We investigated the magnetic proximity effect (MPE) as well as the unidirectional spin Hall magnetoresistance (USMR) and spin-orbit torques (SOTs) in heavy metal/Co/heavy metal trilayer systems compared to Pt/Co and Ta/Co bilayers. By using x-ray resonant magnetic reflectivity, we obtained magnetic depth profiles of the structural, optical and magnetic parameters, and studied the impact of the MPE in Pt on the total magnetic moment of the systems. A detailed analysis of harmonic longitudinal and Hall voltage measurements revealed enhanced SOTs and USMR in the trilayers that include a second heavy metal with the opposite sign of the spin Hall angle.
Ultrathin magnetite (Fe3O4) films are attractive for applications in the field of spintronics due to their ferrimagnetic 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 Fe3O4/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 spintronical applications. The magnetic and magneto optical properties of the Fe3O4/NiO bilayers were probed by the magneto optical Kerr effect. Compared to single Fe3O4 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 Fe3O4/MgO(001) structures making the Fe3O4/NiO bilayers attractive for spintronic applications.
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