Enhanced Spin-Orbit Torque Efficiency in Platinum-Gadolinium Oxide Nanocomposite Films.

Spin-orbit torque (SOT) has emerged as an effective means of manipulating magnetization. However, the current energy efficiency of SOT operation is inefficient due to low damping-like SOT efficiency per unit current bias. In this work, we dope conventional rare earth oxides, GdOy, into highly conductive platinum by magnetron sputtering to form a new group of spin Hall materials. A large damping-like spin-orbit torque (DL-SOT) efficiency of about 0.35 ± 0.013 is obtained in Pt0.70(GdOy)0.30 measured by the spin-torque ferromagnetic resonance (ST-FMR) technique, which is about five times that of pure Pt under the same conditions. The substantial enhancement of the spin Hall effect is revealed by theoretical analysis to be attributed to the strong side jump induced by the rare earth oxide GdOy impurities. Moreover, this large DL-SOT efficiency contributes to a low critical switching current density (8.0 × 106 A·cm-2 in the Pt0.70(GdOy)0.30 layer) in current-induced magnetization switching measurements. This systematic study on SOT switching properties suggests that Pt1-x(GdOy)x is an attractive spin current source with large DL-SOT efficiency for future SOT applications and provides another idea to regulate the spin Hall angle.

Promotion of astrocyte-neuron glutamate-glutamine shuttle by SCFA contributes to the alleviation of Alzheimer's disease.

The brain is particularly susceptible to oxidative damage which is a key feature of several neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease. The shuttling of glutathione (GSH) precursors from astrocytes to neurons has been shown to be instrumental for the neuroprotective activity. Here, we revealed that short chain fatty acids (SCFA), which have been related to AD and PD, could promote glutamate-glutamine shuttle to potentially resist oxidative damage in neurons at cellular level. Furthermore, we performed nine-month-long dietary SCFA supplementations in APPswe/PS1dE9 (APP/PS1) mice, and showed that it reshaped the homeostasis of microbiota and alleviated the cognitive impairment by reducing Aß deposition and tau hyperphosphorylation. Single-cell RNA sequencing analysis of the hippocampus revealed SCFA can enhance astrocyte-neuron communication including glutamate-glutamine shuttle, mainly by acting on astrocyte in vivo. Collectively, our findings indicate that long-term dietary SCFA supplementations at early aging stage can regulate the neuroenergetics to alleviate AD, providing a promising direction for the development of new AD drug.

Structural and magnetic properties of Y3(GaAlFe)5O12 liquid-phase epitaxy films with low ferromagnetic resonance losses.

Ultra-thin rare earth iron garnet (RIG) films with a narrow ferromagnetic resonance (FMR) line width and a low damping factor have attracted a great deal of attention for microwave and spintronic applications. In this work, 200 nm Y3(GaAlFe)5O12 garnet (GaAl-YIG) films were prepared on gadolinium gallium garnet (GGG) substrates by liquid-phase epitaxy (LPE) with low saturation magnetization. The microstructural properties, chemical composition, and magnetostatic and dynamic magnetization characteristics of the films are discussed in detail. According to the structural analysis, these films exhibit a low surface roughness of less than 0.5 nm. The GaAl-YIG films show an obvious temperature dependence of lattice parameter and strain state, and the film's parameter is perfectly matched with that of the GGG substrate at 810°C. There is a clear variation in the Pb level, which brings about a gradual enhancement of the coercivity and a diminution of the squareness ratio of magnetic hysteresis loops as the growth temperature is reduced. Slight changes in surface roughness, strain condition and content of Pb induce the FMR line width and damping factor to vary on a small scale. The line width is less than 10.17 Oe at 12 GHz and the damping factor is of the order of 10-4. All these properties demonstrate that these ultra-thin GaAl-YIG films are of benefit for the development of devices operated at lower frequencies and in lower fields.

