Sprial magnets as magnetoelectrics

An old but emerging class of materials that combine coupled electric and magnetic dipole order is "magnetoelectric multiferroics". In these materials, ferroelectric and magnetic (ferromagnetic or antiferromagnetic) states coexist or compete with each other. The interaction leads to a so-called magnetoelectric effect, which is defined as the induction of magnetization by an electric field or electric polarization by a magnetic field. In the past few years, a new set of magnetoelectric multiferroics such as TbMnO3 and Ni3V2O8 has been discovered. In these magnetoelectric multiferroics, ferroelectric order develops upon magnetic phase transition into a spiral magnetic ordered phase. In addition, these systems show large magnetoelectric effects accompanied by metamagnetic transitions. The noncollinear spiral magnetism is the key to understanding the magnetoelectric properties in these systems. In this article, I discuss the magnetoelectric coupling in spiral magnets and review recent advances in understanding of ferroelectricity and magnetoelectric effect in these new multiferroics. The studies presented here indicate that spiral magnets are promising candidates for magnetoelectrics showing large magnetoelectric effects at low magnetic fields.