Measurement of d15 in Fe100−xGax (x=12.5,15,18.4,22), Fe50Co50, and Fe81Al19 highly textured polycrystalline rods

We report the first measurements of d15, which relate torsion to an applied field, in the high magnetostriction Galfenol alloys Fe100−xGax (x=12.5,15,18.4,22), Fe50Co50, and Fe81Al19. Measurements were performed on highly textured polycrystalline 6.4×50.8mm2 rods by simultaneously applying a longitudinal magnetic field H∥ (−1200<H∥<1200Oe) along the rod axis and a circumferential magnetic field H⊥ generated by a current i (−60<i<+60A) through the sample. We obtained d15 from the twist ξ using du Tremolet de Lacheisserie’s [Magnetostriction (CRC, Boca Raton, 1993), 212] results for H⊥⪡H∥, modified for our nearly cubic samples: d15=2ξ∕j, where j is the current density in the sample. In the Fe100−xGax system, d15 (in nm/A) were 4.5±1, x=12.5 (sample 1); 7±2, x=12.5 (sample 2); 2.8±0.5, x=15; 16±3, x=22 (stress annealed); and 11.4±0.4, x=22. The Fe81.6Ga18.4 measurements did not yield a value. For Fe50Co50, d15=29±4 and for Fe81Al19, d15=8±1. Estimated values of λ111 were obtained by fitting ξ to 1∕H∥ and are...