Magnetic relaxation and thermal properties of a two-dimensional array of dipolar-coupled nanoparticles

We investigate through Monte Carlo simulations the thermal properties of a triangular array of identical magnetic nanoparticles with random uniaxial anisotropy axes in three dimensions. They are coupled by dipolar forces and we determine the blocking temperature of the system as a function of the anisotropy strength and magnitude of the dipolar coupling. We calculate the magnetization, susceptibility, specific heat and Binder cumulant as a function of temperature, and we see that, in the non-interacting case, these properties exhibit a maximum at the blocking temperature. We have found that the increase of blocking temperature is related to an increase in the effective energy barrier due to the dipolar interactions. We have also determined the dependence of the remanence and coercive field as a function of temperature and dipolar strength. At very low temperatures, the coercive field displays a minimum as a function of dipolar strength. The magnetic relaxation is studied as a function of temperature and dipolar strength for an assembly of nanoparticles possessing the same uniaxial anisotropy energy. We have also considered the behaviour of the almost non-thermal relaxation that occurs at the very beginning of the relaxation process as a function of the dipolar coupling strength.