A long-standing puzzle in materials science is understanding the origins of magnetic hysteresis in ferromagnetic materials. These materials have an intrinsic magnetic dipole that can be reversed under an applied magnetic field, and this magnetization reversal traces out a characteristic hysteresis loop. Reducing the width of this loop is critical to develop spintronic and energy conversion devices. Currently, a widely accepted strategy to lower the hysteresis in cubic ferromagnetic alloys is based on changing its chemical composition to reduce the magnitude of a material constant, called the anisotropy constant. While this strategy has resulted in soft magnetic alloys it does not explain the complete story of coercivity. For example, in the iron–nickel system or the Sendust system, a sharp drop in coercivity is observed at 78.5% Ni-composition, at which к1 ≠ 0. Infact in Fe-Ni alloys, tuning to the anisotropy constant to zero noticeably increases its hysteresis. We are developing a coercivity tool that for the first time combines micromagnetics and nonlinear stability analysis in a theoretical framework to predict hysteresis in magnetic alloys; We have successfully applied our coercivity tool to solve a longstanding permalloy problem in soft magnets—that is why a 78.5% Ni-composition shows the lowest coercivity—and provides fundamental insights into the “Coercivity Paradox” of W.F. Brown.
