  We discuss a pseudospin representation of the two-dimensional t-J model. We
introduce pseudospins associated with empty sites, deriving a new
representation of the t-J model that consists of local spins and spinless
fermions. We show, within a mean-field approximation, that our representation
of t-J model corresponds to the {\it isotropic} antiferromagnetic Heisenberg
model in an effective magnetic field. The strength and the direction of the
effective field are determined by the hole doping ${\delta}$ and the
orientation of pseudospins associated with empty sites, respectively. We find
that the staggered magnetization in the standard representation corresponds to
the component of magnetization perpendicular to the effective field in our
pseudospin representation. Using a many-body Green's function method, we show
that the staggered magnetization decreases with increasing hole doping
${\delta}$ and disappears at ${\delta \approx 0.06-0.15}$ for $t/J=2-5$. Our
results are in good agreement with experiments and numerical calculations in
contradistinction to usual mean-field methods.
