Fig. 3: Characterization of MFe@FeOx (M = Co, Ni, Mn).

The Mössbauer spectra of the a CoFe@C and b CoFe@FeOx. c HRTEM image, d the corresponding lattice fringes, as well as e STEM image and the corresponding elemental mapping images of the MnFe@FeOx. f HRTEM image, g the corresponding lattice fringes, as well as h STEM image and the corresponding elemental mapping images of the NiFe@FeOx.