  Using the Resonant Valence Bond (RVB) concept and the Schwinger-boson mean
field approximation, we investigate a two dimensional anisotropic Heisenberg
antiferromagnet. We find that increasing the coupling ratio
($\alpha=J_{y}/J_{x}$), a disordered-ordered phase transition appears beyond a
critical value ($\alpha_{c}$). When $\alpha>\alpha_{c}$ there exists a finite
$T_{N}$ beyond which an ordered-disordered phase transition occurs, while for
$\alpha<\alpha_{c}$ there always exists a gap. Also we find that a decoupling
temperature $T_{D}$ exists for 1D and 2D isotropic case, when $T$ approaches
$T_{D}$ the RVB order parameter decreases rapidly to zero.
