Effect of Oxygen Stoichiometry onMicrostructural andMagnetic Properties of FePt/TaO Bilayer Fabricated by Ion-Beam-Bombardment Deposition

The effect of TaO capping layer on microstructures and magnetic properties of FePt thin films via annealing was studied. The structuralordering of FePt fromface-centered cubic to face-centered tetragonal phases depends strongly on the oxygen contents in the cappingTaO layer. The role of the TaO layer is used to separate the FePt grains, as revealed by TEM. The annealed FePt/TaO (15%O /Ar)exhibited the largest out-of-plane coercivity ( kOe) amongst all samples, compared to that ( kOe) in the reference FePtlayer. At low oxygen content in FePt/TaO bilayers, the Ta atomsmay act as defects to obstruct the FePt ordering whereas at high oxygencontents, the excess oxygen atoms diffuse into the FePt layer and react with Fe to form iron oxides which give rise to the low coercivities,as characterized by the XPS depth profile and binding energy analysis