Magnetostriction of single crystal and polycrystalline Tb0.60Dy0.40 at cryogenic temperatures

At cryogenic temperatures, single crystals of TbDy alloys exhibit giant mag netostrictions of nearly 9000 ppm, making these materials promising for eng ineering service in cryogenic actuators, valves, and positioners. The prepa ration of single crystals is difficult and costly. Preliminary results on t he magnetostriction of textured polycrystalline materials are presented her e. For instance, polycrystalline Tb0.60Dy0.40, plane-rolled (one direction of applied stress) to induce crystallographic texture, has shown magnetostr ictions at 77 K of 3000 ppm for an applied field of 4.5 kOe and an applied load of 23 MPa, or 48% that of a single crystal under similar conditions. C omparisons are presented between the magnetostrictive response of plane- an d form-rolled (two orthogonal directions of applied stress) polycrystalline Tb0.60Dy0.40 at 10 and 77 K. It is reported that at 10 K plane-rolled Tb0. 60Dy0.40 exhibits 1600 ppm magnetostriction at an applied field of 4.4 kOe with a minimal applied load of 0.28 MPa. An observed restoration of the ini tial unstrained state may be a useful feature of polycrystalline materials for engineering service. Finally it is reported that thermal expansion meas urements provide a measure of crystallographic texture for comparison with the magnetostriction. (C) 1999 American Institute of Physics. [S0021-8979(9 9)44008-3].