Ferroelectricity

In physics and materials science, ferroelectricity is the property of certain materials that exhibit a spontaneous electric polarization—an internal electric alignment that arises naturally without an external source. This polarization can be reversed when an external electric field is applied. All ferroelectric materials are also piezoelectric (they generate an electric charge when mechanically stressed) and pyroelectric (they generate a charge when heated or cooled). Their distinctive feature is that the natural electrical polarization is reversible. The term ferroelectricity was coined in analogy to ferromagnetism, where a material exhibits a permanent magnetic moment. Ferromagnetism was already well established when ferroelectricity was first observed in 1920 in Rochelle salt by American physicist Joseph Valasek. The prefix ferro (meaning iron) was adopted even though most ferroelectric materials do not contain iron. Materials that are both ferroelectric and ferromagnetic are known as multiferroics, and they are of particular interest because they combine electric and magnetic ordering in a single system.