We here model the radiation-induced microstructure evolution in bcc iron using the creation-relaxation algorithm directly driven by density functional theory calculations and compare to interatomic potential simulations. The method is in essence a relatively simplified model without thermally driven diffusion. The microstructure evolution in this model is driven mostly by the stress field introduced by sequential direct damage insertions. The defect populations and the corresponding defect cluster characteristics have been analyzed as a function of irradiation dose. Different distribution functions have been investigated for the self-interstitial atom implantation, to make model predictions as close as possible to actual irradiation conditions under which defects are produced. The stability and magnetic characteristics of the defect structures that are formed are studied. Our first-principles simulations revealed that the C15 structure can be dynamically formed during the irradiation of the material and that the constituent atoms align antiferromagnetically to the lattice. For doses on the order of a fraction of 1 displacement per atom, the model material Fe experiences mechanical changes caused by continuous irradiation and approaches a saturation state of about 2% swelling. The radiation-induced change in the local magnetic moments as well as the charge density differences for some isolated and clustered defects have been investigated. The results revealed a net reduction in total magnetization per atom and a tendency for interstitial sites to have a spin polarization opposing the intrinsic atomic site spins when the coordination number was increased compared to that of the initial lattice structure. It is suggested that radiation-induced damage could be traced using nondestructive measures of bulk magnetization changes.

The honeycomb lattice of silicene exhibits a variety of nontrivial reconstructions on the Ag(111) surface, whose diversity hampers the theoretical prediction of experimentally unidentified structures using computationally expensive density functional theory (DFT) calculations. We here apply an efficient method based on an evolutionary algorithm and a Gaussian process, which is trained on the fly with DFT calculations, to the search for the stable structures of silicene on Ag(111). We demonstrate that the structure search method can not only reproduce the well-known structures, but also predict the existence of metastable structures that are close in stability to the most stable ones. Detailed analyses of the obtained results reveal that such metastable structures play crucial roles in the stabilization of less ordered phases often observed experimentally. The present method can replace the conventional manual search based on intuition and is widely applicable to the investigations of new systems such as emerging two-dimensional materials.

The puzzling question about the floating of the topological surface state on top of a thick Pb layer has now possibly been answered. A photoemission study of the interface made by Pb on ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ for different temperatures and adsorbate coverage conditions, allowed us to demonstrate that the evidence reported in the literature can be related to the surface diffusion phenomenon exhibited by the Pb atoms, which leaves the substrate partially uncovered. Comprehensive density functional theory calculations show that despite the specific arrangement of the atoms at the interface, the topological surface state cannot float on top of the adlayer but rather tends to move inward within the substrate.

We study spin-orbit torques (SOTs) in Ni/Pt bilayers and multilayers by ferromagnetic resonance (FMR) and harmonic-Hall measurements. The effect of multilayering and crystal orientation on fieldlike (FL) and dampinglike (DL) torque efficiencies is examined by exploiting the samples with different crystal orientations: epitaxial and polycrystalline structures on sapphire and ${\mathrm{SiO}}_2$ substrates, respectively. We find that both DL and FL torque efficiencies are larger in multilayer samples and there is no complete cancellation of torque efficiencies that is generally expected for ideal symmetric stacking structures. The results of SOT-FMR indicate that the epitaxial samples show higher efficiency for SOT generation compared to the polycrystalline samples, suggesting that SOT generation is modified depending on the interfacial contribution. In addition, the spin Hall conductivity of the epitaxial multilayer is the largest among the samples. The present results signify the importance of crystal orientation, multilayering, and interface quality in improving the efficiency of SOT generation combined with larger spin Hall angle for developing future spintronic devices.

We investigate the magnetic field induced spectral properties of metamaterials incorporating indium antimonide (InSb), using electromagnetic probes in the low terahertz frequency regime. An effective medium theory has been developed to explore the behavior of InSb interspersed with a simple dielectric in a gratinglike structure with various thicknesses and grating filling factors. The metamaterial grating structure impacts the light-matter interactions and substantially modifies reflectivity. Our numerical results demonstrate how nonreciprocal reflection can be enhanced and controlled in this spectral region through the composition of the magnetic grating. The current need for higher frequency communication technology drives the relevancy of this study for application to directional-dependent terahertz devices.

