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The ability to induce and control the perpendicular magnetic anisotropy (PMA) of ferromagnetic layers has been widely investigated, especially those that offer additional functionalities (e.g., skyrmion stabilization, voltage-based magnetization switching, rapid propagation of domain walls). Out-of-plane magnetized ferromagnetic layers in direct contact with an oxide belong to this class. Nowadays, investigation of this type of system includes antiferromagnetic oxides (AFOs) because of their potential for new approaches to applied spintronics that exploit the exchange bias (EB) coupling between the ferromagnetic and the AFO layer. Here, we investigate PMA and EB effect in NiO/Co/Au and NiO/Co/NiO layered systems. We show that the coercive and EB fields increase significantly when the Co layer is coupled with two NiO layers, instead of one. Surrounding the Co layer only with NiO layers induces a strong PMA resulting in an out-of-plane magnetized system can be obtained without a heavy metal/ferromagnetic interface. The PMA arises from a significant surface contribution (0.74 mJ/m2) that can be enhanced up to 0.99 mJ/m2 by annealing at moderate temperatures (~450 K). Using field cooling processes for both systems, we demonstrate a wide-ranging control of the exchange bias field without perturbing other magnetic properties of importance.

In this work, we study magnetization switching induced by spin-orbit torque in $\mathrm{W}$ ($\mathrm{Pt}$)/$\mathrm{Co}$/$\mathrm{Ni}\mathrm{O}$ heterostructures with variable thickness of $\mathrm{W}$ and $\mathrm{Pt}$ heavy-metal layers, a perpendicularly magnetized $\mathrm{Co}$ layer, and an antiferromagnetic $\mathrm{Ni}\mathrm{O}$ layer. Using current-driven switching and magnetoresistance and anomalous-Hall-effect measurements, we determine the perpendicular and in-plane exchange-bias field. Several Hall-bar devices possessing in-plane exchange bias from both systems are selected and analyzed in relation to our analytical switching model of the critical current density as a function of $\mathrm{Pt}$ and $\mathrm{W}$ thickness, resulting in estimation of the effective spin Hall angle and perpendicular effective magnetic anisotropy. We demonstrate in both the $\mathrm{Pt}$/$\mathrm{Co}$/$\mathrm{Ni}\mathrm{O}$ system and the $\mathrm{W}$/$\mathrm{Co}$/$\mathrm{Ni}\mathrm{O}$ system deterministic $\mathrm{Co}$ magnetization switching without an external magnetic field, which is replaced by an in-plane exchange-bias field. Moreover, we show that due to a higher effective spin Hall angle in the $\mathrm{W}$-based system than in the $\mathrm{Pt}$-based system, the relative difference between the resistance states in the magnetization current switching to the difference between the resistance states in magnetic field switching determined by the anomalous Hall effect ($\mathrm{\ensuremath{\Delta}}R/\mathrm{\ensuremath{\Delta}}{R}_{\mathrm{AHE}}$) is about twice as high in $\mathrm{W}$-based devices than in $\mathrm{Pt}$-based devices, while the critical switching-current density in $\mathrm{W}$-based devices is 1 order lower than in $\mathrm{Pt}$-based devices. The current-switching stability and the training process are discussed in detail.

The determination of the interfacial Dzyaloshinskii-Moriya interaction for perpendicularly magnetized thin layered films is not trivial and therefore needs some experimental efforts to determine its sign and magnitude, especially in the exchange biased system. Here, we developed a method proposed by D.-S. Han et al. [Nano Lett. 16, (2016) 4438], which opens a way to investigate this interaction using a conventional PMOKE magnetometer, also in exchange biased systems. Using our approach we demonstrated that the Au/Co/NiO layered system has a strong negative Dzyaloshinskii-Moriya interaction, which is independent of the direction of perpendicular interlayer exchange bias coupling., Comment: 10 pages, 4 figures