Multiferroics

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Multiferroics are materials that have coupled electric, magnetic and structural order parameters that result in simultaneous ferroic properties (i.e. ferroelectric, ferromagnetic, or ferroelastic). Some materials having not ferromagnetic but antiferromagnetic, ferrimagnetic, ferrotoroidic, or helimagnetic ordering are accepted as multiferroics as well.

Only a few single phase multiferroic materials exist. This is, amongst other reasons, because the classical ferroelectric perovskites (BaTiO₃, PZT, etc) contain d ions with empty shells (e.g. Ti⁴⁺ is 3d0) and thus bear no magnetic moment. Exceptions include some orthorhombic manganites, like TbMnO₃, and Bi-based perosvkites like BiFeO₃ or BiMnO₃. In addition, most multiferroics are antiferromagnetic or weak-ferromagnets, BiMnO₃ being one of the very few ferromagnetic and ferroelectric multiferroics. Some multiferroics, like TbMnO₃, exhibit the magnetoelectric effect. The scientific community has a large interest in this subgroup of multiferroic materials, because promising phenomena exist in these materials for technical applications.