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As a paradigmatic phenomenon in condensed matter physics, the quantum anomalous Hall effect (QAHE) in stoichiometric Chern insulators has drawn great interest for years. Using model Hamiltonian analysis and first-principles calculations, we establish a topological phase diagram and map different 2D configurations to it, which are taken from the recently grown magnetic topological insulators MnBi_{4}Te_{7} and MnBi_{6}Te_{10} with superlatticelike stacking patterns. These configurations manifest various topological phases, including the quantum spin Hall effect with and without time-reversal symmetry and QAHE. We then provide design principles to trigger the QAHE by tuning experimentally accessible knobs, such as the slab thickness and magnetization. Our work reveals that superlatticelike magnetic topological insulators with tunable exchange interactions are an ideal platform to realize the long-sought QAHE in pristine compounds, paving a new path within the area of topological materials.
RESUMO
Magnetic topological materials have drawn markedly attention recently due to the strong coupling of their novel topological properties and magnetic configurations. In particular, the MnBi2Te4/(Bi2Te3)n family highlights the researches of multiple magnetic topological materials. Via first-principles calculations, we predict that Mn(Bi, Sb)4Se7, the close relatives of MnBi2Te4/(Bi2Te3)n family, are topological nontrivival in both antiferromagnetic and ferromagnetic configurations. In the antiferromagnetic ground state, Mn(Bi, Sb)4Se7 are simultaneously topological insulators and axion insulators. Massless Dirac surface states emerge on the surfaces parallel to the z axis. In ferromagnetic phases, they are axion insulators. Particularly, when the magnetization direction is along the x axis, they are also topological crystalline insulators. Mirror-symmetry-protected gapless surface states exist on the mirror-invariant surfaces. Hence, the behaviors of surface states are strongly dependent on the magnetization directions and surface orientations. Our work provides more opportunities for the study of magnetic topological physics.
RESUMO
In order to cut down the usage amount of binder, mix it more evenly with the biomass raw materials and improve the quality of pellets in the densification process, this study explored the feasibility of promoting the densification of biomass by using a high-pressure spraying method to add liquid binder. In the study, a high-pressure sprayer was used to spray saturated brown sugar water into sawdust for densification tests. A three-factor orthogonal experiment was designed to analyze the physical characteristics of the pellets under different variables. Through analysis of range and multiple linear regression, the effect curve was drawn to analyze the impact of the high-pressure spraying method on densification. The results showed that under low compaction pressure of 14.9 MPa, the raw materials with adding 6% saturated brown sugar water can be densified into pellets, while the raw materials without binder cannot. Moreover, compared with the method of adding binder by stirring, the high-pressure spraying method obtained the pellets with fewer cracks on the surface and increased the relaxation density of pellets by 8.65%. Under high compaction pressure (75, 100, 124 and 149 MPa), the high-pressure spraying method has a significant effect on increasing the relaxation density, not only on the compressive strength.
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The binder can improve the physical characteristics of biomass pellets by forming solid bridges and increasing the adhesion of biomass materials. Taking pine sawdust as raw material and brown sugar water with different concentration as a binder, this study adopted spraying and stirring methods, respectively, and mixed brown sugar water with biomass in diverse proportions. The characteristic of pellets such as durability, relaxation ratio and compressive strength were studied by orthogonal design. Through range analysis, BP (Back Propagation) neural network factor significance analysis and mapping the relationship between physical properties and factors according to the importance of each factor, the effect of densification variables on the physical characteristics of biomass pellets was studied, and the outcome of adding brown sugar water binder to raw material by spraying method in improving the densification quality of biomass was explored. Results showed the brown sugar water binder added to pine sawdust by spraying method could mix the binder and biomass raw material more evenly compared with the stirring method. The relaxation ratio of pellets obtained by spraying method was reduced by 13.47%. The optimal densification conditions of pine sawdust were when the compaction pressure was 100 MPa, the mass ratio of brown sugar to water was 2:1, the proportion of brown sugar water to biomass material was 3%, and the adding method was spraying.
RESUMO
With no requirements for lattice matching, van der Waals (vdW) ferromagnetic materials are rapidly establishing themselves as effective building blocks for next-generation spintronic devices. We report a hitherto rarely seen antisymmetric magnetoresistance (MR) effect in vdW heterostructured Fe3GeTe2 (FGT)/graphite/FGT devices. Unlike conventional giant MR (GMR), which is characterized by two resistance states, the MR in these vdW heterostructures features distinct high-, intermediate-, and low-resistance states. This unique characteristic is suggestive of underlying physical mechanisms that differ from those observed before. After theoretical calculations, the three-resistance behavior was attributed to a spin momentum locking induced spin-polarized current at the graphite/FGT interface. Our work reveals that ferromagnetic heterostructures assembled from vdW materials can exhibit substantially different properties to those exhibited by similar heterostructures grown in vacuum. Hence, it highlights the potential for new physics and new spintronic applications to be discovered using vdW heterostructures.