Giant Magneto-Optical Effect in van der Waals Room-Temperature Ferromagnet Fe_(3)GaTe_(2)

The discovery of ferromagnetic two-dimensional(2D)van der Waals(vdWs)materials provides an opportunity to explore intriguing physics and to develop innovative spin electronic devices.However,the main challenge for practical applications of vd Ws ferromagnetic crystals lies in the weak intrinsic ferromagnetism and small perpendicular magnetic anisotropy(PMA)above room temperature.Here,we report the intrinsic vd Ws ferromagnetic crystal Fe_(3)GaTe_(2),synthesized by the self-flux method,exhibiting a Curie temperature(TC)of 370 K,a high saturation magnetization of 33.47 emu/g,and a large PMA energy density of approximately 4.17×10^(5)J/m^(3).Furthermore,the magneto-optical effect is systematically investigated in Fe_(3)GaTe_(2).The doubly degenerate E_(2g)(Γ)mode reverses the helicity of incident photons,indicating the existence of pseudoangular-momentum(PAM)and chirality.Meanwhile,the non-degenerate non-chiral A_(1g)(Γ)phonon exhibits a significant magneto-Raman effect under an external out-of-plane magnetic field.These results lay the groundwork for studying phonon chirality and magneto-optical phenomena in 2D magnetic materials,providing the feasibility for further fundamental research and applications in spintronic devices.

Negative-to-Positive Tunnel Magnetoresistance in van der Waals Fe_(3)GeTe_(2)/Cr_(2)Ge_(2)Te_(6)/Fe_(3)GeTe_(2)Junctions

The emergent van der Waals magnetic material is a promising component for spintronic devices with novel functionalities.Here,we report a transition of negative-to-positive magnetoresistance in Fe_(3)GeTe_(2)/Cr_(2)Ge_(2)Te_(6)/Fe_(3)GeTe_(2)van der Waals all-magnetic tunnel junctions with increasing the applied bias voltage.A negative magnetoresistance is observed first in Fe_(3)GeTe_(2)/Cr_(2)Ge_(2)Te_(6)/Fe_(3)GeTe_(2)tunnel junctions,where the resistance with antiparallel aligned magnetization of two Fe_(3)GeTe_(2)electrodes is lower than that with parallel alignment,which is due to the opposite spin polarizations of two Fe_(3)GeTe_(2)electrodes.With the bias voltage increasing,the spin polarization of the biased Fe_(3)GeTe_(2)electrode is changed so that the spin orientations of two Fe_(3)GeTe_(2)electrodes are the same.Our experimental observations are supported by the calculated spin-dependent density of states for Fe_(3)GeTe_(2)electrodes under a finite bias.The significantly bias voltage-dependent spin transport properties in van der Waals magnetic tunnel junctions open a promising route for designing electrical controllable spintronic devices based on van der Waals magnets.

Broadband polarized photodetector based on p-BP/n-ReS2 heterojunction

Two-dimensional(2D) atomic crystals,such as graphene,black phosphorus(BP) and transition metal dichalcogenides(TMDCs) are attractive for use in optoelectronic devices,due to their unique crystal structures and optical absorption properties.In this study,we fabricated BP/ReS2 van der Waals(vdWs) heterojunction devices.The devices realized broadband photoresponse from visible to near infrared(NIR)(400–1800 nm) with stable and repeatable photoswitch characteristics,and the photoresponsivity reached 1.8 mA/W at 1550 nm.In addition,the polarization sensitive detection in the visible to NIR spectrum(532–1750 nm) was demonstrated,and the photodetector showed a highly polarization sensitive photocurrent with an anisotropy ratio as high as 6.44 at 1064 nm.Our study shows that van der Waals heterojunction is an effective way to realize the broadband polarization sensitive photodetection,which is of great significance to the realization and application of multi-functional devices based on 2D vdWs heterostructures.

Large Room-Temperature Magnetoresistance in van der Waals Ferromagnet/Semiconductor Junctions

A magnetic tunnel junction(MTJ)is the core component in memory technologies,such as the magnetic random-access memory,magnetic sensors and programmable logic devices.In particular,MTJs based on twodimensional van der Waals(vd W)heterostructures offer unprecedented opportunities for low power consumption and miniaturization of spintronic devices.However,their operation at room temperature remains a challenge.Here,we report a large tunnel magnetoresistance(TMR)of up to 85%at room temperature(T=300 K)in vdW MTJs based on a thin(<10 nm)semiconductor spacer WSe_(2)layer embedded between two Fe_(3)GaTe_(2e)lectrodes with intrinsic above-room-temperature ferromagnetism.The TMR in the MTJ increases with decreasing temperature up to 164%at T=10 K.The demonstration of TMR in ultra-thin MTJs at room temperature opens a realistic and promising route for next-generation spintronic applications beyond the current state of the art.

