Inverted Hysteresis, Magnetic Domains, and Hysterons

In this letter, we use magnetooptical Kerr effect magnetometry on extended samples to measure local hysteresis curves as a function of an externally applied field in a magnetostriction-free amorphous ribbon and an elliptical Permalloy film element. Although these materials are magnetically soft and have almost zero coercive field, we find that the local hysteresis curves have a highly nonlinear hysteretic character, displaying both counterclockwise and clockwise rotation senses when cycling the loops. This unexpected result can be explained by looking at the total hysteresis curve of the materials as a superposition of local curves and can be described mathematically using the formalism of the Preisach model. Within the framework of this model, we derive the conditions under which a superposition of clockwise and counterclockwise hysteresis loops can lead to a hysteresis-less system, and devise a technique to map the hysterons that define the first-order reversal-curve distribution to physical regions in the specimens.