Soft and hard elastic moduli of Galfenol transduction elements (invited)

In materials with high magnetostriction, e.g., Galfenol (Fe(100-x)Ga(x)), strong magnetoelastic coupling produces a strong dependence of the modulus on the magnetic state of the system. This is manifested in stress-strain curves which depend on the applied magnetic field H. Highly textured free standing zone melt Fe(81.6)Ga(18.4) rods approximately 2 in. X 1/4 in diameter in both as-grown and stress-annealed conditions were measured; one rod was grown at a faster than normal rate. In addition, an Fe(81.6)Ga(18.4) steel (Ga alloyed with 1003 steel) and an Fe(81)Al(19) rod were measured for comparison. Stress-strain curves at an actively controlled fixed magnetic field were obtained and the modulus at constant H, Y(H), was determined by numerical differentiation. All curves exhibit a minimum in the modulus at a stress that depends on H. At low and high stresses Y(H) saturates and equals Y(B), the modulus at constant flux density B. A single domain rotation model originally used to model the magnetization and magnetostriction in these materials was able to capture the major features of the stress-strain behavior and modulus, including the position of the minimum Y(H) and the Delta E effect but did not describe the details accurately. The average YB of five Fe(81.6)Ga(18.4) samples grown at normal rates was 76 +/- 3 GPa. Y(H) was highly dependent on sample, field, and stress and varied between 22 and 65 GPa. Magnetomechanical coupling factors k(33) were calculated to be similar to 0.65. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3058645]