Soft magnetic properties of Co-doped FeSiBC amorphous and nanocrystalline alloys

•(Fe0.82Si0.04B0.13C0.01)95Co5 amorphous alloy with 5 at. % Co addition exhibits a high Bs of 1.73 T and a low Hc of 8.9 A/m.•The (Fe0.82Si0.04B0.13C0.01)90Co10 alloy without nucleating elements could form a controllable amorphous/nanocrystalline dual-phase microstructure.•Magnetic properties and domain wall structure of amorphous and amorphous/nanocrystalline two-phase alloy are characterized.•The coarse grains result in strong pinning of the domain walls, leading to poor magnetic properties. Amorphous ribbons of (Fe0.82Si0.04B0.13C0.01)100-xCox (x = 0, 5, 10, and 15) were prepared by the melt-spinning technique, and their microstructure and magnetic properties were investigated. It was observed that the saturation magnetic flux density (Bs) of the alloys could be efficiently increased from 1.64 to 1.78 T by Co addition. Particularly, the (Fe0.82Si0.04B0.13C0.01)95Co5 amorphous alloy with 5 at. % Co exhibited a high Bs of 1.73 T and a low coercivity (Hc) of 8.9 A/m, which implies a potential industrial application. The (Fe0.82Si0.04B0.13C0.01)90Co10 alloy developed a dual-phase microstructure composed of the bcc-Fe(Co) crystalline phase of size 54 nm that was nonuniformly embedded in the amorphous matrix and exhibited an approximately linear hysteresis loop after annealing at 380 ℃ for 20 min. Magnetic domain walls were observed to support the variation of soft magnetic properties with different annealing temperatures. It is demonstrated that the (Fe0.82Si0.04B0.13C0.01)90Co10 alloy can form a controllable amorphous/nanocrystalline dual-phase microstructure after appropriate heat treatment even without the nucleating elements such as Cu or Au.