Influence of dislocations and twin walls in BaTiO3 on the voltage-controlled switching of perpendicular magnetization

We investigate the influence of dislocations and twin walls in ${\mathrm{BaTiO}}_{3}$ on its ferroelectric response and the resulting effect on the perpendicular magnetic anisotropy (PMA) of a strain-coupled ${[\mathrm{Co}\ensuremath{\setminus}\mathrm{Ni}]}_{\mathrm{n}}$ film. A dense twinned structure in conjunction with a high dislocation density significantly reduces the converse piezoelectric effect of ${\mathrm{BaTiO}}_{3}$ by hindering the propagation of newly nucleated domains with an applied electric field. This, in turn, results in a modest reduction of the PMA of the ferromagnetic layer. On the other hand, the ferroelectric polarization reorients from [100] to [001] direction in a dislocation-free ${\mathrm{BaTiO}}_{3}$, inducing the maximum achievable in-plane compressive strain of 1.1%. A large fraction of this uniaxial strain is transferred to the magnetoelastically coupled ferromagnetic layers whose magnetization switches to in plane via the inverse magnetostriction effect. This work reveals the critical role of the interplay between twin walls and dislocations within a ferroelectric substrate in the performance of multiferroic heterostructures and provides insight into the development of highly energy-efficient magnetoelectric devices.