  By deriving a generalized Harper's equation, we investigate the effects of
temperature $T$ and hole doping $\d$ on antiferromagnetically correlated
electrons under the influence of an applied magnetic field. We obtain a phase
diagram in a $T$-$\d$ plane for staggered magnetization under the external
field. We find that away from half filling the maximum values of staggered
magnetization occur with rapid convergence to a finite temperature constant
near half filling. We discover the reentrant behavior of the staggered
magnetization in the presence of the magnetic field.
