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.

Two-dimensional (2D) chiral halide perovskites have emerged as promising platforms for light emission, yet the microscopic origin of their broadband photoluminescence remains unresolved. Here, we reveal a mechanism whereby molecular chirality induces structural asymmetry in the inorganic lattice, giving rise to chiral polar deformations that stabilize large polarons, providing a direct pathway toward white-light emission. By integrating tight-binding effective models, first-principles simulations, and structural-optical characterization of two 2D chiral lead bromide perovskites based on the S-enantiomer of the chiral α-methylbenzylamine (MBA) and 1-cyclohexylethylamine (CHEA) organic spacers in the form of ${\left(\text{S-MBA}\right)}_2{\mathrm{PbBr}}_4$ and ${\left(\text{S-CHEA}\right)}_2{\mathrm{PbBr}}_4$, we formulate a predictive framework that links symmetry breaking to electronic localization. The combined results reveal how molecular packing governs the emergence of polarons and tunes the spectral width of emission. The more distorted CHEA-based compound supports a continuum of midgap states and exhibits broadband white-light emission, while its MBA analog remains narrowband. Effective models show that long-range asymmetric potentials hybridize with extended states to produce spectrally broad recombination. This work establishes a design principle in which chirality distortions induced in the inorganic layers enable polaron formation and lattice polarization, offering a route toward single-component white-light emitters with intrinsic asymmetry and tunable spectra.

The rare-earth nitrides are ferromagnetic semiconductors whose electronic properties can be tuned by nitrogen vacancy doping, while magnetic properties are selectable by the choice of lanthanide cation. Here, we demonstrate continuous control of the exchange energy in epitaxial thin films of ${\mathrm{Gd}}_x{\mathrm{Lu}}_{1-x}\mathrm{N}$ via cation substitution. Magnetometry shows that the Curie temperature and the effective exchange decrease with increasing Lu content, yet remain robust enough to facilitate ferromagnetic alignment down to compositions as low as $x=0.2$. First-principles calculations combined with Monte-Carlo simulations reproduce the composition dependence of the Curie temperature, and further indicate two exchange channels: an intrinsic mechanism present in stoichiometric films and an additional carrier-mediated contribution activated by nitrogen vacancies. These results establish (Gd,Lu)N as a material with a finely tunable exchange energy and, as such, a weak ferromagnetic semiconductor, compatible with thin-film growth, relevant for application in high-resistance magnetic Josephson junctions.

We study stacking fault (SF) formation in compressed Cu thin films using harmonic transition state theory (HTST), harmonic variational transition state theory (HVTST), and molecular dynamics (MD). Motivated by prior simulations showing extremely large transition rates, we quantify the temperature, strain, and size dependence of SF nucleation free-energy barriers. Due to a very large change in vibrational entropy along the SF nucleation pathway, HTST predicts prefactors up to ${10}^{46}/\sec$, around 34 orders of magnitude higher than so-called standard prefactors. HTST rates are, however, significantly higher than direct MD observations. HVTST reconciles these two approaches by predicting the occurrence of strong non-Arrhenius behavior at high temperatures due to the displacement of the optimal dividing surface for the reaction. Our results demonstrate that entropic effects can dominate defect formation in strained metallic films, leading to strongly anomalous kinetics and underscoring the necessity of a variational treatment for obtaining quantitatively reliable nucleation rates.

This study presents and tests several approaches for predicting fatigue failure in metals using acoustic emission data analysis. We demonstrate that conventional single-valued AE features (event rate, amplitude, power-law exponents) fail to correlate with fatigue damage progression in selective laser melted additively manufactured AlSi10Mg specimens. Instead, we develop two complementary methods based on spectral density analysis of complete acoustic emission waveforms: (1) a physics-based approach that identifies fatigue-related events through their enhanced excitation of an axial resonant mode, and (2) a data-driven method using dimensionality reduction combined with statistical metrics. Both methods demonstrate the ability to predict approaching failure, with the data-driven approach showing superior consistency. Furthermore, both methods are unsupervised, require no extensive training datasets, and are grounded in physical principles, suggesting potential applicability across different materials and geometries. These findings offer promising pathways for nondestructive fatigue monitoring.

The magnetic damping of ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ [Permalloy (Py)] thin films is studied via temperature- and frequency-dependent ferromagnetic resonance (FMR) as a function of the Py layer thickness for two different thickness series, Al/Py/sapphire and Al/Py/Al/sapphire, respectively. Additional magnetic and structural characterization is done by superconducting quantum interference device magnetometry as well as x-ray reflectivity and transmission electron microscopy. The frequency dependence of the FMR linewidth allows us to separate the Gilbert-like contributions from non-Gilbert-like ones like two-magnon scattering (TMS) processes. The thickness dependence allows us to separate the derived magnetic parameters such as saturation magnetization $M_{\mathrm{s}}$, TMS contribution $\mathrm{\Gamma }$, and Gilbert damping parameter $\alpha$ into their respective bulk and interfacial contributions. While the bulk contribution ${\alpha }^{\mathrm{bulk}}$ monotonously decreases with temperature from 0.0061(1) down to 0.0054(1) for both samples series, the interfacial contribution ${\alpha }^{\mathrm{interface}}$ shows a subsequent increase at low temperature. This is rather pronounced for the Al/Py/sapphire series, caused by a temperature-dependent TMS contribution. For the Al/Py/Al/sapphire series, the increase at low temperatures is much less pronounced, and a temperature-independent TMS contribution is only found for the thinnest sample due to a wavy Py film morphology. Correcting for the TMS contributions allows us to extract ${\alpha }^{\mathrm{bulk}}\left(T\right)$ which reflects the intrinsic magnetic damping properties of sputtered Py thin films.

