Skyrmions-based logic gates in one single nanotrack completely reconstructed via chirality barrier

Reconfigurable Skyrmion-Based Logic Gates: Versatile Design and Full-Scale Implementation

Herein, we investigate the behavior of skyrmions within a racetrack design incorporating voltage-controlled magnetic anisotropy (VCMA) gates. Our analysis encompassed multiple forces, including spin currents and anisotropy gradients induced by bias voltages. As a result, the efficient control of skyrmion dynamics was achieved across various VCMA gate configurations. Building upon these findings, we propose an efficient approach to reconfigurable skyrmion logic (RSL) in a thin antiferromagnetic (AFM) film through a versatile design. Our RSL harnesses the selective integration of VCMA, spin-polarized currents, and skyrmion-skyrmion (sky-sky) interactions to implement multiple logic gates, including AND, OR, XOR, NOT, NAND, XNOR, and NOR. The design brings a significant advantage with its simplified fabrication process, making the implementation of the RSL practical and accessible for various applications. Furthermore, the RSL enables seamless dynamic switching between logic gates, thereby enhancing its multifunctionality. Additionally, the strategic incorporation of sky-sky interactions and skyrmion-edge repulsion prominently facilitates the realization of complex gates, such as NAND, XNOR, and NOR gates, that typically require intricate design efforts. Hence, this streamlined integration of RSL, coupled with its adaptability to changing computational needs, underscores its potential as a practical solution for implementing high-functionality skyrmion-based logic gates.

Flexible nanomechanical bit based on few-layer graphene

Mechanical computers have gained intense research interest at size scales ranging from nano to macro as they may complement electronic computers operating in extreme environments. While nanoscale mechanical computers may be easier to integrate with traditional electronic components, most current nanomechanical computers are based on volatile resonator systems that require continuous energy input. In this study, we propose a non-volatile nanomechanical bit based on the quasi-stable configurations of few-layer graphene with void defects, and demonstrate its multiple quasi-stable states by deriving an analytic relationship for the void configuration based on a competition between the bending energy and the cohesive energy. Using this nanomechanical bit, typical logic gates are constructed to perform Boolean calculations, including NOT, AND, OR, NAND and NOR gates, and demonstrate reprogrammability between these logic gates. We also study the accuracy and the stability of the nanomechanical bits based on the few-layer graphene. These findings provide a novel approach to realize the nanomechanical computing process.

Ultralow Power and Shifting-Discretized Magnetic Racetrack Memory Device Driven by Chirality Switching and Spin Current

Magnetic racetrack memory has significantly evolved and developed since its first experimental verification and is considered one of the most promising candidates for future high-density on-chip solid-state memory. However, both the lack of a fast and precise magnetic domain wall (DW) shifting mechanism and the required extremely high DW motion (DWM) driving current make the racetrack difficult to commercialize. Here, we propose a method for coherent DWM that is free from the above issues, which is driven by chirality switching (CS) and an ultralow spin-orbit-torque (SOT) current. The CS, as the driving force of DWM, is achieved by the sign change of the Dzyaloshinskii-Moriya interaction, which is further induced by a ferroelectric switching voltage. The SOT is used to break the symmetry when the magnetic moment is rotated in the Bloch direction. We numerically investigate the underlying principle and the effect of key parameters on the DWM by micromagnetic simulations. Under the CS mechanism, a fast (∼102 m/s), ultralow energy (∼5 attoJoule), and precisely discretized DWM can be achieved. Considering that skyrmions with topological protection and smaller size are also promising for future racetracks, we similarly evaluate the feasibility of applying such a CS mechanism to a skyrmion. However, we find that the CS causes it to "breathe" instead of moving. Our results demonstrate that the CS strategy is suitable for future DW racetrack memory with ultralow power consumption and discretized DWM.

Hole doping induced ferromagnetism and Dzyaloshinskii-Moriya interaction in the two-dimensional group-IVA oxides

Based on the first-principles calculations, we examine the effect of hole doping on the ferromagnetism and Dzyaloshinskii-Moriya interaction (DMI) for PbSnO₂, SnO₂and GeO₂monolayers. The nonmagnetic to ferromagnetic transition and the DMI can emerge simultaneously in the three two-dimensional IVA oxides. By increasing the hole doping concentration, we find the ferromagnetism can be strengthened for the three oxides. Due to different inversion symmetry breaking, isotropic DMI is found in PbSnO₂, whereas anisotropic DMI presents in SnO₂and GeO₂. More appealingly, for PbSnO₂with different hole concentrations, DMI can induce a variety of topological spin textures. Interestingly, a peculiar feature of synchronously switch of magnetic easy axis and DMI chirality upon hole doping is found in PbSnO₂. Hence, Néel-type skyrmions can be tailored via changing hole density in PbSnO₂. Furthermore, we demonstrate that both SnO₂and GeO₂.with different hole concentrations can host antiskyrmions or antibimerons (in-plane antiskyrmions). Our findings demonstrate the presence and tunability of topological chiral structures in p-type magnets and open up new possibility for spintronics.