Novel features of multiferroic and magnetoelectric ferrites and chromites exhibiting magnetically driven ferroelectricity
A few oxides such as YMnO3, TbMnO3, YMn2O5 and BiFeO3 constituted the small family of well-characterized multiferroics until recently, but this area of research has been enlarged significantly due to the advent of a novel class of oxides exhibiting interesting multiferroic and magnetoelectric properties arising from magnetically induced ferroelectricity. Interestingly, these materials are simple transition metal oxides, most of them possessing the perovskite structure. In this review article, we present the significant features of multiferroic and magnetoelectric ferrites and chromites which owe their ferroelectricity to magnetic interactions. Some of the important systems discussed are BiFeO3 whose properties are affected by magnetic and electric fields, rare-earth orthoferrites LnFeO3 (Ln = Dy, Gd and Sm) and rare-earth orthochromites LnCrO3, where exchange-striction plays a significant role. Perovskite oxides of the type Y(A1−xBx)O3 (A, B = Fe, Cr, Mn) exhibit multiferroic properties, although the existence of these properties in YFeO3 and YCrO3 is in doubt. Such oxides with a non-magnetic rare-earth cation at the A site and two transition metal ions in the B-site permit tuning the transition temperatures by varying the B site ions and their relative proportions or the Ln ion. Multiferroic properties of simple ferrites such as Al(Ga)FeO3 where cation disorder appears to play a role are also discussed. Problems and challenges in this area of research are indicated.