Abstract ：

Insights into wave propagation in prestressed porous rocks have great interest in geophysical applications, such as remote monitoring in situ stresses. Wave-induced small dynamic fields superposed onto statically deformed objects can be addressed traditionally by acoustoporoelastic theory that extends the classical acoustoelasticity of solids to porous media by incorporating Biot's theory. Stress-induced deformations in porous rocks are of a progressively scaling feature with increasing prestress, undergoing linear elastic, hyperelastic (nonlinearly elastic), and inelastic deformations prior to mechanical failure. Conventional acoustoporoelastic theory is based on the Taylor expansion for the cubic strain-energy function with linear strains under finite-magnitude prestress. The theory with third-order elastic constants (3oeCs) only accounts for stress-induced hyperelasticity, insufficient to handle inelastic deformations with nonlinear strains of compliant microstructures. We replace the Taylor expansion with the Pade approximation to the strain energy function, leading to Pade acoustoporoelastic equations for inelastic deformations under large-magnitude prestress. Theoretical results from plane-wave analyses agree well with the laboratory measurements of fluid-saturated Portland sandstones under confining and uniaxial prestresses. Finite-difference simulations are implemented to solve the first-order velocity-stress formulation of Pade acoustoporoelastic equations for elastic wave propagation in prestressed porous media under isotropic (confining) and anisotropic (uniaxial and pure shear) prestresses. The resulting wavefield snapshots show the propagation of fast-P and slow-P and slow-S waves in acoustoporoelastic media, illustrating stress-induced velocity orthotropies, strongly related to the direction of prestress. Comparisons with conventional acoustoporoelastic simulations provide a framework to estimate stress-induced inelastic strains from seismic responses in velocity and anisotropy.

Keyword ：

prestressed porous media Acoustoporoelasticity Pade approximation elastic waves

Cite：

Copy from the list or Export to your reference management。

Abstract ：

A multiscale method is presented to develop a constitutive model for anisotropic soils in a three-dimensional (3D) stress state. A fabric tensor and its evolution, which quantify the particle arrangement at the microscale, are adopted to describe the effects of the inherent and induced anisotropy on the mechanical behaviors at the macroscale. Using two steps of stress mapping, the deformation and failure of anisotropic soil under the 3D stress state are equivalent to those of isotropic soil under the triaxial compression stress state. A series of discrete element method (DEM) simulations are conducted to preliminarily verify this equivalence. Based on the above method, the obtained anisotropic yield surface is continuous and smooth. Then, a fabric evolution law is established according to the DEM simulation results. Compared with the rotational hardening law, the fabric evolution law can also make the yield surface rotate during the loading process, and it can grasp the microscopic mechanism of soil deformation. As an example, an anisotropic modified Cam-clay model is developed, and its performance validates the ability of the proposed method to account for the effect of soil anisotropy.

Keyword ：

soil fabric tensor modified stress anisotropy constitutive model

Cite：

Copy from the list or Export to your reference management。

Abstract ：

为了解决软击穿导致的压控磁各向异性磁隧道结(voltage-controlled magnetic anisotropy magnetic tunnel junction,VCMA-MTJ)及其读电路性能下降的问题,在对VCMA-MTJ软击穿机理深入分析的基础上,修正了VCMA-MTJ的电学模型,设计了一种具有固定参考电阻的VCMA-MTJ读电路和一种具有参考电阻调控单元的VCMA-MTJ读电路,研究了软击穿对VCMA-MTJ电阻Rt、隧穿磁阻比率M、软击穿时间Ts以及VCMA-MTJ读电路读错误率的影响.结果表明:软击穿的出现会导致Rt和M均随应力时间t的增加而降低,Ts随氧化层厚度tox的增大而缓慢增加,却随脉冲电压Vb的增大而迅速减少,与反平行态相比,平行态的Ts更短且M降低50％所需时间更少;具有固定参考电阻的VCMA-MTJ读电路可有效避免读"0"错误率的产生,但读"1"错误率却随t的增加而上升,而具有参考电阻调控单元的VCMA-MTJ读电路可在保持读"0"正确率的同时,对读"1"错误率改善达54％,在一定程度上削弱了软击穿对VCMA-MTJ读电路的影响.

