ANISOTROPIC PERPENDICULAR AXIS MAGNETOSTRICTION IN TWINNED TBXDY1-XFE1.95

The longitudinal magnetostriction (Δl/l) for twinned Tb xDy1-xFe1.95 material, prepared by the free-standing float-zone method, has been previously measured and found to be very large (2000×10-6) at room temperature. The magnetostrictions for the [111] and [11̄0] crystallographic axes perpendicular to the applied stress and magnetic-field [112̄] direction are presented as functions of temperature, applied stress, and applied magnetic field. The temperature range is ±60°C centered about the anisotropy compensation temperature of Terfenol-D (+10°C). The stress ranges from 2 to 32 MPa and the magnetic field to ±2000 Oe. The temperature dependence of the perpendicular axes magnetostriction is similar to that of the conventional magnetostriction measured parallel to the [112̄] growth axis. Relative values for the saturation magnetostriction exhibit a large anisotropy in the perpendicular direction, ranging from -117% for the [111] to +19% for the [11̄0] direction. This ratio stays constant as a function of temperature above the compensation temperature for a given prestress above 8 MPa. The largest absolute value of magnetostriction (2260×10-6) occurs in the [111] direction at 10°C at a prestress pressure of 12 MPa. Above this temperature the magnetostriction falls at a rate of -8.5×10 -6/°C. The volume magnetostriction is shown to be small and highly sample dependent. All data is consistent with the parent-twin magnetization model and also the magnetostriction values along nonprincipal axes.