Phase evolution and magnetic properties of a Co-rich multi-component magnetic nanocomposite film

•As-grown film favours FCC-like ordering; upon annealing HCP short range ordering noted.•Atom probe reveals Mn partitioning in as-deposited, non-ideal amorphous mixed state.•Annealing equates thin film and melt spun nano/microstructures. The effect of annealing on the chemical partitioning, microstructural evolution, and magnetic properties of a magnetron sputter deposited Co-2.8Fe-2.7Mn-3.5-Nb-2.4Si-7.2B (at%) alloy was investigated using transmission electron microscopy, atom probe tomography, and vibrating-sample magnetometry. While no crystallinity was observed in the as-deposited film, nonideal mixing in this amorphous state was noted by the Mn enrichment around the film’s ~ 7 nm diameter columnar morphology that spanned the thickness of the film parallel to the growth direction. Following annealing at 520 °C for either 5 min or 20 min, the columnar morphology transformed to a partially crystallised microstructure with Co and Fe enriching 7.0 ± 1.4 nm crystallites encased by an amorphous region enriched with Nb, B, Si, and Mn. The magnetic coercivity, ~ 26 Oe, was invariant upon annealing while the saturation magnetisation increased from 828 to 953 emu/cm3.