  In a recent paper [Phys. Rev. Lett. 91, 117201 (2003)], it is argued that an
itinerant antiferromagnet in an external magnetic field undergoes a spin-flip
transition, in marked contrast with the behavior of a localized
antiferromagnet: for a weak magnetic field, the magnetization is parallel to
the field, and flips to the perpendicular configuration at a critical value of
the field. In this Comment we show that these conclusions are incorrect. The
canted state (not considered in the Letter) is the antiferromagnetic ground
state of the system up to a critical value of the field where the normal state
is restored, in qualitative agreement with the behavior of the magnetization in
a localized antiferromagnet.
