  Magnetic fields are generated in ionized objects rotating with respect to a
radiation background. Based on conservation of canonical ion momentum, it has
been previously suggested that even if the radiation intensity is unrestricted
the maximum field strength generated this way is ~(10^{-4}\Omega) Gauss, where
\Omega is the initial angular velocity of the object. We show that this limit
is valid only for an object made of fully ionized and optically thin plasma.
The limit can be relaxed by orders of magnitude in the presence of a high
neutral fraction or if the plasma is coupled to other forms of matter such as
stars or compact clouds.
