Controlled Individual Skyrmion Nucleation at Artificial Defects Formed by Ion Irradiation

Abstract

Magnetic skyrmions are particle‐like deformations in a magnetic texture. They have great potential as information carriers in spintronic devices because of their interesting topological properties and favorable motion under spin currents. A new method of nucleating skyrmions at nanoscale defect sites, created in a controlled manner with focused ion beam irradiation, in polycrystalline magnetic multilayer samples with an interfacial Dzyaloshinskii–Moriya interaction, is reported. This new method has three notable advantages: 1) localization of nucleation; 2) stability over a larger range of external field strengths, including stability at zero field; and 3) existence of skyrmions in material systems where, prior to defect fabrication, skyrmions were not previously obtained by field cycling. Additionally, it is observed that the size of defect nucleated skyrmions is uninfluenced by the defect itself—provided that the artificial defects are controlled to be smaller than the inherent skyrmion size. All of these characteristics are expected to be useful toward the goal of realizing a skyrmion‐based spintronic device. This phenomenon is studied with a range of transmission electron microscopy techniques to probe quantitatively the magnetic behavior at the defects with applied field and correlate this with the structural impact of the defects.

Temporal Memory With Magnetic Racetracks

“…This however can worsen the skyrmion readability as this scales up the size of the read MTJs, or makes skyrmions miss the MTJ as discussed above. While the use of synthetic antiferromagnet racetracks with compensation for Magnus force can considerably reduce this issue, use of reflecting edges through anisotropy engineering, such as using ion beam irradiation, or geometry engineering by using thicker edges can also help with this issue [34], [35]. By using reflective edges, the skyrmion will more reliably reach the MTJ position, as the repulsive force from the edges will confine the skyrmion to the middle of racetrack.…”

Anisotropy-induced depinning in the Zn-substituted skyrmion host Cu2OSeO3

“…This pinning can affect other dynamic behaviors such as current-induced skyrmion motion-a phenomenon crucial to proposed skyrmion racetrack devices [57,58]. Extrinsic defects and impurities can attract or repel skyrmions [59], or act as nucleation or annihilation sites [60], which might be exploited for technological implementation. In combination with alterations to the energy balance mentioned above, these dynamical pinning effects must be considered when engineering the properties of skyrmion materials for future applications.…”

Skyrmion battery effect via inhomogeneous magnetic anisotropy

“…In these setups, only the central or edge magnetization are anchored by magnetic field or local spin current, due to the fact that the local energy density of the skyrmion decays from the center towards the edge 41 , i.e., a stable skyrmion favors a spatially inhomogeneous energy density. Skyrmions can also be generated in the vicinity of crystal grain 42 , defect [43][44][45][46] and a constrained boundary by a current 47,48 . In this case, local magnetization that is tilted inhomogeneously evolves into a spin spiral and further into a vortex in the constrained region.…”

“…Key ingredient to this setup is the material variation along the radial direction (of the disk) that is realized by a capping layer deposited at the center (region I) and is surrounded by a circular defective region (region II). The defective region can be etched using a side mask 49 or a focused ion beam microscope 46 . The capping layer is expected to enhance the perpendicular magnetic anisotropy (PMA).…”