First Principles Study of (111)-Epitaxially Strained Multiferroic Perovskites

First principles calculations are used to explore the effect of (111) epitaxial strain in the spin-phonon and strain-polarization couplings of transition metal perovskite oxides. Using SrMnO₃ as a prototypical model system, we find that (111)-strain drives the antiferromagnetic-paraelectric cubic phase of SrMnO₃ to a previously unreported monoclinic multiferroic ferroelectric-ferromagnetic phase that is not present in either bulk or (001)-strained form. Under tensile (111)-strain, ferromagnetism stabilizes ferroelectricity at smaller strain values than the 001 case, and displays an out of plane polarization component P_s ~ 10 μC/cm². We further estimate magnetic ordering temperatures and compute lowest phonon frequencies as a function of (111)-strain.