Anisotropic magnetostriction in a 〈 110 〉 oriented crystal Tb_0.36 Dy_0.64 (Fe_0.85Co_0.15) ₂ after coaxial field annealing

Axial magnetostriction of Terfenol-D oriented crystals is highly anisotropic when changing the magnetization direction. Magnetostrictions of a 〈 110 〉 oriented crystal Tb_0.36Dy_0.64(Fe _0.85Co_0.15)₂ were investigated under magnetic fields with a series of angles θ to its axis. Totally different anisotropic magnetostrictive behaviors are observed after annealing under a coaxial field of 240 kA/m. The magnetostriction for the field annealed specimen seems unsaturated even under 640 kA/m for angles θ in the range from 0° to 55°. At these angles, magnetostriction "ascending" is observed during the final magnetization process, while magnetostriction "dropping" occurs at angles above 35° for the untreated crystal. With the increase in angle θ, the corresponding field where magnetostriction starts dropping decreases for the untreated crystal, while the field at which magnetostriction starts ascending increases for the field annealed one. A simplified model based on moment "jump" and "rotation" is proposed to explain such anisotropic behaviors.