Technologies based on magnetic skyrmions such as novel computational devices that can operate at high speed or low energy consumption have been proposed by many researchers.Recently, synthetic antiferromagnetic (SyAF) structures have been proposed to increase the stability and mobility of skyrmions by reducing or eliminating the skyrmion Hall effect. Here, we numerically study the current-induced dynamics of skyrmions on SyAF bilayer structures.We demonstrate the effective control and manipulation of SyAF skyrmions, including the directional displacement and alignment. Besides, we design SyAF skyrmion-based logic gates such as the AND, OR, XOR and NOT gates. Our design provides guidance for future development of spintronic computing devices that use topological nanoscale spin textures as information carriers.

We investigate experimentally the effects of strain on the injection of 180° domain walls (DWs) from a nucleation pad into magnetic nanowires, as typically used for DW-based sensors. In our study, the strain, generated by substrate bending, induces in the material a uniaxial anisotropy due to magnetoelastic coupling. To compare the strain effects, Co40Fe40B20, Ni, and Ni82Fe18 samples with in-plane magnetization and different magnetoelastic coupling are deposited. In these samples, we measure the magnetic field required for the injection of a DW, by imaging using differential contrast in a magneto-optical Kerr microscope. We find that strain increases the DW injection field and that the switching mechanism depends strongly on the strain direction. We observe that low magnetic anisotropy facilitates the creation of a domain wall at the junction between the pad and the wire, whereas a strain-induced magnetic easy axis significantly increases the coercive field of the nucleation pad. Moreover, we find that these effects of strain-induced anisotropy can be counteracted by an additional magnetic uniaxial anisotropy perpendicular to the strain-induced easy axis. We perform micromagnetic simulations to support the interpretation of our experimental findings showing that the above described observations can be explained by the effective anisotropy in the device. The anisotropy influences the switching mechanism in the nucleation pad as well as the pinning of the DW at the wire entrance. As the DW injection is a key operation for sensor performances, the observations show that strain is imposing a lower limit for the sensor field operating window.

Relying on both electromechanical and micromagnetic simulations, we propose a method to control the trajectory of current-driven skyrmions using electric field in hybrid piezoelectric/magnetic systems. By applying a voltage between two lateral electrodes a transverse strain gradient is created as a result of the non-uniform electric field profile in the piezoelectric. Due to magnetoelastic coupling, this transverse gradient leads to a lateral force on the skyrmions that can be used to suppress the skyrmion Hall angle for any given current density if proper voltage is applied. We show that this method works under realistic conditions, such as the presence of disorder in the ferromagnet, and that skyrmion trajectories can be controlled with moderate voltages. Moreover, our method allows for increasing the maximum current density that can be injected before the skyrmion is annihilated at the nanostrip edge, which leads to an increase in the maximum achievable velocities.

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The influence of mechanical strain on the static and dynamic properties of chiral domain walls (DWs) in perpendicularly magnetized strips is investigated using micromagnetic simulations and a one-dimensional model. While a uniform strain allows one to reversibly switch the domain-wall configuration at rest between Bloch and Néel patterns, strain gradients are suggested as an energy-sustainable means to drive domain-wall motion without the need for magnetic fields or electrical currents. It is shown that an in-plane strain gradient creates a force on a domain wall that drives it towards a region of higher tensile (compressive) strain for materials with positive (negative) magnetostriction. Moreover, due to the dependence of the domain-wall internal energy on the in-plane strain, a damping torque proportional to the local strain arises during motion that opposes the precessional torque due to the driving force, which is proportional to the strain gradient. After a transient period, where both the internal DW angle and the velocity change nonmonotonically, reaching their maximum values asynchronously, the two torques balance each other. This compensation prevents the onset of turbulent domain-wall dynamics, and steady domain-wall motion with a constant velocity is asymptotically reached for an arbitrarily large strain gradient. Despite this complex dynamics, our work shows that average domain-wall velocities in the range of 500 m/s can be obtained using voltage-induced strain in piezoelectric/ferromagnetic devices under realistic conditions.