Search Results (271)

Current-driven manipulation of magnetic domain walls (DWs) in perpendicularly magnetized nanowires is promising for spintronic memory and logic applications. In this work, micromagnetic simulations are used to investigate the depinning of DMI-stabilized Néel domain walls from a stepped pinning site under unipolar square-pulse current excitation. The effects of current density, pulse frequency, duty cycle, Dzyaloshinskii–Moriya interaction (DMI), and temperature are examined. The results show that pulse frequency and duty cycle strongly influence the oscillatory response of the pinned DW and can promote depinning through efficient coupling with localized DW dynamics. Increasing the current density enhances the oscillation amplitude and facilitates escape from the pinning region, while variations in DMI produce marked changes in pinning stability and magnetic configuration. Thermal fluctuations further modify the depinning behavior, particularly for stronger DMI, where the system evolves from stable pinning to thermally assisted escape and, at higher temperatures, to less stable magnetic states. Overall, the results show that pulse parameters, DMI strength, and temperature jointly control DW depinning and stability, providing further insight into the tuning of current-driven DW transport in geometrically confined spintronic structures. Full article

Magnetic hyperthermia is a promising therapeutic technique in which magnetic nanoparticles (MNPs) generate heat when exposed to a high-frequency alternating magnetic field. The magnetic dipolar interactions between magnetic nanoparticles play an important role in the relaxation dynamics and overall magnetic heating efficiency. In this work, the thermal response of a tumoral tissue was studied considering the dipole–dipole interactions in chain-like nanoparticle assemblies. A 3D space–time model implemented in COMSOL Multiphysics 6.2 is used to investigate the temperature field and thermal damage in tumoral tissue considering magnetic relaxation mechanisms for both (i) parallel and (ii) perpendicular anisotropy configurations with respect to the applied magnetic field. Dipole–dipole interactions significantly modify the effective energy barriers involved in magnetic relaxation mechanisms, when nanoparticles are closely spaced. Interparticle spacing and MNP size are two very important parameters that influence the effective anisotropy barrier and, implicitly, the heating efficiency of magnetic nanoparticles. Moderate dipolar interactions lead to optimal SAR values, while strong interactions reduce heating efficiency due to magnetic locking. This study provides guidelines for the design of magnetic nanoparticles for hyperthermia applications. Full article

The exchange bias (EB) effect is widely used for stabilizing reference magnetic layers in traditional spintronic devices, yet the EB strength strongly depends on the interfacial quality. Van der Waals antiferromagnets provide an ideal physical platform to study the interfacial magnetic properties for device design in the 2D limit. Herein, we construct CrSBr/Fe₃GeTe₂ heterostructures and investigate the interfacial coupling via first-principles calculations. The results reveal that robust EB coupling in the heterostructure breaks the intrinsic in-plane magnetic limitation of CrSBr, inducing a stable tilted magnetic structure with magnetic moments tilting toward the out-of-plane direction. Such EB-driven magnetic reconstruction dramatically boosts the perpendicular magnetic anisotropy energy to ~6.5 meV/Cr and increases the AFM-FM energy difference to 1.97 meV/f.u. from 0.32 meV/f.u., achieving simultaneous enhancement of magnetic anisotropy and thermodynamic stability. The transport simulations of the CrSBr/Fe₃GeTe₂-based magnetic tunnel junction demonstrate that ~65% TMR can be achieved with the use of such an EB-pinned reference layer. This work clarifies the EB modulation mechanism in 2D CrSBr/Fe₃GeTe₂ heterostructures and provides a reliable theoretical basis for the design of high-performance CrSBr-based reference layers in spintronic devices. Full article

