Order Parameters and Phase Diagrams of Multiferroics
  The symmetry properties, order parameters, and magnetoelectric phase diagrams of multiferroics are discussed. After brief reviews of Ni$_3$V$_2$O$_8$, TbMnO$_3$, and RbFe(MoO$_4$)$_2$, we present a detailed analysis of RMn$_2$O$_5$ (with R=Y, Ho, Dy, Er, Tb, Tm). 
A. B. Harris, Amnon Aharony, and O. Entin-Wohlman