Here, first-principles calculations help us understand solid-state electrolytes within the framework of point defects, considering Schottky, cation, and anion Frenkel defects, Li as interstitial defects, Li deficiencies as vacancies, and isovalent/anisovalent substitutional defects by anions. The defect formation energies, which capture electrons and holes, the diffusivity of Li, the mechanical and thermal stability, and the electrochemical windows are studied for halide solid electrolytes with monoclinic and trigonal phases, respectively. The diffusion pathways along both the $c$ axis and $\mathit{ab}$ plane are observed and the activation energies ($\sim 0.44$ eV) and room-temperature Li-ion conductivities for all structures have been determined. It is observed that anisovalent substitution (${\mathrm{O}}_{\text{Cl}}$) is an effective way to promote Li-ion conductivity for ${\mathrm{Li}}_3{\mathrm{InCl}}_6$ increasing the ionic conductivity from 1.34 mS/cm to 6.23 mS/cm at room temperature, whereas isovalent substitution (${\mathrm{F}}_{\text{Cl}}$) and interstitial (${\mathrm{Li}}_i$) defects help achieve similar conductivity values as those shown by ${\mathrm{Li}}_3{\mathrm{YCl}}_6$ and ${\mathrm{Li}}_3{\mathrm{ErCl}}_6$. Furthermore, the defect structures exhibit a lower reduction potential than sulfide solid electrolytes and, due to the incorporation of defects, the band gaps increase. These results highlight the significance of defects in halide solid electrolytes.

In this work, we determine the dielectric function of ScN in a spectral range from 0.9 to $6.4\mathrm{eV}$ by spectroscopic ellipsometry from nondegenerate doped, bulk-like samples. Several models are applied to the obtained dielectric functions yielding the main critical-point transition energies. These results are compared with state-of-the-art computations, where the band structure of ScN is calculated using Heyd-Scuseria-Ernzerhof (HSE06) hybrid functionals and quasiparticle corrections in the $G_0{W}_0$ approach. Furthermore, the dielectric function of ScN is derived from the computed band structure by solving the Bethe-Salpeter equation to account for electron-hole-pair interactions. We find exceptional agreement between computed and experimentally determined dielectric functions, where discrete excitons are not observed experimentally. We extrapolate an intrinsic direct band gap of $(2.182\pm 0.004)\mathrm{eV}$ and an intrinsic indirect band gap of $(1.08\pm 0.02\mathrm{eV}$) by taking into account many-body effects, while higher energy critical-point transition energies of $\mathrm{\Gamma }$-point transitions are averaged over all samples, yielding $E_{\mathrm{\Gamma }}=(3.853\pm 0.006)\mathrm{eV}$ and $E_{{\mathrm{\Gamma }}^{\prime }}=(5.21\pm 0.02)\mathrm{eV}$. Critical-point transitions in the computed band structure, although, deviate from the experimental ones due to the omission of electron-hole-interaction, where the deviation increases with increasing energy. The dielectric limit of the electronic system is determined as ${\varepsilon }_{\infty }=8.38\pm 0.04$ from experiment, where the computed dielectric function reveals almost the same value (${\varepsilon }_{\infty }=8.33$). Along with other previous publications, we conclude that solving the Bethe-Salpeter equation is indispensable for the computation of the dielectric function of semiconductors even in the absence of discrete excitons.

We present a comprehensive study of the magnetic structure evolution, employing bulk magnetization and neutron powder diffraction (NPD) measurements down to 3.5 K, across the spin reorientation transition in orthorhombic (Pnma) ${\mathrm{TmCrO}}_3$. Magnetic susceptibility reveals canted antiferromagnetic (CAFM) ordering at $T_N=125\mathrm{K}$, followed by the magnetization reversal, showing minima between the two compensation points $T_{\mathrm{comp}1}$ and $T_{\mathrm{comp}2}$. Heat capacity shows a λ-transition at $T_N$, associated with long-range antiferromagnetic order of Cr, followed by a broad feature at ∼ 9 K, arising due to Schottky-type anomaly. Magnetic refinement of NPD data establishes the $P{n}^{\prime }{m}^{\prime }a$: Γ2($C_x,G_y;C_x^{Tm},F_z^{Tm}$) CAFM structure below $T_N$. A gradual change in magnetic structure occurs during the spin-reorientation (SRO) transition below 30 K. During this, the magnetic structure gradually changes from $P{n}^{\prime }{m}^{\prime }a$ (Γ2) to $P{n}^{\prime }m{a}^{\prime }$ (Γ4): $A_x,F_y,G_z;F_y^{Tm}$. Below 30 K, however, neither Γ2 nor Γ4 alone adequately fit the intensity of magnetic reflections. A satisfactory refinement could only be achieved in the monoclinic subgroup $P{2^{\prime }}_1/c^{\prime }$ derived from a combination of Γ2 and Γ4. The observed gradual SRO of Tm and Cr moments is consistent with the magnetic symmetry $P{2^{\prime }}_1/c^{\prime }$: $C_x,G_y,G_z;C_x^{Tm},F_y^{Tm},F_z^{Tm}$. Furthermore, the ordered moments Cr and Tm in ${\mathrm{TmCrO}}_3$ exhibit a complex, nonmonotonic temperature dependence as expected during SRO. Anomalies in lattice parameters suggest magnetoelastic coupling, linking structural distortions to the SRO.