Stress dependence of magnetostrictions and strains in 〈111〉-oriented single crystals of Terfenol-D

Abstract

Single crystals of Tb_0.27Dy_0.73Fe₂ were prepared successfully by the Czochralski (CZ) method using a magnetic levitation cold crucible first in this laboratory. The Laue x‐ray technique and metallography verified its twin‐free single crystalline perfection. Weidmanstatten precipitation (WSP) slightly exists in these specimens with WSP platelets parallel to the {111} planes of Terfenol‐D. Saturation magnetostriction were measured along three principal crystallographic axes [111], [11 2̄] and [1 1̄0] of single crystal Tb_0.27Dy_0.73Fe₂ with magnetic field parallel and then perpendicular to the measuring direction, which gives an intrinsic magnetostriction λ₁₁₁=1640×10⁻⁶ for 〈111〉 easy axis. Stress dependence of magnetostrictions and strains measured along three mutually perpendicular axes, [111], [11 2̄], and, [1 1̄0] on 〈111〉‐oriented single crystalline rods of Terfenol‐D indicates that apparent magnetostriction for 〈111〉 direction increases with increasing applied compressive stress along the rod axis, and reaches 2375×10⁻⁶ under a stress of 24 MPa and a magnetic field of 20 kOe. Maximum d₃₃ decreases with the increment of applied stresses and the amount of WSP, and ranges from 1×10⁻⁶/Oe to 6×10⁻⁶/Oe at about 500 Oe. Less hysteresis appears. Magnetizing processes are calculated and compared with the measured changes of magnetostriction. The authors conclude that 〈111〉‐oriented single crystal of Terfenol‐D is suitable for precise displacement actuators although it would be much better to eliminate the WSP precipitation.