Variation of the magnetoelastic properties of Terfenol-D with sample thickness

Abstract

The effect of sample thickness on the static magnetostrain and dynamic magnetoelastic properties of Terfenol-D has been determined by slicing a 25 mm long, 20 mm diameter rod into progressively thinner samples. The static saturation magnetostrain (/spl lambda/sat) showed a gradual change through the cross-section of the rod believed to be due to variations in composition and crystallographic orientation. The static saturation magnetostrain was not found to depend on the sample thickness, unlike the dynamic properties, which were found to depend largely on the thickness of the sample. In reducing the sample thickness from 17.35 mm to 1.17 mm, the maximum dynamic strain coefficient (d/sub 33/) increased by 100% and 279% at 240 and 3840 Hz respectively toward a maximum of 5 nmA/sup -1/. Classical eddy current theory has been used to model the fields within the samples and mechanical modeling further used to predict the surface strain. Eddy currents are found only to be responsible for some of the increase in dynamic properties with decreasing sample thickness. The discrepancy between the expected dynamic properties and those measured was as much as 135% and may be due to different domain wall motions occurring at the surface compared to those in the bulk.