We use ab initio calculations to systematically study the phase diagram of multiferroic ${\mathrm{Sr}}_{1-x}{\mathrm{Ba}}_x{\mathrm{MnO}}_3$ ($0\le x\le 1$) as a function of chemical doping, epitaxial strain, and external pressure. We find that by replacing Sr with Ba in cubic ${\mathrm{SrMnO}}_3$ and imposing epitaxial strain, the material can be tuned to the vicinity of a first order transition between two multiferroic phases, one antiferromagnetic with a smaller polarization and one ferromagnetic with a larger polarization. A giant effective magnetoelectric coupling and cross-field control (electric field control of magnetism or magnetic field control of polarization) can be achieved in the vicinity of the transition. The dependence of the theoretically computed transition point on the choice of exchange correlation functionals is determined and is found to be non-negligible. We also show that the perovskite structure of ${\mathrm{BaMnO}}_3$ can be stabilized relative to its hexagonal polymorphs at pressures larger than 20 GPa.

• Received 21 September 2015
• Revised 16 August 2016

DOI:https://doi.org/10.1103/PhysRevB.94.165106