Keyword ：

压控磁各向异性 参考电阻调控单元 读电路 磁隧道结 应力时间 软击穿

Cite：

Copy from the list or Export to your reference management。

Abstract ：

Two-dimensional (2D) layered materials have been studied in depth during the past two decades due to their unique structure and properties. Transition metal (TM) intercalation of layered materials have been proven as an effective way to introduce new physical properties, such as tunable 2D magnetism, but the direct growth of atomically thin heteroatoms-intercalated layered materials remains untapped. Herein, we directly synthesize various ultrathin heteroatoms-intercalated 2D layered materials (UHI-2DMs) through flux-assisted growth (FAG) approach. Eight UHI-2DMs (V1/3NbS2, Cr1/3NbS2, Mn1/3NbS2, Fe1/3NbS2, Co1/3NbS2, Co1/3NbSe2, Fe1/3TaS2, Fe1/4TaS2) were successfully synthesized. Their thickness can be reduced to the thinnest limit (bilayer 2D material with monolayer intercalated TM), and magnetic ordering can be induced in the synthesized structures. Interestingly, due to the possible anisotropy-stabilized long-range ferromagnetism in Fe1/3TaS2 with weak interlayer coupling, the layer-independent magnetic ordering temperature of Fe1/3TaS2 was revealed by magneto-transport properties. This work establishes a general method for direct synthesis of heteroatom-intercalated ultrathin 2D materials with tunable chemical and physical properties. The intercalation of heteroatoms has been demonstrated to be an effective approach to introduce new physical properties in 2D layered materials (2DMs). Here, the authors report a flux-assisted growth method to synthesize various ultrathin heteroatoms-intercalated 2DMs, showing evidence of anisotropy-stabilized long-range ferromagnetism in Fe1/3TaS2.

Cite：

Copy from the list or Export to your reference management。

Abstract ：

The discovery of room-temperature ferromagnetism in van der Waals (vdW) materials opens new avenues for exploring low-dimensional magnetism and its applications in spintronics. Recently, the observation of the room-temperature topological Hall effect in the vdW ferromagnet Fe3GaTe2 suggests the possible existence of room-temperature skyrmions, yet skyrmions have not been directly observed. In this study, real-space imaging was employed to investigate the domain evolution of the labyrinth and skyrmion structure. First, Neel-type skyrmions can be created at room temperature. In addition, the influence of flake thickness and external magnetic field (during field cooling) on both labyrinth domains and the skyrmion lattice is unveiled. Due to the competition between magnetic anisotropy and dipole interactions, the specimen thickness significantly influences the density of skyrmions. These findings demonstrate that Fe3GaTe2 can host room-temperature skyrmions of various sizes, opening up avenues for further study of magnetic topological textures at room temperature.

Keyword ：

magnetic domain magnetic force microscope van der Waals magnet Fe3GaTe2

Cite：

Copy from the list or Export to your reference management。

Abstract ：

Electrides have attracted significant attention in the fields of physics, materials science, and chemistry due to their distinctive electron properties characterized by weak nuclear binding. In this study, based on first-principles calculations and symmetry analysis, we report that the pure zirconium with alpha-phase (alpha-Zr) is expected to be the electrically neutral electride with topological nodal loop. Furthermore, the nodal loop located at the k(z) = 0 plane exhibits a clear drumhead-like surface state. The energy levels of the topological nodal loop can be regulated by applying uniaxial strain, resulting in the topological nodal loop being closer to the Fermi level. Remarkably, the work function of the electride Zr shows a significant anisotropy along the (001), (100), and (110) directions, particularly with a low work function of 3.14 eV along the (110) surface. Therefore, we predict that alpha-Zr provides a promising platform for future research on topological electrides.

Keyword ：

DFT calculations topological nodal loop inorganic electride work function

Cite：

Copy from the list or Export to your reference management。

Abstract ：

In situ synthesized (Ti, V)C reinforced Ni-based composite coatings were prepared using laser cladding method. The phase composition, microstructure, hardness, and wear resistance of the composite coatings with different carbide contents were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), hardness tester, and wear tester. The evolution process of the melt pool was elucidated. In comparison with the Ni45 laser-clad coating, the microhardness and wear resistance of the Ni-based composite coatings containing (Ti, V)C were significantly enhanced. The best wear resistance and highest average hardness of 835.9 HV of the composite coatings was achieved at a design content of 10 wt.% of (Ti, V)C. Compared to the Ni45 coating, the wear resistance increased from 1.6 to 17.1 min/mg, an improvement of approximately 9.76 times. First-principles calculations were employed to assess the mechanical properties, anisotropy, and electronic properties of the composite ceramic phase (Ti, V)C. Hardness calculations were conducted using a predictive model. The computational results indicated that (Ti, V)C exhibits strong covalent bonding characteristics, with a calculated hardness of 3235 HV exceeding that of TiC and VC.

