M. TEODORESCU, G. A. LUNGU, Band ferromagnetism in systems of variable dimensionality, Journal of Optoelectronics and Advanced Materials Vol. 10, Iss. 11, pp. 3058-3068 (2008)