We demonstrate unambiguous evidence of the electric field control of magnetic anisotropy in a wedge-shaped Co film of varying thickness. A copolymer ferroelectric of 70% vinylidene fluoride with 30% trifluoroethylene, P(VDF-TrFE) overlays the Co wedge, providing a large switchable electric field. As the ferroelectric polarization is switched from up to down, the magnetic anisotropy of the Co films changes by as much as 50%. At the lowest Co thickness the magnetic anisotropy switches from out-of-plane to in-plane as the ferroelectric polarization changes from up to down, enabling us to rotate the magnetization through a large angle at constant magnetic field merely by switching the ferroelectric polarization. The large mismatch in the stiffness coefficients between the polymer ferroelectric and metallic ferromagnet excludes typical magnetoelectric strain coupling; rather, the magnetic changes arise from the large electric field at the ferroelectric/ferromagnet interface.

Shireen, "Magnetoelectric effects in ferromagnetic cobalt/ferroelectric copolymer multilayer films" (2010). Stephen Ducharme Publications. 69.

The sweep rate dependence of the coercive field in magnetic thin films is well-known. Here we present an experimental investigation of the dependence of electric field control of magnetization on the magnetic field sweep rate. Our sample is a ferroelectric/ferromagnetic heterostructure, with a soft polymer ferroelectric in contact with a transition metal ferromagnet, Co. Previous work on these heterostructures revealed a large change in coercive field and anisotropy when the ferroelectric polarization was switched from up to down. The present work shows that faster sweep rates increase the changes in coercive field that arise from switching the ferroelectric polarization. Our data indicate that the field sweep rate is an important parameter in the investigation of magnetoelectric coupling.