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International audience; In this study we report on the analysis of magnetic domain wall (DW) curvature due to magnetic field induced motion in Ta/CoFeB/MgO and Pt/Co/Pt wires with perpendicular magnetic anisotropy. In wires of 20µm and 25µm a large edge pinning potential produces the anchoring of the DWs ends to the wire edges which is evidenced as a significant curvature of the DW front as it propagates. As the driving magnetic field is increased the curvature reduces as the result of the system moving away from the creep regime of DW motion, which implies a weaker dependence of the DW dynamics on the interaction between the DW and the wire edge defects. A simple model is derived to describe the dependence of the DW curvature on the driving magnetic field and allows to extract the parameter σ E which accounts for the strength of the edge pinning potential. The model describes well systems with both weak and strong bulk pinning potentials like Ta/CoFeB/MgO and Pt/Co/Pt, respectively. This provides a means to quantify the effect of edge pinning induced DW curvature in magnetic DW dynamics. Keywords: magnetic micro wires, domain wall curvature, perpendicular magnetic anisotropy, Understanding the behaviour of magnetic domain walls (DWs) when transitioning from full films into patterned structures is of great importance for developing nanodevices for DW based technologies 1. The analysis of DW dynamics in the so called creep regime of motion 2-5 , where defects play a central role, is a key aspect. In Ta/CoFeB/MgO/Ta films with perpendicular anisotropy bulk defect densities, and therefore depinning fields (H dep), are relatively low 6-8. In Pt/Co/Pt films, for example, the values of H dep can be more than one order of magnitude higher 2,4,5. Due to this low bulk pinning potential the DW dynamics can be easily controlled even in full films by artificial pinning imposed through homogeneous material engineering processes, like light ion irradiation 9-11 or pre-patterned substrates 12. Defects generated through micro/nanostructuring can also have a great impact in pristine materials. DW velocities even in micrometer size wires have been found to experience a critical decrease below the creep law dependence at low drive which scales with the wire width 13. This effect is also accompanied by an increase in the curvature of the DW front and has therefore been attributed to edge pinning. A deeper analysis of the DW curvature in wires is therefore needed in view of miniaturisation for technological applications. In this study we present the analysis of the DW curvature in a series of 20µm wide Ta/CoFeB/

Magnetic domain wall motion could be the key to the next generation of data storage devices, shift registers without mechanically moving parts. Various concepts of such so-called ‘racetrack memories’ have been developed, but they are usually plagued by the need for high current densities or complex geometrical requirements. We introduce a new device concept, based on the interfacial Dzyaloshinskii-Moriya interaction (DMI), of which the importance in magnetic thin films was recently discovered. In this device the domain walls are moved solely by magnetic fields. Unidirectionality is created utilizing the recent observation that the strength with which a domain wall is pinned at an anisotropy barrier depends on the direction of the in-plane field due to the chiral nature of DMI. We demonstrate proof-of-principle experiments to verify that unidirectional domain-wall motion is achieved and investigate several material stacks for this novel device including a detailed analysis of device performance for consecutive pinning and depinning processes.

Canted magnetization is obtained in ultrathin, antiferromagnetically coupled magnetic bilayers with\ud thicknesses around the spin reorientation transition. The canting angle is controlled by both the\ud magnetic layer thickness and interlayer coupling strength, which are tuned independently. Hysteresis\ud loops are obtained, where magnetization components parallel and transverse to the applied field are\ud measured, and analyzed by comparison to micromagnetic simulations. This enables the canting angle\ud to be extracted and the behavior of the individual layers to be distinguished. Two types of canted\ud systems are obtained with either single-layer reversal or complex, coupled two-layer reversal, under\ud moderate external magnetic fields. Controlling the magnetization canting and reversal behavior of\ud ultra-thin layers is relevant for the development of magnetoresistive random-access memory and\ud spin-torque oscillator devices.

Domain-wall (DW) motion in magnetic nanostrips is intensively studied, in particular because of the possible applications in data storage. In this work, we will investigate a novel method of DW motion using magnetic field pulses, with the precession torque as the driving mechanism. We use a one dimensional (1D) model to show that it is possible to drive DWs in out-of-plane materials using the precession torque, and we identify the key parameters that influence this motion. Because the DW moves back to its initial position at the end of the field pulse, thereby severely complicating direct detection of the DW motion, depinning experiments are used to indirectly observe the effect of the precession torque. The 1D model is extended to include an energy landscape in order to predict the influence of the precession torque in the depinning experiments. Although preliminary experiments did not yet show an effect of the precession torque, our calculations indicate that depinning experiments can be used to demonstrate this novel method of DW motion in out-of-plane materials, which even allows for coherent motion of multiple domains when the Dzyaloshinskii-Moriya interaction is taken into account.

We have designed a bilayer synthetic antiferromagnet where the order of layer reversal can be selected by varying the sweep rate of the applied magnetic field. The system is formed by two ultra-thin ferromagnetic layers with different proximities to the spin reorientation transition, coupled antiferromagnetically using Ruderman-Kittel-Kasuya-Yosida interactions. The different dynamic magnetic reversal behavior of both layers produces a crossover in their switching fields for field rates in the kOe/s range. This effect is due to the different effective anisotropy of both layers, added to an appropriate asymmetric antiferromagnetic coupling between them. Field-rate controlled selective switching of perpendicular magnetic anisotropy layers as shown here can be exploited in sensing and memory applications.