Qing-lin Xia

Strain-induced gap transition and anisotropic Dirac-like cones in monolayer and bilayer phosphorene

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.

Strain engineering band gap, effective mass and anisotropic Dirac-like cone in monolayer arsenene

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.

An analytical approach to the interaction of a propagating spin wave and a Bloch wall

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.

Spin-wave resonance reflection and spin-wave induced domain wall displacement

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 complica...

Steady-state domain wall motion driven by adiabatic spin-transfer torque with assistance of microwave field

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.

Conversion of electronic to magnonic spin current at a heavy-metal magnetic-insulator interface

Electronic spin current is convertible to magnonic spin current via the creation or annihilation of thermal magnons at the interface of a magnetic insulator and a metal with a strong spin-orbital coupling. So far this phenomenon was evidenced in the linear regime. Based on analytical and fulledged numerical results for the non-linear regime we demonstrate that the generated thermal magnons or magnonic spin current in the insulator is asymmetric with respect to the charge current direction in the metal and exhibits a nonlinear dependence on the charge current density, which is explained by the tuning effect of the spin Hall torque and the magnetization damping. The results are also discussed in light of and are in line with recent experiments pointing to a new way of non-linear manipulation of spin with electrical means.

Spin waves in the soft layer of exchange-coupled soft/hard bilayers

The magnetic dynamical properties of the soft layer in exchange-coupled soft/hard bilayers have been investigated numerically using a one-dimensional atomic chain model. The frequencies and spatial profiles of spin wave eigenmodes are calculated during the magnetization reversal process of the soft layer. The spin wave modes exhibit a spatially modulated amplitude, which is especially evident for high-order modes. A dynamic pinning effect of surface magnetic moment is observed. The spin wave eigenfrequency decreases linearly with the increase of the magnetic field in the uniformly magnetized state and increases nonlinearly with field when spiral magnetization configuration is formed in the soft layer.

Spin wave modes of width modulated Ni80Fe20/Pt nanostrip detected by spin-orbit torque induced ferromagnetic resonance

We study magnetic dynamics of Ni80Fe20/Pt magnonic crystals made of width periodically varied nanostrips using the spin-torque induced ferromagnetic resonance technique. DC voltage signals are detected when nanostrip magnonic crystals (MCs) are driven resonantly. The DC voltage originates dominantly from the spin rectification effect due to the coupling between the AC electrical current and the oscillated anisotropic magnetoresistance. In addition to uniform magnetization precession across the MC, localized spin wave modes are also observed. Their evolution with the strength and direction of the magnetic field are studied. Micromagnetic simulations are performed to illustrate the experimental results.We study magnetic dynamics of Ni80Fe20/Pt magnonic crystals made of width periodically varied nanostrips using the spin-torque induced ferromagnetic resonance technique. DC voltage signals are detected when nanostrip magnonic crystals (MCs) are driven resonantly. The DC voltage originates dominantly from the spin rectification effect due to the coupling between the AC electrical current and the oscillated anisotropic magnetoresistance. In addition to uniform magnetization precession across the MC, localized spin wave modes are also observed. Their evolution with the strength and direction of the magnetic field are studied. Micromagnetic simulations are performed to illustrate the experimental results.