Two-dimensional (2D) van der Waals (vdW) magnetic materials have recently been introduced as a new horizon in materials science, and they enable potential applications for next-generation spintronic ...devices. Here, in this communication, the observations of stable Bloch-type magnetic skyrmions in single crystals of 2D vdW Fe3GeTe2 (FGT) are reported by using in situ Lorentz transmission electron microscopy (TEM). We find the ground-state magnetic stripe domains in FGT transform into skyrmion bubbles when an external magnetic field is applied perpendicularly to the (001) thin plate with temperatures below the Curie temperature T C. Most interestingly, a hexagonal lattice of skyrmion bubbles is obtained via field-cooling manipulation with magnetic field applied along the 001 direction. Owing to their topological stability, the skyrmion bubble lattices are stable to large field-cooling tilted angles and further reproduced by utilizing the micromagnetic simulations. These observations directly demonstrate that the 2D vdW FGT possesses a rich variety of topological spin textures, being of great promise for future applications in the field of spintronics.
Upon environmental weathering, plastic materials form smaller sized microplastics, of which the contamination in agricultural fields is of significant importance and increasing social concern. ...Plastic mulch films are considered a major source of agricultural soil microplastic pollution. However, the mechanism and kinetics of microplastic formation from plastic mulch films were rarely understood. In this study, the rate of microplastic generation from typical mulch films, such as oxodegradable, biodegradable, and conventional non-degradable (polyethylene, PE) mulch films, were quantified in soil under simulated UV irradiation. Results showed that microplastic formation was more rapid from biodegradable mulch film, followed sequentially by oxodegradable mulch film, white PE mulch film, and black PE mulch film. The kinetics of microplastic generation strictly followed the Schwarzchild's law, with exponential growth at indexes between 1.6309 and 2.0502 in the microplastic generation model. At a cumulative UV irradiation of 2.1 MJ/m2, the average quantity of microplastics released from biodegradable, oxodegradable, and white and black non-degradable mulch films were 475, 266, 163, 147 particles/cm2, respectively; with particle sizes largely distributed within 0.02–0.10 mm range. Concurrent increase in crystallinity and surface erosion of the mulch films were observed upon UV irradiation, which further determined the accessibility and activity of the materials to photo-oxidation (reflected as HI indexes), therefore played a critical role on the quantity and size ranges of microplastic debris.
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•Kinetics of microplastic generation from mulch films were studied upon UV irradiation.•Biodegradable films were most rapid in microplastic formation, followed by oxo-film and PE film.•Kinetics of microplastic generation strictly followed the Schwarzchild's law.•Crystallinity and chemical composition are critical for the size and quantity of microplastics.•At cumulative UV exposure of 2.1 MJ/m2, 147–475 microparticles/cm2 could be released.
A field experiment was conducted to investigate the effect of long-term (30-year) fertilizer and organic manure treatments on grain yield, soil chemical properties and some microbiological properties ...of arable soils in Pingliang, Gansu, China. Six treatments were chosen for this work: unfertilized control (CK), nitrogen fertilizer annually (N), nitrogen and phosphorus (P) fertilizers annually (NP), straw plus N added annually and P fertilizer added every second year (NP
+
S), farmyard manure added annually (FYM), and farmyard manure plus N and P fertilizers added annually (NP
+
FYM). Mean winter wheat yields for the 20
years ranged from 1.60
Mg
ha
−
1
for the CK treatment to 4.62
Mg
ha
−
1
for the NP+FYM treatment. Maize yields for the 8
years averaged 3.40 and 7.66
Mg
ha
−
1
in the same treatments. The results showed that there was no interaction between farmyard manure and NP fertilizers. Compared with the CK treatment, the average soil organic carbon (SOC) and total nitrogen (TN) content were 2.0 and 3.1%, 1.9 and 13.3%, 32.7 and 24.5%, 23.0 and 19.4%, and 39.9 and 27.6% larger, respectively, for N, NP, FYM, NP
+
S and NP
+
FYM. The N only resulted in not only lowering of pH but also deficient of both P and K in the soil. Soil available K declined rapidly without straw or manure additions. The microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) contents increased with the application of nitrogen and phosphorus inorganic fertilizers. However, there was greater increase of these parameters when organic manure was applied along with inorganic fertilizers. Organic manure application also increased soil dehydrogenase, alkaline phosphatases, β-glucosidasen and urease activity significantly. The results indicated that long-term additions of organic manure have the most beneficial effects on grain yield and soil quality among the investigated types of fertilization.
