Multiferroics

Multiferroics are compounds that exhibit two or more of the following ferroic order parameters: anti-, ferri- or ferromagnetism, ferroelectricity, ferroelasticity and ferrotoroidicity. Multiferroicity is both of academic and technological interest. The academic interest is caused by the fact that the interaction of two or more order parameters may lead to new physical effects. The technological interest originates particularly from multiferroics that show ferromagnetic and ferroelectric characteristics. If both are present, the so-called magnetoelectric effect may occur, which results in a coupling of magnetization and electric polarization. This interaction can be used in future storage technologies. Even now only a very few multiferroic compounds are known, among them TbMnO₃, the Bi-based perovskites (BiFeO₃, BiMnO₃), and the Brownmillerites (Ca₂(Al,Fe³⁺)₂O₅). In our group we concentrate on Brownmillerites and their ferrimagnetic and ferroelectric properties.