${\mathrm{NH}}_4\mathrm{SCN}$ exhibits successive phase transitions from monoclinic to orthorhombic, and then to tetragonal. The former phase transition is accompanied by an inverse colossal barocaloric effect and a huge negative thermal expansion. This transition is complicated by the possibly coexisting orientational disorder of ${\mathrm{NH}}_4^{+}$ and $\mathrm{SC}{\mathrm{N}}^{-}$, and the mechanism is still unclear. Here, ${\mathrm{NH}}_4\mathrm{SCN}$ is investigated using high-resolution neutron powder diffraction, pair distribution function analysis, and Raman scattering. Both the average and local structural analyses indicate that only ${\mathrm{NH}}_4^{+}$ is orientationally disordered in the orthorhombic phase, and $\mathrm{SC}{\mathrm{N}}^{-}$ becomes subsequently disordered in the tetragonal phase. Both temperature-induced and pressure-induced hardening behaviors of $\mathrm{SC}{\mathrm{N}}^{-}$-related vibrations are observed, which lead to the breakage of hydrogen bonds-linked ${\mathrm{NH}}_4^{+}$ with $\mathrm{SC}{\mathrm{N}}^{-}$ and further facilitate phase transition. Our findings provide a solid standing point of atomic structures and dynamics on which the scenario of the phase transition and the associated physical properties are established.

Today, the capture of post-combustion ${\mathrm{CO}}_2$ has become a global priority, particularly in order to curb rising temperatures in the coming decades. ${\mathrm{CO}}_2$ physisorption in porous materials such as metal-organic frameworks is likely one of the most effective approaches to addressing this problem, thanks to its low energy requirement and improved regeneration process. In this study, I investigated ${\mathrm{CO}}_2$ capture in humid conditions using the Al-MIL-53-TDC metal-organic framework through molecular simulations. I observed that water filling occurs gradually through pore capillary condensation. Remarkably, the presence of water (at a hydration rate of 4.4 wt%) resulted in a significant increase of 283% in the adsorbed amount of ${\mathrm{CO}}_2$ (1.8 mmol/g at 0.2 bar) due to a unique transparency property. The thin molecular walls between the uniaxial channels enable van der Waals and electrostatic interactions between water and adsorbed gas, which allow media on opposite sides of the walls to influence each other. The increase in isosteric heat of adsorption (46 kJ/mol) is attributed to the contribution of water/water energy resulting from the truncation of the hydration shell of water. This truncation increases the number of hydrogen bonds, which can be linked to a kosmotropic effect. Additionally, the selectivity of hydrated Al-MIL-53-TDC for ${\mathrm{CO}}_2$/${\mathrm{N}}_2$ increased by 185% at 0.2 bar (composition 20:80), compared to the unhydrated MOF material with QsT $<$ 50 kJ/mol.

We present a study by scanning tunneling microscopy, supported by ab initio calculations, of the interaction between graphene and monolayer (semiconducting) $\mathrm{Pt}{\mathrm{Se}}_2$ as a function of the twist angle $\theta$ between the two layers. We analyze the $\mathrm{Pt}{\mathrm{Se}}_2$ contribution to the hybrid interface states that develop within the band gap of the semiconductor to probe the interaction. The experimental data indicate that the interlayer coupling increases markedly with the value of $\theta$, which is confirmed by ab initio calculations. The moiré patterns observed within the gap are consistent with a momentum conservation rule between hybridized states, and the strength of the hybridization can be qualitatively described by a perturbative model.

There is ongoing interest in strongly correlated spin systems where the interplay between structural, charge, and spin degrees of freedom produces novel phenomena, including helical spin order, topologically protected spin textures (e.g., skyrmions), unconventional electronic band physics (e.g., flat bands), and other emergent states. Here we report results for ${\mathrm{GdNiAl}}_4{\mathrm{Ge}}_2$, which crystallizes in a rhombohedral structure that features geometrically frustrated triangular nets of lanthanide ions. Magnetic, thermodynamic, and electrical transport measurements reveal metallic behavior with antiferromagnetic-like ordering in small magnetic fields, which strongly evolves to produce a spin-flop transition and hysteresis for magnetic fields applied in the $ab$ plane. This results in a region of the temperature-field phase space where the magnetic susceptibility of the field-cooled curves is smaller than that of the zero-field-cooled curves and where the ac magnetic response exhibits frequency- and field-dependent peaks only in the zero-field-cooled curves. This suggests the formation of history-dependent spin structures or domains with complex spin relaxation dynamics, possibly resembling what is seen in other materials with nontrivial spin textures. This establishes ${\mathrm{GdNiAl}}_4{\mathrm{Ge}}_2$ as a host for intriguing spin states and further focuses attention on this family of materials.

