In this work, an ultrafast nucleation of an isolated anti-ferromagnetic (AFM) skyrmion was reported in an AFM layer with DMi strengths of 0.47$$-$$ - 0.32 $$\mathrm{mJ}/{\mathrm{m}}^{2}$$ mJ / m 2 using spin-transfer torque by locally injecting pure spin currents into magnetic tracks. Besides, we revealed the key advantages of AFM skyrmion-based racetrack memories by comparing the motion of AFM and FM skyrmions driven by spin–orbit torques (SOTs) for different skyrmion sizes along racetrack memories with various notch sizes. Our results indicate that for AFM skyrmion, the skyrmion Hall effect does not exist during the skyrmion motion, therefore at small skyrmion sizes, we succeeded to overcome the repulsive forces developed in the notch area for low and large SOTs. The obtained findings were carefully analyzed by computing the variation of energy barriers associated with the notch for different skyrmion sizes using minimum energy path (MEP) calculations. We showed that the larger the skyrmion size, the harder it is to shrink the skyrmion in the notch which produces a high energy barrier (Eb) for large skyrmion sizes. Moreover, as the notch size increases, the skyrmion size shrinks further, and hence Eb increases proportionally. Nevertheless, we proved that AFM skyrmions are more efficient and flexible than FM skyrmions against boundary forces.

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We investigated the magnetization switching by means of a spin-polarized current via spin-transfer torque (STT) in a half-metallic Heusler Co 1.5 Fe 1.5 Ge alloy by numerically solving the Landau-Lifshitz-Gilbert-Slonczewski equation including the STT term in a spin-valve nanopillar Co 1.5 Fe 1.5 Ge/Ag/Co 1.5 Fe 1.5 Ge using micromagnetic simulation. In this work, we use Co 1.5 Fe 1.5 Ge film of 2 nm thickness, and then we inject a spin polarization current perpendicular to plane of the multilayers in order to flip the free layer magnetization and therefore get the magnetization switching between the two layers. Half-metallic Heusler Co 1.5 Fe 1.5 Ge is characterized by a small Gilbert damping constant α = 0.0025 and a complete spin polarization at the Fermi level. Using these specific parameters, we obtain the magnetization switching between the free layer and the pinned layer with a critical current density of about 10 6 A/cm 2 , as well the magnetization switching process of nanopillar are discussed and analyzed. Also, we deeply examine the behavior of magnetization switching dynamic as a function of the current density within a weak external magnetic field which helps to trig switching. Finally, we studied the impact of free layer thickness on magnetization switching dynamic and STT energy in order to immunize further the switching time and the critical current density.

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