AVS 46th International Symposium
    Magnetic Interfaces and Nanostructures Technical Group Monday Sessions
       Session MI-MoM

Paper MI-MoM9
Low-temperature Gaseous Nitriding and Subsequent Oxidation of Epitaxial Ni/Fe Bilayers

Monday, October 25, 1999, 11:00 am, Room 618/619

Session: New Magnetic Materials
Presenter: A.V. Mijiritskii, University of Groningen, The Netherlands
Authors: A.V. Mijiritskii, University of Groningen, The Netherlands
M.A. James, University of Groningen, The Netherlands
D.O. Boerma, University of Groningen, The Netherlands
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Fe-nitrides are of interest due to their anti-corrosive, mechanical and magnetic properties. From a technological point of view, one of the most attractive ways to form Fe-nitrides is gaseous nitriding of Fe in a NH@sub 3@+H@sub 2@ mixture. The disadvantage of this method is the necessity to apply relatively high temperatures upon the nitriding. Lately, a method has been discovered allowing fabrication of pore-free Fe-N phases in a mixture of NH@sub 3@+H@sub 2@ at relatively low temperatures (550-625 K) by using a Ni cap-layer as a catalyst. In the present work we study the behaviour of epitaxial Ni/Fe bilayers upon low-temperature gaseous nitriding as well as the subsequent oxidation of the Ni/Fe-N systems formed. A number of experimental techniques was employed including XRD, RBS, XPS, and CEMS. Epitaxial Ni/Fe bilayers were grown on MgO(100) in-situ by molecular beam epitaxy (MBE) or ex-situ by laser ablation deposition (LAD). Nitriding was done in a dedicated N-oven at 575 K at different nitriding potentials of the NH@sub 3@+H@sub 2@ mixture depending on the nitride phase to be produced. Oxidation of the Ni/Fe-N systems obtained was performed in an O-oven at 525 K in P(O@sub 2@)=1x10@sup -6@ mbar. Upon nitriding in NH@sub 3@+H@sub 2@, oxidation of Fe was observed due to small fraction of H@sub 2@O present in the N-oven. On the basis of the RBS measurements it was concluded that to prevent the oxidation, the thickness of the capping Ni layer should exceed 200 Å. XRD measurements performed on as-nitrided samples revealed that Fe-nitride phases form at higher nitriding potential values in the case of epitaxial Ni/Fe bilayers compared to policrystalline Ni/Fe bilayers. This is probably due to the absence of nucleation sites in the epitaxial layers. The epitaxial relationships of the phases produced and the details of the nitriding and oxidation kinetics are being discussed.