Experimental Preisach analysis of the Wohlfarth relation (abstract)

Abstract

The Wohlfarth relation1 states that, for noninteracting particles, the ascending normalized remanent major loop, mD(H), is twice the shifted normalized virgin remanent magnetization. Researchers2 claim to measure the interaction field and characterize it as ‘‘positive’’ and ‘‘negative’’ depending on whether it is ‘‘above’’ or ‘‘below’’ the axis on a Henkel plot or a ΔM plot. It has been shown3 that the moving Preisach model can compute all observed types of ΔM plots by varying only the moving parameter, α, and over only positive values. This type of behavior is characterized by the ratio of α to the standard deviation of the interaction field. In this paper the measured ΔM plot for two commercial recording media, namely longitudinal BaFe and γ-Fe2O3, is presented and the positive moving parameter of each sample is identified. Let us define the operative field of the system by Hop=H+αM, where M is the total magnetization. It is then shown that, when plotted as a function of Hop, all samples deviate from the Wohlfarth relation in the same way, even though they exhibit ‘‘positive’’ and ‘‘negative’’ ΔM when plotted as a function of the applied field, H, as seen in Fig. 1. It will also be shown that deviations from the Wohlfarth relation are due to a combination of parameters, not only the interaction field. The model and the identification algorithm has been used to simulate all the observed ΔM plots.