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PhD thesis defense of Magdalena Krupska-Klimczak

Badanie i modyfikacja cienkowarstwowych układów na bazie magnetytu

Investigation and modification of magnetite-based thin film systems Magnetite (Fe3O4) is considered as a potential material for spintronic applications in the room temperature. Spintronic devices would consist of magnetite thin films. However, external conditions (high temperatures, exposure to air or to high-energy beam) can destroy the structure or change the composition of magnetite layers. Therefore, it is important to determine the stability of the magnetite layers.

The aim of the dissertation was to investigate the quality and to determine the stability of the Fe3O4 thin films under the expose to external conditions such as annealing and high-energy argon (Ar+), krypton (Kr+) and gold (Au+) ion irradiation.

The Single layer and bilayer thin films were grown on the MgO(001) substrate (Fe3O4/MgO(001), Fe3O4/Fe/MgO(001) and Fe/Fe3O4/MgO(001)) by molecular beam epitaxy technique (MBE). Two series of thin film systems are described in this work – nine samples in total, with different thickness and sequence of the layers. All of them were investigated in the as-grown state and after modification (upon annealing and high-energy ion irradiation) by X ray reflectometry (XRR), Rutherford’s backscattering spectrometry (RBS) and RBS with the channeling effect (RBS-C). For data analysis SIMNRA and SRIM computer simulations were used.

It was shown that single layer film Fe3O4/MgO(001) possesses a very good quality and in the bilayer Fe3O4/Fe/MgO(001) film, on the surface there is always a stoichiometric Fe3O4 layer. The important outcome is finding the high stability of the Fe3O4 layer on the surface of the bilayer films upon irradiations. For all investigated films, despite the reduction of the layer thickness and even the full oxidation of the Fe buffer layer, the surface Fe3O4 layer is always preserved after irradiation with ion fluences smaller than e.g. ϕ(Ar)= 20,731016 Ar+/cm2, ϕ(Kr)=3,841016 Kr+/cm2, ϕ(Au)= 11016 Au+/cm2 ion.