Effect of Stress Annealing on the Saturation Magnetostriction of Nanocrystalline Fe$_{73.5}$Cu$_{1}$Nb$_{3}$Si$_{15.5}$B$_{7}$

Abstract

Ribbons of amorphous Fe73.5Cu1Nb3Si15.5B7 have been crystallized by annealing under tensile stress. As typical for this composition, the annealed ribbons reveal a nanocrystalline structure with low coercivity, near-zero magnetostriction, and a strong creep-induced anisotropy proportional to the annealing stress. The present work shows that the tensile stress, ?a, applied during annealing also affects the saturation magnetostriction ?s. Accordingly, ?sdecreases linearly with increasing magnitude of ?a. The samples have an initially small positive magnetostriction and, hence, ?s even changes its sign from positive to negative with increasing annealing stress. This change of sign provides qualitative evidence that the effect is clearly beyond experimental error. Our finding is compared to the elastic stress dependence of the saturation magnetostriction constant. The latter is a well-established phenomena for amorphous Co-base alloys and, as we will demonstrate, can also be observed in nanocrystalline alloys. The results will be discussed theoretically in terms of the strain dependence of the magnetic anisotropy energy which ultimately provides the physical origin of magnetostrictive phenomena.