  CoAl2O4 spinel with magnetic Co2+ ions on the diamond A-lattice is known to
be magnetically frustrated. We compare neutron single crystal diffraction
patterns measured in zero and applied magnetic fields with the ones obtained
from classical Monte-Carlo models. In simulations we test the influence of
various parameters on diffraction patterns: the ratio of nearest-, J1, and
next-nearest, J2, neighbor interactions, magnetic field applied along the
principal crystallographic directions, and random disorder on the A(Co2+)- and
B(Al3+)- sites. We conclude that the models considered so far explain the
broadening of magnetic Bragg peaks in zero magnetic field and their anisotropic
response to applied magnetic field only partly. As bulk properties of our
single crystal are isotropic, we suggest that its microstructure, specifically
<111>-twin boundaries, could be a reason of the nonconventional magnetic order
in CoAl2O4.
