Colossal Orbital Current Induced by Gradient Oxidation for High-Efficiency Magnetization Switching.

Orbital angular momentum flow can be used to develop a low-dissipation electronic information device by manipulating the orbital current. However, efficiently generating and fully harnessing orbital currents is a formidable challenge. In this study, an approach is presented that induces a colossal orbital current by gradient oxidation in Pt/Ta to enhance spin-orbit torque (SOT) and achieve high-efficiency magnetization switching. The maximum efficiency of the SOT before and after the gradient oxidation of Ta is improved relative to that of Pt by ≈600 and 1200%, respectively. The large SOT originates from the colossal orbital current because of the orbital Rashba-Edelstein effect induced by the gradient oxidation of Ta. In addition, a large spin-to-charge conversion efficiency is observed in yttrium iron garnet/Pt/TaOx because of the inverse orbital Rashba-Edelstein effect. Harnessing the orbital current can help effectively minimize the critical current density of the current-induced magnetization switching to 2.26-1.08 × 106 A cm-2, marking a 12-fold reduction compared to that using Pt. This findings provide a new path for research on low-dissipation spin-orbit devices and improve the tunability of orbital current generation.

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.

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.

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.

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.

Magnetite/Iron Foil as an Effective and Nonfiltration Catalyst for Heterogeneous Fenton-like Reactions under Neutral Conditions.

A magnetite/iron foil (MIF) composite was synthesized as a heterogeneous Fenton-like catalyst. The MIF catalyst effectively degraded Rhodamine B under neutral conditions (degradation efficiency = 86%), avoiding the procedure of pH adjustment. The MIF catalyst could be conveniently recycled without filtration, and the advantages of the stability and reusability of a MIF catalyst made it promising in practical wastewater treatment.

Semiconductor terahertz modulator arrays: the size and edge effect.

A terahertz spatial modulator is the critical component for active terahertz imaging using compressive sensing. Here small silicon pieces were put in arrays on flexible polymer substrate to fabricate semiconductor terahertz spatial modulators. By doing this, the inter-diffusion of photo-generated charge carriers is prevented for better resolution, and flexibility is achieved. Since the size of silicon is comparable to the wavelength of the terahertz wave, and the dielectric properties of the gap are very different from silicon, the optical modulation of each element is very different from the large silicon. In this Letter, the terahertz wave interaction and optical modulation of the small silicon are systematically studied by time domain spectroscopy. Notably, a strong resonance-like absorption peak was observed in a transmittance spectrum for the small silicon due to the size and edge effect. The spatial modulation of the terahertz wave was also compared between the silicon array and the large silicon samples.

Fabrication of Heterostructured Metal Oxide/TiO2 Nanotube Arrays Prepared via Thermal Decomposition and Crystallization.

Heterostructured TiO2 materials are of great importance in electronic and photochemical related applications. We report herein a simple, low-cost, and scalable fabrication of metal oxides heterostructured TiO2 nanotube arrays (NTAs) through a combined strategy of thermal decomposition and crystallization. Various M xO y/TiO2 heterostructured films (M = Zn, Ce, Cu, Cr...) were obtained by using TiO2 NTAs as "nano-containers" as well as "nano-reactors", while using M(CH3COO) x solutions as the precursors. SEM, XRD, EDS results demonstrated that Cu2O/TiO2 NTAs, ZnO/TiO2 NTAs, Cr2O3/TiO2 NTAs, and CeO2/TiO2 NTAs were successfully fabricated. Photocatalytic results revealed that the heterostructured M xO y/TiO2 films could either enhance the UV photocatalytic activities or enable the visible light photocatalytic activities of the TiO2 NTAs. This study provides a facile general approach to prepare M xO y/TiO2 NTAs films, which could be very useful for environmental and energy areas.

Synthesis of Highly Uniform and Compact Lithium Zinc Ferrite Ceramics via an Efficient Low Temperature Approach.

LiZn ferrite ceramics with high saturation magnetization (4πMs) and low ferromagnetic resonance line widths (ΔH) represent a very critical class of material for microwave ferrite devices. Many existing approaches emphasize promotion of the grain growth (average size is 10-50 µm) of ferrite ceramics to improve the gyromagnetic properties at relatively low sintering temperatures. This paper describes a new strategy for obtaining uniform and compact LiZn ferrite ceramics (average grains size is ∼2 µm) with enhanced magnetic performance by suppressing grain growth in great detail. The LiZn ferrites with a formula of Li0.415Zn0.27Mn0.06Ti0.1Fe2.155O4 were prepared by solid reaction routes with two new sintering strategies. Interestingly, results show that uniform, compact, and pure spinel ferrite ceramics were synthesized at a low temperature (∼850 °C) without obvious grain growth. We also find that a fast second sintering treatment (FSST) can further improve their gyromagnetic properties, such as higher 4πMs and lower ΔH. The two new strategies are facile and efficient for densification of LiZn ferrite ceramics via suppressing grain growth at low temperatures. The sintering strategy reported in this study also provides a referential experience for other ceramics, such as soft magnetism ferrite ceramics or dielectric ceramics.

High-speed and broadband terahertz wave modulators based on large-area graphene field-effect transistors.

We present a broadband terahertz wave modulator with improved modulation depth and switch speed by cautiously selecting the gate dielectric materials in a large-area graphene-based field-effect transistor (GFET). An ultrathin Al2O3 film (∼60 nm) is deposited by an atomic-layer-deposition technique as a high-k gate dielectric layer, which reduces the Coulomb impurity scattering and cavity effect, and thus greatly improves the modulation performance. Our modulator has achieved a modulation depth of 22% and modulation speed of 170 kHz in a frequency range from 0.4 to 1.5 THz, which is a large improvement in comparison to its predecessor of SiO2-based GFET.

Asymmetric Manipulation of Perpendicular Exchange Bias and Programmable Spin Logical Cells by Spin-Orbit Torque in a Ferromagnet/Antiferromagnet System.

Antiferromagnets are competitive candidates for the next generation of spintronic devices owing to their superiority in small-scale and low-power-consumption devices. The electrical manipulation of the magnetization and exchange bias (EB) driven by spin-orbit torque (SOT) in ferromagnetic (FM)/antiferromagnetic (AFM) systems has become focused in spintronics. Here, the realization of a large perpendicular EB field in Co/IrMn and the effective manipulation of the magnetic moments of the magnetic Co layer and EB field by SOT in Pt/Co/IrMn system is reported. During the SOT-driven switching process, an asymmetrically manipulated state is observed. Current pulses with the same amplitude but opposite directions induce different magnetization states. Magneto-optical Kerr measurements reveal that this is due to the coexistence of stable and metastable antiferromagnetic domains in the AFM. Exploiting the asymmetric properties of these FM/AFM structures, five spin logic gates, namely AND, OR, NOR, NAND, and NOT, are realized in a single cell via SOT. This study provides an insight into the special ability of SOT on AFMs and also paves an avenue to construct the logic-in-memory and neuromorphic computing cells based on the AFM spintronic system.

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.

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.

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.

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.

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.