MnPtGa is a hexagonal intermetallic compound with a rich variety of magnetic orders. Its magnetic state is reported to range from collinear ferromagnetism, to noncollinear skyrmion-type order. MnPtGa is a system with strongly localized magnetic moments at the Mn atoms, as was demonstrated using calculations for disordered local moments. The magnetic moments at the Mn sites stay at $\approx 3.9{\mu }_B$ even above the calculated magnetic transition temperatures ($T_N=220\mathrm{K}$ or $T_C=285\mathrm{K}$). In the present work, a special emphasis was placed on the possible noncollinear magnetic order using first-principles calculations. The investigations included magnetic anisotropy, static noncollinear orders in the form of spin canting, and dynamic noncollinearity in spin spirals. It is found that the energy differences between ferromagnetic, antiferromagnetic, canted, or spiral magnetic order are in the order of not more than 30 meV, which is in the order of thermal energies at ambient temperature. This hints that a particular magnetic state—including skyrmions, antiskyrmions, or spin glass transitions—may be forced when an external field is applied at finite temperature.

Deep level defects in silicon carbide (SiC) are of great importance for developing both power electronics and quantum technology applications based on SiC material. While the more technologically mature $4H$ polytype has been widely explored, electrical identification of deep level defect states in $6H$-SiC has not been completed. This work aims to identify irradiation-induced charge state transition levels arising from intrinsic defects in $6H$-SiC using deep level transient spectroscopy (DLTS) and the formation energy diagram formalism based on density functional theory (DFT) calculations. By comparing experimental results of $6H$-SiC epitaxial layers with measurements of $4H$-SiC material that has been grown under identical conditions, combined with DFT calculations, we assign possible origins for the observed DLTS-signatures.

Hydrogen embrittlement (HE), degradation of the mechanical properties of metals due to the presence of hydrogen, is a persistent problem that has been attracting the attention of the material science community for about fifteen decades. Extensive experimental observations indicate the presence of nanovoids and the increase of free volume at the grain boundaries in hydrogen contaminated metals. This rate-dependent phenomenon motivates theoretical investigations of the underlying mechanisms. Here, a hydrogen enhanced cross-slip (HECS) mechanism in the close vicinity of the grain boundaries is demonstrated by direct molecular dynamics simulations and theoretical calculations. To this end, the interaction of screw dislocations with a variety of symmetric tilt grain boundaries in H-charged and H-free bicrystalline nickel is examined. The presence of segregated H atoms at the grain boundaries induces a stress field in their vicinity, and thus,- the barrier for cross-slip of screw dislocations considerably decreases. The enhanced cross-slip of dislocations facilitates the formation of jogs on bowedout dislocations. These jogs can form vacancies during the glide process. This mechanism of defect production shows nanoscale evidence of enhanced vacancy formation and subsequent increase in the free volume along the grain boundaries in the presence of H.

Cadmium sulphide/zinc sulphide nanocomposites embedded in polyaniline (PANI/CdS/ZnS) were prepared by a simple two-step sol-gel method. The as-synthesized nanocomposites were characterized using different spectroscopic and structural characterization techniques. The optical properties, structure, composition, and morphology of the as-prepared nanocomposites were studied using UV-Vis spectrophotometry, photoluminescence spectrophotometry (PL), x-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive x-ray spectroscopy (EDAX/EDS), and transmission electron microscopy (TEM). The synthesized nanocomposite was found to be of spherical shape, with an average particle size in the nanometer range. The photocatalytic activity of the prepared nanocomposite was examined toward the degradation of an organic dye as a model for wastewater treatment. The PANI/CdS/ZnS nanocomposite exhibited prominent catalytic activity toward the tested dye, methyl orange (MO), with a degradation efficiency of ∼96.4% in a short reaction time of 50 mins for the sample with the highest shell concentration. Kinetic study of the photocatalytic degradation reactions was performed and showed pseudo-first-order kinetics.

The binary metal borides provide a promising platform for searching for unique materials with superconductivity and superhardness under high pressure, owing to the distinctive bonding characteristics of boron. In this work, we combined the first-principles calculations and crystal structure predictions, and we predicted four exotic stoichiometries and eight unique U-B compounds under high pressure. The predicted compounds have layered or caged structure units, and four of them host high hardness under ambient pressure. By removal of the U atoms, we predicted three metastable boron clathrates at ambient pressure. Remarkably, the Vickers hardness of the predicted $C2/m\text{−}{\mathrm{B}}_6$ is estimated to be 49–53 GPa, and the $C2/m\text{−}{\mathrm{B}}_{12}$ is superconducting with the $T_{\mathrm{c}}$ value of 16.12 K. Our calculations enrich the phase diagram of binary metal borides and boron allotropes, providing insights for the future theoretical and experimental studies on unique materials.

