Effect of cobalt doping on structural and magnetic characterization of nanocrystalline Fe72−xCoxCr28 (10 < X < 22) alloys

Highlights: • Preparation of nanocrystalline Fe-Cr-Co alloys with different content of cobalt was carried out. • The effect of substitution of Fe with Co on magnetic properties was done. • Optimization of the alloying composition and annealing condition were carried out. In this study, the effect of substitution of Co with Fe on structural and magnetic characteristics of nanocrystalline Fe-Co-Cr alloys has been investigated. In this regard, different combinations of Fe, Co and Cr elements with nominal composition of Fe_72−xCo_xCr₂₈ (10 < X < 22) were mechanically milled and subsequently annealed in the range of 560–640 °C. The samples were characterized using X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. Based on results, during milling process Cr and Co elements have been dissolved in Fe matrix and Fe-Cr-Co solid solution (with combination of α₁ and α₂ spinodal phases) has been formed. The coercivity and saturation of magnetization of formed alloys were in the range of 110–187 Oe and 150–175 emu/g, respectively. The coercivity of Fe_72−xCo_xCr₂₈ (10 < X < 22) alloys showed an anomalous behavior at 18 at.% of Co as a result of optimal interaction between α₁ and α₂ phases in this composition. The formed Fe-Co-Cr α-phase solid solutions were not stable and transformed to σ and γ phases during annealing process at temperatures higher than 600 °C. The formation of non-magnetic σ and γ phases had destructive effect on magnetic properties of prepared samples with different composition.