Inverted shear-strain magnetoelastic coupling at the Fe/BaTiO₃ interface from polarised x-ray imaging

The elastic degree of freedom is widely exploited to mediate magnetoelectric coupling between ferromagnetic films and ferroelectric substrates. For epitaxial Fe films grown on clean BaTiO₃ substrates, shear strain can determine the underlying magnetoelastic coupling. Here, we use PhotoEmission Electron Microscopy of ferroic Fe and BaTiO₃ domains, combined with micromagnetic simulations, to directly reveal an inverted interfacial magnetoelastic coupling in the low-dimensional limit. We show that the magnetocrystalline anisotropy competes with the epitaxial shear strain to align the local magnetization of ultrathin Fe films close to the local polarization direction of the ferroelectric BaTiO₃ in-plane domains. Poling the BaTiO₃ substrate creates c-domains with no shear strain contribution with the local magnetization rotated by ~45°. Tuning shear strain magnetoelastic contributions suggests new routes for designing magnetoelectric devices.