Pancharatnam Lecture
Magnets in a Time-Varying Field: Hysteresis
Speaker: Prof. Deepak Dhar (I.N.S.A. Distinguished Professor, International Center for Theoretical Sciences:- Tata Institute of Fundamental Research.)
If a magnet is subjected to a time-varying oscillating magnetic field, the magnetization also changes in time, but there is time-lag between the perturbation and the response. This general phenomena of response lagging behind the imposed field is called hysteresis. Because of its important applications in power transmission technology, this has been studied for about 140 years now. In theoretical statistical physics, this is of interest as a prototypical example of a periodic steady state of a driven non-equilibrium system. In this lecture, I will like to share our perspective of the understanding of hysteresis gained from these studies, based on a recent review article Sanjib Saphapandit and I wrote on this topic. I will discuss the basic models of hysteresis, variation of the area of the loop with frequency and amplitude of the field, and dynamical phase transitions in this system. I will also discuss Barkhausen noise, in which a smoothly varying field gives rise to burstlike response, which is used as a model of similar behavior in ferroelectrics, earthquakes, and climate changes etcetera.
