13.

(a) The synthesis process for metal oxides. SEM and TEM images for (b) NiFe-oxide, (c) CoFe-oxide, (d) CoNiFe-oxide, (e) NiCuFe-oxide, (f) NiZnFe-oxide, (g) CuZnFe-oxide, (h) CoMnFe-oxide, and (i) CoNiCuMnZnFe-oxide. The SEM images have scale bars set to 500 nm. (j,k) High-resolution TEM images and selected area electron diffraction (SAED) pattern of CoNiCuMnZnFe-oxide. (l) High-angle annular dark-field STEM image and associated elemental mapping of CoNiCuMnZnFe-oxide. Reproduced with permission from ref. . Copyright 2022, Wiley-VCH GmbH.