Engineering magnetoelectric coupling in 4H-SrMnO3 through chemical pressure

New multiferroic materials are sought to enable transformative next-generation technologies such as ultralow-power memory devices. Magnetoelectric (ME) coupling between ferromagnetic (FM) and ferroelectric (FE) orderings provides the key functionality in this pursuit, but it is difficult to engineer these into a single material due to their competing chemical requirements. We recently developed a symmetry-based approach to design ME coupling in perovskite materials, and now we seek to showcase its wider utility in more complex structure types. 4H-SrMnO3 exhibits several structural and magnetic instabilities which render it amenable to our ME coupling scheme, but the octahedral tilts in this system must be reoriented to induce an improper FE mode – this represents the final symmetry-breaking ingredient required to induce ME coupling. We seek to perform a variable-temperature neutron diffraction experiment on GEM on the series 4H-Sr1-xCaxMnO3 to assess whether chemical pressure effects unlock the FE mode in this system, thus providing the critical symmetry-required ingredients for ME coupling. Our results will highlight the potential of hexagonal perovskite polytypes to demonstrate technologically useful ferroic behaviours, hence illustrating the generality of our symmetry approach to realise new ME multiferroics for next-generation device applications.