15-01U

The rectangular-lattice spin-1/2 Heisenberg model with nearest-neighbor, and next-nearest-neighbor interactions is considered by means of the Jordan-Wigner transformation. We use a mean-field type approximation for phase factors as well as for the terms which describe the spinless fermion interaction in the fermionized Hamiltonian. In the case of Néel phase the dependence of the magnetic order on frustration parameter is obtained in the ground-state. The obtained result is compared with the result of other analytical and numerical methods.