We report the growth of high-quality rhombohedral boron nitride (rBN) crystals by the iron flux method at atmospheric pressure. In contrast to the lamellar structure of standard hexagonal boron nitride (hBN) covering the metal ingot, the current synthesized BN shell is composed of many triangular bulk crystallites, of submillimeter size, predominantly in the rhombohedral phase, with only weak traces of hBN detected by high-resolution x-ray diffraction. The low-temperature photoluminescence emission confirms the excellent quality of the rhombohedral stacking with unprecedented width for all phonon replicas at the band edge. The Raman spectra are characterized by the absence of any low-energy modes at $\sim 50 {\mathrm{cm}}^{-1}$, the presence of an extended band around $800{\mathrm{cm}}^{-1}$, and an asymmetric high-energy mode at $1366{\mathrm{cm}}^{-1}$. These observations are in very good agreement with the phonon dispersion calculated for the rhombohedral primitive cell with $C_{3v}$ symmetry.

Nearly all ultrawide-bandgap oxides are affected by hole localization that limits $p$-type conductivity and thus potential applications for these materials. Highly localized holes, also known as hole polarons, are trapped in the vicinity of acceptor dopants, giving rise to large ionization energies and severely constraining free hole concentrations. Though this hole-trapping behavior affects wurtzite zinc oxide, rocksalt zinc oxide has been recently found to be resistant to the formation of hole polarons. Moreover, $p$-type doping using lithium acceptors was predicted to be achievable. While rocksalt zinc oxide is metastable and has a band gap near $\sim 3\mathrm{eV}$, here it is found that zinc magnesium oxide (${\mathrm{Zn}}_x{\mathrm{Mg}}_{1-x}\mathrm{O}$) alloys remain $p$-type dopable within the stable rocksalt crystal structure, in addition to exhibiting band gaps in excess of 4 eV. As in rocksalt zinc oxide, alkali acceptors are shallow in zinc magnesium oxide and do not appear to be affected by donor compensation. These results indicate that alkali-doped ${\mathrm{Zn}}_x{\mathrm{Mg}}_{1-x}\mathrm{O}$ alloys are a promising system for achieving a $p$-type dopable ultrawide-bandgap oxide.

${\mathrm{Ti}}^{4+}/{\mathrm{Ti}}^{3+}$ dopants in oxides are known to significantly influence optical and electronic properties, yet a systematic understanding of their defect levels across different hosts remains limited. In this study, we employ dielectric-dependent hybrid density functional theory (PBE0-$\alpha$) to compute the band gaps and ${\mathrm{Ti}}^{4+}/{\mathrm{Ti}}^{3+}$ charge transition levels (CTLs) in a range of host materials. The calculated CTLs relative to the valence band maxima show good agreement with experimental data, typically deviating by less than $10\%$, which is considered acceptable given the uncertainties in experimental measurements. By combining these computational results with experimentally derived vacuum-referenced valence band maxima, we construct band diagrams that clarify the energetic positions of Ti-related defects. These results demonstrate the accuracy and predictive power of the PBE0-$\alpha$ approach and provide a robust computational framework and valuable reference data for the analysis and design of Ti-doped functional oxides.

While dislocation-based plasticity is often the dominant deformation mechanism for fcc alloys, twinning and dynamic recrystallization play important roles under certain loading conditions. Reducing temperature or increasing rates favors twinning in fcc metals with low stacking fault energies. Here, large-scale molecular dynamics simulations reveal that loading triaxiality can also induce twinning and twinning-mediated grain refinement. At strain rates between ${10}^8{\mathrm{s}}^{-1}$ and ${10}^9{\mathrm{s}}^{-1}$, we observe a transition from a dislocation-dominated regime for uniaxial tension to one dominated by twinning and, eventually, grain refinement as the deformation triaxiality is continuously changed toward biaxial tension. The simulations reveal how strain rate and stacking fault energy affect the transitions between regimes and underlying mechanisms.

