Giant magnetostriction in amorphous (Tb1−xDyx)(Fe0.45Co0.55)y films

The magnetization and magnetostriction have been studied in amorphous (Tb1−xDyx)(Fe0.45Co0.55)y films. A well-defined easy axis is created by magnetic field annealing and the sperimagnetic cone structure, characteristic of these amorphous alloys, is reduced. The anisotropy has a minimum at x=0.73 as in the R Fe2 Laves phase. This points to the similarity between the local environments in the amorphous and crystalline states. A giant magnetoelastic coupling coefficient b of 60 MPa is developed at 300 K in low applied field for x=0, optimally annealed films. Assuming a Young’s modulus and a Poisson ratio of 80 GPa and 0.31, respectively, the magnetostriction is evaluated at 1020×10−6. This is much larger than previously reported values in other amorphous films.