Enhanced magnetostriction of Tb-Dy-Fe via simultaneous ⟨111⟩ crystallographic orientation and -morphological alignment induced by directional solidification in high magnetic fields

The giant magnetostriction exhibited by pseudobinary Tb-Dy-Fe compounds has attracted considerable attention for use in magneto-mechanical actuators and sensors. However, simultaneously producing a crystallographic orientation and a morphological alignment of the (Tb,Dy)Fe-2 phase along the ⟨111⟩ direction has proven difficult and inhibits further increase in the desired property. This work demonstrates that, by coupling the directional solidification and a high magnetic field, a ⟨111⟩-orientation and -alignment were simultaneously created. In addition, the pores and the defects in the alloys were eliminated, leading to an enhancement of the magnetostrictive performance. Analyses indicate that the controlled growth of the (Tb,Dy)Fe-2 crystal was owing to the collaboration of the multiple magnetic field effects on both the liquid and the solid phases during the directional solidification. Specifically, the magnetic torque induced a rotation of the crystals aligning their easy axis of magnetization (i.e., ⟨111⟩) along the magnetic field direction. Further, the Lorentz force stabilized the directional growth of the crystals by suppressing the convection, while the magnetic force exerted a compressive stress on the paramagnetic alloy melt to remove the gases in the melt. As a result, a highly ⟨111⟩-oriented and -aligned and defect-free Tb-Dy-Fe compound was produced. This strategy may also be expanded to other alloy systems whose phases exhibit a magnetic anisotropy and thereby fabricate anisotropic functional compounds.