Magnetostriction measurements of (Fe–Co)–Mo–Cu–B alloys with varying atomic Fe/Co ratio

Amorphous rapidly quenched ribbons of (Fe–Co)79Mo8Cu1B12 (numbers indicate at.%) with the ratio Co/Fe = 0, 1/12, 1/9, 1/6, 1/4, 1/3, 1/2 and 1 were prepared by planar flow casting. The dependence of Curie temperature TC on Co/Fe ratio was determined from temperature dependencies of sample dilatation measured using a special dilatometer designed for these materials. 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 TC. Using special disc shaped samples-field dependencies of magnetostriction in parallel and perpendicular directions of applied magnetic field were obtained by direct measurement. 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 15 ppm, depending both on the Co/Fe ratio and on the shift of TC with composition. The alloy with ratio Co/Fe = 0 exhibits TC in the vicinity of room temperature, thus field dependencies of magnetostriction are practically linear functions of applied field and approach saturation only for high field values.