Microstructure and magnetic properties of nanocrystalline Co-doped Sendust alloys prepared by melt spinning

(Fe1−xCox)85Si9.6Al5.4 (wt.%) (x = 0, 0.05, 0.10, 0.15, 0.20) nanocrystalline flakes have been prepared by high-energy planetary ball milling method from melt-spun ribbons. The as-milled powders were annealed at various temperatures ranging from 573 to 973 K for 30 min under the protection of nitrogen. XRD, SEM and VSM were used to characterize the microstructure and magnetic properties of the nanocrystalline powder samples. It was found that D03 superlattice phase was detected in the melt-spun ribbons, coexisting with α-Fe(Co) matrix phase. As the milling time reached 20 h or longer, the D03 superlattice structure of Co-doped samples disappeared. When the milling time was prolonged to 70 h, thin flakes with aspect ratio higher than 10:1 were achieved, and the corresponding average grain size was about 10 nm. After 30 min heat treatment, the D03 superlattice reappeared in the ball milled flakes when the annealing temperature was higher than 773 K. In addition, heat treatment has an evident effect on internal stress relief. The saturation magnetization Ms of Co-doped samples is larger than Co free samples. Moreover, the substitution of Co for Fe is beneficial to increase the Curie temperature (TC) of nanocrystalline D03 phase from 733 K for x = 0 to 1000 K for x = 0.20, indicating a potential application in elevated temperatures.