This study explores the influence of heat treatment paths on the structural relaxation of metallic glasses (MGs) in the regime of fast dynamics. We create MG samples using various quenching rates, from ${10}^9$ to ${10}^{11}$ K/s, and expose these samples to near-$T_{\mathrm{g}}$ heat treatments with assorted combinations of heating (cooling) rates, from $5\times {10}^{10}$ to $5\times {10}^{12}$ K/s, and annealing durations, from 10 ps to 10 ns. Results show that the effect of the heating rate is intricately tied to the initial structure of the MG, while a decrease in the cooling rate invariably intensifies the aging process. Extending the annealing duration may induce either aging or rejuvenation, subject to the specific thermal history. To interpret these findings, we hypothesize that the memory effect, governed by the activation and annihilation of reversible and irreversible flow units, underpins the rejuvenation-aging competition in MGs. Moreover, we suggest viewing the cooling stage as an annealing phase controlled by gradient temperature and fine-tuning its rate to achieve the targeted active-flow unit distributions. This study illuminates the role of fast dynamics during the glass relaxation process and offers practical strategies for tailoring heat treatments to optimize MG structures and mechanical performance.

We report the electronic structure of ${\mathrm{In}}_{1.8-x}{\mathrm{Mn}}_x{\mathrm{Sn}}_{0.2}{\mathrm{O}}_3$ ($x=0.0$, 0.2, and 0.3), which combines transparency, ferromagnetism, and semiconducting properties, by means of hard x-ray photoemission spectroscopy (HAXPES), soft x-ray resonant photoemission spectroscopy (RPES), and x-ray absorption spectroscopy (XAS). The spectral shape of the Mn $L$-edge XAS spectra indicates that the valence of the substitutional Mn ions is divalent. The peak position of the In $3d$ and O $1s$ core-level spectra shifts toward lower binding energy with Mn concentration suggest the hole doping due to the ${\mathrm{Mn}}^{2+}$ ions. The valence-band spectra exhibit the well-defined features associated with the donor states across the Fermi level $E_{\mathrm{F}}$ and the valence-band edge. The valence-band maximum (VBM) shifts to lower binding energy and the spectral weight near $E_{\mathrm{F}}$ decreases with increasing Mn concentration, which is consistent with the hole doping nature observed in the core-level shift. The Mn $2p\text{−}3d$ RPES reveals that the hump structure around 1.9 eV above the VBM originates from the Mn $3d$ impurity band and the valence-band state consists of the O $2p$ band strongly hybridized with the Mn $3d$ orbital. Furthermore, there is no contribution of the Mn $3d$ orbital to the spectral weight close to $E_{\mathrm{F}}$. Our results reveal the entire valence-band structure of ${\mathrm{In}}_{1.8-x}{\mathrm{Mn}}_x{\mathrm{Sn}}_{0.2}{\mathrm{O}}_3$ and the effect of the Mn substitution, which provides the important information related to the physical properties such as transparency, electrical conductivity, and ferromagnetism for the functional materials.

A true understanding of the properties of pnictide superconductors requires the development of high-quality materials and performing measurements designed to unravel their intrinsic properties and short-range nematic correlations which are often obscured by extrinsic effects such as poor crystallinity, inhomogeneity, domain formation, and twinning. In this paper, we report the systematic growth of high-quality Na-substituted $\mathrm{Ba}{\mathrm{Fe}}_2{\mathrm{As}}_2$ single crystals and their characterization using pulsed magnetic fields x-ray diffraction and x-ray diffuse scattering. Analysis of the properties and compositions of the highest-quality crystals shows that their actual Na stoichiometry is about 50–60% of the nominal content and that the targeted production of crystals with specific compositions is accessible. We derived a reliable equation to estimate the Na stoichiometry based on the measured superconducting $T_c$ of these materials. Attempting to force spin reorientation and induce tetragonality, orthorhombic ${\mathrm{Ba}}_{1-\mathrm{x}}{\mathrm{Na}}_{\mathrm{x}}{\mathrm{Fe}}_2{\mathrm{As}}_2$ single crystals subjected to out-of-plane magnetic fields up to 31.4T are found to exhibit strong in-plane magnetic anisotropy demonstrated by the insufficiency of such high fields in manipulating the relative population of their twinned domains or in suppressing the orthorhombic order. Broad x-ray diffuse-intensity rods observed at temperatures between 30 and 300 K uncover short-range structural correlations. Local structure modeling together with 3D–Δ pair-distribution function mapping of real-space interatomic vectors show that the diffuse scattering arises from in-plane short-range chemical correlations of the Ba and Na atoms coupled with short-range atomic displacements within the same plane due to an effective size difference between the two atomic species.

