  The HH 111 protostellar disk has recently been found to host a pair of spiral
arms. Here we report the dust polarization results in the disk as well as the
inner envelope around it, obtained with the Atacama Large
Millimeter/submillimeter Array in continuum at lambda ~ 870 micron and ~ 0. 05"
resolution. In the inner envelope, polarization is detected with a polarization
degree of ~ 6% and an orientation almost everywhere parallel to the minor axis
of the disk, and thus likely to be due to the dust grains magnetically aligned
mainly by toroidal fields. In the disk, the polarization orientation is roughly
azimuthal on the far side and becomes parallel to the minor axis on the near
side, with a polarization gap in between on the far side near the central
protostar. The disk polarization degree is ~ 2%. The polarized intensity is
higher on the near side than the far side, showing a near-far side asymmetry.
More importantly, the polarized intensity and thus polarization degree are
lower in the spiral arms, but higher in between the arms, showing an
anticorrelation of the polarized intensity with the spiral arms. Our modeling
results indicate that this anticorrelation is useful for constraining the
polarization mechanism and is consistent with the dust self-scattering by the
grains that have grown to a size of ~ 150 micron. The interarms are sandwiched
and illuminated by two brighter spiral arms and thus have higher polarized
intensity. Our dust self-scattering model can also reproduce the observed
polarization orientation parallel to the minor axis on the near side and the
observed azimuthal polarization orientation at the two disk edges in the major
axis.
