Figure 1: Triangle

A big push in the field of multiferroics has focused on engineering strong magnetoelectric coupling. The magnetoelectric effect describes the coupling between electric and magnetic fields in matter. Strong magnetoelectric coupling in materials would enable a new generation of devices where we could say manipulate magnetic data bits with an electric field. Another idea is to evolve computational capabilities to utilize not only the presence of charge, but the spin of the electrons. The so called field of spintronics would need materials that can respond quickly to small applied fields (typically we envision materials working with small electric fields to keep power consumption, heating, etc. to a minimum) and have deterministic control of electron spins (i.e., magnetic order). Magnetoelectric materials – like some multiferroics – offer exciting opportunities for making these types of devices a reality. 

Figure 2: Switching

This figure describes the main essence of the paper we’ve been discussing. We were attempting to show that we could control ferromagnetism with an electric field. On the left is a schematic of a cross-sectional view of the device we used in this study. Very simply, it consisted of a ferromagnetic materials (Co_0.9Fe_0.1, here called CoFe) in contact with the magnetoelectric, multiferroic BiFeO₃. The device structure allowed us to apply electric fields in the plane of the film between the blue electrodes. This enabled deterministic control of the ferroelectric switching in the BiFeO₃. The antiferromagnetic order in BiFeO₃, in turn, coupled to the ferroelectric order and upon a change in the ferroelectricity a corresponding change in the antiferromagnetism is obtained. This antiferromagnetic order is then coupled to the ferromagnetic order in CoFe via an exchange interaction. Demonstrated on the right is what happens to the ferromagnet upon application of an electric field. The magnetic domain structure is observed to switch back-and-forth by 90° rotations as imaged via x-ray magnetic circular dichroism photoemission electron microscopy.