Effects of a Uniform Applied Magnetic Field and Temperature on the Magnetic Properties of the Dipolar Anti-ferromagnetic planar System: Parametric Study

The effects of a uniform external magnetic field, with strength parameter of h, on the magnetic properties of a two-dimensional square dipolar antiferromagnetic planar system, with sizes (104 X 104,64 X 64,32 X 32), have been determined for both zero and finite temperatures. In this study, the classical spins are confined to the plane of the system and interact through a nearest neighbor antiferromagnetic exchange interaction, the long-range dipolar interaction, and a uniform external magnetic field along the axis of the lattice. Throughout, the strength of the exchange interaction is assumed to be antiferromagnetic and fixed at −1.2g, where g is the strength of the dipolar interaction. At zero temperature, the ground state calculations show that the system switches from ferromagnetic phase (FE phase) to the dipolar antiferromagnetic phase (AF phase) at ho = 6.00g as the applied field is decreased. As the applied field is decreased further, the spin configuration starts to turn antiferromagnetically perpendicular to the applied field in a continuous manner. As the applied field goes to zero, the system favors the dipolar antiferromagnetic in which the spins are aligned perpendicular to the field (AF1 phase). At finite temperature, the magnetic phase diagram for the system has been determined as a function of both h and T using Monte Carlo simulations. At low temperatures, the results from simulations show that the system exhibits a first order transition from the ferromagnetic phase to the dipolar phase (AF phase) as the field is decreased. When the applied field goes to zero, the system favors the dipolar phase in which the spins are ordered at   with the axis of the lattice (AF2 phase). At low fields, the Monte Carlo results indicate that the system exhibits a second order transition from the dipolar antiferromagnetic phase to the paramagnetic phase as the temperature is increased. However, at high fields and for low temperatures the system favors the ferromagnetic phase. As the temperature is increased the system gradually disorders. In addition, Monte Carlo simulation results show that there exists a range of the magnetic field values in which the system exhibits a first order reorientation transition from the dipolar antiferromagnetic phase to the ferromagnetic phase as the temperature is increased.