Engineering Multiferroism inCaMnO3

Structural instabilities of ${\mathrm{CaMnO}}_3$ are investigated from first principles. We point out that, on top of a strong antiferrodistortive instability responsible for its orthorhombic ground state, the cubic perovskite structure of ${\mathrm{CaMnO}}_3$ also exhibits a weak ferroelectric instability. Although ferroelectricity is suppressed by antiferrodistortive motions, we show that it can be favored using strain or chemical engineering in order to make ${\mathrm{CaMnO}}_3$ multiferroic. We finally highlight that the ferroelectric instability of ${\mathrm{CaMnO}}_3$ is Mn-dominated. This illustrates that, contrary to common belief, ferroelectricity and magnetism are not necessarily exclusive but can be driven by the same cation.