Application of the ratio d/χ to the investigation of magnetization processes in giant‐magnetostrictive materials

The change in magnetostriction Δλ with change in magnetization ΔM for domain‐wall motion is shown to depend only on the wall type, the magnetostriction constants, and the saturation magnetization and not on the field required to effect the change. The quantity Π=Δλ/ΔM (or the dynamic equivalent d/χ) is therefore a valuable parameter for use in investigating magnetization processes. Theoretical values of Π are given for different wall processes in ⟨111⟩ and ⟨100⟩ easy materials and used to interpret experimental measurements in different (Tb, Dy, Ho)Fe2 materials. It is shown that Π vs M curves are more sensitive to the detail of the magnetization process than λ vs M curves. In ⟨111⟩ easy compositions the processes are found to be complex with the combination of wall motion processes changing continuously with increasing magnetization and no region where a single process dominates. In contrast, for ⟨100⟩ easy materials, there is an extended region in which 90° wall processes dominate. In both cases, quasistatic and dynamic processes are shown to be equivalent, independent of temperature, and independent of the frequency and magnitude of the drive field