High surface stability of magnetite on bi-layer Fe3O4/Fe/MgO(0 0 1) films under 1 MeV Kr+ ion irradiation

N-T H Kim-Ngan, M Krupska, A G Balogh, P Malinsky and A Mackova

Abstract

We investigate the stability of the bi-layer Fe₃O₄/Fe(0 0 1) films grown epitaxially on MgO(0 0 1) substrates with the layer thickness in the range of 25–100 nm upon 1 MeV Kr⁺ ion irradiation. The layer structure and layer composition of the films before and after ion irradiation were studied by XRR, RBS and RBS-C techniques. The interdiffusion and intermixing was analyzed. No visible change in the RBS spectra was observed upon irradiation with ion fluence below 10¹⁵ Kr cm⁻². The bi-layer structure and the stoichiometric Fe₃O₄ layer on the surface were well preserved after Kr⁺ ion irradiation at low damage levels, although the strong intermixing implied a large interfacial (Fe _x O _y ) and (Fe, Mg)O _y layer respective at Fe₃O₄–Fe and Fe–MgO interface. The high ion fluence of 3.8  ×  10¹⁶ Kr cm⁻² has induced a complete oxidization of the buffer Fe layer. Under such Kr fluence, the stoichiometry of the Fe₃O₄ surface layer was still preserved indicating its high stability. The entire film contains Fe _x O _y -type composition at ion fluence large than 5.0  ×  10¹⁶ Kr cm⁻²