The letters under the peaks are the assignment by De Jesús Ruíz-Baltazar and coworkers. "Additionally, the band associated to the magnetite and hematite phases are corroborated with Raman spectra obtained from the RRUFF Raman Mineral Spectra database (University of Arizona)". It "Is important to note that the magnetite and hematite phases are presents in the experimental Raman spectrum, however, the majority phase observed is the magnetite" (De Jesús Ruíz-Baltazar et al., 2019).