interaction, like Pt/Co, but surprisingly also at FM-oxide interfaces. [2] This is attributed to the hybridization between the metal and the oxygen electronic orbitals across the interfaces, as confirmed by ab initio calculations. [3] The amplitude of this interaction is strongly sensitive to the degree of oxidation of the metal/oxide interface. Previous studies carried out for several Pt/Co/oxide stacks show that the PMA evolves with the cobalt oxidation rate following a typical bell-like curve. [2,[4][5][6][7] The maximum PMA is obtained for the optimal oxidation of the FM/oxide interface, when all the metal interfacial FM atoms are bonded to oxygen atoms. If the contribution of the Pt/FM interface to the PMA is not sufficient to promote out-ofplane magnetization, an increase of the FM oxidation may help driving the magnetization from in-plane (IP) to out-plane (OOP) (see Figure 3b)The interfacial anisotropy at the FMoxide interface can be manipulated by an electric field via electronic [8][9][10] or magneto-ionic effects. [1] The largest effects of the electric field on the PMA were obtained by triggering the oxidation of cobalt via the migration of oxygen ions. [11][12][13] Up to recent years, this mechanism was observed to be slow and to require high temperatures, since the voltage-driven switching between IP and OOP magnetization was shown to require several minutes at room temperature. [11] A voltage-driven mechanism in which the modification of interfacial PMA is attributed to the migration of hydrogen, rather than to the less mobile oxygen ions, was recently proposed as a more efficient [14,15] and faster (down to 2 ms) [16] way to switch the magnetization easy axis direction.In this work, we show that by depositing on top of the magnetic stack a thin ZrO 2 layer acting as an oxygen ion conductor, a huge voltage-driven variation of the PMA can be obtained for two model systems for spintronic applications, Pt/Co/AlO x and Pt/Co/TbO x trilayers. While Pt/Co/AlO x was the first system in which chiral domain walls could be driven efficiently by spin-orbit torque, [17] Pt/Co/TbO x may become ferrimagnetic, with reduced magnetization, and acquire interesting domain wall dynamics properties, if terbium is sufficiently reduced. [18] As reported in our previous work, [19] the PMA of these systems Magneto-ionics is a fast developing research field which opens the perspective of energy efficient magnetic devices, where the magnetization direction is controlled by an electric field which drives the migration of ionic species. In this work, the interfacial perpendicular magnetic anisotropy (PMA) of Pt/ Co/oxide stacks covered by ZrO 2 , acting as a ionic conductor, is tuned by a gate voltage at room temperature. A large variation of the PMA is obtained by modifying the oxidation of the cobalt layer through the migration of oxygen ions: the easy magnetization axis can be switched reversibly from in-plane, with under-oxidized Co, to in-plane, with over-oxidized Co, passing through an out-of-plane magnetization state. T...

Magnetic skyrmions are localized chiral spin textures, which offer great promise to store and process information at the nanoscale. In the presence of asymmetric exchange interactions, their chirality, which governs their dynamics, is generally considered as an intrinsic parameter set during the sample deposition. In this work, we experimentally demonstrate that a gate voltage can control this key parameter. We probe the chirality of skyrmions and chiral domain walls by observing the direction of their current-induced motion and show that a gate voltage can reverse it. This local and dynamical reversal of the chirality is due to a sign inversion of the interfacial Dzyaloshinskii-Moriya interaction that we attribute to ionic migration of oxygen under gate voltage. Micromagnetic simulations show that the chirality reversal is a continuous transformation, in which the skyrmion is conserved. This control of chirality with 2–3 V gate voltage can be used for skyrmion-based logic devices, yielding new functionalities.

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We present an experimental study of the magnetization reversal in Au/Co layers with perpendicular anisotropy versus variable magnetic field. Changes in domain structure were recorded simultaneously with the measurement of the hysteresis loop by a Kerr microscope in polar configuration. The magnetization reversal is performed by domain wall propagation in the two-way up to down and inversely. In addition, it was shown experimentally that the evolution of the domain structure is almost the same along both branches of the hysteresis loop. The magnetization reversal is always triggered at the same places of the sample independently of the applied magnetic field direction.

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