Effect of Co addition and annealing conditions on the magnetic properties of nanocrystalline FeCoSiBPCu ribbons

•Addition of Co on the glass formation of Fe80CoxB14−xSi2P3Cu1 alloys was investigated.•Co addition enlarged the temperature region for heat treatment of this alloy family.•Higher Co addition leads to smaller grain size of nanocrystals and better soft magnetic properties.•The Fe80Co4B10Si2P3Cu1 alloy possesses excellent soft magnetic performance with Bs of 1.84 T and Hc of 5.3 A/m. We report the effect of substituting Co for a metalloid element on the glass formation, thermal properties, and magnetic behaviors of Fe80CoxB14−xSi2P3Cu1 (x = 0, 2, 4, 6) alloy ribbons. The addition of Co decreased the thermal stability of the alloy against crystallization and expanded the heat treatment temperature region of this alloy family. Fe80Co4B10Si2P3Cu1 alloy, which was annealed under optimal conditions, exhibited good soft magnetic performance that was characterized by a high saturation magnetic flux density of 1.84 T, a high effective magnetic conductivity of 12,601 at 1000 Hz, a low coercivity of 5.3 A/m, and a low core loss of 62 W/kg at 1000 Hz and 1.5 T.