Magnetic properties of interacting nanoparticles in a triangular lattice: Monte Carlo simulations

We study the magnetic properties of a system of interacting nanoparticles in a triangular lattice through Monte Carlo simulations. The small particles are subjected to an in-plane magnetic field and are coupled via long-range dipolar interactions. They also present uniaxial anisotropy energy, with the easy axes pointing randomly in three dimensions. We assume a Gaussian distribution for the strengths of the uniaxial anisotropy energy. We calculate the blocking temperature of the system from the zero-field-cooled curve as a function of the ratio between the dipolar and mean uniaxial anisotropy energy contributions. The blocking temperature increases linearly with this ratio, showing that the net effect of the dipolar interactions is to increase the height of the effective energy barriers seen by the nanoparticles. The hysteresis curves are also determined as a function of this ratio and we show that the coercive field exhibits a slight minimum for a small value of the dipolar strength. When the dipolar interactions are not negligible, we observe a steep variation in the component of the magnetization that is perpendicular to the magnetic field in the neighborhood of the coercive field.