Magnetic relaxation in terms of microscopic energy barriers in a model of dipolar interacting nanoparticles

Abstract

The magnetic relaxation and hysteresis of a system of single domain particles with dipolar interactions are studied by Monte Carlo simulations. We model the system by a chain of Heisenberg classical spins with randomly oriented easy-axis and log-normal distribution of anisotropy constants interacting through dipole-dipole interactions. Extending the so-called $T\ln (t/{\tau }_0)$ method to interacting systems, we show how to relate the simulated relaxation curves to the effective energy barrier distributions responsible for the long-time relaxation. We find that the relaxation law changes from quasi-logarithmic to power-law when increasing the interaction strength. This fact is shown to be due to the appearence of an increasing number of small energy barriers caused by the reduction of the anisotropy energy barriers as the local dipolar fields increase.

arXiv comment11 pages, 10 figures

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• The magnetic structure factor of correlated moments in small-angle neutron scattering
• Dipolar interactions and thermal stability of two-dimensional nanoparticle arrays
• Elementary transitions and magnetic correlations in two-dimensional disordered nanoparticle ensembles
• Morphology and magnetism of multifunctional nanostructured $\gamma$-Fe${}_2$O${}_3$ films: Simulation and experiments
• Ferromagnetic resonance of a magnetic dimer with dipolar coupling
• Vortex fluctuations and freezing of dipolar-coupled granular moments in thin ferromagnetic films
• Magnetic Relaxation in Two Dimensional Assembly of Dipolar Interacting Nanoparticles
• Non-Arrhenius relaxation of the Heisenberg model with dipolar and anisotropic interactions
• Tailoring Heat Dissipation in Ordered Arrays of Dipolar Coupled Magnetic Nanoparticles