Shear-wave time-of-flight (TOF) measurement enables controlled assessment of frequency-dependent wave propagation, but its feasibility in biological tissues remains insufficiently established. This study evaluated whether a custom shear-wave TOF device could detect frequency- and direction-dependent responses in ex vivo tissues. Three porcine liver samples and three chicken breast samples were examined. Chicken breast was measured with propagation parallel and perpendicular to visible muscle fibers. One-cycle sinusoidal excitations were applied at 40–160 Hz, with 50 acquisitions ensemble-averaged per sample–frequency measurement. TOF was estimated using Tx threshold detection and cumulative-energy-based Rx onset detection, and TOF-derived apparent shear-wave propagation speed was calculated from the Tx–Rx distance and the measured TOF. Frequency-dependent data were fitted using the Kelvin–Voigt fractional derivative model to obtain model-dependent KVFD fit parameters. Signal quality was assessed, and a preliminary descriptive comparison with HISKY EQTouch UD3000 (Wuxi Hisky Medical Technologies Co., Ltd., Wuxi, China) SWE was performed. All 63 averaged sample–frequency measurements satisfied the predefined primary-detection criteria. Mean apparent shear-wave speed was 3.145 m/s in porcine liver, 6.133 m/s in chicken breast measured parallel to the fibers, and 5.914 m/s in chicken breast measured perpendicular to the fibers, giving a parallel-to-perpendicular speed ratio of 1.037. Mean post-averaging, post-processing SNR ranged from 24.47 to 31.52 dB. The UD3000 comparison showed the same tissue ranking. The device detected frequency- and direction-dependent responses in averaged ex vivo signals, supporting its feasibility as a controlled research platform. Claims of absolute stiffness accuracy and intrinsic muscle anisotropy require independent calibration and validation. Full article

Three-dimensional topological magnetic defects, such as Bloch points, are of significant interest for high-frequency spintronics due to their unique particle-like properties and effective inertial mass. We investigate the nucleation, stabilization, and driven dynamics of an isolated Bloch point in a ferromagnetic multilayer with alternating in-plane and perpendicular magnetic anisotropy. Using micromagnetic simulations, we show that a perpendicular magnetic field stabilizes a head-to-head Bloch point state, while a transient in-plane field pulse drives the defect into gyrotropic and nutation motion. To model the dynamics, we develop a collective-coordinate Lagrangian description of the Bloch point core. We further demonstrate that the time-dependent core displacement generates a transverse charge current via spin pumping and inherent spin-to-charge conversion within the multilayer system. The resulting current spectrum contains low-frequency and high-frequency components, including an intrinsic nutation mode in the gigahertz range. Our findings expand the capabilities for electrical control and identification of complex spin configurations, contributing to the development of active three-dimensional spintronic devices. Full article

Dimensional accuracy and surface roughness in material extrusion (MEX) have been widely studied; however, the effect of part scale on the simultaneous fulfilment of geometrical tolerances and surface finish remains less clearly established. This study evaluates the scale-dependent quality of PLA parts manufactured by material extrusion (MEX) using a full 3 × 3 × 3 factorial design, combining three scales (1×, 0.75×, and 0.5×), three commercial PLA filaments, and three printing speeds (40, 60, and 80 mm/s). A dedicated test artefact was inspected by a coordinate measuring machine to quantify GD&T-related deviations, including flatness, perpendicularity, parallelism, angularity, circularity, cylindricity, and coaxiality. Surface roughness was characterized by 2D profilometry using Ra, Rz, and Rq on representative horizontal and vertical surfaces. Results showed that part scale was the dominant factor affecting geometrical conformity, especially for orientation- and location-related tolerances such as perpendicularity, parallelism, and coaxiality, which deteriorated markedly as specimen size decreased. Filament type also influenced several geometrical responses, whereas printing speed showed no significant main effect on geometrical tolerances within the evaluated range. Surface roughness exhibited clear anisotropy, with vertical surfaces showing higher values and stronger statistical dependence on process factors. Unlike studies focused only on dimensional accuracy or surface roughness, this work provides an integrated GD&T-based and surface-texture assessment of scale-dependent quality loss in PLA parts manufactured by MEX. These findings may help designers and manufacturers define inspection criteria, select suitable commercial PLA filaments, and identify critical geometrical features when scaled MEX parts are intended for functional applications. Full article

