The symmetry properties, order parameters, and magnetoelectric phase diagrams
of multiferroics are discussed. After brief reviews of Ni3V2O8,
TbMnO3, and RbFe(MoO4)2, we present a detailed analysis of
RMn2O5 (with R=Y, Ho, Dy, Er, Tb, Tm).Comment: 23 pages, 7 figures, 3 tables. For FOCUS ON MULTIFERROICS (IOP