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2012 Physics Colloquium Non–linear magnetic modeling: breaking through the materials barrier David Jiles Department of Electrical and Computer Engineering Iowa State University Ames, Iowa 50011, USA When magnetic materials are exposed to external magnetic field the change in magnetization extends beyond the simple linear regime. Under these conditions it is found that the response of the materials is no longer reversible. This phenomenon, hysteresis, is well documented in the experimental literature and properties such as magnetic coercivity can range from less than 1 A/m in soft materials to 1,000,000 A/m in hard materials. Description of the non-linear response of hysteresis is a topic at the leading edge of research with important technological applications. The complexity of the problem arises because many different factors compete to determine the overall response. Therefore the description of hysteresis is poorly developed compared with the understanding of low amplitude, linear/reversible effects. In this lecture discussion will focus on the underlying concepts used to explain, and practical models used to describe, hysteresis in different materials. In general all of these descriptions are simplified approximations to complicated systems with many different and competing interactions on length scales ranging from the atomistic (10-9 m) to the macroscopic continuum (10-2 m). Therefore depending on the relative importance of the interactions, and the length scale of interest, different models are appropriate to different situations. 4:00 pm on December 6, 2012 245 Physics Building Refreshment starts 3:45 pm