Magnetic two-dimensional van derWaals materials for spintronic devices

Magnetic two-dimensional(2D)van derWaals(vdWs)materials and their heterostructures attract increasing attention in the spintronics community due to their various degrees of freedom such as spin,charge,and energy valley,which may stimulate potential applications in the field of low-power and high-speed spintronic devices in the future.This review begins with introducing the long-range magnetic order in 2D vdWs materials and the recent progress of tunning their properties by electrostatic doping and stress.Next,the proximity-effect,current-induced magnetization switching,and the related spintronic devices(such as magnetic tunnel junctions and spin valves)based on magnetic 2D vdWs materials are presented.Finally,the development trend of magnetic 2D vdWs materials is discussed.This review provides comprehensive understandings for the development of novel spintronic applications based on magnetic 2D vdWs materials.

Spin-filter effect and spin-polarized optoelectronic properties in annulene-based molecular spintronic devices

Using Fe, Co or Ni chains as electrodes, we designed several annulene-based molecular spintronic devices and investigated the quantum transport properties based on density functional theory and non-equilibrium Green＇s function method.Our results show that these devices have outstanding spin-filter capabilities and exhibit giant magnetoresistance effect,and that with Ni chains as electrodes, the device has the best transport properties. Furthermore, we investigated the spinpolarized optoelectronic properties of the device with Ni electrodes and found that the spin-polarized photocurrents can be directly generated by irradiating the device with infrared, visible or ultraviolet light. More importantly, if the magnetization directions of the two electrodes are antiparallel, the photocurrents with different spins are spatially separated, appearing at different electrodes. This phenomenon provides a new way to simultaneously generate two spin currents.

High-performance spin-filtering and spin-rectifying effects in Blatter radical-based molecular spintronic device

We design a Blatter radical-based molecular spintronic device, and investigate its spin-polarized transport properties using density functional theory and non-equilibrium Green's function technique. High-performance spin-rectifying and spin-filtering effects are realized. The physical mechanism is explained by the spin-resolved bias voltage-dependent transmission spectra, the energy levels of the corresponding molecular projected self-consistent Hamiltonian orbitals, and their spatial distributions. The results demonstrate that the Blatter radical has great potential in the development of highperformance multifunctional molecular spintronic devices.

Spin transfer nano-oscillator based on synthetic antiferromagnetic skyrmion pair assisted by perpendicular fixed magnetic field

As a microwave generator, spin transfer nano-oscillator(STNO) based on skyrmion promises to become one of the next-generation spintronic devices. However, there still exist a few limitations to the practical applications. In this paper, we propose a new STNO based on synthetic antiferromagnetic(SAF) skyrmion pair assisted by a perpendicular fixed magnetic field. It is found that the oscillation frequency of this kind of STNO can reach up to 5.0 GHz, and the multiple oscillation peak with higher frequency can be realized under a fixed out-of-plane magnetic field. Further investigation shows that the skyrmion stability is improved by bilayer antiferromagnetic coupling, which guarantees the stability process of skyrmion under higher spin-polarized current density. Our results provide the alternative possibilities for designing new skyrmionbased STNO to further improve the oscillation frequency, and realize the output of multiple frequency microwave signal.

Angle-dependent spin wave spectra of permalloy ring arrays

We investigated the angle-dependent spin wave spectra of permalloy ring arrays with the fixed outer diameter and various inner diameters by ferromagnetic resonance spectroscopy and micromagnetic simulation.When the field is obliquely applied to the ring,local resonance mode can be observed in different parts of the rings.And the resonance mode will change to perpendicular spin standing waves if the magnetic field is applied along the perpendicular direction.The simulation results demonstrated this evolution and implied more resonance modes that maybe exist.And the mathematical fitting results based on the Kittel equation further proved the existence of local resonance mode.

Nanoscale control of low-dimensional spin structures in manganites

Due to the upcoming demands of next-generation electronic/magnetoelectronic devices with low-energy consumption,emerging correlated materials（such as superconductors,topological insulators and manganites） are one of the highly promising candidates for the applications.For the past decades,manganites have attracted great interest due to the colossal magnetoresistance effect,charge-spin-orbital ordering,and electronic phase separation.However,the incapable of deterministic control of those emerging low-dimensional spin structures at ambient condition restrict their possible applications.Therefore,the understanding and control of the dynamic behaviors of spin order parameters at nanoscale in manganites under external stimuli with low energy consumption,especially at room temperature is highly desired.In this review,we collected recent major progresses of nanoscale control of spin structures in manganites at low dimension,especially focusing on the control of their phase boundaries,domain walls as well as the topological spin structures（e.g.,skyrmions）.In addition,capacitor-based prototype spintronic devices are proposed by taking advantage of the above control methods in manganites.This capacitor-based structure may provide a new platform for the design of future spintronic devices with low-energy consumption.

A realistic topological p-n junction at the Bi2Se3 （0001） surface based on planar twin boundary defects

We propose a realistic topological p-n junction （TPNJ） by matching two Bi2Se3 （0001） slabs with opposite arrangements of planar twin boundary defects. The atomistic modeling of such a device leads to dislocation defects in the hexagonal lattice in several quintuple layers. Nevertheless, total energy calculations reveal that the interface relaxes, yielding a smooth geometrical transition that preserves the nearest-neighbors fcc-type geometry throughout these defect layers. The electronic, magnetic, and transport properties of the junction have then been calculated at the ab initio level under open boundary conditions, i.e., employing a thin-film geometry that is infinite along the electron transport direction. Indeed, a p-n junction is obtained with a built-in potential as large as 350 meV. The calculations further reveal the spin texture across the interface with unprecedented detail. As the main result, we obtain non-negligible transmission probabilities around the F point, which involve an electron spin-flip process while crossing the interface.