Competing cubic and uniaxial anisotropies on the energy barrier distribution of interacting magnetic nanoparticles

Abstract

We study the magnetic behavior of a two-dimensional set of interacting magnetic nanoparticles. The single-domain nanoparticles exhibit competing cubic and uniaxial anisotropies, and they interact themselves through long-range dipolar interactions. We employ the stochastic Landau-Lifshitz-Gilbert equation to describe the time evolution of the magnetic moments of the system. We determine the magnetic relaxation of the system as a function of the ratio between cubic and uniaxial anisotropies, and from the strength of dipolar coupling. From the relaxation curves we calculate the effective energy barrier distribution by considering both situations where the uniaxial axes are completely aligned or randomly oriented relative to an external magnetic field. When the axes are randomly oriented, two peaks are observed in the distribution of energy barriers depending on the ratio of cubic and uniaxial anisotropies, as well as on the intensity of dipolar coupling. Through the zero-field-cooled curves we also determine the blocking temperature of the system and we show that it increases both with the ratio between the cubic and uniaxial anisotropies, as well as with the magnitude of dipolar interactions.