Non-centrosymmetric Weyl semimetal state and strain effect in the twisted-brick phase transition metal monochalcogenides.

Weyl semimetals are a class of gapless electronic excitation topological quantum materials upon breaking time-reversal or inversion symmetry. Here, we demonstrate the existence of the Weyl semimetal state in the non-centrosymmetric twisted-brick phase MoTe theoretically. The topological properties and strain effects of MoTe have been systematically studied based on first-principles calculations and the Wannier-based tight-binding method. In the absence of spin-orbit coupling (SOC), MoTe exhibits gapless nodal loop states related to the mirror reflection symmetry. When the SOC is turned on, the two nodal loops split into 22 pairs of Weyl points (WPs) with opposite chirality. When the effect of uniaxial (εz) strain is taken into account, the Weyl semimetal phase of MoTe shows great robustness and striking tunable topological strength. In particular, the total number of WPs changes significantly under strain. MoTe under +4% and +8% uniaxial strains have only four pairs of WPs with a relatively large separation in momentum space. These results show that MoTe under weak strain is a promising partly ideal type I Weyl semimetal candidate, while the isolog structure WTe both opens a direct gap with and without SOC, showing a compensated semimetal state.

Study on laser-induced damage of TbBiIG crystal at 1064†nm.

With the development of miniaturization of high-energy laser systems, a new Faraday rotator material must be studied to realize the miniaturization and integration of optical isolators. In this paper, high-quality (TbBi)3Fe5O12 (TbBiIG) and Ca-doped (TbBi)3Fe5O12 (Ca: TbBiIG) single crystal films with hundreds of microns thickness were grown by liquid phase epitaxy method on (111) oriented garnet substrate. The crystal structure, magneto-optical (MO), optical and laser induced damage properties were investigated in detail. We found that the (TbBi)3Fe5O12 film has outstanding magneto-optical and laser-induced damage properties. Optical and MO properties indicate that TbBiIG films have a high specific faraday rotation angle of 1452 deg/cm at 1310 nm, and 2812 deg/cm at 1064 nm, absorption coefficient (α) is 5.63 cm-1 and 15.7 cm-1 at 1310 nm and 1064 nm, respectively. The laser-induced damage threshold (LIDT) of TbBiIG irradiated by a multi-frequency laser is 8.91 J/cm2. The light absorption has a significant impact on LIDT value. Rare-earth ion doped iron garnet (RIG) material is a very potential MO material, which can greatly reduce the size and weight of optical isolators in the 1064 nm band.

Tune the resonance of VO2 joined metamaterial dimers by adjacent cut wires.

Two terahertz metamaterials were joined by a conductivity variable VO2 patch to obtain a metamaterial dimer. By applying voltage or heat to the VO2 patches, active modulation of terahertz wave could be achieved. A cut-wire metamaterial was placed adjacent to the VO2 joined dimer to affect its electromagnetic response. It was found that the cut wire could heavily impact the resonance mode of the VO2 joined dimer, which gives dual resonance dips in transmission spectrum for both insulating and conducting states of VO2 patches. As a result, by tuning the conductivity of VO2, active dual band phase modulation could be achieved with high transmission window by this dimer-cut wire coupling system.

Direct investigation of the atomic structure and decreased magnetism of antiphase boundaries in garnet.

The ferrimagnetic insulator iron garnets, tailored artificially with specific compositions, have been widely utilized in magneto-optical (MO) devices. The adjustment on synthesis always induces structural variation, which is underestimated due to the limited knowledge of the local structures. Here, by analyzing the structure and magnetic properties, two different antiphase boundaries (APBs) with individual interfacial structure are investigated in substituted iron garnet film. We reveal that magnetic signals decrease in the regions close to APBs, which implies degraded MO performance. In particular, the segregation of oxygen deficiencies across the APBs directly leads to reduced magnetic elements, further decreases the magnetic moment of Fe and results in a higher absorption coefficient close to the APBs. Furthermore, the formation of APBs can be eliminated by optimizing the growth rate, thus contributing to the enhanced MO performance. These analyses at the atomic scale provide important guidance for optimizing MO functional materials.

