Design of soft magnetic materials

Abstract

We present a strategy for the design of ferromagnetic materials with exceptionally low magnetic hysteresis, quantified by coercivity. In this strategy, we use a micromagnetic algorithm that we have developed in previous research and which has been validated by its success in solving the "Permalloy Problem" -- the well-known difficulty of predicting the composition 78.5% Ni of lowest coercivity in the Fe-Ni system -- and by the insight, it provides into the "Coercivity Paradox" of W. F. Brown. Unexpectedly, the design strategy predicts that cubic materials with large saturation magnetization $m_s$ and large magnetocrystalline anisotropy constant $\kappa_1$ will have low coercivity on the order of that of Permalloy, as long as the magnetostriction constants $\lambda_{100}, \lambda_{111}$ are tuned to special values. The explicit prediction for a cubic material with low coercivity is the dimensionless number $(c_{11}-c_{12}) \lambda_{100}^2/\kappa_1 = 81$ for $\langle 100 \rangle$ easy axes. The results would seem to have a broad potential application, especially to magnetic materials of interest in energy research.