Burst magnetostriction in Tb0.3Dy0.7Fe1.9

Abstract

The magnetostriction and magnetic induction calculated by a continuous, anisotropic, anhysteric, magnetization model are compared with magnetostriction and magnetic induction measurements on burst and nonburst magnetostrictive ${\mathrm{Tb}}_{\mathrm{0.3}}{\mathrm{Dy}}_{\mathrm{0.7}}{\mathrm{Fe}}_{\mathrm{1.9}}$ twinned single crystal rods. The model shows that the magnetostriction and permeability suppression occurring at low applied field is the result of the rotation, and subsequent capture, of initial field antiparallel magnetization into field transverse [111̄] or [1̄1̄1] local magnetoelastic energy minima. The model further shows that the interval of high magnetostriction applied field derivative, $\mathrm{d\lambda /dH}$ , characteristic of burst magnetostrictive material, is the result of the rotation of field transverse [111̄] or [1̄1̄1] oriented magnetization into the [111] near field magnetocrystalline minima. The occurance of burst magnetostriction is therefore contingent on obtaining sufficient magnetocrystalline anisotropy and sufficiently tight magnetization energy distribution in experimental ${\mathrm{Tb}}_{\mathrm{0.3}}{\mathrm{Dy}}_{\mathrm{0.7}}{\mathrm{Fe}}_{\mathrm{1.9}}$ twinned single crystal rods so as to minimize the applied field interval over which this magnetization rotation process occurs. A final analysis shows that the present model is able to correctly approximate the applied field dependence of the burst magnetostriction response and the applied field dependence of the simultaneous magnetostriction and permeability suppression with a single set of parameters for a range of constant [112] applied compressive stresses. The model additionally exhibits approximately correct saturation magnetostrictions for a range of experimentally applied compressive stresses. However, the model fails to match the experimental behavior above a simultaneous $\mathrm{d\lambda /dH}$ , permeability and field hysteresis transition, located approximately 1000 microstrain from the saturation magnetostriction. The experimental transition clearly indicates a change in magnetization mechanism not accommodated by the present model.