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/sub w/ (for weak pinning) and V/sub 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/sub fw/ (using V/sub w/) and H/sub fs/ (using V/sub s/), for each of the specimens. Comparing the values of H/sub fw/ and H/sub fs/ with the Barbier's plot which relates magnetic viscosity to the coercive field H/sub 0/ of a wide variety of magnetic materials, it was found that H/sub fw/ of the low age specimens plotted against their H/sub 0/ exhibited similar behaviour as in the Barbier's plot. However, when values of H/sub 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/2F/sub 0/ in the case when the material has a weak pinning regime, where F and F/sub 0/ are the pinning force per unit area with and without the demagnetizing consideration respectively, and by a factor of 1/4 in the case of strong pinning.<
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