Influence of a Continuous Activation Energy Spectrum on the Aging Behavior of Magnetic Thin Films

Abstract

Skew aging and its dependence on stabilization treatments have been investigated in cylindrical electroplated Permalloy films by annealing in hard‐axis magnetic fields. The skew field H_β was measured using the Belson test method. Plots of H_β vs a logarithmic time scale show nearly straight lines over a range of four decades for temperatures between the ambient temperature and 200°C. This behavior may be explained by assuming that the activation energies of the relaxation processes have a continuous distribution between 0.8 and 1.6 eV, independent of the stabilization treatment. The frequency factor is found to be a function of the stabilization temperature, lying between 10⁹ and 10¹⁰ sec⁻¹. These values can be interpreted as being due to first‐order kinetic processes, which is not possible if discrete activation energies are assumed. The reason for the distribution is the highly defected structure of thin films, especially at grain boundaries and dislocations and around impurities. Stabilization treatments reduce the total volume of these regions and the vacancy concentration. Only the Fe–Fe pair ordering mechanism is necessary to interpret the annealing data if one assumes that pairs in local defected regions also contribute to the anisotropy.