  The slave-rotor mean-field theory of Florens and Georges is generalized to
the antiferromagnetic phase of the Hubbard model. An effective action
consisting of a spin rotor and a fermion is derived and the corresponding
saddle-point action is analyzed. Zero-temperature phase diagram of the
antiferromagnetic Hubbard model is presented. While the magnetic phase persists
for all values of the Hubbard interaction U, the single-particle spectral
function exhibits a crossover into an incoherent phase when the magnetic moment
m (and the corresponding U values) lies within a certain window m_c < m <
1-m_c, indicating a possible deviation from the Hartree-Fock theory.
