Interpretation of thermal dependence of magnetic aftereffect for magnetic nanocomposite with slow decay rates

A new experimental characterization is presented of time-, field-, and temperature-dependent dynamic effects in magnetization of a nanocomposite which displays slow decay. Field and temperature variations of irreversible susceptibility, χ irr , decay coefficient, S, fluctuation field, hf , and activation volume, V, have been calculated for the nanocomposite sample (Co80Ni20) using a recently developed modified Preisach–Arrhenius (MPA) model. The sample is composed of non-interacting nanoparticles having negligible reversible magnetization. Non-Arrhenius behavior is observed in both the maximum decay coefficient, S max, and the fluctuation field, hf , as a function of temperature T. The peak of both temperature curves are identical and occur at a critical temperature Tk of ∼50 K, which agrees with our experimental results. Based on the effect of a temperature-dependent chemical potential on energy barrier, hf is studied for T < Tk and T ≥ Tk , respectively. A more complete MPA model that can predict the magnetization as function of time, field and temperature for a magnetic material with slow decay rates is proposed. This model uses a multi-variable analytical formula, , which incorporates the characteristic parameters.