Ternary Mn-Co-Fe metallic thin films were deposited by RF-magnetron co-sputtering on SiO2/Si wafers and on ZMG232L (Hitachi Metals®), a special ferritic stainless steel for Solid Oxide Fuel Cell applications. The deposition was followed by heat treatment in an oxidizing atmosphere in order to convert the metallic thin films to (Mn,Co,Fe)3O4 spinel oxides. Coated and uncoated steel samples were analyzed after 1 h heat treatment in order to confirm the presence of the spinel structure on top of the steel, as well as to investigate and characterize the growth of oxides, namely (Mn,Cr)3O4 and Cr2O3, at the internal steel/coating interface. From Grazing Incidence X-ray Diffraction (GI-XRD) investigations together with Energy Dispersive X-ray analysis – Scanning Electron Microscopy and Time of Flight – Secondary Ions Mass Spectroscopy sputtering depth profiling the presence of well adherent (Mn,Co,Fe)3O4 coatings with approximately 500 nm thickness and a grain size of about 150 nm was confirmed. After the preparation annealing, some samples were heat-treated in simulated cathodic atmospheres at 800 °C for 500 h in order to assess the stability of the coatings. GI-XRD spectra still showed the presence of the protective coatings, however sputtering depth profile analysis indicated the presence of Cr on the surface.