  We apply the theory of radiative torque (RAT) alignment for studying
protoplanetary disks around a T-Tauri star and perform 3D radiative transfer
calculations to provide the expected maps of polarized radiation to be compared
with observations, such as with ALMA. We revisit the issue of grain alignment
for large grains expected in the protoplanetary disks and find that mm-sized
grains at midplane do not align with the magnetic field as the Larmor
precession timescale for such large grains becomes longer than the gaseous
damping timescale. Hence, for these grains the RAT theory predicts that the
alignment axis is determined by the grain precession with respect to the
radiative flux. As a result, we expect that the polarization will be in the
azimuthal direction for a face-on disk. It is also shown that if dust grains
have superparamagnetic inclusions, magnetic field alignment is possible for
(sub-)micron grains at the surface layer of disks, and this can be tested by
mid-infrared polarimetric observations.
