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Skyrmion-based magnonic crystal (MC) provides the dynamic tunability of manipulating magnonic band structure, and this brings obvious advantages over geometry or material-modulated MCs with a static band. But the existence of stable skyrmion usually requires strong Dzyaloshinskii–Moriya interaction (DMI) in combination with an external magnetic field under specific strength, and all these features limit the experimental realization and practical designing of the skyrmion-based MC. Here, we introduce the concept of artificial magnetic skyrmion-based MC. The artificial skyrmion lattice is realized by patterning an array of magnetic nanodisks on a thin film. The coupling between nanodisks and thin film generates an array of skyrmions possessing the same period as the nanodisk array. Via applying the pulsed magnetic field, one can turn on and off the skyrmion lattice, which allows switching between two very different magnonic band structures. Furthermore, via a honeycomb lattice, we extend this design to the dynamic on and off for chiral magnon edge state. The on and off switching is fast and in the range of nanoseconds. Considering that the coupling from nanodisks can greatly enhance the stability of skyrmions, no matter whether the DMI or magnetic field exists or not, our design points to a simple realization of dynamic skyrmion MC and topological magnonic devices.

The electronic properties of two-dimensional puckered arsenene have been investigated using first-principles calculations. The effective mass of electrons exhibits highly anisotropic dispersion in intrinsic puckered arsenene. Futhermore, we find that out-of-plane strain is effective in tuning the band gap, as the material undergoes the transition into a metal from an indirect gap semiconductor. Remarkably, we observe the emergence of Dirac-like cone with in-plane strain. Strain modulates not only the band gap of monolayer arsenene, but also the effective mass. Our results present possibilities for engineering the electronic properties of two-dimensional puckered arsenene and pave a way for tuning carrier mobility of future electronic devices.

The electronic properties of two-dimensional monolayer and bilayer phosphorene subjected to uniaxial and biaxial strains have been investigated using first-principles calculations based on density functional theory. Strain engineering has obvious influence on the electronic properties of monolayer and bilayer phosphorene. By comparison, we find that biaxial strain is more effective in tuning the band gap than uniaxial strain. Interestingly, we observe the emergence of Dirac-like cones by the application of zigzag tensile strain in the monolayer and bilayer systems. For bilayer phosphorene, we induce the anisotropic Dirac-like dispersion by the application of appropriate armchair or biaxial compressive strain. Our results present very interesting possibilities for engineering the electronic properties of phosphorene and pave a way for tuning the band gap of future electronic and optoelectronic devices.

The magnetic domain wall (DW) motion driven by a spin-polarized current opens a new concept for memory and logic devices. However, the critical current density required to overcome the intrinsic and/or extrinsic pinning of DW remains too large for practical applications. Here, we show, by using micromagnetic simulations and analytical approaches, that the application of a microwave field offers an effective solution to this problem. When a transverse microwave field is applied, the adiabatic spin-transfer torque (STT) alone can sustain a steady-state DW motion without the sign of Walker breakdown, meaning that the intrinsic pinning disappears. The extrinsic pinning can also be effectively reduced. Moreover, the DW velocity is increased greatly for the microwave-assisted DW motion. This provides a new way to manipulate the DW motion at low current densities.

We have studied the current-induced displacement of a 180° Bloch wall by means of micromagnetic simulation and analytical approach. It is found that the adiabatic spin-transfer torque can sustain a steady-state domain wall (DW) motion in the direction opposite to that of the electron flow without Walker Breakdown when a transverse microwave field is applied. This kind of motion is very sensitive to the microwave frequency and can be resonantly enhanced by exciting the domain wall thickness oscillation mode. A one-dimensional analytical model was established to account for the microwave-assisted wall motion. These findings may be helpful for reducing the critical spin-polarized current density and designing DW-based spintronic devices.

Spin-wave propagation and spin-wave induced domain wall motion in nanostrips with a Neel wall are studied by micromagnetic simulations. It is found that the reflection of spin waves by the wall can be resonantly excited due to the interaction between spin waves and domain-wall normal modes. With the decrease of the saturation magnetization Ms (and the consequent increase of the wall width), the reflection is diminished and complete transmission can occur. The domain wall motion induced by spin waves is closely related to the spin-wave reflectivity of the wall, and may exhibit different types of behavior. The reflected spin waves (or magnons) give rise to a magnonic linear momentum-transfer torque, which drives the wall to move along the spin wave propagation direction. The maximal velocity of the domain wall motion corresponds to the resonance reflection of the spin waves. The transmitted spin waves (or magnons) lead to a magnonic spin-transfer torque, which drags the wall to move backwardly. The complicated domain wall motion can be described qualitatively by a one-dimensional model incorporating both the magnonic linear momentum-transfer torque and the magnonic spin-transfer torque. The results obtained here may find use in designing magnonic nanodevices.

The spin wave propagation and the spin-wave induced domain wall motion in a nanostrip with a Bloch domain wall are studied. The spin-wave dispersion relation and the transmission coefficients across the wall are derived analytically. A one-dimensional model for the domain wall motion is constructed. It is found that the spin wave can drive the wall to move either in the same direction or in the opposite direction to that of spin-wave propagation depending on the transmission coefficient. The transmitted magnons drag the wall moving backward without inertia by the adiabatic and nonadiabatic spin-transfer torques, while the reflected magnons push the wall moving forward by the linear momentum transfer torque.

We investigate effects of a small DC spin-polarized current on the pulse field-induced precessional magnetization reversal in a thin elliptic magnetic element by micromagnetic simulations. We find that the spin-polarized current not only broadens the time window of the pulse duration, in which a successful precessional reversal is achievable, but also significantly suppresses the magnetization ringing after the reversal. The pulse time window as well as the decay rate of the ringing increase with increasing the current density. When a spin-polarized current with 5 MA/cm2 is applied, the time window increases from 80 ps to 112 ps, and the relaxation time of the ringing decreases from 1.1 ns to 0.32 ns. Our results provide useful information to achieve magnetic nanodevices based on precessional switching.