The characterization of short-range order (SRO) and its influence on performance are a widely debated topics in high-entropy alloys (HEAs). In this work, taking the Co-Fe-Ni-Ti alloy without complicated magnetism as a benchmark of $3d$ HEAs, we investigate the effect of SRO on local lattice distortion (LLD), general stacking fault energy (GSFE), tensile and shear strength of FCC ${\mathrm{Co}}_{30}{\mathrm{Fe}}_{16.66}{\mathrm{Ni}}_{36.67}{\mathrm{Ti}}_{16.67}$ via the combination of Monte Carlo (MC) and molecular dynamics (MD). This alloy shows the typical SRO of Ti-$X$ $(X=\mathrm{Fe},\mathrm{Co})$ atomic pairs, while the segregation of Ti-Ti atomic pairs. The SRO has a minor inhibition on LLD. Considering the thermal vibration induced atomic displacement, the degree of LLD increases nonlinearly with increasing temperature. Both the severe LLD and SRO are helpful to tune the GSFE at finite temperature. The SRO enhances the degree of deformation twinning and delays the appearance of the HCP phase but increases the number of HCP-type atoms as the energy buffers. For the polycrystalline systems, SRO promotes the precipitation of BCC phase at grain boundaries and the number of HCP-type atoms in the grain and activates the deformation of slip surfaces. Therefore SRO could play a key role for the outstanding strength and plasticity of Co-Fe-Ni-Ti HEAs.

We studied the electronic structure of a layered antiferromagnetic metal, EuSnP, in the paramagnetic and in the antiferromagnetic phase using angle-resolved photoemission spectroscopy (ARPES) alongside density-functional theory (DFT)-based first-principles calculations. The temperature dependence of the magnetic susceptibility measurements exhibits an antiferromagnetic transition at a Néel temperature of 21 K. Employing high-resolution ARPES, the valence-band structure was measured at several temperatures above and below the Néel temperature, which produced identical spectra independent of temperature. Through analysis of the ARPES results presented here, we attribute the temperature-independent spectra to the weak coupling of the Sn and P conduction electrons with Eu $4f$ states.

We have succeeded for the first time in synthesizing single crystals of nanolaminated borides ${\left({\mathrm{Fe}}_{1-x}{\mathrm{Mn}}_x\right)}_2{\mathrm{AlB}}_2$ in the entire Fe–Mn composition range using the Al self-flux method, and have established $T-x$ and $H-T$ magnetic phase diagrams from the results of magnetization measurements. The ferromagnetic correlation of ${\mathrm{Fe}}_2{\mathrm{AlB}}_2$ is weakened with the Mn substitution, whereas the antiferromagnetic correlation of ${\mathrm{Mn}}_2{\mathrm{AlB}}_2$ is enhanced with the Fe up to $x=0.65$. The spin direction in the magnetically ordered states changes from the $a$ to the $b$ axis with increasing Mn concentration and temperature. At $x$ = 0.31–0.46, there are three magnetic phases; ferromagnetic, antiferromagnetic, and intermediate phases in between. At $x$ = 0.65 and 0.74, a spin-flop-like metamagnetic transition was observed at a finite field parallel to the spin direction. These observations indicate that in ${\left({\mathrm{Fe}}_{1-x}{\mathrm{Mn}}_x\right)}_2{\mathrm{AlB}}_2$ the ferromagnetic and antiferromagnetic correlations coexist and the uniaxial magnetic anisotropy competes between the $a$ and $b$ axes.

Magnetism-driven nonrelativistic spin splittings (NRSS) are promising for highly efficient spintronics applications. Although 2D centrosymmetric (in four-dimensional spacetime) antiferromagnets are abundant, they have not received extensive research attention owing to symmetry-forbidden spin polarization and magnetization. Here, we demonstrate a paradigm to harness NRSS by twisting the bilayer of centrosymmetric antiferromagnets with commensurate twist angles. We observe $i$-wave altermagnetic spin-momentum coupling by first-principles simulations and symmetry analysis on prototypical ${\text{MnPSe}}_3$ and MnSe antiferromagnets. The strength of NRSS (up to 80 meV Å) induced by twisting is comparable to SOC-induced linear Rashba-Dresselhaus effects. The results also demonstrate how applying biaxial strain and a vertical electric field tune the NRSS. The findings reveal the untapped potential of centrosymmetric antiferromagnets and thus expand the material's horizons in spintronics.

