Field evaporation in atom probe tomography (APT) includes known processes related to surface migration of atoms, such as the so-called roll-up mechanism. They lead to trajectory aberrations and artifacts on the detector. These processes are usually neglected in simulations. The inclusion of such processes is crucial for providing reliable models for the development and verification of APT reconstruction algorithms, a key part of the whole methodology. Here, we include stochastic lateral velocity perturbations and a roll-up mechanism to simulations performed using the Robin-Rolland model. By comparing with experimental data from Al and Ni systems, we find the stochastic perturbation energy distributions that allow us to very accurately reproduce the detector patterns seen experimentally and thus greatly improve the accuracy of the simulations. We also explore the possible causes of remaining discrepancies between the experimental and simulated detector patterns.

High power consumption, leakage currents, and fatigue in conventional electrical switches motivate the development of alternative switching paradigms for low-power and high-contrast signal control. In this study, a twisted bilayer SnTe switching architecture based on interlayer-twist-induced polarization switching is proposed. Introducing a finite twist disrupts the intrinsic symmetry of few-layer α-SnTe, generating an out-of-plane polarization and enabling a large-contrast switching response. Near a twist angle of $27.8^{\circ }$, with a gradual rotation of $0.{323}^{\circ }$, the polarization undergoes a pronounced evolution from a virtually negligible value to a maximum of $3.26\times {10}^{-11}\mathrm{C}/\mathrm{m}$, with the polarization differing by $3.24\times {10}^{-11}\mathrm{C}/\mathrm{m}$ between the two stable states. The remarkable polarization response induced by the subdegree interlayer twist establishes a viable strategy for designing low-power logic devices and multifunctional quantum electronic systems at the nanoscale.

We report on the epitaxial growth of nm-thick films of bismuth-substituted yttrium iron garnet (BiYIG) by high-temperature off-axis radio-frequency magnetron sputtering. We demonstrate accurate control of the magnetic properties by tuning of the sputtering parameters and epitaxial strain on various (111)-oriented garnet substrates. BiYIG films with up to −0.80% lattice mismatch with the substrate remain fully strained up to 60 nm thick, maintaining a high crystalline quality. Transmission electron microscopy and energy-dispersive x-ray spectroscopy confirm coherent epitaxial growth, the absence of defects, and limited interdiffusion at the BiYIG/substrate interface. Varying the tensile or compressive strain between −0.80% and $+0.56\%$ in BiYIG allows for accurate compensation of the total magnetic anisotropy through magnetoelastic coupling. The effective magnetic anisotropy of sputtered BiYIG films can be further tuned via the off-axis deposition angle and the oxygen flow during growth, which determine the cation stoichiometry. Under optimized growth conditions, a ferromagnetic resonance (FMR) linewidth of 1 mT at 10 GHz is reliably obtained even for thicknesses as low as 10 nm. We also report small FMR linewidths in ultrathin (2–5 nm) BiYIG films grown on diamagnetic substrate yttrium scandium gallium garnet. These findings highlight the promise of low-damping, strain-engineered nm-thick BiYIG films for implementing advanced functionalities in spin-orbitronic and magnonic devices. Specifically, the magnetic-anisotropy compensation and low damping enable large cone-angle magnetization dynamics immune to magnon-magnon nonlinear scattering.

We report a method to grow B20 MnGe thin films using molecular-beam epitaxy, which employs an ultrathin CrSi template layer on Si(111). This layer is expected to be nonmagnetic, in contrast to MnSi and FeGe buffer layers that have been used previously. This template layer permits an investigation of the intrinsic properties of MnGe in the ultrathin-film limit without the influence of a neighboring magnetic layer. Single-phase MnGe(111) films were grown with thicknesses between 2 and $40\mathrm{n}\mathrm{m}$, which exhibited low interfacial roughnesses on the order of $0.6\mathrm{n}\mathrm{m}$. The films crystallized in a B20 structure with a small rhombohedral distortion. Magnetometry measurements in out-of-plane fields are consistent with a cone phase derived from helimagnetic order propagating along the film normal. However, an unexpected remanent moment develops below $35\mathrm{K}$, concomitant with features in the field dependence of the transport data. This provides indirect evidence for the presence of a low-temperature phase which has been identified by others as either a triple-$Q$ topological spin-hedgehog lattice, or a multidomain single-$Q$ helical state.

