Effect of fine-particle interactions on minor loops: Magnetic flip-flop

Minor hysteresis loops often do not close on themselves on the first cycle. Néel described three phenomena which have this effect: Magnetic aftereffect (trainage magnétique), creep (reptation) and magnetic flip-flop (bascule). The flip-flop is due to interaction fields attaining values during the minor Joop which had not been attained previously. This may cause the first minor loop to cross itself (positive effect), or to remain unclosed (negative effect). In the region where the Preisach diagram is statistically stable, we have analyzed the effect of changing interaction fields as a perturbation. If interactions between pairs of magnetic grains are considered we conclude that the flip-flop effect should be negative for a minor loop with one vertex on the major loop. This result implies that the minor loop actually goes outside of the major loop at the end of its first cycle. Néel has demonstrsted that this is possible for a two particle system. We conclude that a minor loop extending outside of the major loop should be observable in fine grained magnetic material with a low packing factor.