  The control of magnetic materials and devices by voltages without electric
currents holds the promise of power-saving nano-scale devices. Here we study
the temperature-dependent voltage control of the magnetic anisotropy caused by
rare-earth (RE) local moments at an interface between a magnetic metal and a
non-magnetic insulator, such as Co|(RE)|MgO. Based on a Stevens operator
representation of crystal and applied field effects, we find large dominantly
quadrupolar intrinsic and field-induced interface anisotropies at room
temperature. We suggest improved functionalities of transition metal tunnel
junctions by dusting their interfaces with rare earths.