A trainable descriptor based on artificial neural networks (ANN), developed in our recent study [M. Uchida et al., Phys. Rev. Mater. 8, 103805 (2024)], is integrated into a neural-network potential (NNP) and applied to various lattice defects in molecular simulations of silicon. The ANN descriptor achieves higher predictive accuracy for point defects, surfaces, and symmetric tilt grain boundaries (STGBs) than analytic-function-based descriptors. As a case study of crystallographically complex defects, the ANN descriptor is applied to asymmetric tilt grain boundaries (ATGBs), where favorable atomic structures are governed by the competition between multiple structural units. For the Σ9(111)||(115) ATGB, the predicted atomic structure shows a grain boundary energy close to the DFT value and agrees with previous electron microscopy observations. Similarly, Σ3, Σ5, and Σ9 ATGBs are also systematically examined with the combination of the ANN descriptor and DFT calculations. ATGBs in the Σ5 system can be described by structural units of two STGBs with the same Σ value, indicating that Σ5 ATGBs ideally facet into Σ5 STGB structures. In contrast, this trend does not hold for the Σ3 and Σ9 ATGBs due to the crystallographic incompatibility of the constituent STGBs. As a result, Σ3 and Σ9 ATGBs involve structural units that cannot be predicted by the crystallographic misorientation of the two gains. Electronic-structure analysis reveals that specific atoms at ATGBs create defect levels within the band gap, depending on the inclination angle of ATGBs. These results highlight that the high-accuracy ANN descriptor provides a deeper understanding of atomic and electronic structures and energetics of complex lattice defects.

Pt/Co-based thin films of varying thicknesses were sputtered onto thermally oxidized Si substrates and capped with Cu, Au, or MgO layers. Vibrating sample magnetometry was employed to extract the magnetization at saturation ($M_s$) and the magnetic dead layer thickness ($t_d$) from the Co thickness dependence of the surface magnetic moment, following measurements at selected temperatures (${25}^{\circ }\mathrm{C}$, ${150}^{\circ }\mathrm{C}$, and ${250}^{\circ }\mathrm{C}$) and cooling back to room temperature. By linear extrapolation of these data, $M_s$ and $t_d$ were determined for each temperature, enabling the analysis of their temperature dependence. The influence of the temperature on the perpendicular magnetic anisotropy (PMA), on the interfacial Dzyaloshinskii-Moriya interaction (DMI), and on the magnetic damping was investigated using a custom-built in situ system integrated into Brillouin light scattering and microstrip line ferromagnetic resonance (MS-FMR) setups. The damping constant showed a nonlinear dependence on the inverse effective thickness of the Co layer, attributed to a strong interfacial two-magnon scattering, particularly pronounced in Pt/Co/Au and Pt/Co/Cu structures. With increasing temperature, both the surface PMA and DMI constants decrease (in absolute value), although with a different dynamic of changes between different systems. This behavior is partly due to enhanced thermal fluctuations, which tend to reduce both DMI and anisotropy constants. Additionally, heating during measurements promotes interdiffusion and structural modifications, further influencing magnetic properties. In the case of Pt/Co/MgO, thermal treatment likely acts as an annealing process, enhancing both PMA and DMI by driving the demixing of oxygen atoms from the Co layer and promoting Co/O interface formation. This results in reduced temperature dependence of PMA and DMI for Pt/Co/MgO. Finally, clear correlations were observed between the surface PMA constant and $t_d$ and between the inhomogeneous FMR linewidth and the effective damping constant in the as-grown samples, which diminished with increasing measurement temperature.

Perovskites with tunable and switchable polarization hold immense promise for unlocking novel functionalities. Using density-functional theory, we reveal that intrinsic defects can induce, enhance, and control polarization in nonferroelectric perovskites, with ${\mathrm{SrTiO}}_3$ as our model system. At high defect concentrations, these systems exhibit strong spontaneous polarization—comparable to that of conventional ferroelectrics. Crucially, this polarization is switchable, enabled by the inherent symmetry-equivalence of defect sites in ${\mathrm{SrTiO}}_3$. Strikingly, polarization switching not only reverses the polarization direction and modulates its magnitude but also modifies the spatial distribution of localized defect states. This dynamic behavior points to unprecedented responses to external stimuli, opening new avenues for defect-engineered materials design.