Giant Extrinsic Spin Hall Effect in Platinum-Titanium Oxide Nanocomposite Films.

Although the spin Hall effect provides a pathway for efficient and fast current-induced manipulation of magnetization, application of spin-orbit torque magnetic random access memory with low power dissipation is still limited to spin Hall materials with low spin Hall angles or very high resistivities. This work reports a group of spin Hall materials, Pt1 -x (TiO2 )x nanocomposites, that combines a giant spin Hall effect with a low resistivity. The spin Hall angle of Pt1 -x (TiO2 )x in an yttrium iron garnet/Pt1 -x (TiO2 )x double-layer heterostructure is estimated from a combination of ferromagnetic resonance, spin pumping, and inverse spin Hall experiments. A giant spin Hall angle 1.607 ± 0.04 is obtained in a Pt0.94 (TiO2 )0.06 nanocomposite film, which is an increase by an order of magnitude compared with 0.051 ± 0.002 in pure Pt thin film under the same conditions. The great enhancement of spin Hall angle is attributed to strong side-jump induced by TiO2 impurities. These findings provide a new nanocomposite spin Hall material combining a giant spin Hall angle, low resistivity and excellent process compatibility with semiconductors for developing highly efficiency current-induced magnetization switching memory devices and logic devices.

Noncentrosymmetric Weyl phase and topological phase transition in bulk MoTe.

Ideal topological materials are those stable materials with less nontrivial band crossing near the Fermi surface and a long Fermi arc. By means of first-principles calculations, here we present that the 3D monochalcogenide molybdenum telluride (Pm-MoTe) without an inversion center shows a type-II Weyl semimetal (WSM) phase which cannot checked by symmetry index method. A total of eight Weyl points (WPs) are found in different quadrants of the Brillouin zone (BZ) of Pm-MoTe, which guarantee a long Fermi arc. The WSM phase is robust against the spin-orbit coupling (SOC) effect because of mirror symmetry and time reversal symmetry. It is also found that a topological phase transition can be tuned by strain. For different types of strain, the number of WPs can be effectively modulated to a minimum number, and their energies could be closer to Fermi level. These findings propose a promising material candidate that partly satisfies the ideal WSM criteria and extends the potential applications of the tunable topological phase.

High-Performance Multifunctional Photodetector and THz Modulator Based on Graphene/TiO2/p-Si Heterojunction.

In this paper, we have reported a multifunctional device from graphene/TiO2/p-Si heterojunction, followed by its systematical analysis of optical response in a device under ultraviolet-visible-infrared band and transmission changes of terahertz waves in the 0.3-1.0 THz band under different bias voltages. It is found that photodetector in the "back-to-back" p-n-p energy band structure has a seriously unbalanced distribution of photogenerated carriers in the vertical direction when light is irradiated from the graphene side. So this ensures a higher optical gain of the device in the form of up to 3.6 A/W responsivities and 4 × 1013 Jones detectability under 750 nm laser irradiation. Besides, the addition of TiO2 layer in this terahertz modulator continuously widens the carrier depletion region under negative bias, thereby realizing modulation of the terahertz wave, making the modulation depth up to 23% under - 15 V bias. However, almost no change is observed in the transmission of terahertz wave when a positive bias is applied. A similar of an electronic semiconductor diode is observed that only allows the passage of terahertz wave for negative bias and blocks the positive ones.

New Opportunities for High-Performance Source-Gated Transistors Using Unconventional Materials.