Strontium iron oxide undergoes a voltage-driven topotactic phase transition between an insulating brownmillerite (BM) and a conductive perovskite (PV) structure. Understanding this redox-based transition requires, first, a detailed characterization of and, second, a detailed description of field-driven oxide-ion transport in both phases. In this study, we used classical molecular dynamics (MD) simulations to determine the oxide-ion mobility $u_{\mathrm{O}}$ in anisotropic ${\mathrm{Sr}}_2{\mathrm{Fe}}_2{\mathrm{O}}_{5\pm \delta }$ (BM phase) and in isotropic ${\mathrm{SrFeO}}_{2.5\pm \delta /2}$ (PV phase) as a function of electric field strength, $0.5\le E/\mathrm{M}\mathrm{V}\mathrm{c}{\mathrm{m}}^{-1}\le 10$, and as a function of temperature, $1300\le T/\mathrm{K}\le 3000$. The use of oxygen-excess ($+\delta$) and oxygen-deficient ($-\delta$) BM systems permits, respectively, interstitialcy and interstitial migration, and vacancy migration, to be probed. From $u_{\mathrm{O}}$ results obtained at low fields (i.e., within the linear regime), we obtain the activation enthalpies and effective attempt frequencies of oxygen-vacancy migration and oxygen-interstitial/oxygen-interstitialcy migration; and, together with literature data for tracer diffusivities, we determine Haven ratios $H_{\mathrm{r}}\left(T\right)$ for BM and PV phases. At higher fields (i.e., within the nonlinear regime), $u_{\mathrm{O}}\left(E\right)$ data shows a strong nonlinear response for all three migration mechanisms. In each case, the behavior is described within an existing analytical framework that uses as input the zero-field activation enthalpies and effective attempt frequencies. Interstitialcy migration displays a stronger nonlinear response compared with interstitial or vacancy migration, and this is ascribed to its longer effective charge displacement arising from its collective nature. Finally, the MD simulations at high field strengths indicate a field-driven BM-to-PV phase transition (at constant oxygen stoichiometry).

Brittle or ductile failure of materials is typically governed by a competition between crack propagation and plastic deformation. For ductile crystals like aluminum, this framework shows that brittle fracture does not occur, regardless of preexisting cracks. However, it does not account for environmental effects that can promote embrittlement. We show that self-assembled organic monolayer adsorbates of varying chain length can induce a ductile-to-brittle transition in crystals under bending and shear. These adsorbates impose a surface stress that varies from compressive to tensile with increasing chain length, driving the transition. We develop an analytical model incorporating adsorbate-induced surface stress into the criterion for dislocation emission and compare it against crack propagation. This yields an embrittlement map demarcating regimes of ductile and brittle behavior in load-surface stress space. Our findings suggest a critical role for surface stress in environmentally assisted cracking, as well as opportunities for utilizing this stress to enhance manufacturing processes such as machining, polishing, and comminution.

This research establishes a systematic, high-throughput computational framework for designing radiation-resistant, dilute ternary copper-based alloys by addition of solutes that bind to vacancies and reduce their mobility, thus promoting interstitial-vacancy recombination. The first challenge in developing alloys by this method is mitigating the vacancy-mediated solute drag effect, since density functional theory (DFT) calculations show that solutes that bind strongly to vacancies are also rapidly dragged to point-defect sinks, and thus removed from the matrix. To overcome this problem, two types of solutes are added to the Cu matrix: a first solute with a strong vacancy binding energy ($B$-type species) and another solute that binds to ‘‘B’’ and is a slow diffuser in Cu ($C$-type species). Using DFT, 21 synergistic solute pairs are screened, with “B”$=\mathrm{Zr}$, Ge, Sn and “C”$=\mathrm{Fe}$, Co, Mo, Ni, Nb, W, Cr. Two promising alloys, Cu(Zr,Co) and Cu(Zr,Fe) are then investigated in detail in the dilute regime. Diffusion and solute drag in these alloys are modeled using the kinetic cluster expansion approach (KineCluE) under irradiation conditions. It is shown that strong Zr-‘‘C’’ thermodynamic binding, especially between Zr and Co, significantly reduces the mobility of Zr solute and suppresses the vacancy-mediated solute drag. Using an analytical framework for the standard five-jump frequency model for diffusion in binary alloys, it is found that vacancy-Zr-Co triplets disrupt the kinetic circuits that promote solute drag in the binary alloy by raising the dissociation barrier for the vacancy from the solute.

