  We predicted the ferroelectric-ferromagnetic multiferroic properties of
EuTiO3 nanowires and generated the phase diagrams in coordinates of temperature
and wire radii. The calculations were performed within the
Landau-Ginzburg-Devonshire theory with phenomenological parameters extracted
from tabulated experimental data and first principles calculations. Since bulk
EuTiO3 is antiferromagnetic at temperatures lower than 5.5 K and paraelectric
at all temperatures, our goal was to investigate the possibility of inducing
the ferroelectric and ferromagnetic properties of EuTiO3 by reducing the bulk
to nanosystems. Our results indicate that ferroelectric spontaneous
polarization of ~0.1-0.5C/m2 is induced in EuTiO3 nanowires due to the
intrinsic surface stress, which is inversely proportional to the nanowire
radius. The spontaneous polarization exists at temperatures lower than 300 K,
for the wire radius less than 1 nm and typical surface stress coefficients ~ 15
N/m. Due to the strong biquadratic magnetoelectric coupling, the spontaneous
polarization in turn induces the ferromagnetic phase at temperatures lower than
30 K for 2 nm nanowire, and at temperatures lower than 10 K for 4 nm nanowire
in EuTiO3. Thus we predicted that the EuTiO3 nanowires can be the new
ferroelectric-ferromagnetic multiferroic.