Magnetic Weyl semimetalsWeyl semimetals (WSMs)—materials that host exotic quasiparticles called Weyl fermions—must break either spatial inversion or time-reversal symmetry. A number of WSMs that ...break inversion symmetry have been identified, but showing unambiguously that a material is a time-reversal-breaking WSM is tricky. Three groups now provide spectroscopic evidence for this latter state in magnetic materials (see the Perspective by da Silva Neto). Belopolski et al. probed the material Co2MnGa using angle-resolved photoemission spectroscopy, revealing exotic drumhead surface states. Using the same technique, Liu et al. studied the material Co3Sn2S2, which was complemented by the scanning tunneling spectroscopy measurements of Morali et al. These magnetic WSM states provide an ideal setting for exotic transport effects.Science, this issue p. 1278, p. 1282, p. 1286; see also p. 1248Bulk–surface correspondence in Weyl semimetals ensures the formation of topological “Fermi arc” surface bands whose existence is guaranteed by bulk Weyl nodes. By investigating three distinct surface terminations of the ferromagnetic semimetal Co3Sn2S2, we verify spectroscopically its classification as a time-reversal symmetry-broken Weyl semimetal. We show that the distinct surface potentials imposed by three different terminations modify the Fermi-arc contour and Weyl node connectivity. On the tin (Sn) surface, we identify intra–Brillouin zone Weyl node connectivity of Fermi arcs, whereas on cobalt (Co) termination, the connectivity is across adjacent Brillouin zones. On the sulfur (S) surface, Fermi arcs overlap with nontopological bulk and surface states. We thus resolve both topologically protected and nonprotected electronic properties of a Weyl semimetal.
Magnetic Weyl semimetals with broken time-reversal symmetry are expected to generate strong intrinsic anomalous Hall effects, due to their large Berry curvature. Here, we report a magnetic Weyl ...semimetal candidate, Co
Sn
S
, with a quasi-two-dimensional crystal structure consisting of stacked Kagomé lattices. This lattice provides an excellent platform for hosting exotic topological quantum states. We observe a negative magnetoresistance that is consistent with the chiral anomaly expected from the presence of Weyl nodes close to the Fermi level. The anomalous Hall conductivity is robust against both increased temperature and charge conductivity, which corroborates the intrinsic Berry-curvature mechanism in momentum space. Owing to the low carrier density in this material and the significantly enhanced Berry curvature from its band structure, the anomalous Hall conductivity and the anomalous Hall angle simultaneously reach 1130 Ω
cm
and 20%, respectively, an order of magnitude larger than typical magnetic systems. Combining the Kagomé-lattice structure and the out-of-plane ferromagnetic order of Co
Sn
S
, we expect that this material is an excellent candidate for observation of the quantum anomalous Hall state in the two-dimensional limit.
Abstract
The interplay between electronic correlations and topological protection may offer a rich avenue for discovering emergent quantum phenomena in condensed matter. However, electronic ...correlations have so far been little investigated in Weyl semimetals (WSMs) by experiments. Here, we report a combined optical spectroscopy and theoretical calculation study on the strength and effect of electronic correlations in a magnet Co
3
Sn
2
S
2
. The electronic kinetic energy estimated from our optical data is about half of that obtained from single-particle ab initio calculations in the ferromagnetic ground state, which indicates intermediate-strength electronic correlations in this system. Furthermore, comparing the energy and side-slope ratios between the interband-transition peaks at high energies in the experimental and single-particle-calculation-derived optical conductivity spectra with the bandwidth-renormalization factors obtained by many-body calculations enables us to estimate the Coulomb-interaction strength (
U
∼ 4 eV) in Co
3
Sn
2
S
2
. Besides, a sharp experimental optical conductivity peak at low energy, which is absent in the single-particle-calculation-derived spectrum but is consistent with the optical conductivity peaks obtained by many-body calculations with
U
∼ 4 eV, indicates that an electronic band connecting the two Weyl cones is flattened by electronic correlations and emerges near the Fermi energy in Co
3
Sn
2
S
2
. Our work paves the way for exploring flat-band-generated quantum phenomena in WSMs.
Abstract
The physical realization of Chern insulators is of fundamental and practical interest, as they are predicted to host the quantum anomalous Hall (QAH) effect and topologically protected ...chiral edge states which can carry dissipationless current. Current realizations of the QAH state often require complex heterostructures and sub-Kelvin temperatures, making the discovery of intrinsic, high temperature QAH systems of significant interest. In this work we show that time-reversal symmetry breaking Weyl semimetals, being essentially stacks of Chern insulators with inter-layer coupling, may provide a new platform for the higher temperature realization of robust chiral edge states. We present combined scanning tunneling spectroscopy and theoretical investigations of the magnetic Weyl semimetal, Co
3
Sn
2
S
2
. Using modeling and numerical simulations we find that depending on the strength of the interlayer coupling, chiral edge states can be localized on partially exposed kagome planes on the surfaces of a Weyl semimetal. Correspondingly, our d
I
/d
V
maps on the kagome Co
3
Sn terraces show topological states confined to the edges which display linear dispersion. This work provides a new paradigm for realizing chiral edge modes and provides a pathway for the realization of higher temperature QAH effect in magnetic Weyl systems in the two-dimensional limit.