The stability of Fe-Si compounds under extreme pressure is critical for understanding the composition and evolution of Earth's core and terrestrial planetary interiors. Using first-principles calculations and adaptive genetic algorithm crystal structure prediction method, we systematically investigated the thermodynamic stability of Fe-Si compounds and their structural evolution as a function of silicon concentration over pressures ranging from 0 GPa to 1 TPa. At 0 K, B2-FeSi is identified as the sole thermodynamically stable phase at high pressures. Through structural characterization analysis of metastable structures, we found that as the Si content increases, there is a transition in structural motifs from hcp to bcc and then to fcc. Furthermore, electronic and vibrational entropies significantly enhance the thermodynamic stability of certain alloy structures. Our study highlights the synergistic effects of composition, pressure, and volume in regulating phase stability, providing theoretical insights into the composition and structural evolution of planetary cores.

$\mathrm{HfZr}{\mathrm{O}}_2$(HZO) is a promising ferroelectric material compatible with CMOS technology, retaining functionality at nanometer-scale thicknesses. Its ferroelectricity arises from metastable polar phases—orthorhombic ($Pca{2}_1$) and rhombohedral (R3m)–coexisting with the thermodynamically stable, non-polar monoclinic phase ($P{2}_1/c$). Accurate quantification of these coexisting phases is essential for optimizing device performance. Here, we use first-principles calculations to estimate core-level shifts in the O 1s X-ray photoelectron spectroscopy (XPS) peak, revealing a distinct, up to 0.84 eV higher binding energy component for oxygen atoms in the polar sublattice compared to those in non-polar environments. These shifts incorporate both initial and final state effects in photoemission. Experimental validation through X-ray diffraction (XRD) and XPS on HZO films with varying phase composition confirms our predictions. Our findings provide a clear, spectroscopically accessible fingerprint to distinguish polar and non-polar phases in HZO via O 1s XPS analysis, offering a practical tool for phase quantification and enabling targeted integration of ferroelectricity in advanced nanoelectronic devices.

Skyrmion lattices, composed of densely packed ferromagnetic skyrmions, possess unique topological domain structures and can be tuned by external factors like force, magnetic fields, and temperature, making them promising for next-generation spintronic devices. Similar to atomic crystals, lattice defects, such as grain boundaries, exist within skyrmion lattices and are expected to have significant impact on the behaviors of skyrmion lattices. However, even the fundamental structures and external condition dependence of skyrmion grain boundaries remain poorly understood. In this study, we systematically investigated the skyrmion grain boundary structures and their dependence on external fields using phase-field simulations. Our results reveal that skyrmion grain boundaries are stabilized through skyrmion deformation, forming unique quasiparticle-based structures, while they consist of five to seven pair dislocations, analogous to those in conventional crystals. The degree of deformation strongly depends on both temperature and magnetic field: at low temperature and low magnetic field, skyrmions near the grain boundary undergo enhanced deformation, in order to reduce Dzyaloshinskii-Moriya interaction energy. Furthermore, our strain analysis shows that such local skyrmion deformations fundamentally alter the lattice mismatch relaxation mechanisms. These findings not only deepen the fundamental understanding of defect structures in topological magnetic systems but also provide insights relevant to the design of advanced spintronic devices.

While the short-range order structure and properties of phosphate-based glasses have been extensively studied, limited studies have focused on their medium-range order (MRO) structure, including the structural origin of the first sharp diffraction peak (FSDP) in the structure factor. In this work we perform molecular dynamics simulations, based on a machine learning interatomic potential, of calcium phosphate and calcium aluminophosphate glasses to investigate their MRO structures. We do so based on both classical ring analyses and persistent homology, clarifying the relation between different MRO features and the position of the FSDP. Furthermore, by classifying loops based on geometric descriptors (roundness and eccentricity), we show that the density distribution of loops with an eccentricity between 0.6 and 0.8 and those exhibiting high roundness are found at similar $Q$ values as the FSDP. Compositional variations, especially with increasing Ca/P ratio, systematically leads to larger loops, including more loops with high eccentricity. Overall, our work provides new insights into the geometry of MRO structures identified by persistent homology and classical ring analysis in phosphate glass networks.

