The unique effect of in-plane anisotropic strain in the magnetization control by electric field

A model for \(La_{1-x}Sr_xMnO_3\) which incorporates the physics of dynamic Jahn-Teller and double-exchange effects is presented and solved via a dynamical mean field approximation. In an intermediate coupling regime the interplay of these two effects is found to reproduce the behavior of the resistivity and magnetic transition temperature observed in \(La_{1-x} Sr_x MnO_3\).

Magnetoelectric coupling permits a magnetic order parameter to be addressed electrically or vice versa, and could find use in data storage, field sensors and actuators. Coupling constants for single phase materials such as chromium dioxide, boracites and manganites are typically as low as 10^{-12} - 10^{-9} s/m, e.g. because the polarisations and magnetisations are small. Two phase multiferroics with strain mediated coupling, such as laminates, composites and epitaxial nanostructures, are more promising because each phase may be independently optimised. The resulting magnetoelectric switching can be larger, e.g. 10^{-8} s/m, but it is not sharp because clean coupling is precluded by the complexity of the microstructures and concomitant strain fields. Here we report a giant sharp magnetoelectric effect at a single epitaxial interface between a 40 nm ferromagnetic stress-sensitive La_{0.67}Sr_{0.33}MnO_3 film, and a 0.5 mm BaTiO_3 substrate that is ferroelectric, piezoelectric and ferroelastic. By applying a small electric field (4-10 kV/cm) across the entire structure, we achieve persistent changes in film magnetisation of up to 65% near the BaTiO_3 structural phase transition at around 200 K. This represents a giant magnetoelectric coupling (2.3*10-7 s/m) that arises from strain fields due to ferroelastic non-180 degree domains whose presence we confirm using x-ray diffraction. The coupling persists over a wide range of temperatures including room temperature, and could therefore inspire a range of sensor and memory applications.