Discovery of giant magnetostriction in annealed Co1-xFex thin-films

Abstract

Chemical and structural heterogeneity and resulting interaction of coexisting phases can lead to extraordinary behaviors in oxides as observed in piezoelectric materials at morphotropic phase boundaries and relaxor ferroelectrics. But such phenomena are rare in metallic alloys. Here, we show that by tuning the presence of structural heterogeneity in textured Co1-xFex thin films, effective room-temperature magnetostriction λeff as large as 260 ppm can be achieved at low saturation field of 1000 ppm, rivaling magnetostriction attained in rare-earth containing Terfenol, which requires saturation field > 0.1 T. Synchrotron diffraction and electron microscopy analyses of our Co1-xFex films indicate that the maximum in magnetostriction occurs at compositions close to the (fcc+bcc)/bcc phase boundary and originates from the precipitation of an equilibrium Co-rich fcc phase embedded in a Fe-rich bcc matrix. These results together with reported observations of large magnetostriction in Fe1-xGax alloys indicate that the recently proposed heterogeneous magnetostriction mechanism can be used to guide exploration of other novel compounds with unusual magnetoelastic properties.