New routes to multiferroics

Multiferroic materials are those which possess both ferroelectric and ferromagnetic properties. Clearly, there is a contradiction here since ferromagnetism requires d-electrons while ferroelectricity generally occurs only in the absence of d-electrons. Several multiferroics demonstrating magnetoelectric coupling effects have, however, been discovered in the past few years, but they generally make use of alternative mechanisms in attaining these properties. Several new ideas and concepts have emerged in the past two years, typical of them being magnetic ferroelectricity induced by frustrated magnetism, lone pair effect, charge-ordering and local non-centrosymmetry. Charge-order driven magnetic ferroelectricity is interesting in that it would be expected to occur in a large number of rare earth manganites, $Ln_{1-x}A_xMnO_3$ (A = alkaline earth), well known for colossal magnetoresistance, electronic phase separation and other properties. In this article, we discuss novel routes to multiferroics, giving specific examples of materials along with their characteristics