The influence of different tillage practices on soil organic carbon levels is more significant under long-term tillage compared to short-term tillage. Despite the great interest in the effect of ...no-tillage (NT) management practice on carbon sequestration, the long-term effect of NT practice on soil organic carbon and its fractions in northern China remain unclear. We evaluated the long-term effects (after 17years) of NT and conventional tillage (CT) practices on soil organic carbon and its fractions at different depths ranging from 0 to 60cm using a cinnamon soil in Shanxi, China. A randomised block design with three replications was used to evaluate both the tillage and its effects on the yield performance of winter wheat (Triticum aestivum L.). After 17years, the soil organic carbon (SOC) concentration in the NT soil was greater than that of the CT soil, but only in the layer that was located between 0 and 10cm. There was a significant accumulation of SOC (0–60cm) in the NT soil (50.2MgCha−1) compared to that observed in the CT soil (46.3MgCha−1). The particulate organic matter C (POM-C), dissolved organic C (DOC), and microbial biomass C (MBC) levels in the 0–5cm layer under NT treatment were 155%, 232%, and 63% greater, respectively, compared to the CT treatment. The POM-C, DOC, and MBC in the 5–10cm layer under NT treatment were 67%, 123%, and 63% greater, respectively, compared to the CT treatment. Below 10cm, the labile carbon observed in the NT treatment did not differ from that of the CT treatment. Significantly positive correlations were observed between the SOC and the labile organic C fractions. Moreover, the winter wheat (T. aestivum L.) yield increased 28.9% in the NT treatment compared to the CT treatment. The data show that NT is an effective and sustainable management practice that improves carbon sequestration and increases soil fertility, resulting in higher winter wheat yields in the rainfed dryland farming areas of northern China.
•No-tillage (NT) has a great role on carbon sequestration in northern China.•NT increased SOC, POM-C, MBC and DOC in the upper layers than CT.•The labile C fractions were highly correlated with the SOC.•The yield from the winter wheat showed 29% higher in NT practice.
Nitrogen (N) is a major fertiliser for agriculture and food production. About 67.84 million tons of N are annually applied to agricultural fields, without which nearly half of the world’s population ...would not be alive today. Returning plant residues to the soil is an alternative and sustainable way of N fertilisation. Although impacts of returning plant residues on plant available N in soil have been widely studied, there is still no systematic review of their mechanisms and models. In this review we highlight the following advances: (1) When plant residues are returned to the soil, N undergoes biotic immobilisation–remineralisation, abiotic immobilisation, soil organic N mineralisation and plant residue organic N mineralisation. (2) Plant residues modify inorganic N fate using three mechanism mineralisation, immobilisation–mineralisation and immobilisation, depending on plant residue nature and soil properties. (3) The use of plant residue C/N ratio is not always effective to predict the effect of plant residues. Instead, soil properties and the forms of carbon and nitrogen should be considered. (4) Mineralisation always promotes N uptake by crops and increases the risk of N loss. In addition, although net immobilisation is involved in immobilisation–mineralisation and immobilisation, it does not necessarily induce lower crop nitrogen uptake. Results also depend on the synchronism between the changing soil inorganic N and the crop N uptake. (5) N loss during mineralisation can be reduced by an immobiliser. Net N immobilisation during immobilisation–mineralisation and immobilisation can be reduced by changing the timing of ploughing and fertilising or by changing the plant residues placement.
The discovery of magnetic topological semimetals has recently attracted significant attention in the field of topology and thermoelectrics. In a thermoelectric device based on the Nernst geometry, an ...external magnet is required as an integral part. Reported is a zero‐field Nernst effect in a newly discovered hard‐ferromagnetic kagome‐lattice Weyl‐semimetal Co3Sn2S2. A maximum Nernst thermopower of ≈3 µV K−1 at 80 K in zero field is achieved in this magnetic Weyl‐semimetal. The results demonstrate the possibility of application of topological hard magnetic semimetals for low‐power thermoelectric devices based on the Nernst effect and are thus valuable for the comprehensive understanding of transport properties in this class of materials.
A zero‐field Nernst effect in the ferromagnetic Weyl‐semimetal Co3Sn2S2 is reported. A maximum Nernst thermopower of ≈3 µV K−1 at 80 K in zero field is achieved. This study shows the potential of the search for new hard magnets from the library of topological materials for the generation of larger and potentially useful levels of Nernst thermopower.
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