The interfaces between ferromagnetic electrodes and tunnel oxides play a crucial role in determining the performances of spin-based electronic devices, such as magnetic tunnel junctions. Therefore, a deep knowledge of the structural, chemical, and magnetic properties of the buried interfaces is required. We study the influence of rapid thermal annealing treatments up to 500° C on the interfacial properties of the Fe/Lu2O3 system. As-grown stacks reveal the presence of hydrogenated Fe–Lu–H intermetallic phases at the Fe/Lu2O3 interface most likely due to the H absorption on the Lu2O3 surface upon exposure to air and/or to the oxide growth. The annealing treatments induce remarkable changes of the structural, chemical, and magnetic properties at the interface, as evidenced at the atomic scale by the sub-monolayer sensitivity of conversion electron Mössbauer spectroscopy …