Field-anneal-induced magnetic anisotropy in highly textured Fe-Al magnetostrictive strips

Highly textured (011)[100] Goss-oriented rolled sheet Fe-Al alloy is a promising magnetostrictive material for use in bending mode sensors and vibrational energy harvesters. In this paper, we performed magnetic field annealing (FA) to induce magnetic anisotropy in strips of highly textured Fe-Al. Prior work suggests FA as a viable alternative to stress annealing (SA), which leads to buckling of Fe-Al rolled sheet samples. The Fe-Al strips studied here exhibited tetragonal magnetostriction values ((3/2)λsat = λ∥ − λ⟂) of ∼136 ppm along their length, which corresponds to ∼78% of the single crystal value along a <100> orientation. The effectiveness of FA on magnetic moment rotation was inferred by comparing post-FA magnetostriction measurements with the maximum possible yield, where λ∥= 0 and λ⟂= (3/2)λsat. Strain gauge data from the middle of the strip indicates that FA achieved ∼27% of the desired built-in uniaxial anisotropy along the parallel direction of the strip length, decreasing λ∥ by 25 ppm of the 95 ppm. Hall effect sensor data was used to assess the potential effect of FA on sensing and energy harvesting performance. FA improved the bending-stress-induced changes in magnetization near the clamped end of the strips by ∼45%. These results suggest that the FA was more effective in the region near the end of the strip than toward the middle of the strip, which we explain may be a result of the use of high temperature permanent magnets at the ends of the strips for the FA protocol.