Magnetostriction Measurements of (Fe-Co)-Mo-Cu-B Alloys with Varying Atomic Fe/Co Ratio

Amorphous rapidly quenched ribbons of $(Fe-Co)_{76}Mo_8Cu_1B_{15}$ with the ratio Co/Fe = 0, 1/9, 1/6, 1/4, 1/3, 1/2, 1/1 and 2/1 were prepared by planar flow casting. The dependence of the Curie temperature $T_C$ on Co/Fe ratio was determined. Due to the presence of the invar effect it was possible to measure the spontaneous volume magnetostriction in the temperature interval between 300 K and $T_C$. Field dependences of magnetostriction in parallel and perpendicular directions of applied magnetic field were obtained by direct measurement method. Subsequently, saturation magnetostriction and volume magnetostriction as well as forced magnetostriction were computed. Saturation magnetostriction increases with increasing Co/Fe ratio from 0 up to 17 ppm, depending both on the Co/Fe ratio and on the shift of $T_C$ with composition. The alloy with ratio Co/Fe = 0 exhibits $T_C$ near room temperature, thus field dependences of magnetostriction, corresponding to the dependences of a paramagnetic system are practically linear functions of applied field, corresponding to paramagnetic state