Magnetic relaxation of a system of interacting magnetic nanoparticles at finite temperature

We investigate the magnetic relaxation of a system of interacting single-domain magnetic nanoparticles, where the uniaxial energy density depends on temperature. Particles of different sizes are placed in random positions along a linear chain. For each value of temperature, the stochastic Landau-Lifshitz-Gilbert equation is numerically integrated. Applying an appropriate scaling function we determine the magnetic relaxation as a function of time and temperature as well as the energy barrier distribution of the system as a function of the mean distance between neighbor particles. We show that the typical energy barrier is not a monotonic function of the dipolar coupling. It decreases with the separation between particles until it reaches a minimum. For weaker dipolar interactions, the antiferromagnetic part could be responsible for enhancing the local uniaxial energy barriers. The decrease of the energy barrier for small values of the dipolar coupling was seen experimentally for the magnetoferritin nanoparticle.