This study evaluates the mechanical performance, anisotropy, and spatial variability of 3D-printed cementitious and alkali-activated composites under laboratory, atmospheric, and freeze–thaw conditions. Alkali-activated composites exhibited substantially higher shrinkage than cement-based mixtures, reflecting differences in their reaction mechanisms and pore structure development. Compressive strength was measured in two orthogonal directions representing perpendicular ($⟂$) and parallel ($\parallel$) behaviour. Non-activated mixtures exhibited compressive strength of 11–12 MPa, whereas alkali-activated composites reached 19–20 MPa in the reference condition. Atmospheric exposure increased compressive strength by 10–22%, while freeze–thaw cycles did not significantly affect perpendicular strength. Flexural strength of non-activated mixtures remained low (3.7–5.3 MPa), whereas activated composites showed higher values in the reference state (8.8–15.0 MPa) but decreased after atmospheric exposure to 5.3–5.8 MPa. The degree of anisotropy increased significantly for alkali-activated mixtures (from 0.09 to 0.24) while remaining relatively stable for non-activated materials (0.04–0.11). Glass fibres showed no significant degradation after environmental and freeze–thaw exposure, while merino wool fibres exhibited only minor surface irregularities, confirming the potential of both fibre types for use in sustainable lightweight 3D-printed cementitious and alkali-activated composites. Full article

Vertical cracks in concrete present a major challenge for many conventional nondestructive testing methods (NDT) and structural health monitoring (SHM) methods. Elastic wave-based approaches offer strong interaction with crack faces and depth sensitivity; however, their effectiveness is often limited by the lack of repeatable and tunable excitation sources. Repeatability is critical because scattered and attenuated signals require stacking to achieve adequate signal-to-noise ratios, while tunability is essential because key crack attributes are frequency-dependent and must be probed at appropriate wavelengths. In this study, we develop an active sensing system utilizing a linear impact actuator as a repeatable and tunable mechanical source for elastic-based NDT and apply it to a 0.24 m thick concrete slab containing three surface-breaking vertical cracks with depths of 6, 12, and 18 cm, respectively. The actuator is tuned by adjusting impact conditions to generate $A_0$-dominated Lamb wave responses. For each crack, two linear arrays are deployed, one parallel and one perpendicular to the crack trace, to investigate directional anisotropy. Phase-velocity anisotropy is quantified using the $A_0$ Lamb wave dispersion curves, while the effective quality factor is used as a complementary indicator of direction-dependent attenuation. Our results show that phase velocities are consistently higher for crack-parallel propagation than for crack-perpendicular propagation, and that the degree of anisotropy increases with crack depth. The quality factor decreases with increasing crack depth and exhibits anisotropic behavior, with systematically lower values for crack-perpendicular measurements compared to crack-parallel measurements. Overall, the results demonstrate that controllable and repeatable impact excitation establishes a reliable framework for elastic-wave-based characterization of idealized vertical cracks in concrete. Full article

Terahertz time-domain spectroscopy (THz-TDS) is a widely used technique for characterizing a broad range of materials in the terahertz frequency region. Conventional THz-TDS requires both reference and sample signals to extract optical parameters such as refractive index and absorption coefficient. Determining optical anisotropy, specifically birefringence and linear dichroism, typically requires separate measurements of the optical parameters of the sample parallel and perpendicular to the terahertz electric field. This process increases measurement time and depends heavily on a stable reference scan. In this work, we present a simple and accurate method to directly obtain birefringence and linear dichroism without the need for a reference measurement. The proposed approach extracts anisotropic parameters solely from the sample signals by analyzing the differential phase delay and amplitude attenuation between orthogonally polarized terahertz electric field components. We validate this method experimentally using optically anisotropic materials such as TiO₂ and bamboo samples and confirm that the results agree closely with those from conventional reference-based THz-TDS. This technique offers a practical route to measure the optical anisotropy of materials, particularly in situations where acquiring a reference signal is challenging. Full article

