Theoretical Models for Magnetic Properties of Iron Pnictides Part I: Spin Formalism

We attempt to describe the magnetic properties of parent pnictide compounds by using the J1 - J2 - Jc Heisenberg model Hamiltonian. In order to obtain the ground state magnetization and spin wave dispersion we use the Green's functions method for spin operators. The equations of motion for Green's functions are decoupled by employing the random phase approximation. We analyze the results numerically and after comparison with experimental data we conclude that the model is to be modified to make it more relevant to iron pnictides.