  By studying the zero-temperature and nonzero-temperature phase diagrams of
the ferromagnetic spin-1 Bose-Hubbard model under an external magnetic field,
we find that the competition between ferromagnetism and the quadratic Zeeman
energy yields two superfluid phases, which feature discontinuous first-order
phase transitions between them for a strongly spinor Bose gas such as ${}^7$Li,
contrary to the corresponding continuum system.