Two-dimensional (2D) intrinsic ferromagnets with perpendicular magnetic anisotropy (PMA) have been experimentally verified as promising candidates for nanoscale spintronic devices and magnetic random-access memories. In this work, we systematically investigate the stability, electronic structure, and magnetic properties of monolayer MOCl (M = Ti, V, Cr, Mo) via first-principles calculations. The results demonstrate that allshi ciju monolayers MOCl (M = Ti, V, Cr, Mo) are intrinsic ferromagnetic semiconductors, with magnetic moments of 1.0 μ_B/Ti atom, 2.0 μ_B/V atom, 2.5 μ_B/Cr atom and 3.0 μ_B/Mo atom, respectively. Notably, both monolayers TiOCl and CrOCl exhibit perpendicular magnetic anisotropic energy (MAE), which is mainly contributed by metal atoms Ti and Cr, respectively. Drawing on the second-order perturbation theory, we conduct an analysis of the density of states and the magnetic anisotropy energy (MAE) resolved by d orbitals for Ti and Cr atoms. Our analysis shows that in monolayer TiOCl, the MAE of Ti atoms mainly stems from the disparities in matrix elements between the d_yz and d_x²−y² (d_xz) orbitals. Conversely, in monolayer CrOCl, the MAE of Cr atoms is largely due to the differences in matrix elements between the d_xy (d_yz) and d_x²−y² (d_z²) orbitals. Biaxial strain can efficiently regulate the MAE of monolayer CrOCl. Specifically, when under tensile strain, the MAE of monolayer CrOCl experiences a substantial increase. Our research results indicate that both monolayers TiOCl and CrOCl have significant potential for use in spintronic devices and high-density data storage systems. Full article

The manufacturing of personalized implants from Ti–6Al–4V alloy using additive manufacturing technologies is a promising direction in modern medicine. However, components produced by these methods are characterized by a non-equilibrium microstructure, high residual stresses, and anisotropy of mechanical properties, which necessitates subsequent heat treatment. The aim of the present work was a systematic comparative study of the effect of three heat treatment regimes—stress relief annealing (600 °C, 3 h), subtransus annealing in the (α + β) region (950 °C, 1 h, furnace cooling), and solution treatment followed by aging (STA: 950 °C, 0.5 h, water quenching + aging at 675 °C, 3 h)—on the microstructure and mechanical properties of Ti–6Al–4V alloy manufactured by laser powder bed fusion (L-PBF) and plasma arc directed energy deposition (PA-DED). The microstructure was examined using scanning electron microscopy, transmission electron microscopy, and electron backscatter diffraction (EBSD). Tensile mechanical properties were determined in two directions: parallel and perpendicular to the build direction. Stress-relief annealing led to an increase in the ductility of the alloy without a noticeable decrease in strength and without significant changes in the microstructure. Subtransus annealing resulted in the formation of an equilibrium lamellar (α + β) structure, which provided a substantial increase in ductility with a moderate decrease in strength. Solution treatment and aging resulted in formation of a bimodal microstructure. Subtransus annealing (both alloys), STA (L-PBF) and stress relief annealing (PA-DED) provided properties comparable to those of wrought material. The obtained results form the basis for a scientifically informed selection of both the manufacturing route and the heat treatment regime for biomedical implants made of Ti–6Al–4V alloy. Full article

We demonstrate the molecular beam epitaxy growth of two-dimensional van der Waals ferromagnet Fe₃GaTe₂ films with precisely controlled thicknesses down to a single unit cell. Magneto-optical Kerr effect microscopy measurements reveal robust room-temperature ferromagnetism with perpendicular magnetic anisotropy persisting across all thicknesses, including finite coercivity in monolayer films. The magnetic domain structures show strong thickness dependence: ultrathin films exhibit near-single-domain states without resolved domain nucleation or domain wall propagation, while thicker films develop complex multi-domain configurations featuring bubble-like domains. These findings underscore the pivotal role of dimensional confinement in modulating the magnetic properties of Fe₃GaTe₂ and provide critical insights into thickness-dependent phenomena in two-dimensional magnets, advancing their prospects for room-temperature spintronic applications. Full article

