Berlin 2008 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 20: Multiferroics
MA 20.2: Vortrag
Mittwoch, 27. Februar 2008, 14:15–14:30, EB 202
Towards a microscopic theory of toroidal moments in periodic crystals — •Claude Ederer1 and Nicola A. Spaldin2 — 1School of Physics, Trinity College Dublin, Dublin 2, Ireland — 2Materials Department, University of California, Santa Barbara, CA 93106, USA
A toroidal moment breaks both time- and space-inversion symmetries simultaneously, and thus facilitates coupling between magnetization and electric polarization in magnetoelectric multiferroics. Furthermore, the recent observation of toroidic domains suggests that "ferrotoroidicity" represents a fundamental form of ferroic order, in addition to ferromagnetism, ferroelectricity, and ferroelasticity [1].
Here we review the basic definitions of toroidal moments and illustrate the difficulties in evaluating the toroidal moment of an infinite periodic system. We show that periodic boundary conditions give rise to a multivaluedness of the toroidal moment per unit cell, in close analogy to the case of the electric polarization in bulk periodic crystals. We then evaluate the toroidal moments of several multiferroic and magnetoelectric materials (BaNiF4, LiCoPO4, GaFeO3, and BiFeO3) in the "localized dipole limit", where the toroidal moment is caused by a time and space reversal symmetry-breaking arrangement of localized magnetic moments [2].
[1] B. B. Van Aken, J. P. Rivera, H. Schmid, and M. Fiebig, Nature 449, 702 (2007).
[2] C. Ederer and N. A. Spaldin, arXiv:0706.1974v1 [cond-mat.str.el], Phys. Rev. B, in press (2007).