Source-gated transistors (SGTs), which are typically realized by introducing a source barrier in staggered thin-film transistors (TFTs), exhibit many advantages over conventional TFTs, including ultrahigh gain, lower power consumption, higher bias stress stability, immunity to short-channel effects, and greater tolerance to geometric variations. These properties make SGTs promising candidates for readily fabricated displays, biomedical sensors, and wearable electronics for the Internet of Things, where low power dissipation, high performance, and efficient, low-cost manufacturability are essential. In this review, the general aspects of SGT structure, fabrication, and operation mechanisms are first discussed, followed by a detailed property comparison with conventional TFTs. Next, advances in high-performance SGTs based on silicon are first discussed, followed by recent advances in emerging metal oxides, organic semiconductors, and 2D materials, which are individually discussed, followed by promising applications that can be uniquely realized by SGTs and their circuitry. Lastly, this review concludes with challenges and outlook overview.

Atomic-scale insights into quantum-order parameters in bismuth-doped iron garnet.

Bismuth and rare earth elements have been identified as effective substituent elements in the iron garnet structure, allowing an enhancement in magneto-optical response by several orders of magnitude in the visible and near-infrared region. Various mechanisms have been proposed to account for such enhancement, but testing of these ideas is hampered by a lack of suitable experimental data, where information is required not only regarding the lattice sites where substituent atoms are located but also how these atoms affect various order parameters. Here, we show for a Bi-substituted lutetium iron garnet how a suite of advanced electron microscopy techniques, combined with theoretical calculations, can be used to determine the interactions between a range of quantum-order parameters, including lattice, charge, spin, orbital, and crystal field splitting energy. In particular, we determine how the Bi distribution results in lattice distortions that are coupled with changes in electronic structure at certain lattice sites. These results reveal that these lattice distortions result in a decrease in the crystal-field splitting energies at Fe sites and in a lifted orbital degeneracy at octahedral sites, while the antiferromagnetic spin order remains preserved, thereby contributing to enhanced magneto-optical response in bismuth-substituted iron garnet. The combination of subangstrom imaging techniques and atomic-scale spectroscopy opens up possibilities for revealing insights into hidden coupling effects between multiple quantum-order parameters, thereby further guiding research and development for a wide range of complex functional materials.

Carbon-Graphitic Carbon Nitride Hybrids for Heterogeneous Photocatalysis.

Polymeric graphitic carbon nitride (g-C3 N4 ) and various carbon materials have experienced a renaissance as viable alternates in photocatalysis due to their captivating metal-free features, favorable photoelectric properties, and economic adaptabilities. Although numerous efforts have focused on the integration of both materials with optimized photocatalytic performance in recent years, the direct parameters for this emerging enhancement are not fully summarized yet. Fully understanding the synergistic effects between g-C3 N4 and carbon materials on photocatalytic action is vital to further development of metal-free semiconductors in future studies. Here, recent advances of carbon/g-C3 N4 hybrids on various photocatalytic applications are reviewed. The dominant governing factors by inducing carbon into g-C3 N4 photocatalysts with involving photocatalytic mechanism are highlighted. Five typical carbon-induced enhancement effects are mainly discussed here, i.e., local electric modification, band structure tailoring, multiple charge carrier activation, chemical group functionalization, and abundant surface-modified engineering. Photocatalytic performance of carbon-induced g-C3 N4 photocatalysts for addressing directly both the renewable energy storage and environmental remediation is also summarized. Finally, perspectives and ongoing challenges encountered in the development of metal-free carbon-induced g-C3 N4 photocatalysts are presented.

Porous graphitic carbon nitride for solar photocatalytic applications.

