  Antiferromagnetic condensates are generally believed not to display
modulational instability and subsequent spin-domain formation. Here we
demonstrate that in he presence of a homogeneous magnetic field
antiferromagnetic spin-1 Bose-Einstein condensates can undergo spatial
modulational instability followed by the subsequent generation of spin domains.
Employing numerical simulations for realistic conditions, we show how this
novel effect can be observed in sodium condensates confined in an optical trap.
Finally, we link this instability and spin-domain formation with stationary
modes of the condensate.
