The extra signal at BE near 106 eV can be attributed to the combination of a configuration interaction (CI) satellite from the low-spin multiplet of the Mn ion (predominant in the sample with x = 1.40) and a charge transfer (CT) satellite from the low-spin multiplet of the Fe ion (predominant in the samples with x = 0.37 and 0.47). For the samples with x below 0.5, the energy splitting of the Mn 3s doublet is higher than 6.2 eV, which strongly suggests that the Mn ions are preferentially in the divalent state, with no evidence of oxidized species; these values are consistent with the results reported elsewhere for several manganese ferrites. The contribution of the CI satellite to the broader structure at a BE shifted to +15-16 eV from the low-spin multiplet contribution is a clear hint for the presence of Mn in 3d 5 electronic configuration. Moreover, the higher ΔBE value for the sample with the lowest Mn content (6.5 eV) denotes an enhanced ionicity of the lattice Mn-O bonds, which might indicate that under a low level of Mn doping, the Mn(II) ions entering into the ferrite structure show preference for the octahedral (B) sites. In contrast, the sample with high Mn content (x = 1.40) experiences a reduction (5.9 eV) of the Mn 3s ΔBE that could suggest the coexistence of a Mn 3+ fraction forming oxidized species, though the occurrence of more covalent Mn(II)-containing phases. The recorded XPS spectra also provided a conclusive clue on the heterogeneity of the samples by analyzing the 2p and 3s regions (outermost 4 nm and topmost 6 nm, respectively). We have compared the computed Mn/Fe atomic ratios obtained by fitting the 3s region and the corresponding atomic fractions obtained by integrating the 2p region during the survey scans (see Figure in the SI).