Magnetic viscosity and activation volume in domain wall pinning

When domain wall pinning is due to random arrays of inhomogeneities, the dynamical process of unpinning could be described by the weak or the strong domain wall pinning models. Based on these two models, the values of activation volume V_w (for weak pinning) and V_s (for strong pinning) of bowed domain wall of thermally annealed iron-rich FeAu specimens were estimated. The results were then used to calculate their corresponding fluctuation held H_fw (using V_w) and H_fs (using V_s), for each of the specimens. Comparing the values of H_fw and H_fs with the Barbier´s plot which relates magnetic viscosity to the coercive field H₀ of a wide variety of magnetic materials, it was found that H_fw of the low age specimens plotted against their H₀ exhibited similar behaviour as in the Barbier´s plot. However, when values of H_fs were used in the plotting, similarity with the Barbier´s result was only found in specimens after prolonged aging. It is also found that when the localized demagnetizing effect on the bowed portion of the domain wall due to the presence of the surface free-poles is to be considered in the derivation, the fluctuation field is smaller than that without such consideration by a factor of F/2F₀ in the case when the material has a weak pinning regime, where F and F₀ are the pinning force per unit area with and without the demagnetizing consideration respectively, and by a factor of ¼ in the case of strong pinning