General Synthesis of 2D Magnetic Transition Metal Dihalides via Trihalide Reduction.

Two-dimensional (2D) transition metal dihalides (TMDHs) have been receiving extensive attention due to their diversified magnetic properties and promising applications in spintronics. However, controlled growth of 2D TMDHs remains challenging owing to their extreme sensitivity to atmospheric moisture. Herein, using a home-built nitrogen-filled interconnected glovebox system, a universal chemical vapor deposition synthesis route of high-quality 2D TMDH flakes (1T-FeCl2, FeBr2, VCl2, and VBr2) by reduction of their trihalide counterparts is developed. Representatively, ultrathin (∼8.6 nm) FeCl2 flakes are synthesized on SiO2/Si, while on graphene/Cu foil the thickness can be down to monolayer (1L). Reflective magnetic circular dichroism spectroscopy shows an interlayer antiferromagnetic ordering of FeCl2 with a Neel temperature at ∼17 K. Scanning tunneling microscopy and spectroscopy further identify the atomic-scale structures and band features of 1L and bilayer FeCl2 on graphene/Cu foil.

Strain Tunability of Perpendicular Magnetic Anisotropy in van der Waals Ferromagnets VI3.

Layered ferromagnets with strong magnetic anisotropy energy (MAE) have special applications in nanoscale memory elements in electronic circuits. Here, we report a strain tunability of perpendicular magnetic anisotropy in van der Waals (vdW) ferromagnets VI3 using magnetic circular dichroism measurements. For an unstrained flake, the M-H curve shows a rectangular-shaped hysteresis loop with a large coercivity (1.775 T at 10 K) and remanent magnetization. Furthermore, the coercivity can be enhanced to a maximum of 2.6 T under a 3.8% external in-plane tensile strain. Our DFT calculations show that the increased MAE under strain contributes to the enhancement of coercivity. Meanwhile, the strain tunability on the coercivity of CrI3, with a similar crystal structure, is limited. The main reason is the strong spin-orbit coupling in V3+ in VI6 octahedra in comparison with that in Cr3+. The strain tunability of coercivity in VI3 flakes highlights its potential for integration into vdW heterostructures.

Hard ferromagnetic behavior in atomically thin CrSiTe3 flakes.

The research on two-dimensional (2D) van der Waals (vdW) magnets has promoted the development of ultrahigh-density data storage and nanoscale spintronic devices. However, the soft ferromagnetic behavior in most 2D magnets, which means the absence of remanent magnetization, severely limits their applications in realistic devices. Here, we report a layer-controlled ferromagnetic behavior in atomically thin CrSiTe3 flakes, where a transition from the soft to the hard ferromagnetic state occurs as the thickness of samples decreases down to several nanometers. Phenomenally, in contrast to the negligible hysteresis loop in the bulk counterparts, atomically thin CrSiTe3 shows a rectangular loop with finite magnetization and coercivity as the thickness decreases down to ∼8 nm, indicative of a single-domain and out-of-plane ferromagnetic order. We find that the stray field is weakened with decreasing thickness, which suppresses the formation of the domain wall. In addition, thickness-dependent ferromagnetic properties also reveal a crossover from 3 dimensional to 2 dimensional Ising ferromagnets, accompanied by a drop of the Curie temperature from 33 K for bulk to ∼17 K for the 4 nm sample. Our study paves the way towards exploring and learning much more about atomically thin and layered intrinsic ferromagnets.

Structure-property relationships of photofunctional diiridium(II) complexes with tetracationic charge and an unsupported Ir-Ir bond.

In contrast to the extensively studied dirhodium(II) complexes and iridium(III) complexes, neutral or dicationic dinuclear iridium(II) complexes with an unsupported ligand are underdeveloped. Here, a series of tetracationic dinuclear iridium(II) complexes, featuring the unsupported Ir(II)-Ir(II) single bond with long bond distances (2.8942(4)-2.9731(4) Å), are synthesized and structurally characterized. Interestingly, compared to the previous unsupported neutral or dicationic diiridium(II) complexes, our DFT and high-level DLPNO-CCSD(T) results found the largest binding energy in these tetracationic complexes even with the long Ir(II)-Ir(II) bond. Our study further reveals that London dispersion interactions enhance the stability cooperatively and significantly to overcome the strong electrostatic repulsion between two half dicationic metal fragments. This class of complexes also exhibit photoluminescence in solution and solid states, which, to our knowledge, represents the first example of this unsupported dinuclear iridium(II) system. In addition, their photoreactivity involving the generation of iridium(II) radical monomer from homolytic cleavage was also explored. The experimental results of photophysical and photochemical behaviours were also correlated with computational studies.

Pressure-Enhanced Ferromagnetism in Layered CrSiTe3 Flakes.