In semiconductor detectors designed for capturing dark matter particles or neutrinos, when the detection threshold is constantly improved to increasingly low energies, an “excess” signal of apparent energy release events below a few hundred eV is observed in several different kinds of detectors. This becomes a big obstacle to the observation of actual dark matter signals, hindering the detectors' sensitivity for rare events in this energy range. Using atomistic simulations with a classical thermostat and a quantum thermal bath, we show that this kind of signal is consistent with energy release from long-term annealing events of complex defects that can be formed by any kind of nuclear recoil radiation events. Such energy releases are shown to have a very similar exponential dependence on energy release magnitudes as that observed in experiments. By detailed analysis of the annealing events, we show that crossing very low energy barriers can trigger larger energy releases in an avalanche-like effect. This explains why large energy release events can occur even down to cryogenic temperatures, where the significant migration of point defects in silicon is hardly ever possible.

${\mathrm{La}}_2{\mathrm{NiO}}_4$ is a prototypical member of the Ruddlesden-Popper nickelate series that offers a valuable reference point for elucidating the key ingredients behind the intriguing properties of these systems. However, the structural and electronic properties of ${\mathrm{La}}_2{\mathrm{NiO}}_4$ under pressure and doping remain surprisingly underexplored. Here, we investigate these properties using density-functional-theory calculations. We find that its tetragonal $I4/mmm$ structure can be stabilized, not only under pressure, but also at ambient pressure via the partial substitution of La with Ba. In both cases, we find a pronounced magnetostructural interplay that manifests, in particular, as anomalies in the lattice-parameter evolution with composition, deviating from Vegard's law. Moreover, we show that the combined effects of Ba substitution and pressure leads to qualitative changes in the electronic structure toward the formal $d^{7.5}$ configuration of the superconducting bilayer nickelates. Further, while ${\mathrm{La}}_2{\mathrm{NiO}}_4$ can undergo an insulator-metal transition with pressure retaining G-type antiferromagnetic order, ${\mathrm{La}}_{1.5}{\mathrm{Ba}}_{0.5}{\mathrm{NiO}}_4$ exhibits metallic behavior with an enhanced competition between different magnetic states. Our results thus offer additional insights into the interplay of structure, doping, and magnetism across the Ruddlesden-Popper nickelate series.

The PL6 color center in $4H$-SiC, known for its excellent ambient-temperature spin and optical properties, has an unresolved microscopic origin. In this first-principles study, we systematically investigate potential structures to clarify its nature. We first rigorously examine the DV-antisite hypothesis (a divacancy paired with a carbon antisite, ${\mathrm{C}}_{\mathrm{Si}}$), analyzing the energetic, electronic, and spin properties of various $V_{\mathrm{Si}}{V}_{\mathrm{C}}+{\mathrm{C}}_{\mathrm{Si}}$ configurations. Two ${\mathrm{C}}_{3\mathrm{v}}$-symmetric $\mathrm{kk}+{\mathrm{C}}_{\mathrm{Si}}$ complexes emerge as strong candidates within this framework. Subsequently, a critical comparison of hyperfine interaction signatures is performed between these candidates, the alternative OV model [specifically OV(hh) and OV(kk), an oxygen replacing C together with a Si vacancy], and experimental data. This analysis demonstrates that the OV(hh) structure more accurately reproduces PL6's hyperfine features. Furthermore, reevaluation of the proposed OV(hk) model for the related PL5 center reveals zero-field splitting parameter $E$ inconsistencies with experimental results, suggesting that PL5 and PL6 may have distinct origins. These findings provide crucial theoretical insights and motivate targeted experimental validation for these quantum defects.

Recent experiments highlight second-order nonlinear optics (NLO), including the bulk photovoltaic effect (BPVE) and second-harmonic generation (SHG), in weak interlayer coupling materials, as the photoelectric conversion is enhanced with layer numbers [Nature (London) 613, 53 (2023)]. Here, based on first-principles calculations, we investigate the BPVE and SHG in $\mathrm{Sn}{\mathrm{P}}_2\mathrm{S}{\mathrm{e}}_6$. The small interlayer coupling energy and minor band-gap variation with layer number indicate its weak interlayer coupling. The BPVE and SHG responses increase with layer number, regardless of the parity of the layer number. Moreover, the interlayer sliding has a negligible influence on the BPVE, which guarantees that the BPVE is robust against structural deformation. The parity-independent, sliding-insensitive BPVE, along with the accumulation effect with layer number of BPVE and SHG in $\mathrm{Sn}{\mathrm{P}}_2\mathrm{S}{\mathrm{e}}_6$, indicates its potential applications in NLO devices.