APPLICATION OF THE RATIO D/CHI 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)Fe 2 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.