Hysteresis, d*33 and d33 of Fe81.6Ga18.4 textured polycrystals

Abstract

Measurements of d33* (major and minor loops) and d33 (major loops) were made on three Fe81.6Ga18.4 (Galfenol) highly textured polycrystalline rods, one of which had a small amount of 1002 steel substituted for the iron. Seven ΔT’s between ±25 and ± 0.5 MPa at 100 Oe were used for the minor loops. These measurements are useful for energy harvesting, which is the generation of energy by utilizing vibrations present in the environment. For magnetostrictive materials d33*=∂B/∂THis the relevant parameter, where B is the magnetic flux density, T is the stress and H is held constant. Since real energy harvesting devices will not have active H control, ∂B/∂Twas also measured where H was not held constant. The d33*’s and d33’s (d33=∂S/∂HT) for both binary samples with ΔT ≥ ±5 MPa were well fit by a Gaussian plus a constant. Peak amplitudes for d33 and d33*were ∼80 and ∼60 nm/A, respectively. At smaller ΔT’s, d33*vs. T was flat or showed a broad peak. The steel containing sample had a larger cubic anisotropy which resulted in a double peaked d33 curve with a maximum amplitude of ∼100 nm/A. At the points where the d33* and d33 measurements overlap, the two d-coefficients are within 5 to 50% of one another at 100 Oe. The hysteresis in the S-T and B-H loops was ∼2 and ∼0.9 kJ/m3, respectively.