Magnetic skyrmions are attracting interest as efficient information‐storage devices with low energy consumption, and have been experimentally and theoretically investigated in multilayers including ferromagnets, ferrimagnets, and antiferromagnets. The 3D spin texture of skyrmions demonstrated in ferromagnetic multilayers provides a powerful pathway for understanding the stabilization of ferromagnetic skyrmions. However, the manipulation mechanism of skyrmions in antiferromagnets is still lacking. A Hall balance with a ferromagnet/insulating spacer/ferromagnet structure is considered to be a promising candidate to study skyrmions in synthetic antiferromagnets. Here, high‐density Néel‐type skyrmions are experimentally observed at zero field and room temperature by Lorentz transmission electron microscopy in a Hall balance (core structure [Co/Pt]n/NiO/[Co/Pt]n) with interfacial canted magnetizations because of interlayer ferromagnetic/antiferromagnetic coupling between top and bottom [Co/Pt]n multilayers, where the Co layers in [Co/Pt]n are always ferromagnetically coupled. Micromagnetic simulations show that the generation and density of skyrmions are strongly dependent on interlayer exchange coupling (IEC) and easy‐axis orientation. Direct experimental evidence of skyrmions in synthetic antiferromagnets is provided, suggesting that the proposed approach offers a promising alternative mechanism for room‐temperature spintronics.

Electrical switching of magnetization through spin-orbit torque (SOT) induced by a composition gradient in single-layer L1 0 -FePt has garnered considerable research interest owing to its inherent superior perpendicular magnetic anisotropy (PMA) that provides ultrahigh capacity to magnetic storage and memory devices. However, a large in-plane external magnetic field is typically required to assist SOT-driven switching, which is still a limitation for the practical application of L1 0 -FePt. This study reports realizable field-free magnetization switching by SOT via Cr doping to form a singlelayer magnetic structure with an in-plane magnetization component oriented toward L1 0 -FeCrPt [110] direction that strongly depends on the magnetocrystalline anisotropy. The Cr doping yields a considerable in-plane exchangecoupling effective field that is conducive toward disintegrating the rotational switching symmetry and facilitates field-free switching in single-layer films with PMA. Furthermore, this in-plane effective field exhibits a nonmonotonic evolution with respect to the Cr-doping concentration, which is validated using first-principles calculation with a frustration-based model of magnetic exchange interactions. Thus, this study delivers an attractive method to facilitate the field-free electrical manipulations of magnetization in singlelayer ferromagnets to motivate innovative designs for advanced spintronics devices.

Spin–orbit torque (SOT) offers a promising pathway to electrically manipulate magnetization in perpendicular multilayers, but the ultrahigh current density required for SOT switching limits its applications. Here, we report that field-free SOT switching is achieved in perpendicular Ta/CoFeB/MgO multilayers by inserting ultrathin Mg or Hf layers. A critical current density of 1.18 × 107 A/cm2 is obtained in Ta/CoFeB/Mg(0.1 nm)/MgO multilayers for field-free SOT switching, which is 42% lower than that in the Ta/CoFeB/MgO sample. The results demonstrate that the enhanced SOT switching efficiency is determined by a modified Rashba interface induced by interfacial orbital hybridization due to the presence of an ultrathin inserted layer. Furthermore, SOT exhibits a significant dependence on the interfacial structure, especially the interfacial oxygen content. Our findings provide an effective insight into the interfacial manipulation of SOT-based spintronic devices.

No abstract

High performance of the generation, stabilization and manipulation of magnetic skyrmions prompts the application of topological multilayers in spintronic devices. Skyrmions in synthetic antiferromagnets (SAF) have been considered to be a promising alternative to overcome the limitations of ferromagnetic skyrmions, such as the skyrmion Hall effect and stray magnetic field. Here, by using the Lorentz transmission electron microscopy, the interconversion between the single domain, labyrinth domain and skyrmion state can be observed by the combined manipulation of electric current and magnetic field in a Hall balance (A SAF with the core structure of [Co/Pt]4/NiO/[Co/Pt]4) showing perpendicular magnetic anisotropy). Furthermore, high-density room temperature skyrmions can be stabilized at zero field while the external stimulus is removed and the skyrmion density is tunable. The generation and manipulation method of skyrmions in Hall balance in this study opens up a promising way to engineer SAF-skyrmion-based memory devices.