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In 1914, a magnetic alloy with an unusually high magnetic permeability and low hysteresis was discovered at the Bell Telephone Laboratories. This magnetic alloy resulted from a series of investigations on the iron-nickel alloy system, in which the nickel content was systematically varied. Under a very specific combination of the alloy composition (78.5% Ni-content), a drastic increase in magnetic permeability and a decrease in coercive force were observed. In the past, this unusual behavior of the permalloy has been attributed to the anisotropy constant, however, there is still no theory that explains this drastic decrease in hysteresis in magnetic alloys. This webinar will show how magnetostriction constants, in addition to anisotropy, play a surprisingly important role in reducing hysteresis at the permalloy composition. We build on this finding and present a strategy for the design of ferromagnetic materials with exceptionally low magnetic hysteresis, quantified by coercivity. Unexpectedly, our design strategy predicts that cubic materials with large saturation magnetization m_s and large magnetocrystalline anisotropy constant κ₁ will have low coercivity on the order of that of Permalloy, as long as the magnetostriction constants λ₁₀₀, λ₁₁₁ are tuned to special values. Our results demonstrate agreement with the permalloy experiments and provide theoretical insights into developing novel soft magnetic alloys with negligible hysteresis.

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Dr. Ananya Renuka Balakrishna joined the Department of Aerospace and Mechanical Engineering at USC as an Assistant Professor in Fall 2020. Prior to joining USC, she pursued postdoctoral research as a Lindemann Fellow at MIT (Department of Materials Science), and at the University of Minnesota (Aerospace Engineering and Mechanics). Dr. Renuka Balakrishna received her Ph.D. in Solid Mechanics and Materials Engineering from the University of Oxford. Broadly, her research focuses on developing mathematical models to investigate the links between material instabilities, microstructures, and properties in energy-storage and functional materials