  In ferromagnetic Bose-Einstein condensates (BECs), the quadratic Zeeman
effect controls magnetic anisotropy, which affects on magnetic domain pattern
formation. While the longitudinal magnetization is dominant (similar to the
Ising model) for a negative quadratic Zeeman energy, the transverse
magnetization is dominant (similar to the XY model) for a positive one. When
the quadratic Zeeman energy is positive, the coarsening dynamics is driven by
vortex-antivortex annihilation in the same way as the XY model. However, due to
superfluid flow of atoms, there exist several combinations of vortex-antivortex
pairs in ferromagnetic BECs, which makes the coarsening dynamics more
complicated than that of the XY model. We propose a revised domain growth law,
which is based on the growth law of the two-dimensional XY model, for a
two-dimensional ferromagnetic BEC with a positive quadratic Zeeman energy.