Despite recent advances in layered ferromagnets, ferromagnetic interactions in these materials are rather weak. Here, we report pressure-enhanced ferromagnetism in layered CrSiTe3 flakes revealed by high-pressure magnetic circular dichroism measurements. Below ∼3 GPa, CrSiTe3 undergoes a paramagnetic-to-ferromagnetic phase transition at ∼32 K, and the field-induced spin-flip in the ferromagnetic phase produces nearly zero hysteresis loops, demonstrating soft ferromagnetism. Above ∼4 GPa, a soft-to-hard ferromagnetic transition occurs, signaled by rectangular-shaped hysteresis loops with finite coercivity and remanent magnetization. Interestingly, as pressure increases, the Curie temperature and coercivity dramatically increase up to ∼138 K and 0.17 T at 7.8 GPa, respectively, in contrast to ∼36 K and 0.02 T at 4.6 GPa. It indicates a remarkable influence of pressure on exchange interactions, which is consistent with DFT calculations. The effective interaction between magnetic couplings and external pressure offers new opportunities in pursuit of high-temperature layered ferromagnets.

Epitaxial growth of large-grain-size ferromagnetic monolayer CrI3 for valley Zeeman splitting enhancement.

Two-dimensional (2D) magnetic CrI3 has received considerable research attention because of its intrinsic features, including insulation, Ising ferromagnetism, and stacking-order-dependent magnetism, as well as potential in spintronic applications. However, the current strategy for the production of ambient-unstable CrI3 thin layer is limited to mechanical exfoliation, which normally suffers from uncontrollable layer thickness, small size, and low yet unpredictable yield. Here, via a confined vapor epitaxy (CVE) method, we demonstrate the mass production of flower-like CrI3 monolayers on mica. Interestingly, we discovered the crucial role of K ions on the mica surface in determining the morphology of monolayer CrI3, reacting with precursors to form a KIx buffer layer. Meanwhile, the transport agent affects the thickness and size of the as-grown CrI3. Moreover, the Curie temperature of CrI3 is greatly affected by the interaction between CrI3 and the substrate. The monolayer CrI3 on mica could act as a magnetic substrate for valley Zeeman splitting enhancement of WSe2. We reckon our work represents a major advancement in the mass production of monolayer 2D CrI3 and anticipate that our growth strategy may be extended to other transition metal halides.

Pressure-Dependent Intermediate Magnetic Phase in Thin Fe3GeTe2 Flakes.

We investigated the evolution of ferromagnetism in layered Fe3GeTe2 flakes under different pressures and temperatures using in situ magnetic circular dichroism (MCD) spectroscopy. We found that the rectangular shape of the hysteresis loop under an out-of-plane magnetic field sweep can be sustained below 7 GPa. Above that pressure, an intermediate state appears in the low-temperature region signaled by an 8-shaped skewed hysteresis loop. Meanwhile, the coercive field and Curie temperature decrease with increasing pressures, implying the decrease of the exchange interaction and the magneto-crystalline anisotropy under pressures. The intermediate phase has a labyrinthine domain structure, which is attributed to the increase of the ratio of exchange interaction to magneto-crystalline anisotropy based on Jagla's theory. Moreover, our calculations reveal a weak structural transition around 6 GPa that corresponds to a significant change in the FeI-FeI bond length, which has strong influences on magnetic interaction. Detailed analysis on exchange interaction and magneto-crystalline anisotropy with pressure shows a consistent trend with experiments.

Ecological and human health risk of sulfonamides in surface water and groundwater of Huixian karst wetland in Guilin, China.

Sulfonamide antibiotics are contaminants of emerging concern (CEC). These CECs raise considerable alarm because they are commonly present in water environments. Studies on the environmental existence of CECs in karst areas of Guilin (Southern China) have yet to be reported. Thus, this study aims to investigate the presence, temporal and spatial distributions of sulfonamides in surface water and groundwater of four major aquatic environments (i.e., aquafarm water, ditch water, wetland water, and groundwater) in the Huixian karst wetland system of Guilin. Furthermore, this study aims to determine the ecological and human health risks of individual sulfonamides and their mixtures. Ten sulfonamides (i.e., sulfadiazine, sulfapyridine, sulfamerazine, trimethoprim, sulfamethazine, sulfamethoxypyridazine, sulfachloropyridazine, sulfamethoxazole, sulfadimethoxine, and sulfaquinoxaline) were observed in the study area. The highest average concentrations of aquafarm water, ditch water, wetland water, and groundwater were those of sulfadiazine (48.24 µg/L), sulfamethoxypyridazine (1281.50 µg/L), sulfamethoxazole (51.14 µg/L), and sulfamethazine (20.06 µg/L), respectively. The potential ecological risks of the detected compounds were much higher in ditch water than in aquafarm water, wetland water, and groundwater. The most ecological risks were observed for sulfachloropyridazine with a risk quotient (RQ) reaching 335.5 to green algae and 152 to Daphnia magna in ditch water. Similarly, sulfachloropyridazine posed the highest ecological risks to green algae among the ten sulfonamides in aquafarm water (RQ = 3.39), wetland water (RQ = 2.98), and groundwater (RQ = 3.6). Human health risk for age groups<12 months was observed from sulfonamide in drinking groundwater. Ecological and human health risks caused by sulfonamide mixtures were larger than the individual risks. Overall, ecological and human health risks caused by sulfonamides were observed in the study area.

