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We investigate theoretically the motion of chiral N\'eel domain walls in perpendicularly magnetized systems driven by in-plane strain gradients. We show that such strain drives domain walls efficiently towards increasing tensile (compressive) strain for positive (negative) magnetostrictive materials. During their motion a local damping torque that opposes the precessional torque due to the strain gradient arises. This torque prevents the onset of turbulent dynamics, and steady domain wall motion with constant velocity is asymptotically reached for any arbitrary large strain gradient. Withal, velocities in the range of 500 m/s can be obtained using voltage-induced strain under realistic conditions.

Perpendicular synthetic antiferromagnets (p-SAFs) are of interest for the next generation of ultrafast, high-density spintronic memory and logic devices. However, to efficiently operate their magnetic order by current-induced spin-orbit torques (SOTs), an unfavored high external magnetic field is conventionally required to break the symmetry. Here, we report the field-free SOT switching of a p-SAF through the introduction of an interlayer with Dzyaloshinskii-Moriya interactions (DMIs). We experimentally observe the existence of the DMI interlayer in our SAF sample by an azimuthal angular-dependent anomalous Hall measurement. Deterministic field-free switching is accomplished in such a sample and depicted by macrospin and micromagnetic simulations. The comparison between the uniaxial interlayer DMI and the azimuthal direction-dependent switching behavior strongly suggests its origin from the DMI interlayer. We demonstrate the compatibility of the proposed strategy with magnetic tunnel junction device structure. Our results provide a strategy for p-SAF-based high-performance SOT devices.

We investigate experimentally the effects of externally applied strain on the injection of 180$^\circ$ domain walls (DW) 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, $Co_{40}Fe_{40}B_{20}$, $Ni$ and $Ni_{82}Fe_{18}$ 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 differential contrast in a magneto-optical Kerr microscope. We find that strain increases the DW injection field, however, the switching mechanism depends strongly on the direction of the strain with respect to the wire axis. 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. Additionally, we find that the effects of mechanical strain can be counteracted by a magnetic uniaxial anisotropy perpendicular to the strain-induced easy axis. In $Co_{40}Fe_{40}B_{20}$, we show that this anisotropy can be induced by annealing in a magnetic field. We perform micromagnetic simulations to support the interpretation of our experimental findings. Our simulations show 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.

Nickel nanoparticles stabilized in aqueous emulsion of copolymers were prepared in a few minutes using polyol assisted-microwave (MW) process. This approach based on the reduction of metal salt (NiCl2·6H2O) in the presence of low concentration of hydrazine hydrate (N2H4·H2O) using a commercial copolymer (latex) as both, reducing and stabilizing agents. The reaction parameters such as the precursor concentration, copolymer and MW power affect significantly the reaction rate and the shape/size (2.5 nm to 7 nm) of Ni nanoparticles. Ni NPs were stored at room temperature for approximately 6 months without any visible change, which indicate the important role of latex copolymer as a good stabilizer for Ni NPs, The structural and optical properties have been studied separately using UV–Visible spectroscopy, Transmission Electron Microscopy (TEM) and Energy-Dispersive X-ray Spectroscopy (EDXs). TEM images using high magnifications identified the Ni NPs as spherical shapes. The FTIR spectra indicate that Ni nanoparticles attached to the copolymers (latex) at the surface by the stretching vibration of O–H bond, which gives crucial information on the interface structure Ni NPs/Latex marked by a reduced coupling between spins at NPs surfaces. Magnetic properties were demonstrated using SQUID (Quantum Design Squid/VSM). The shift observed in hysteresis loop (M–H) measured at 2 K due to the spin–spin reduced coupling at the nanoparticles surfaces, which gives spin-glass like behavior in the system. In other hand, the zero-field-cooled (ZFC) and the field-cooled (FC) measurements under magnetic field of 100 Oe exhibited the blocking temperature TB that strongly depends on Ni particle sizes.

