Materials displaying ferromagnetism (long range magnetic order) or ferroelectricity (long range electric order) are omnipresent in our daily life. Ferromagnetism is key to devices like power transformers or computer hard disks, while ferroelectricity is the basis of actuators, sensors, capacitors, and nonvolatile computer memory. A single compound that boasts both properties-a so-called multiferroic-could be the basis of a host of new applications, particularly if electric order can control

more »

... etic order (and vice versa). Now, John Heron at the University of California, Berkeley, and colleagues have achieved one of the longstanding goals of multiferroics research: they show they can reversibly switch the magnetization of a multiferroic system by 180 • with the application of an electric voltage at room temperature. The results, appearing in Physical Review Letters[1], could pave the way to a new generation of compact magnetic devices with unmatched energy efficiency. As early as 1894, Pierre Curie suggested that magnetoelectricity-the interaction between dielectric and magnetic properties-offered a way to change a material's magnetic properties with an electric field. Half a century later, magnetoelectricity was discovered in Cr 2 O 3 , but it was far too small and too rarely occurring in other materials to be of any technological use. Hope resurged when, many years after their actual discovery, multiferroics were recognized as a potential source for pronounced magnetoelectric effects (for a review see Ref. [2]). Yet the marriage between magnetic and electric order is not, it turns out, a happy one. The most prominent mechanisms promoting magnetic order exclude electric order (and likewise the other way around) so multiferroicity is always a compromise [3] . It usually occurs only at low temperature and the magnetization or the polarization (or both) are orders of magnitude smaller than in established ferromagnets and ferroelectrics. This also holds for BiFeO 3 , the only compound so far dis-