  Multiferroic materials, in which ferroelectric and magnetic ordering coexist,
are of fundamental interest for the development of multi-state memory devices
that allow for electrical writing and non-destructive magnetic read-out
operation. The great challenge is to create multiferroic materials that operate
at room-temperature and have a large ferroelectric polarization P. Cupric
oxide, CuO, is promising because of its large P ~ 10^{2} {\mu}C.m^{-2}, but is
unfortunately only multiferroic in a temperature range of 20 K, from 210 to 230
K. Here, using a combination of density functional theory and Monte Carlo
calculations, we establish that pressure-driven phase competition induces a
giant stabilization of the multiferroic phase of CuO, which at 20-40 GPa
becomes stable in a domain larger than 300 K, from 0 to T > 300 K. Thus, under
high-pressure, CuO is predicted to be a room-temperature multiferroic with
large polarization.
