Anomalous time-induced curvature in Henkel plots based on the Preisach model

We have used a finite-temperature version of the Preisach model, in which thermally activated switching events supplement those induced by an applied field h_a, to calculate the magnetizing and demagnetizing remanences, i_r(h_a) and i_d(-h_a), respectively, assuming a Preisach distribution that is Gaussian in both the coercive field h_c and the shift field h_s. Since T≠0, the time t that the magnetization is permitted to relax influences the shape of the hysteresis loop and the Henkel plots constructed from the remanences. If the effective time for relaxation is specific to a given branch of the cycle, due perhaps to the way the system reacts to a given experimental procedure, it is possible to generate Henkel plots with curvature suggestive of mean field interaction effects, even if no such effects are actually present, or with such extreme demagnetizing-like curvature that the plot actually crosses the nominal lower boundary i_d= -i_r. Experimental instances of this behavior are discussed.