  Multifunctional materials composed of ultrathin magnetic films with
perpendicular magnetic anisotropy combined with ferroelectric substrates
represent a new approach toward low power, fast, high density spintronics. Here
we demonstrate Co/Ni multilayered films with tunable saturation magnetization
and perpendicular anisotropy grown directly on ferroelectric PZT
[Pb(Zr_xTi_1-x)O_3] substrate plates. Electric fields up to +/- 2 MV/m expand
the PZT by 0.1% and generate at least 0.02% in-plane compression in the Co/Ni
multilayered film. Modifying the strain with a voltage can reduce the coercive
field by over 30%. We also demonstrate that alternating in-plane tensile and
compressive strains (less than 0.01%) can be used to propagate magnetic domain
walls. This ability to manipulate high anisotropy magnetic thin films could
prove useful for lowering the switching energy for magnetic elements in future
voltage-controlled spintronic devices.