The effects of rainfall regimes and terracing on runoff and erosion in the Three Gorges area, China.

Changes in natural rainfall regimes have taken place and are expected to become more pronounced in future decades. These changes are also likely to be accompanied by changes in crop management practices. The main purpose of this study was to analyze runoff and soil loss in relation to rainfall regimes and terracing in the Three Gorges area, China. Based on 10 years of field observation and k-mean clusters, 101 rainfall events were grouped into three rainfall regimes. Rainfall regime I was the group of events with strong rainfall intensity, high frequency, and short duration. Rainfall regime III consisted of events with low intensity, long duration, and high rainfall amount. Rainfall regime II was the aggregation of events of high intensity and amount, and less frequent occurrence. The results showed that event runoff coefficients were not significantly different among rainfall regimes. However, the average soil erosion rates in rainfall regimes I and II were significantly higher than that in regime III. The average erosion rates under rainfall regimes I, II, and III were 21.6, 39.7, and 9.8 g m-2, respectively. The effect of rainfall regime on soil erosion also was changed by terracing. On unterraced cropland, soil erosion rate in rainfall regime I is significantly higher than that in regime III. However, the situation did not exist in unterraced orchard. Terracing significantly reduced runoff and soil erosion, and compensated the effects of rainfall regime on soil erosion, which indicated that runoff and erosion in terraced system may be little influenced by climate change. Based on these results, it was suggested more attention should be paid to the timing of rainfall events in relation to crop development and the high erosion on unterraced citrus orchard to control soil erosion in this area.

Anomalous enhancement of valley polarization in multilayer WS2 at room temperature.

We probe the polarization of the "A" exciton photoluminescence from monolayer and multilayer WS2 at 10 K and 295 K under near-resonant and off-resonant conditions. The monolayer WS2 exhibits relatively low valley polarization, around 24% at 10 K and 8% at 295 K, while all multilayer WS2 samples show very high valley polarization, which is a more or less constant value of around 80% at 10 K under near-resonant excitation. At room temperature, it is observed experimentally that valley polarization in multilayer WS2 monotonously increases with shrinking of the indirect bandgap energy. The phonon-assisted intervalley scattering via the K-Γ-K(K') valleys is identified as the primary valley polarization relaxation channel, which could be gradually suppressed as the thickness increases, leading to a valley polarization of up to 70% in multilayer WS2 (>3 unit layers).

Bound exciton and free exciton states in GaSe thin slab.

The photoluminescence (PL) and absorption experiments have been performed in GaSe slab with incident light polarized perpendicular to c-axis of sample at 10 K. An obvious energy difference of about 34 meV between exciton absorption peak and PL peak (the highest energy peak) is observed. By studying the temperature dependence of PL and absorption spectra, we attribute it to energy difference between free exciton and bound exciton states, where main exciton absorption peak comes from free exciton absorption, and PL peak is attributed to recombination of bound exciton at 10 K. This strong bound exciton effect is stable up to 50 K. Moreover, the temperature dependence of integrated PL intensity and PL lifetime reveals that a non-radiative process, with activation energy extracted as 0.5 meV, dominates PL emission.

[Treatment of ovarian cyst after ovulation-induction with sanjie zhentong capsule].

OBJECTIVE: To observe the efficacy of Sanjie Zhentong Capsule (SJC) in treating ovarian cyst after ovulation-induction. METHODS: Fifty-eight patients with ovarian cyst were randomly assigned to two groups, 33 in the treated group treated with SJC and 25 in the control group treated with temporization for 1 month. Changes of estradiol (E2), luteinizing hormone (LH) and follicle stimulating hormone (FSH) level as well as condition of cyst before and after treatment were observed and compared. And the time for complete disappearance (TCD) of cyst and the pregnant rate within 4 months were followed-up. RESULTS: Effective rate (no fluid cyst sized over 1.0 cm could be found in bilateral ovary and E2 <280 pmol/L) in the treated group was 81.8% (27/33) and 52.0% (13/25) in the control group, showing significant difference between them (P <0.05). Level of E2 decreased in both groups, but the lowering was more significant in the treated group, after 1 month, it being 220.54 +/- 96.23 pmol/L vs 372.56 +/- 330.62 pmol/L (P <0.05). The changes of LH and FSH levels were of no statistical significance (P >0.05). TCD in the treated group was 1.18 +/- 0.46 months, which was shorter than that in the control group (1.96 +/- 1.34 months, P <0.05). The pregnant rate within 4 months in the two groups was 60.6% (20/ 33) and 32.0% (8/25) respectively, showing significant difference (P < 0.05). CONCLUSION: SJC has good efficacy in treating ovarian cyst after ovulation-induction.