Keyword ：

wear resistance laser cladding nickel-based composite coating (Ti, V)C reinforced phase first-principles calculations

Cite：

Copy from the list or Export to your reference management。

Abstract ：

The advent of NdFeB bonded magnets with freedom of shape design is effective in achieving motor size and weight reductions. In this paper, the NdFeB bonded magnets were produced through calendaring molding, and the effect of powder shape on degree of alignment (DOA) of NdFeB bonded magnets was investigated. The magnetic measurement results demonstrate that platelet-shaped anisotropic Master Quality Authenticated (MQA) powders exhibit a significantly higher DOA compared to sphere-shaped anisotropic HDDR powders. Microstructural analysis reveals the presence of an oriented structure induced by mechanical stress in MQA bonded magnets, resulting in magnetic anisotropy. This observation is consistent with the difference in X-ray diffraction (XRD) patterns between the cross-section and surface of MQA bonded magnets. Conversely, spherical HDDR particles display minimal orientation and maintain a random distribution, resulting in magnetic isotropy. The XRD pattern of the cross-section of HDDR bonded magnets closely resembles that of its surface. In summary, our findings highlight the superior potential of platelet-shaped anisotropic MQA powders for achieving enhancing magnetic properties during the calendaring molding process, in contrast to sphere-shaped anisotropic HDDR powders. This study provides valuable insights into the determinants of mechanical particle orientation during the fabrication of anisotropic NdFeB bonded magnets, with implications for the development of high-performance bonded magnets.

Cite：

Copy from the list or Export to your reference management。

Abstract ：

The crystal structure, orientation, reduced modulus, and hardness of Al 3 Sc single crystal were studied using X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and nanoindentation techniques, combined with Hertzian elastic theory method (Hertz) and Oliver-Pharr method (O & P). Millimeter-sized Al 3 Sc single crystals were prepared using quasi-equilibrium solidification of hypereutectic Al-15(wt %) Sc alloy. The XRD results showed that the samples were composed of L1 2 -Al 3 Sc and Al phases. The EBSD and nanoindentation results showed that for five Al 3 Sc single crystals with different orientations, the reduced moduli measured by Hertz method were 146.6 +/- 0.4-148.3 +/- 0.2 GPa; while measured by O & P method they were 147 +/- 2-150 +/- 3 GPa. The corresponding hardnesses were varied between 3.8 +/- 0.1 and 3.9 +/- 0.1 GPa. The Poisson's ratio and elastic constants were determined through iterative calculation based on the relationship between the reduced modulus and Young's modulus at various orientations. The polycrystal elastic properties, bulk modulus, shear modulus and Young's modulus, were determined. The elastic constants c11, c12, and c44 were 179.2 +/- 0.4, 44.1 +/- 0.1, and 68.3 +/- 0.3 GPa, respectively; the Poisson's ratio was 0.196 +/- 0.001. The Young's modulus of five Al 3 Sc single crystals oriented in different directions was in the narrow range 161-164 GPa. The anisotropy factor of Al 3 Sc crystal was 1.011 +/- 0.002, confirming that it is elastically isotropic. These results provide fundamental information for the research and development of the Al 3 Sc intermetallic compound and related alloys in future.

Keyword ：

Nanoindentation Hertzian elasticity theory Oliver-Pharr method Mechanical properties Al-3 Sc Single crystal

Cite：

Copy from the list or Export to your reference management。

Abstract ：

Due to their novel optical and optoelectronic properties, 2D materials have received increasing interest for optoelectronics applications. However, when the width of the channel layer decreases to the nanoscale, the properties of 2D materials can be seriously influenced due to the boundary defects and the approximation of physical dimensions and mean free path of the electron. That brings many challenges to developing novel electronics. Hence, researchers began to maintain their focus on 1D semiconductors without boundary defects and surfaces. Herein, fibrous phosphorus, another Quasi-1D layered semiconducting phosphorus allotrope with air-stable low symmetry, is reported. We found the in-plane anisotropic Raman response and excitation and exciton emission at room temperature. Moreover, the raw materials of fibrous phosphorus are nontoxic and abundant on the earth. These excellent properties will make it a highly competitive material for future applications in the optoelectronic area.

Cite：

Copy from the list or Export to your reference management。