  We discuss the role of quantum fluctuations in Heisenberg antiferromagnets on
face-centered cubic lattice with small dipolar interaction in which the
next-nearest-neighbor exchange coupling dominates over the nearest-neighbor
one. It is well known that a collinear magnetic structure which contains (111)
ferromagnetic planes arranged antiferromagnetically along one of the space
diagonals of the cube is stabilized in this model via order-by-disorder
mechanism. On the mean-field level, the dipolar interaction forces spins to lie
within (111) planes. By considering 1/S - corrections to the ground state
energy, we demonstrate that quantum fluctuations lead to an anisotropy within
(111) planes favoring three equivalent directions for the staggered
magnetization (e.g., $[11\overline{2}]$, $[1\overline{2}1]$, and
$[\overline{2}11]$ directions for (111) plane). Such in-plane anisotropy was
obtained experimentally in related materials MnO, $\alpha$-MnS, $\alpha$-MnSe,
EuTe, and EuSe. We find that the order-by-disorder mechanism can contribute
significantly to the value of the in-plane anisotropy in EuTe. Magnon spectrum
is also derived in the first order in 1/S.
