Manipulating exchange bias in 2D magnetic heterojunction for high-performance robust memory applications.

The exchange bias (EB) effect plays an undisputed role in the development of highly sensitive, robust, and high-density spintronic devices in magnetic data storage. However, the weak EB field, low blocking temperature, as well as the lack of modulation methods, seriously limit the application of EB in van der Waals (vdW) spintronic devices. Here, we utilized pressure engineering to tune the vdW spacing of the two-dimensional (2D) FePSe3/Fe3GeTe2 heterostructures. The EB field (HEB, from 29.2 mT to 111.2 mT) and blocking temperature (Tb, from 20 K to 110 K) are significantly enhanced, and a highly sensitive and robust spin valve is demonstrated. Interestingly, this enhancement of the EB effect was extended to exposed Fe3GeTe2, due to the single-domain nature of Fe3GeTe2. Our findings provide opportunities for the producing, exploring, and tuning of magnetic vdW heterostructures with strong interlayer coupling, thereby enabling customized 2D spintronic devices in the future.

Carbon Nanotube Fibers Decorated with MnO2 for Wire-Shaped Supercapacitor.

Fibers made from CNTs (CNT fibers) have the potential to form high-strength, lightweight materials with superior electrical conductivity. CNT fibers have attracted great attention in relation to various applications, in particular as conductive electrodes in energy applications, such as capacitors, lithium-ion batteries, and solar cells. Among these, wire-shaped supercapacitors demonstrate various advantages for use in lightweight and wearable electronics. However, making electrodes with uniform structures and desirable electrochemical performances still remains a challenge. In this study, dry-spun CNT fibers from CNT carpets were homogeneously loaded with MnO2 nanoflakes through the treatment of KMnO4. These functionalized fibers were systematically characterized in terms of their morphology, surface and mechanical properties, and electrochemical performance. The resulting MnO2-CNT fiber electrode showed high specific capacitance (231.3 F/g) in a Na2SO4 electrolyte, 23 times higher than the specific capacitance of the bare CNT fibers. The symmetric wire-shaped supercapacitor composed of CNT-MnO2 fiber electrodes and a PVA/H3PO4 electrolyte possesses an energy density of 86 nWh/cm and good cycling performance. Combined with its light weight and high flexibility, this CNT-based wire-shaped supercapacitor shows promise for applications in flexible and wearable energy storage devices.

Proximity-Coupling-Induced Significant Enhancement of Coercive Field and Curie Temperature in 2D van der Waals Heterostructures.

Magnetism in 2D has long been the focus of condensed matter physics due to its important applications in spintronic devices. A particularly promising aspect of 2D magnetism is the ability to fabricate 2D heterostructures with engineered optical, electrical, and quantum properties. Recently, the discovery of intrinsic ferromagnetisms in atomic thick materials has provided a new platform for investigations of fundamental magnetic physics. In contrast to 2D CrI3 and Cr2 Ge2 Te6 insulators, itinerant ferromagnetic Fe3 GeTe2 (FGT), which has a larger intrinsic perpendicular anisotropy, higher Curie temperature (TC ), and relatively better stability, is a promising candidate for achieving permanent room-temperature ferromagnetism through interface or component engineering. Here, it is shown that the ferromagnetic properties of FGT thin flakes can be modulated through coupling with a FePS3 . The magneto-optical Kerr effect results show that the TC of FGT is improved by more than 30 K and that the coercive field is increased by ≈100% due to the proximity coupling effect, which changes the spin textures of FGT at the interface. This work reveals that antiferromagnet/ferromagnet coupling is a promising way to engineer the magnetic properties of itinerant 2D ferromagnets, which paves the way for applications in advanced magnetic spintronic and memory devices.

Two-dimensional ferromagnetism in CrTe flakes down to atomically thin layers.