Crystallographic defects in a topological semimetal can result in charge doping and scattering centers which may mask the exotic spectroscopic and transport properties, respectively. Here, we investigate the possible crystallographic defects including vacancy and antisite in Weyl semimetal LaAlGe using hybrid-density-functional theory calculations. We show that a considerable concentration of Al- and Ge-related defects naturally form during growth due to their low formation enthalpy. Specifically, Al can be easily replaced by Ge in the $I{4}_{1}md$ phase of LaAlGe, forming the Ge-on-Al antisite, ${\mathrm{Ge}}_{\mathrm{Al}}$. The counterpart, Al-on-Ge (${\mathrm{Al}}_{\mathrm{Ge}}$), is also probable. The most abundant defect ${\mathrm{Ge}}_{\mathrm{Al}}$ is donorlike, effectively electron doping, and these defects are therefore not only scattering centers in the electronic transport process but may also induce the substantial vertical shift of the chemical potential. The results imply that the naturally occurring defects hinder both spectroscopic and transport features arising from the Weyl physics in LaAlGe. Our work can be applied to the $R\mathrm{AlGe}$ family ($R=\mathrm{rare}$ earth) and help improve the quality of single-crystal magnetic Weyl semimetal.

Vanadium sesquioxide (${\mathrm{V}}_2{\mathrm{O}}_3$) is a strongly correlated electronic material that famously undergoes a triple coupled first-order transition where it transitions from a paramagnetic metal with a rhombohedral structure at high temperature to an antiferromagnetic insulator with a monoclinic structure. While several studies have used one of both electronic and structural transitions to control the properties of a heterostructure, evidence of magnetic coupling has notoriously yet to be found. In this paper, we report on a robust magnetic coupling between the antiferromagnetic (AFM) ${\mathrm{V}}_2{\mathrm{O}}_3$ and ferromagnetic (FM) Permalloy (Py) layers that results in a significant exchange bias and strain-induced coercivity enhancement. We provide a temperature and angle-dependent study of magnetic properties, which clearly indicates exchange bias at the AFM/FM interface that appears at the onset of the metal-insulator transition. The magnitude of the exchange bias is strongest when the field is applied along the [001] ${\mathrm{V}}_2{\mathrm{O}}_3$ crystallographic orientation which corresponds to an AFM spin configuration on the [110] surface. This opens the door to designing and implementing novel functionalities in transition metal oxide-based computing using the connection between magnetism and the metal-insulator transition.

${\mathrm{LaMnO}}_3$ (LMO) thin films epitaxially grown on ${\mathrm{SrTiO}}_3$ (STO) usually exhibit ferromagnetism above a critical layer thickness. We report the use of scanning SQUID microscopy (SSM) to study the suppression of the ferromagnetism in STO/LMO/metal structures. By partially covering the LMO surface with a metallic layer, both covered and uncovered LMO regions can be studied simultaneously. While Au does not significantly influence the ferromagnetic order of the underlying LMO film, a thin Ti layer induces a strong suppression of the ferromagnetism, over tens of nanometers, which increases with time on a timescale of days. Detailed electron energy loss spectroscopy analysis of the Ti-${\mathrm{LaMnO}}_3$ interface reveals the presence of ${\mathrm{Mn}}^{2+}$ and an evolution of the Ti valence state from ${\mathrm{Ti}}^0$ to ${\mathrm{Ti}}^{4+}$ over approximately 5 nm. Furthermore, we demonstrate that by patterning Ti/Au overlayers, we can locally suppress the ferromagnetism and define ferromagnetic structures down to sub-micrometer scales.