Laser powder bed fusion (LPBF) induces pronounced microstructural anisotropy in NiTi alloys, which strongly governs their corrosion behavior in physiological environments. Here, the orientation-dependent microstructure and corrosion performance of LPBF NiTi alloys were systematically investigated on the XY (perpendicular to build direction) and XZ (parallel to build direction) planes. The XY plane is dominated by polygonal B2 grains, whereas semi-quantitative XRD analysis and TEM observations indicate a relatively larger contribution of lamellar B19′ martensite on the XZ plane. Electrochemical tests in Hank’s solution (pH 3–7) reveal pronounced corrosion anisotropy. At pH 7, the XZ plane exhibits a higher charge transfer resistance (143.9 vs. 109.1 kΩ cm²) and a lower corrosion current density (0.231 vs. 0.599 μA cm⁻²) than the XY plane. After 72 h immersion, the R_ct of the XZ plane remains approximately 31% higher than that of the XY plane at pH 7, while its apparent donor density is lower than that of the XY plane at pH 3 (7.38 × 10²⁹ vs. 12.33 × 10²⁹ cm⁻³). The superior electrochemical response of the XZ plane correlates with its denser lamellar B19′ morphology and lower passive-film donor density. Competition between interface-assisted passivation and interface-related electrochemical heterogeneity is proposed as a possible contributor to the anisotropic corrosion response. Full article

The durability of cement-based materials is strongly affected by ionic ingress and transport within calcium silicate hydrate (C-S-H) nanopores, governing their long-term degradation in saline environments. However, the coupled effects of pore size and salinity on nanoscale ionic behaviors remain insufficiently understood, limiting the mechanistic interpretation of durability evolution in cementitious systems. Existing studies have mainly considered pore size and solution salinity separately, while a systematic understanding of their coupling effects on ionic spatial distribution, transport properties and regime transitions is still lacking. In this study, molecular dynamics simulations are performed for NaCl solutions confined in C-S-H nanopores with pore sizes of 2.5–12.5 nm and salinities of 0–2 M. Results show layered water and ion structures that become increasingly confined with decreasing pore size. Increasing salinity enhances ion accumulation while suppressing water mobility due to competitive adsorption. Ion diffusion is significantly lower than that of water molecules, while transport parallel to the C-S-H surface is much higher than in the perpendicular direction, indicating strong anisotropy. Regime-dependent diffusion behaviors are observed across pore size–salinity conditions. These findings deepen the understanding of water and ionic transport and adsorption, improving durability models for cement-based materials in construction engineering. Full article

Freeze–thaw durability of 3D-printed engineered cementitious composites (3DP-ECC) is strongly affected by print-induced interlayer defects and anisotropy, particularly in cold regions. This study investigated Cast-ECC and Z-direction 3DP-ECC incorporating Yellow River sediment (YRS) as an equal-mass replacement for quartz sand at 0–100%. Compressive, three-point bending, and four-point bending tests, relative dynamic elastic modulus (RDME), XCT, MIP, SEM–EDS, and Weibull damage modeling were used to evaluate degradation up to 150 freshwater freeze–thaw cycles. Moderate YRS replacement (25–50%) improved particle packing, reduced visible defects, and refined the pore structure, thereby enhancing frost resistance. The R50 mixture showed the best residual performance: after 150 cycles, compressive strength decreased from 55 to 46 MPa in Cast-ECC and from 54 to 44 MPa in 3DP-ECC, corresponding to retention rates of 83.6% and 81.5%, respectively. The residual peak load in four-point bending of 3DP-ECC-R50 was 15.4% lower than that of Cast-ECC-R50, confirming the detrimental role of interlayer defects under loading perpendicular to the layers. RDME-based Weibull fitting described the overall damage evolution (R² = 0.876–0.994), while XCT, MIP, and SEM–EDS indicated that interlayer discontinuities, pore-structure evolution, and local microstructural degradation governed anisotropic deterioration. The results support durability-oriented design of YRS-based 3DP-ECC in cold regions. Full article