Data-driven models can accurately describe and predict the dynamical properties of glass-forming liquids from structural data. Accurate predictions, however, do not guarantee an understanding of the underlying physical phenomena and the key factors that control them. In this paper, we illustrate the merits and limitations of linear regression models of glassy dynamics built on high-dimensional structural descriptors. By analyzing data for a two-dimensional glass model, we show that several descriptors commonly used in glass-transition studies display multicollinearity, which hinders the interpretability of linear models. Ridge regression suppresses some of the shortcomings of multicollinearity, but its solutions are not concise enough to be physically interpretable. Only by using dimensional reduction techniques we do eventually obtain linear models that strike a balance between prediction accuracy and interpretability. Our analysis points to a key role of local packing and composition fluctuations in the glass model under study.

We investigated the local Co $3d$ electronic structure of ${\mathrm{Na}}_2\mathrm{BaCo}$$({\mathrm{PO}}_4{)}_2$ using polarization-dependent x-ray absorption spectroscopy (XAS) in combination with full multiplet cluster calculations. We employed the line-fitting inverse partial fluorescence yield (IPFY) technique to obtain accurate XAS spectra from strong insulating materials. Our combined experimental and theoretical analysis reveals a very small effective trigonal distortion of only 11 meV in the ${\mathrm{CoO}}_6$ octahedra, indicating a close to ideal condition to render a ground state with the $J_{\mathrm{eff}}=1\text{/}2$ character. With our cluster model we were also able to simulate magnetic susceptibility measurements along different directions in the crystal. These findings highlight ${\mathrm{Na}}_2\mathrm{BaCo}$$({\mathrm{PO}}_4{)}_2$ as a promising platform for exploring exotic magnetic phenomena associated with $J_{\mathrm{eff}}=1\text{/}2$ ground states on triangular lattices.

We report bulk magnetic properties of ytterbium tantalate in its monoclinic fergusonite modification, $M\text{−}{\mathrm{YbTaO}}_4$. The spin-$\frac{1}{2} {\mathrm{Yb}}^{3+}$ ions in this phase are arranged on a geometrically frustrated “stretched diamond” lattice. $M\text{−}{\mathrm{YbTaO}}_4$ cannot be prepared at ambient pressure and was instead prepared in a belt-type apparatus at 6 GPa and ${1800}^{\circ }\mathrm{C}$. Susceptibility and specific heat data show no long-range ordering down to 1.8 K and are consistent with a $J_{\mathrm{eff}}=\frac{1}{2}$ Kramers doublet which splits in an applied field. Furthermore, under high-pressure synthesis the entire solid solution ${\mathrm{YbNb}}_{\mathrm{x}}{\mathrm{Ta}}_{1-\mathrm{x}}{\mathrm{O}}_4$ ($0\le x\le 1$) can be stabilized in the $M$ phase, in contrast to ambient-pressure synthesis which favors the competing $M^{\prime }$ phase for Ta-rich compositions. Subsequent annealing of the Nb-Ta mixed samples resulted in color changes, suggesting oxygen deficiency in some of the as-prepared high pressure samples. There was little variation in the bulk magnetic properties upon varying either the Nb/Ta ratio or the annealing conditions.

Dislocation motion—the atomic-scale mechanism of crystal plasticity—governs the strength and ductility of materials. In functional materials, external stimuli beyond mechanical stress can also affect dislocation glide. In the wide band-gap semiconductor ZnS, optical illumination suppresses plasticity, whereas electric fields can enhance dislocation motion. Here, we show that the common underlying mechanism for these phenomena is the charged dislocations that respond to the changes in carrier concentration. Our prior theoretical work showed that locally charged dislocations in ZnS trap excess carriers, triggering core reconstructions that modify their mobility, with the positively charged Zn-rich core dislocations showing the most drastic change. Here, we validate this prediction experimentally by showing that either optical excitation or electronic doping selectively inhibits the glide of Zn-rich dislocations in epitaxially grown ZnS. First, imaging individual interface misfit dislocations under different optical excitation conditions shows that Zn-core glide is strongly reduced as optical power is increased, while the S-core dislocations show negligible sensitivity to light, marking the first single misfit dislocation imaging of the photoplastic effect. Next, we show that a similar behavior is observed with direct electron (n-type) doping of ZnS epitaxial layers grown beyond the critical thickness. As the n-type dopant density is increased, the resulting Zn-core dislocation density is reduced by more than one order of magnitude, while the S-core density remains essentially unchanged, causing a sign reversal of the strain-anisotropy with n-type doping. These results demonstrate a common origin for the opto-electronic sensitivity of dislocations in ZnS and provide a pathway for the engineering of dislocation content in compound semiconductors.