Induced magnetic anisotropy in stress-annealed Galfenol laminated rods

Abstract

Iron–gallium (Galfenol) is a promising transducer material that combines highmagnetostriction, desirable mechanical properties and a high permeability. The highpermeability of this material causes a relatively low cutoff frequency in dynamicapplications, above which eddy currents form and introduce significant power losses. Toreduce the eddy current losses, magnetostrictive drivers are commonly laminated. A secondtransducer design consideration is the introduction of an initial alignment of domains insideof the material to maximize the magnetostriction performance without a prestressmechanism. Built-in uniaxial magnetic anisotropy through stress annealing alignsmagnetic moments perpendicular to the direction of actuation. Stress annealing is ahigh temperature process with simultaneous application of an external load andsubsequent cooling under load in which the magnetic moment alignment developed attemperature is retained. The external load needed to build in a useful uniaxialmagnetic anisotropy in Galfenol is greater than the buckling load for Galfenollaminae sized for use in high frequency dynamic applications. In this study, stressannealing of highly textured polycrystalline Galfenol is successfully extended to thinlaminae by introducing fixtures to avoid buckling of the laminae under compressionduring the heat treatment process. The maximum built-in uniaxial anisotropy was11.2 kJ m−3.