Visualization of dynamic processes during ionic migration in oxides can provide us opportunities for direct observation of various ionic phenomena and for understanding mechanisms of various applications that work based on ionic migration in solids. Electrocoloration is a readily accessible means of the direct observation of dynamic processes governed by oxygen ion migration. Here, we investigate the dynamic behavior of color fronts in the lateral devices of Ca-doped $\mathrm{BiFe}{\mathrm{O}}_3$ thin films grown on $\mathrm{SrTi}{\mathrm{O}}_3$ (100) substrates by recording the electrocoloration process with an optical microscope while simultaneously measuring the channel current. Voltage-dependent morphological instabilities, such as kinetic roughening of color fronts, are analyzed. We found that a significant amount of oxidation preceded the propagation of color fronts during electrocoloration and hence oxygen ionic mobility measured from the electrocoloration methods is the property of the intermediate phase, more oxidized than the pristine phase. This work provides intriguing insights into the dynamic behaviors of oxygen ions in oxides and the ionic mobility measurements with electrocoloration methods.

Thin layers of orthorhombic uranium ($\alpha$-U) have been grown onto buffered sapphire substrates by dc magnetron sputtering, resulting in the discovery of new epitaxial matches to Ti(00.1) and Zr(00.1) surfaces. These systems have been characterized by x-ray diffraction and reflectivity and the optimal deposition temperatures have been determined. More advanced structural characterization of the known Nb(110) and W(110) buffered $\alpha$-U systems has also been carried out, showing that past reports of the domain structures of the U layers are incomplete. The ability of this low symmetry structure to form crystalline matches across a range of crystallographic templates highlights the complexity of U metal epitaxy and points naturally toward studies of the low temperature electronic properties of $\alpha$-U as a function of epitaxial strain.

In this study, we investigate the properties of ferrimagnetic ${\mathrm{Tb}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ (TbIG) thin films grown on ${\mathrm{Gd}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ (GGG) substrates using the pulsed laser deposition technique. Some of the films are capped with a thin platinum (Pt) layer. We observe a strong temperature-dependent anomalous Hall effect in the films, with sign reversals at the ferrimagnetic compensation temperature $\left(\sim 240\mathrm{K}\right)$ and lower temperatures. X-ray diffraction and scanning transmission electron microscopy (STEM) confirm the high crystalline quality and smooth surfaces of the films, while the Pt layer is found to be polycrystalline. Polarized neutron reflectometry reveals a weak magnetic moment confined to the TbIG layer, and an interfacial magnetic layer at the substrate-film boundary appears at low temperatures (below 10 K). This observation is supported by STEM-energy dispersive x-ray mapping, which indicates a chemical difference in the ratio of Gd:Ga at the TbIG/GGG interface. Unlike YIG/GGG interfaces, the TbIG/GGG interface does not exhibit magnetic dead layers. Additionally, a small, induced magnetization is detected in the Pt heavy metal layer at low temperature, with ferromagnetic coupling to the garnet, potentially influencing the anomalous Hall effect.

The magnetic properties of [Mn(pyrazinecarboxylate)${}_2{]}_n$, empirical formula ${\mathrm{C}}_{10}{\mathrm{H}}_6{\mathrm{MnN}}_4{\mathrm{O}}_4$, are investigated through susceptibility, heat capacity, and neutron scattering measurements. The structure consists of Mn-Mn dimers linked on a distorted 2D hexagonal structure. The weak out-of-plane interactions create a quasi-2D magnetic material within the larger three-dimensional metal-organic framework structure. We show that this material undergoes a two-stage magnetic transition, related to the low dimensionality of the Mn lattice. First, at 5 K, which is assigned to the initial development of short-range order in the 2D layers. This is followed by long-range order at 3.3 K. Applied field measurements reveal the potential to induce magnetic transitions in moderately small fields of $\sim 2$ T. Neutron powder diffraction enabled the determination of a unique magnetic space group ${P{2}_1}^{\prime }/c$ (No. 14.77) at 1.5 K. This magnetic structure consists of antiferromagnetically coupled Mn-Mn dimers with spins principally along the out-of-plane $a$ axis.

Using an evolutionary algorithm in combination with first-principles density-functional theory calculations, we identify a two-dimensional (2D) ${\mathrm{CaP}}_3$ monolayer as a new Dirac semimetal due to inversion and nonsymmorphic spatial symmetries of the structure. This new topological material, composed of light elements, exhibits high structural stability (higher than the phase known in the literature), which is confirmed by thermodynamic and kinetic stability analysis. Moreover, it satisfies the electron filling criteria, so that its Dirac state is located near the Fermi level. The existence of the Dirac state predicted by the theoretical symmetry analysis is also confirmed by first-principles electronic band structure calculations. We find that the energy position of the Dirac state can be tuned by strain, while the Dirac state is unstable against an external electric field since it breaks the spatial inversion symmetry. Our findings should be instrumental in the development of 2D Dirac fermions based on light elements for their application in nanoelectronic devices and topological electronics.