2D layered chalcogenide semiconductors have been proposed as a promising class of materials for low‐dimensional electronic, optoelectronic, and spintronic devices. Here, all‐2D van der Waals vertical spin‐valve devices, that combine the 2D layered semiconductor InSe as a spacer with the 2D layered ferromagnetic metal Fe3GeTe2 as spin injection and detection electrodes, are reported. Two distinct transport behaviors are observed: tunneling and metallic, which are assigned to the formation of a pinhole‐free tunnel barrier at the Fe3GeTe2/InSe interface and pinholes in the InSe spacer layer, respectively. For the tunneling device, a large magnetoresistance (MR) of 41% is obtained under an applied bias current of 0.1 µA at 10 K, which is about three times larger than that of the metallic device. Moreover, the tunneling device exhibits a lower operating bias current but a more sensitive bias current dependence than the metallic device. The MR and spin polarization of both the metallic and tunneling devices decrease with increasing temperature, which can be fitted well by Bloch's law. These findings reveal the critical role of pinholes in the MR of all‐2D van der Waals ferromagnet/semiconductor heterojunction devices.

The 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 two-dimensional (2D) van der Waals (vdW) 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 WSe2 layer embedded between two Fe3GaTe2 electrodes 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.

Targeted design of organic semiconductors in organic spintronics is relatively limited. Therefore, four conjugated polymers with analogous structures based on isoindigo (IID) units were designed and synthesized to investigate the structure–property relationships in spin and charge carrier transport. Structural design strategies include introduction of pyridinic nitrogen atoms into IID units to change electronic structures and alteration of different branching points of alkyl chains to adjust the aggregation structure. By fabricating polymer field-effect transistors (PFETs) and organic spin valves (OSVs), all of the polymers exhibited good ambipolar field-effect properties (all of the mobilities exceeding 0.3 cm2 V–1 s–1) and relatively high magnetoresistance (MR) values (maximum up to 25%). Most importantly, it is found that the introduction of pyridinic nitrogen into the IID units can improve MR values of OSVs and electron mobilities of PFETs, whereas the extension of alkyl chain branching points can reduce MR values of the conjugated polymers. This work is the first attempt to thoroughly study the structure–property relationship in the OSVs, combined with molecular design of the conjugated polymers, which provides a guideline for molecular engineering, especially for organic spintronics.

Exploiting the spin degree of freedom to store and manipulate information provides a paradigm for future microelectronics. The development of van der Waals (vdW) heterostructures has created a fascinating platform for exploring spintronic properties in the two-dimensional (2D) limit. Transition-metal dichalcogenides such as tungsten diselenide (WSe2) have electronic band structures that are ideal for hosting many exotic spin–orbit phenomena. Here, we report the spin-filtering effect in all-vdW heterostructures with WSe2 barrier. Combining 2D-perpendicular magnetic anisotropy Fe3GeTe2 (FGT) with different thicknesses of WSe2, the FGT/WSe2/FGT spin valve shows distinct charge and spin transport behavior. Moreover, the negative magnetoresistance (−4.3%) could be inverted into positive magnetoresistance (up to +25.8%) with decreasing the WSe2 thickness. Furthermore, we proposed a spin-filtering model based on Δ-symmetry electrons tunneling to explain the crossover from negative to positive MR signal through ab initio calculation. These experimental and theoretical results illustrate the rich potential of the families of TMDC materials to control spin currents in 2D spintronic devices.

A series of aza[4]helicenes have been conveniently synthesized in yields of 71–92 % by a one‐pot procedure involving the Pictet–Spengler reaction. The structures of the aza[4]helicenes were characterized by 1H and 13C NMR spectroscopy, mass spectrometry, and X‐ray crystallography. Moreover, it was found that the aza[4]helicenes self‐assemble into 2D layers or herringbone‐like structures in the solid state. In addition, the optical properties were investigated by UV and fluorescence spectroscopic methods.

No abstract

recombination in organic light-emitting diodes and organic magnetoresistance (MR) devices. [9][10][11][12] Moreover, organic semiconductors have obvious advantages, lower cost, and better flexibility, and they have greater possibility in wearable and large area applications. [13][14][15][16][17][18][19][20] The most common prototype organic device using spin freedom is organic spin valves (OSVs), [5,11,[21][22][23][24][25] which consist of a nonmagnetic spacer sandwiched between two ferromagnetic (FM) electrodes, and based on the alignment of the electron spin relative to the FM layer magnetization orientation. In this research field, there are tunneling and diffusive regimes. [26] The tunneling regimes occur in relatively thinner spacers (<15 nm), and the mode is weakly dependent on temperature. The diffusive regimes are also called hoping in organic spintronics. This mode occurs in relatively thicker layers (≥15 nm), and it is strongly dependent on temperature. In addition, the present study lies in the diffusive regime owing of the conductivity mismatch problem and more abundant phenomena like Hanle effect in organic spintronics. For organic semiconductor, both spin-orbit interaction and the hyperfine interaction play very significant parts in determining the spin relaxation, but the origin of determining the spin relaxation in organic semiconductors is still unknown. Herein, OSV effect is characterized by the MR ratios, defined as MR = (R ap − R p )/R p , where R ap and R p denote the resistance in the antiparallel and parallel states of FM electrode magnetization direction, respectively. There are lots of efforts to explore organic spintronics Organic materials are proposed to be excellent spin transport layers due to their weak hyperfine and spin-orbit coupling interaction. Donor−acceptortype polymers PTDCNTVT-420 and PTDCNTVT-320 with diketopyrrolopyrrole (DPP) units are employed as the spacers in the organic spin valves, which have more advantages such as solution processing, higher mobility, and large area fabrication. The performance of polymers spin valves based on DPP units with different alkyl side chain lengths are studied. The different top ferromagnetic (FM) electrodes Co and Ni 80 Fe 20 are used for spin detection resulting in obvious distinct magnetoresistance (MR) values. The MR ratio of approaching 30% at 10 K is achieved with the Ni 80 Fe 20 electrodes using PTDCNTVT-420 with longer alkyl side chain lengths. Moreover, the MR behaviors are observed depending on various temperatures, which are related with the FM electrodes spin injection efficiency. The direct spinterface are also investigated by transmission electron microscopy (TEM) and atomic force microscopy (AFM). In addition, the series of results indicate that the PTDCNTVT polymers can be used as good spin transport model materials and give clues for future polymers spintronic studies.

Among the numerous two-dimensional van der Waals (vdW) magnetic materials, Fe3GeTe2 (FGT), due to its outstanding properties such as metallicity, high Curie temperature and strong perpendicular magnetic anisotropy, quickly emerged...