Photocatalysis is attracting increased attention in solving the energy crisis and environmental pollution. Graphitic carbon nitride (g-C3N4), a non-metal photocatalyst, has been regarded as an ideal photocatalyst to solve these problems because of its chemical stability and unique optical properties. However, traditional g-C3N4 exhibits moderate photocatalytic activity due to its low specific surface area and fast recombination rate of photogenerated electrons. Among the many modified g-C3N4 materials, porous carbon nitride (PCN) can solve the shortcomings of traditional g-C3N4 because of PCN's increased number of surface-active sites, specific surface area, light harvesting, diffusion and adsorption/activation. However, a frontier, comprehensive summary of the development of PCN is less reported. Thus, a review on recent developments in PCN research is urgently needed to further promote its advancement. In this review, the synthesis methods, structures and properties and photocatalytic applications of PCN photocatalysts are described in detail. The current challenges and future development of PCN/PCN-based photocatalysts are discussed. This review may present an up-to-date view of the PCN development to provide an in-depth understanding of PCN-based photocatalysts.

Effect of Interfacial Roughness Spin Scattering on the Spin Current Transport in YIG/NiO/Pt Heterostructures.

Interfacial properties play a vital role in spin current injection from the ferromagnetic (FM) layer into the nonmagnetic (NM) layer. So far, impedance matching and spin-orbit coupling are two important, well-known factors in spin current transport in FM/NM heterostructures. In this work, the spin current transport in Y3Fe5O12 (YIG)/NiO/Pt heterostructures was investigated by spin Hall magnetoresistance and inverse spin Hall effect measurements. By inserting a layer of antiferromagnetic insulator NiO, the magnetic proximity effect affecting the Pt atoms owing to YIG and the anomalous spin Hall voltage can be efficiently blocked. Ferromagnetic resonance and spin pumping measurements verified that the ferromagnetic/antiferromagnetic exchange coupling inhibits transmission of the spin current at the YIG/NiO interface when the NiO layer is thick. Atomic force microscopy and spherical aberration-corrected transmission electron microscopy proved that the strong interfacial roughness-enhanced spin scattering between NiO and Pt can greatly increase both the inverse spin Hall voltage and the spin Hall magnetoresistance when the NiO layer is thin or even discontinuous. This interface roughness-dominated spin scattering mechanism based on the YIG/NiO/Pt heterostructure is a new discovery, and there is significant potential for exploiting this mechanism in the construction of low-dissipation spintronic devices with an efficient spin current injection.

Interfacial modification of titanium dioxide to enhance photocatalytic efficiency towards H2 production.

Strong demand for affordable clean energy to support applications ranging from conventional energy supply to space propulsion places spotlight on advanced energy generation using photovoltaic and wind power. Yet, the intermittent nature of solar and wind sources drives the search for energy storage solutions that would permit the needed level of resilience and support further growth in the use of renewable sources of power. Hydrogen generation using sunlight is a promising pathway to decouple demand from supply. Herein, we show how exposure to reactive Ar-H2, Ar-H2-N2, and Ar-O2 plasma environments can notably enhance surface properties of photocatalytic TiO2 nanosheets used in advanced energy generation systems. Treatment using Ar-H2 plasmas produced highly hydrogenated, surface-disordered TiO2 nanosheets with oxygen vacancies, whereas exposure to Ar-H2-N2 plasmas resulted in N doping. Surprisingly, Ar-O2 plasma treatment did not change surface properties of TiO2. Optical emission spectroscopy was used to monitor transient species to further understand surface modification in plasma. Direct measurements demonstrated that among thus-produced samples, hydrogenated TiO2 nanosheets exhibit the highest photocatalytic H2-generation activity under visible-light irradiation, which is also greater than the activity of pure, untreated nanosheets. The mechanism of enhancing the visible-light photocatalytic H2-generation activity on hydrogenated TiO2 nanosheets is also proposed. The level of surface disorder and oxygen vacancies plays an important role in enhancing visible-light absorption and reducing the recombination of photogenerated electrons and holes.

Constructing functionalized plasmonic gold/titanium dioxide nanosheets with small gold nanoparticles for efficient photocatalytic hydrogen evolution.

