Friday, September 15, 2006
4:00 PM
Physics Building, Room 204
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"The Unusual Symmetry of Ferroelectricity in Incommensurate Magnets"

Brooks Harris , University of Pennsylvania
[Host: Seunghun Lee]
The coupling between electric and magnetic properties in condensed matter systems is usually very weak. In part this may be viewed as being a result of the fact that the electric and magnetic fields exhibit different symmetries which do not naturally couple to one another. Here I discuss a class of materials which display a very unusual phase transition in which magnetic ordering and the development of ferroelectricity occur simultaneously. This coupling has drawn great interest recently mainly due to various experimental results for this fascinating coupling whereby magnetic ordering induces erroelectricity. My main objective is to understand the phenomonology of this magnetoelectric coupling via a Landau expansion whose consequences depend crucially on the symmetry properties of the magnetic order and the consistency of this order with ferroelectric ordering. Even this simple phenomenological theory explains a number of nontrivial ferroelectric properties which have been observed. I discuss briefly the advantages of such a symmetry analysis versus specific microscopic models.

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