Current-driven coherent skyrmion generation

Device geometry dependent deterministic skyrmion generation from a skyrmionium

A magnetic skyrmionium can be perceived as an association of two magnetic skyrmions with opposite topological charges. In this work, we have investigated the transformation of skyrmionium into multi-skyrmionic states via domain wall pairs in three different devices with variable geometric configurations. The same device geometries are considered for single ferromagnetic layer and synthetic antiferromagnetic system. It is observed that by tuning the current density, deterministic generation of skyrmions is possible via the spin transfer torque. The proposed device is efficiently adjustable to change the number of skyrmions also at room temperature. The results may lead to development of skyrmion-based devices for neuromorphic and unconventional computing.

Stabilizing magnetic skyrmions in constricted nanowires

Magnetic skyrmions are topologically-protected chiral nano-scale spin structures that offer low power and high-density functionalities for spintronic devices. They behave as particles that can be moved, created and annihilated. These characteristics make them promising information-carrying bits, hence a precise control of the skyrmion motion is essential. This study shows that stabilizing skyrmion is possible using a stepped nanowire geometry. The nanoconstriction dimension and materials properties are found to strongly affect the pinning, depinning and annihilation of the skyrmion. It is also observed that near the stepped region, the skyrmion slows down and its velocity changes direction before its stability. Moreover, a reduction of skyrmion size as it squeezes through the stepped region is observed. Our results will open a new strategy for the design and development of skyrmion-based devices.

Multibit racetrack memory

We present a hybrid usage of domain walls and skyrmions in the same racetrack memory which can enable developing a platform for many-valued magnetic data storage technology, by numerically solving the Landau-Lifshitz-Gilbert equation. The conversion of domain-walls to magnetic skyrmions in a plain nanotrack without geometrical restrictions allowed us to realize a ternary racetrack memory. Annihilation, conversion, and passing over of the reverse domains are considered as the three-state of ternary logic. We anticipate that multibit racetrack memory will influence the development of data storage platforms for emergent computing technologies.

Strain-enhanced Dzyaloshinskii-Moriya interaction at Co/Pt interfaces

The interfacial Dzyaloshinskii-Moriya interaction (DMI) is an essential ingredient for stabilizing chiral spin configurations in spintronic applications. Here, via first-principles calculations, we reveal the influence of lattice strain on DMI in Co/Pt interface. We observed a considerable enhancement for a certain lattice strain. Furthermore, a direct correlation is established between the DMI and interlayer distances dominated by the strain, which is attributed to a hybridization of electronic orbitals. This hybridization has also been presented as the microscopic origin of the interfacial DMI. We anticipate that our predictions provide new insights into the control of interfacial DMI for skyrmion-based spintronic devices.

Direct current-tunable MHz to multi-GHz skyrmion generation and control

Skyrmions offer high density, low power, and nonvolatile memory functionalities due to their nanoscale and topologically-protected chiral spin structures. For integrated high-bandwidth devices, one needs to control skyrmion generation and propagation rates using current. Here, we introduce a skyrmion initialization and control method to generate periodic skyrmions from 114 MHz to 21 GHz using spin-polarized direct current. We first initialize a stable magnetic domain profile that is pinned between a notch and a rectangular constriction using a DC pulse. Next, we pass spin-polarized DC charge current to eject periodic skyrmions at a desired frequency. By changing the DC current density, we demonstrate in micromagnetic simulations that skyrmion generation frequencies can be controlled reversibly over more than seven octaves of frequencies. By using domain pinning and current-driven skyrmion motion, we demonstrate a highly tunable and DC-controlled skyrmion signal source, which pave the way towards ultra wideband, compact and integrated skyrmionic circuits.