Magnetostriction of a (110) oriented Tb0.3Dy0.7Fe1.95 polycrystals annealed under a noncoaxial magnetic field
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Æ110æ oriented Tb0.3Dy0.7Fe1.95 alloy rod was annealed at 500 °C under a magnetic field of 0.3 T, which was applied 35° away from the rod axis. X-ray diffraction characterization and optical microscopy observation showed that both the crystal orientation and morphologies were retained after magnetic annealing. Magnetic force microscopy images exhibited obvious change of the magnetic domain configurations. The magnetostrictive performance was changed drastically. Saturation axial magnetostriction kks increased from 1023 to 1650 ppm by the ratio of 61.3%, but saturation perpendicular magnetostriction k⊥s decreased from 802 to 624 ppm. Maximum magnetostrictive strain coefficients d33 and d31 were found to be enhanced by 29.3% and 32.6%, respectively. In addition, the fields for obtaining both optimum d33 and d31 decreased, which indicates that better magnetostrictive performance can be achieved at lower external fields after magnetic annealing.
I. INTRODUCTION
Giant magnetostrictive materials Terfenol-D have attracted considerable interest for applications in linear motors, precise actuators, and high-power underwater acoustic transducers.1–5 In general, the giant magnetostriction originates mainly from the (Tb, Dy)Fe2 Laves phase. With the application of a uniaxial compressive prestress, the Æ110æ or Æ112æ oriented (Tb, Dy)Fe2 crystals possess improved magnetostrictive performance, which is the so-called “jump” effect.6 The magnetostriction “jump” effect is ascribed to specific moment rotation processes. Under the uniaxial compressive stress, the magnetic moments orient along the Æ111æ easy magnetization directions (EMDs), which are perpendicular to the crystal axis. As an external field is applied, the moments “jump” toward the nearest EMD, which lies only 19.5° from the Æ112æ axis or 35.2° from the Æ110æ axis, resulting in a significant improvement in axial magnetostriction.6,7 Alternatively, magnetic annealing can also redistribute the magnetic moments and control the magnetostrictive responses of Terfenol-D oriented crystals.8–12 When annealing under a magnetic field transverse to the rod axis, the magnetostrictive strain coefficient, d33, of a Tb0.3Dy0.7Fe1.95 Æ112æ oriented crystal can be improved by 44%.9 Without applying any compressive prestress, saturation axial magnetostriction of a Æ110æ oriented crystal Tb0.3Dy0.7Fe1.95 is significantly improved by 58% after annealing under a transverse magnetic field of a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2010.48 J. Mater. Res., Vol. 26, No. 1, Jan 14, 2011
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0.3 T.10 Previous investigation also demonstrates that both axial magnetostriction kk and perpendicular magnetostriction k⊥ of the Æ110æ oriented crystal are significantly improved through transverse field annealing, while negative kk and positive k⊥ are found after annealing under a coaxial field of 0.3 T.11 Therefore, differential magnetostrictive responses can be achieved in the Æ110æ oriented crystal through chang
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