Magnetostrictive Properties of Galfenol Alloys Under Compressive Stress

Abstract

Fe–Ga alloys, in which the α-Fe structure is maintained, are rich sources of high strength, low cost magnetostrictive alloys for transducer and vibration reduction applications. Although the magnetostriction of Fe itself is very low, when a relatively small fraction of the Fe atoms are replaced by Ga, the magnetostriction, (3/2)λ100, increases greatly. Until recently, the highest magnetostriction was found with the replacement of Fe by Al (Alfenol). In this paper, we present our measurements of magnetostriction on Fe1−x Gax , 0.13 ≤ x ≤ 0.24, (Galfenol). With the substitution of 19% Ga for Fe in Fe1−x Gax , a 12-fold increase in magnetostriction to ∼ 400 ppm occurs, even though Ga is non-magnetic. In these alloys, the saturation magnetizations remain high, Ms ∼= 1.7 T, and the Curie temperatures are far above room temperature, TC ∼= 700◦C. In most alloys studied, the magnetostrictions and magnetizations are fully saturated in fields less than 24 kA/m, even under compressive stresses >100 MPa. For x = 0.24 (near Fe3Ga), an anomalous increase in magnetostriction with temperature occurs with a peak magnetostriction above room temperature. Small additions of Ni and Mo to the binary Fe–Ga alloys decrease the room temperature value of λ100.