  Within Dyson-Maleev (DM) transformation and self-consistent mean-field
treatment, the N\'eel order/disorder transition is studied for an
antiferromagnetic Heisenberg model which is defined on a square lattice with a
nearest neighbour exchange $J_1$ and a next-nearest neighbour exchange $J_2$
along only one of the diagonals. It is found that the N\'eel order may exist up
to $J_2/J_1=0.572$, beyond its classically stable regime. This result
qualitatively improves that from linear spin-wave theory based on
Holstein-Primakoff transformation.