可压缩壁湍流物理与建模研究进展

对高速边界层转捩与湍流的理解、建模与控制不但具有广泛的学术兴趣,而且对高速飞行器的设计与节能有至关重要的意义,因为转捩和湍流会急剧增加壁面摩阻和热流.根据Morkovin假设,高速流动具有一些与不可压缩流动本质上相似的特征,但另一方面,由于存在热力学过程、激波、高焓效应等多物理场耦合,与不可压缩流动也有显著区别.本文综述了高速边界层转捩与湍流的物理和建模方面的最新研究进展,其中较大部分内容为湍流研究.为了物理过程描述的完整性,我们首先简要综述了高速流动转捩,主要关注气动加热原理和推迟转捩的被动控制策略.随后,我们总结了近期在湍流平均流向速度和温度的标度率方面的一些令人鼓舞的发现,这些标度率能够用于构建一系列新颖的壁面模型以提高模式精度.此外,作为湍流建模的基础之一,我们还总结了湍流结构方面的研究,尤其关注边界层对数区含能运动的标度率与建模.另外,我们综述了各种用于预测壁湍流的线性模型.尽管湍流通常被认为是高度非线性的,这些线性模型在过去二十年的研究中取得了较大的成功.最后,我们对综述进行总结,并简要展望未来研究.

Highly Stretchable Ionic and Electronic Conductive Fabric

Wearable devices redefine the way people interact with machines.Despite the intensive effort in the design and fabrication of synthetic fibers to improve wearable device properties in terms of electronic and ionic conductivity,stretchability,com-fort,and washability,challenges remain in fabricating single fiber materials that optimize all properties simultaneously.In this work,we demonstrate a highly stretchable,ionic,and electronic conductive fabric via(1)the natural nanoscale chan-nels in fibers for effective ion transportation,(2)confining the electronic conductive material with the cellulose fibers,and(3)decoupling the property degradation of the fiber from deformation using the knitted pattern.The hierarchical structure created by cotton fibers can serve as ionic conductive channels as well as a robust multiscale scaffold to host infiltrated elec-tronic conductive materials.Cotton strands with ionic and electronic conductivity can be knitted into fabrics that are highly stretchable(~300%).Moreover,high ionic and electronic conductivity are observed with 2 S/m and 5 S/m,respectively,even under a strain of 175%.With the inherent advantages of cotton fabrics such as moisture-wicking,washability,comfort,and light-weightiness for wearable applications,our approach of directly functionalized cellulose can potentially be a promising route towards highly stretchable and wearable mixed conductors.

基于Fe3GeTe2范德华同质结的无间隔层多态垂直自旋阀

不同于共价键合的磁性多层薄膜体系,由二维层状磁性材料构成的范德华结中的无悬挂键高质量范德华界面为实现新的器件功能提供了可能.与广泛应用的传统三明治结构(铁磁金属/非磁性间隔层/铁磁金属)自旋阀不同,本文报道了无间隔层的、基于范德华同质结的多态垂直自旋阀,这里铁磁电极和/或中间层都为机械剥离获得的二维Fe3GeTe2纳米片.通过制备由两片和三片Fe3GeTe2二维纳米片组成的同质结器件,作者分别演示了两态和三态自旋阀磁阻行为.本文提出的基于范德华同质结的全金属自旋阀具有较小的电阻面积和较低的工作电流密度以及垂直两端器件结构.这种新型的简单自旋阀结构将可能实现更多态的磁学存储和逻辑器件.这项工作揭示了基于二维磁性同质结实现多态非易失磁学存储和逻辑的可能性,并强调范德华界面是自旋电子学器件的基本组成部分.

波纹壁面上的高超声速边界层气动降热

Hypersonic boundary layer transition is of fundamental importance for the design of high-speed vehicles because of its direct relevance to drag and aerodynamic heating.As the focus of transition and turbulence research is shifting towards higher velocities,research on compressible flows,especially hypersonic flows,is becoming increasingly attractive to researchers worldwide[1,2].

Generation of acoustic waves in the hypersonic boundary layer over a wavy wall

The effects of a wavy wall on a hypersonic boundary layer of a flared cone are investigated using experimental measurements and direct numerical simulations(DNSs). Non-contact optical measurements using a focused laser differential interferometer(FLDI) show that a wavy wall can significantly suppress the second mode, and multiple perturbations of new frequencies are generated over the wavy surface, which agrees well with numerical results. Using Lagrangian tracking of marked particles, it is demonstrated that the wavy wall geometry can induce mean flow oscillations while exciting acoustic waves. The frequencies of the excited disturbances over a wavy wall agree with the classical Rossiter model. The superposition of a disturbance propagating downstream and an acoustic wave propagating upstream at the same frequency but with different amplitudes and propagation velocities results in a spatial distribution with a streamwise-oscillatory pattern over the wavy surface. A simple two-wave superposition model that takes into account the phase velocities and wavenumbers of the convective disturbance and acoustic wave can well describe the modal behavior of excited disturbances over a wavy wall.

Notes on the hypersonic boundary layer transition

A brief discussion is given in this note to clarify the transition path of the hypersonic boundary layer.The first mode plays an important role in the hypersonic boundary layer transition and should not be ignored.The second mode may enhance the boundary layer transition,but it is not the decisive factor affecting the transition.