Micromagnetics of Galfenol

摘要

We study the micromagnetics of soft cubic ferromagnets with large magnetostriction, with the goal of understanding the microstructure and behavior of recently reported single-crystal Galfenol samples [Chopra and Wuttig in Nature 521(7552):340-343,2015]. First, taking the no-exchange formulation of the micromagnetics energy [De Simone and James in J Mech Phys Solids 50(2):283-320,2002], we construct minimizing sequences that yield local average magnetization and strain curves matching the experimental findings of Chopra and Wuttig (2015). Then, reintroducing a sharp-interface version of the exchange energy [Choksi and Kohn in Commun Pure Appl Math 51(3):259-289,1998], we construct normal and zig-zag Landau states; within the parameter regime of Galfenol, we show that the latter achieves lower-energy scaling via equipartition of energy between the 90 degrees wall energy, 180 degrees wall energy and the anisotropy energy. This forms the first step in adapting the program of Kohn and Muller [Philos Mag A 66(5):697-715,1992] to explain why certain magnetic microstructures are observed over others.