Ab-initio prediction of a new multiferroic with large polarization and magnetization

We describe the design of a new magnetic ferroelectric with large spontaneous magnetization and polarization using first-principles density functional theory. The usual difficulties associated with the production of robustly-insulating ferromagnets are circumvented by incorporating the magnetism through {\it ferri-}magnetic behavior. We show that the the ordered perovskite \BFCO will have a polarization of $\sim$80 $\mu$C/cm$^2$, a piezoelectric coefficient of 283 $\mu$C/cm$^{2}$, and a magnetization of $\sim$160 emu/cm$^3$ (2 $\mu_B$ per formula unit), far exceeding the properties of any known multiferroic.