Electrical control of magnetic properties is crucial for device applications in the field of spintronics. Prof Ono and his research team at the Institute for Chemical research, together with NEC cooperation, have demonstrated the room-temperature electrical control of the ferromagnetic phase transition in cobalt, a representative of the transition-metal ferromagnet family. Solid-state field effect devices, consisting of an ultra-thin cobalt film covered by a dielectric layer and a gate-electrode on top of that, were fabricated (Figure 1). They found that the ferromagnetic state of the film could be turned on and off isothermally and reversed simply by applying an electric field between the cobalt layer and the gate electrode at room temperature. The shift of the Curie temperature was found to be up to 12 Kelvin by applying an electric field of about ±2 MV/cm.
The result is a significant development for future low-power magnetic devices. In addition, the demonstrated electric field effect of the two dimensional ferromagnet opens up a new way to explore and control magnetism in relation to the dimensionality.
Figure 1 Ferromagnetic phase transition of a metal ferromagnet of Cobalt (Co) was induced by applying a gate voltage (VG) at room temperature. The device for the transport measurements consists of a metal gate (Au/Cr), an insulator layer (HfO2), and an ultra-thin Co layer.