The Symmetry of Multiferroics
Abstract
Description
This paper represents a detailed instruction manual for constructing the Landau expansion for magnetoelectric coupling in incommensurate ferroelectric magnets. The first step is to describe the magnetic ordering in terms of symmetry adapted coordinates which serve as complex valued magnetic order parameters whose transformation properties are displayed. In so doing we use the previously proposed technique to exploit inversion symmetry, since this symmetry had been universally overlooked. Having order parameters of known symmetry which describe the magnetic ordering, we are able to construct the trilinear interaction which couples incommensurate magnetic order to the uniform polarization in order to treat many of the multiferroic systems so far investigated. The role of this theory in comparison to microscopic models is discussed.
29 pages, 6 figures. In Table XVIII I corrected (for NVO) G_3 to G_4. For TbMn_2O_5 I called the analysis of Appendix B "simplfied" because I only used one wavevector out of the star of q. The reader might not like this, but the results using inversion symmetry seem to be OK. I also added a clarifying sentence to the fourth conclusion ("By considering...")
29 pages, 6 figures. In Table XVIII I corrected (for NVO) G_3 to G_4. For TbMn_2O_5 I called the analysis of Appendix B "simplfied" because I only used one wavevector out of the star of q. The reader might not like this, but the results using inversion symmetry seem to be OK. I also added a clarifying sentence to the fourth conclusion ("By considering...")