Structural, magnetic and magneto optical properties of Fe_3O_4/NiO bilayers on MgO(001)

摘要

Ultrathin magnetite (Fe_3O_4) films are attractive for applications in the field of spintronics due to their ferrimag-netic behavior with assumed high degree of spin polarized electrons at the Fermi energy. For these applications, it is necessary to form epitactical bilayer structure combining ferrimagnetic magnetite with an antiferromagnetic layer. Therefore, here we study Fe_3O_4/NiO bilayers on MgO(001) substrates. Bilayers grown by reactive molecular beam epitaxy are stoichiometric and have well-developed surface and interface structures. The NiO layers are laterally pinned to the structure of the MgO(001) substrate while the magnetite films gradually relax. The interfaces show smooth morphologies and the films have very homogeneous film thickness necessary for spin-tronical applications. The magnetic and magneto optical properties of the Fe_3O_4/NiO bilayers were probed by the magneto optical Kerr effect. Compared to single Fe_3O_4 layers on MgO(001), the bilayers show complicated ferrimagnetic behavior depending on the azimuthal direction of the external applied field. The coercive field of the bilayers, however, is increased with the coercive field of single layer Fe_3O_4/MgO(001) structures making the Fe_3O_4/NiO bilayers attractive for spintronic applications.