Designing switchable room-temperature multiferroics via the discovery of a novel magneto-electric coupling

Magnetoelectric (ME) coupling is the key ingredient for realizing the cross control of magnetism and ferroelectricity in multiferroics. However, multiferroics are not only rare in nature, especially at room temperature, but also the overwhelming majority of known multiferroics does not exhibit an highly-desired switching of magnetization when the polarization is reversed by an electric field. Here, we report group theory analysis and ab-initio calculations demonstrating, and revealing the origin of the existence of a novel form of ME coupling term in a special class of materials that does allow such switching. This term naturally explains the previously observed electric-field control of magnetism in the first known multiferroics, i.e., the Ni-X boracite family. It is also presently used to design a switchable room-temperature multiferroic having a rather large ferroelectric polarization, strong spontaneous magnetization, and strong ME coupling.