  We investigate the effect of magnetic fields on a Kondo insulator by using
the periodic Anderson model. The analysis by dynamical mean field theory
combined with quantum Monte Carlo simulations reveals that the magnetic field
drives the Kondo insulator to a transverse antiferromagnetic insulator at low
temperatures. We calculate the staggered spin susceptibility and find its
divergence signaling the antiferromagnetic instability. Further investigation
of the spin correlation functions and the magnetization process clarifies how
the magnetic field suppresses the Kondo singlet formation and induces the
transverse antiferromagnetic ordering.