Small plasmonic Au nanoparticles (NPs)-decorated with TiO2 nanosheets were fabricated to improve the photocatalytic performance. The Au/TiO2 nanosheets with Au NPs of different sizes ranging from ∼3 nm to 28 nm were prepared by using hydrothermally obtained TiO2 nanosheets as substrate via urea and light reduction method. During synthesis, the obtained Au NPs through urea reduction treatment in different calcination temperatures possessed smaller size (∼3-13 nm) than those of the light reduction method (∼28 nm). The introduced Au NPs were tightly loaded on the surface of TiO2 nanosheets through in situ growth reduction process of chloroauric acid. The emergence of smaller Au NPs promoted the photocatalytic performance over Au/TiO2 nanosheets. The as-prepared Au/TiO2 nanosheets with small Au NP sizes of ∼3-5 nm showed the highest photocatalytic rate of hydrogen production (∼230 µmol·h-1) under xenon lamp illumination, exceeding more than twice that of Au/TiO2 nanosheets with loading of larger Au NPs (∼28 nm). The favorable constituents and combination of Au/TiO2 nanosheets provided large surface adsorptive sites for reactant adsorption, introduced plasmonic effects and formed Schottky barrier junction via surface plasmon resonance. The Schottky barrier height was lower due to the presence of smaller Au NPs, thereby enhancing the charge separation through the Schottky transfer hub to neighboring TiO2 nanosheets. The synergistic effect between the plasmonic hot carrier-driven Au NPs and TiO2 nanosheets was discussed. The photocatalytic mechanism was also proposed for the fabrication of visible light-restricted photocatalysts with smaller Au NPs.

Two-Dimensional Transition Metal MXene-Based Photocatalysts for Solar Fuel Generation.

The exploration of advanced and novel photocatalytic materials has been widely investigated in recent years. MXene, a new two-dimensional (2D) transition metal material, is gaining attention as a suitable alternative for promoting photocatalytic performance because of its flexible adjustability of elemental composition, regular layered structure, and excellent electrical conductivity. This Perspective summarizes the recent significant advancements in 2D MXene-based photocatalysts for solar fuel conversion. The rational design and specific effects of MXene-based photocatalysts for photocatalytic solar fuel generation are described. Moreover, the different roles of MXene in MXene-based photocatalysts, such as functional group provider, photocatalytic electronic acceptor, substrate, and cocatalyst, for improving photocatalytic performance are discussed. Further discussion about the challenges and optimizations for improvements of 2D MXene and MXene-based photocatalysts in the context of promising solar fuel generation is also presented.

High-Performance All-Optical Terahertz Modulator Based on Graphene/TiO2/Si Trilayer Heterojunctions.

In this paper, we demonstrate a trilayer hybrid terahertz (THz) modulator made by combining a p-type silicon (p-Si) substrate, TiO2 interlayer, and single-layer graphene. The interface between Si and TiO2 introduced a built-in electric field, which drove the photoelectrons from Si to TiO2, and then the electrons injected into the graphene layer, causing the Fermi level of graphene to shift into a higher conduction band. The conductivity of graphene would increase, resulting in the decrease of transmitted terahertz wave. And the terahertz transmission modulation was realized. We observed a broadband modulation of the terahertz transmission in the frequency range from 0.3 to 1.7 THz and a large modulation depth of 88% with proper optical excitation. The results show that the graphene/TiO2/p-Si hybrid nanostructures exhibit great potential for terahertz broadband applications, such as terahertz imaging and communication.

Reconfigurable nanoscale spin-wave directional coupler using spin-orbit torque.

We present a reconfigurable nanoscale spin-wave directional coupler based on spin-orbit torque (SOT). By micromagnetic simulations, it is demonstrated that the functionality and operating frequency of proposed device can be dynamically switched by inverting the whole or part of the relative magnetic configuration of the dipolar-coupled waveguides using SOT. Utilizing the effect of sudden change in coupling length, the functionality of power divider can be realized. The proposed reconfigurable spin-wave directional coupler opens a way for two-dimensional planar magnonic integrated circuits.