Two-dimensional (2D) ferromagnetism has attracted intense attention as it provides a platform for the investigation of fundamental physics and the emerged devices. Recently, the discovery of intrinsic 2D ferromagnet has enabled researchers to fabricate ultrathin devices, which can be controlled by external fields. Nevertheless, 2D ferromagnetic materials are mostly obtained by mechanical exfoliation methods with uncontrollable size and thickness, which make the device fabrication processes time-consuming and difficult to expand in industries. Therefore, the development of a controllable fabrication process for the synthesis of 2D intrinsic magnetic materials is necessary. In this study, a new 2D ferromagnet, chromium tellurium (CrTe), was successfully synthesized by the chemical vapor deposition (CVD) method, and the magnetism was studied by the magneto-optical Kerr effect (MOKE) technique. The results demonstrated that CrTe flakes exhibit hard magnetism with strong perpendicular anisotropy. As the thickness varies from 45 nm to 11 nm, the hard magnetism sustains quite well, with the Curie temperature TC decreasing from 205 K to 140 K. Our study presents a new ultrathin hard magnetic material, which has the potential to be fabricated and applied in spintronic devices massively.

Simultaneous growth of three-dimensional carbon nanotubes and ultrathin graphite networks on copper.

A new way to simultaneously grow carbon nanotubes (CNTs) and ultrathin graphite on copper (Cu) foils has been investigated. This one-step growth process yields three-dimensional networks of CNTs on graphitic layers (3D CNTs/G) on Cu foils. Their synthesis conditions and growth mechanism are discussed in detail taking their structural properties into account. Individual CNTs and the 3D CNTs/G networks by means of an in-situ conductive atomic force microscope inside a scanning electron microscope are electrically characterized. Time-resolved photoluminescence demonstrated fast charge transfer and high carrier collection efficiency superior to two-dimensional ultrathin graphite only. Their facile and tunable growth and excellent electrical properties show that the 3D CNTs/G are strongly attractive for various applications such as solar cells, sensors, supercapacitors, photovoltaics, power generation, and optoelectronics.

Gap-Induced Giant Third-Order Optical Nonlinearity and Long Electron Relaxation Time in Random-Distributed Gold Nanorod Arrays.

The third-order optical nonlinearities and the hot electron relaxation time (τ) of random-distributed gold nanorods arrays on glass (R-GNRA) have been investigated by using Z-scan and optical Kerr effect (OKE) techniques. Large third-order optical susceptibility (χ(3)) with the value of 2.5 × 10-6 esu has been obtained around the plamsonic resonance peak under the excitation power intensity of 0.1 GW/cm2. Further decrease of the excitation power intensity down to 0.3 MW/cm2 will lead to the significant increase of χ(3) up to 6.4 × 10-4 esu. The OKE results show that the relaxation time of R-GNRA around the plasmonic peak is 13.9 ± 0.4 ps, which is more than 4 times longer than those of the individual gold nanostructures distributed in water solutions. The Finite-difference time domain simulations demonstrate that this large enhancement of χ(3) and slow down of τ are caused by the gap-induced large local field enhancement of GNRs dimers in R-GNRA. These significant results offer great opportunities for plasmonic nanostructures in applications of photonic and photocatalytic devices.

Plasmon-enhanced versatile optical nonlinearities in a Au-Ag-Au multi-segmental hybrid structure.

A Au-Ag-Au multi-segmental hybrid structure has been synthesized by using an electrodeposition method based on an anodic aluminum oxide (AAO) membrane. The third-order optical nonlinearities, second harmonic generation (SHG) and photoluminescence (PL) properties containing ultrafast supercontinuum generation and plasmon mediated thermal emission have been investigated. Significant optical enhancements have been obtained near surface plasmon resonance wavelength in all the abovementioned nonlinear processes. Comparative studies between the Au-Ag-Au multi-segmental hybrid structure and the corresponding single-component Au and Ag hybrid structures demonstrate that the Au-Ag-Au multi-segmental hybrid structure has much larger optical nonlinearities than its counterparts. These results demonstrate that the Au-Ag-Au hybrid structure is a promising candidate for applications in plasmonic devices and enhancement substrates.