Skyrmions are considered as topologically protected magnetic textures; they are covering a large area of applications. In this work, we studied using micromagnetic simulations the emergence of skyrmions in a nanodisk stacked in a FM/NM/FM multilayer system. We show how the skyrmion is formed through the antiferromagnetic interlayer exchange coupling (IEC). We also show the impact of the IEC on skyrmion size in both layers. We try as a conclusion to identify the range of IEC where skyrmions could exist in such systems.

In this paper, we study the magnetization behavior in Co40Fe40B20 nanodisks with Dzyaloshinskii-Moriya interaction, which is induced by a Pt layer. The known giant perpendicular magnetic anisotropy (PMA) in thin films elaborated from this kind of materials improves the topological structures nucleation. Our work consists in investigating the skyrmions apparition and stability in amorphous CoFeB nanodisks. The detected skyrmions are not spontaneously nucleated. Their nucleation is induced by an applied external field. We also study reversal magnetization of CoFeB and we elucidate skyrmions nucleation and annihilation.

[EN] Relying on both electromechanical and micromagnetic simulations, we propose a method to control the trajectory of current-driven skyrmions using an 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 nonuniform electric field profile in the piezoelectric material. 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 a 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 the maximum current density that can be injected before the skyrmion is annihilated at the nanostrip edge to be increased, which leads to an increase in the maximum achievable velocities., European Union H2020 Program (MSCA MagnEFi ITN Grant No. 860060) Ministerio de Education y Ciencia (Project No. MAT2017-87072-C4-1-P) Ministerio de Ciencia e Innovacion (Project No. PID2020-117024GB-C41) Consejeria de Educación of Castilla y León (Projects No. SA114P20 and No.SA299P18).

Vortices are topological structures, which are characterized by circular organization of magnetic moments and by chirality. In this paper, we investigate the impact of film lateral dimensions and thicknesses on magnetization reversibility by applying an in-plane external magnetic field on Co(tCo)/Py (3 nm) bilayers where the Py is the permalloy, a ferromagnetic alloy of nickel and iron (Ni80Fe20). The study is achieved by using appropriate micromagnetic simulations. We also show that the vortices number and their sizes can be controlled by playing on the lateral dimensions and the thickness of the bilayer.

Nanometric spin structures such as skyrmions are covering a large area of applications related to new technologies. In this paper, we carry out a computational study on magnetic skyrmions behavior in Pt/CoFeB/Ru/CoFeB antiferromagnetic-exchange coupled systems. We aim to explore the possibilities of skyrmions nucleation in such multilayer. We demonstrated that skyrmions could be hosted in such system under specific conditions. We also studied the in-plane and out-of-plane reversal magnetization processes for these magnetic multilayers in order to check the skyrmion behavior under magnetic field loops.

Skyrmions are viewed as the basic elements for the future generation of magnetic memories. Their small sizes and good dynamical properties give them the ability to store and transport information easily. In this paper, we used micromagnetic simulation to study the contribution of interlayer exchange coupling and the geometrical confinement on scaling magnetic skyrmions. We started the work by comparing the utility of interlayer exchange coupling to the perpendicular magnetic field in scaling magnetic skyrmions. Then, we investigated the effect of combining the interlayer exchange coupling and geometrical confinement to reduce skyrmions size.

Magnetic skyrmions have attracted a great deal of interest in the last decades. They are widely used for many spintronic applications. In this manuscript, we study by micromagnetic simulation the emergence of a hexagonal Neel-type skyrmion lattice in a square thin film of CeFeB. We specifically examine the formation and annihilation of the skyrmion lattice. Moreover, we show the decrease of the skyrmion sizes with the increase of the magnetic field, while the lattice parameter remains unchanged during this rise.

Technologies based on magnetic skyrmions, such as computational devices that can operate at high speed or with low energy consumption, have been proposed by many researchers. Recently, synthetic antiferromagnetic (SAF) 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 SAF bilayer structures. We demonstrate the effective control and manipulation of SAF skyrmions, including directional displacement and alignment. Furthermore, we design SAF-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.