Density of energy barriers in fine magnetic particle systems

Using a numerical method based on the minimization of the Onsager-Machlup functional, we have studied the energy barrier distributions in systems of fine magnetic particles with the uniaxial anisotropy and the dipolar interaction. In such systems, the interplay of the single particle anisotropy and the dipolar interaction strength (particle concentration) determines whether the single-particle or collective remagnetization dominates the system behavior (including barrier heights). Our main conclusion is that the influence of the dipolar interparticle interaction on the energy barrier density ρ(E) depends qualitatively on the single particle anisotropy. For low anisotropies ρ(E) shifts toward higher barriers when increasing interaction strength, whereby for moderate and high anisotropy values, the opposite shift takes place. We propose the explanation for this phenomenon.