Figure 5. Co-Fe alloyed nanoparticles embedded in the carbon fibres.

(a) The ⁵⁹Co zero field FNR spectra recorded at 2 (black), 4.2 (magenta) and 77 K (blue). The inset optical photo shows the tested sample in the setup (left) and a totally expended sample (right) with the same mass (∼100 mg, with size around 3 cm by 5 cm). (b) TDFNR spectra: in black spectrum measured at 2 K minus spectrum measured at 4.2 K; in magenta spectrum at 4.2 K minus spectrum at 77 K; in blue spectrum at 77 K. The inset structure models display the B2 ordered Co and Fe atoms (blue spectrum) and the same ordered structure but with an excess of Co atoms (magenta and black spectra). (c) High-resolution TEM image of typical Co-Fe alloyed nanoparticles embedded in the porous carbon fibres. (d) Representative HAADF-STEM image of various size particles embedded in carbon fibres, and (e) relative Co and Fe atomic concentration in big (30±3 nm, black) and small (10± 3 nm, magenta) alloyed nanoparticles measured by EDS mapping. (f) Relative map with Co in red and Fe in green showing the Co and Fe elements dispersed in different size of alloyed nanoparticles. The scale bars in c,d and f are 5, 100 and 30 nm, respectively.