Significance of phase difference in magnetism and the magneto-electric effect

Abstract

For the new class of multi-ferroics, in which inversion symmetry is broken by magnetic ordering, a number of models have been developed to describe the exchange interactions that might give rise to net polarisation. We explore the importance of phase factors in these theories and how this concept brings together existing ideas within a common motif. Phase differences appear ubiquitous within the subject and they are fixed or free dependent upon the symmetry of the magnetic atoms. Further, we state restrictions upon which representations and co-representations a system displaying electric polarisation can order under. © 2009 IOP Publishing Ltd.