  We demonstrate that magnetic properties of ultra-thin Co films adjacent to
Gd2O3 gate oxides can be directly manipulated by voltage. The Co films can be
reversibly changed from an optimally-oxidized state with a strong perpendicular
magnetic anisotropy to a metallic state with an in-plane magnetic anisotropy,
or to an oxidized state with nearly zero magnetization, depending on the
polarity and time duration of the applied electric fields. Consequently, an
unprecedentedly large change of magnetic anisotropy energy up to 0.73 erg/cm2
has been realized in a nonvolatile manner using gate voltages of only a few
volts. These results open a new route to achieve ultra-low energy magnetization
manipulation in spintronic devices.
