Henkel plots in a temperature and time dependent preisach model

The effect of finite temperature T and observation time t on the Henkel plots of ac and thermally demagnetized systems has been investigated within Ihe framework of a generalized Preisach model in which it is assumed that thermally activated hopping will occur over all energy harriers W < W= k_BTIn(t/t0) where Tn is a microscopic time and will systematically drive the Preisach plane towards equilibrium. The Preisach distribution function is assumed to be a factorized produrt of a Gaussian coercive field distribution with mean value hc and dispersion <r. and a Gaussian interaction field distribution with a self-consistent mean-field average h_int -km and dispersion <rs. Increases in temperature or observation time cause a progressive collapse of the hysteresis cycle as expected and also enhance dcmagnetizing-like curvature in Henkel plots at least for ac demagnetized systems. An exception is a thermally demagnetized system with k = 0 which has a linear Henkel plot independent of W. Varying the effective time for thermal relaxation of the magnetization from branch to branch of the hysteresis cycle can have the effect of imitating mean field interactions of both magnetizing-like and demagnetizing-like sign in systems with A = 0 and can even lead to Henkel plots which violate the lower boundary idir.