Magnetostrictions and Curie temperature measurements of (Fe-Co)91−xMo8Cu1Bx alloys with varying Co/Fe ratio

Amorphous rapidly quenched ribbons of (Fe-Co)79Mo8Cu1B12 and (Fe-Co)76Mo8Cu1B15 with the ratio of Co/Fe from 0 to 1 and 0 to 2, respectively, 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, which is of the order of 10−3. Using special disc-shaped samples field dependencies of magnetostriction in parallel and perpendicular directions of the applied magnetic field were obtained by direct measurement. Subsequently, saturation magnetostriction and volume magnetostriction as well as forced magnetostriction were computed. Saturation magnetostriction λS increases with increasing Co/Fe ratio from 0 up to 15 and from 0 up to 17 ppm for both alloy systems, respectively, depending both on the Co/Fe ratio and on the shift of TC with composition. After attaining the maximal value and further increase of the Co/Fe ratio the saturation magnetostriction decreases. Both alloy systems with ratio Co/Fe=0 exhibit TC near room temperature and the system passes into paramagnetic state. TC for higher Co/Fe ratios approaches the glass transition region. In paramagnetic state the field dependencies of magnetostriction are practically linear functions of applied field and approach saturation only for high-field values.