Comparative measurements of the field dependence of Young’s modulus and shear modulus in Fe-based amorphous wire

In this paper we present measurements of the field dependence of Young’s modulus E(H) and shear modulus G(H) for amorphous wires of composition Fe77.5B15Si7.5. E(H) was measured by a vibrating reed method and G(H) by means of a torsional pendulum. For as-cast wire the maximum change in either modulus is about 2%, and the form of the field dependence is consistent with the rotation of moments in the outer sheath from a radial to an axial direction, analogous to the moment rotation model for transversely field annealed ribbons. The small magnitude of the modulus changes is a consequence of the rather high anisotropy of a few kJ/m3 associated with the casting stress. The modulus changes in current annealed wires are much greater than in the as-cast state, with ratios Emin/Emax approaching the largest values found in transversely field annealed ribbons. This is consistent with the reduction of the radial stress by annealing, but also indicates the retention of a substantial proportion of off-axis moments. The significance of these results in the light of present understanding of domain structure in amorphous wires is discussed.