Potassium sodium niobate lead-free piezoelectric thin films are of great potential for integrated functional devices. Metal-organic vapor-phase epitaxy enables high-quality wafer-scale fabrication of epitaxial piezoelectric thin films, whereas the film domain structure and evolution, which particularly originate from the strain and strongly impact the film properties, require further study. We report in this paper an in-depth study of the piezoelectric domain structure as well as the domain evolution induced by an external electric field in ${\mathrm{K}}_{0.5}\mathrm{N}{\mathrm{a}}_{0.5}\mathrm{Nb}{\mathrm{O}}_3$ films. Epitaxially strained $c_{\mathrm{pc}}$ oriented ${\mathrm{K}}_{0.5}\mathrm{N}{\mathrm{a}}_{0.5}\mathrm{Nb}{\mathrm{O}}_3$ films were grown on $\mathrm{SrRu}{\mathrm{O}}_3/\mathrm{DySc}{\mathrm{O}}_3$ (110) substrates, and four different superdomain variants consisting of monoclinic ${90}^{\circ } M_{\mathrm{C}}$ stripe domains were verified and studied in detail. The domain switching behavior was examined by piezoresponse force microscopy (PFM), which suggests that both the in-plane and out-of-plane polarization can be reversed by an external out-of-plane positive electric field. However, application of a negative bias leads to the accumulation of surface charges concurrently accompanied by small morphology changes. We tentatively attribute this observation to the injection of vacancies in the film surface under negative voltage. Therefore, the out-of-plane polarization component cannot be switched, and in-plane orientation of the stripe domains is only reoriented at the edges of the litho-window, which could be attributed to either an inhomogeneous electric field below the PFM tip or trailing fields caused by the movement of the PFM tip across the surface. However, surface charges dissipate within 1 h. These results are beneficial for understanding the domain evolution mechanism and intentional tuning of ferroelectric thin-film properties.

Magnetic properties of bulk thulium crystals have been studied, with most works dating back to the 1960s, but to our knowledge, studies of thulium thin films are lacking. Here, we report the growth of Tm(0001) epitaxial films on SiC(0001) by means of molecular beam epitaxy. Clear Laue oscillations and narrow rocking curves in the x-ray diffraction scans indicate the high crystalline quality of the films. Magnetic circular dichroism and the anomalous Hall effect are utilized to probe magnetic properties. Periodic changes of remanent magnetization indicate a ferrimagnetic order with a period of seven monolayers along the $c$ axis, in agreement with the ferrimagnetic properties of the bulk. The realization of Tm thin films opens the door to explore physics that could not be probed in the bulk.

Using first principles density functional theory calculations, we explore the atomic and electronic structure of TiOF, aiming to understand the impact of fluoride substitution on the rutile ${\mathrm{TiO}}_2$ framework. We identify the ground state atomic structure of TiOF and uncover the driving forces behind the experimentally observed anion ordering along rutile (110) planes. The anion ordering stems from the interplay between Ti-F cation-anion interactions and the tendency of $d^1{\mathrm{Ti}}^{3+}$ cations to form singlet Ti-Ti dimers through enhanced metal-metal bonding. As the on-site Coulombic interactions increase, we observe suppression of the singlet state formation and the induction of local magnetic moments on the ${\mathrm{Ti}}^{3+}$ sites. Lastly, we show that the $d$-electron filling of the transition metal cation dictates the long-range anion ordering in $3d$ rutile oxyfluorides.

The low symmetry of monoclinic $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ leads to elaborate intrinsic defects, such as Ga vacancies split amongst multiple lattice sites. These defects contribute to fast, anisotropic Ga diffusion, yet their complexity makes it challenging to understand dominant diffusion mechanisms. Here, we predict the 3D diffusivity tensors for Ga interstitials ($\mathrm{Ga}{}_{\text{i}}^{3+}$) and vacancies ($\mathrm{V}{}_{\text{Ga}}^{3-}$) via first principles and direct solution of the master diffusion equations. We first explore the maximum extent of configurationally complex “$N$-split” Ga interstitials and vacancies. With dominant low-energy defects identified, we enumerate all possible elementary hops connecting defect configurations to each other, including interstitialcy hops. Hopping barriers are obtained from nudged elastic band simulations. Finally, the comprehensive sets of (i) defect configurations and their energies and (ii) the hopping barriers that connect them are used to construct the master diffusion equations for both $\mathrm{Ga}{}_{\text{i}}^{3+}$ and $\mathrm{V}{}_{\text{Ga}}^{3-}$. The solution to these equations yields the Onsager transport coefficients, i.e., the components of the 3D diffusivity tensors $D_{{\text{Ga}}_{\text{i}}}$ and $D_{{\text{V}}_{\text{Ga}}}$ for $\mathrm{Ga}{}_{\text{i}}^{3+}$ and $\mathrm{V}{}_{\text{Ga}}^{3-}$, respectively. It further reveals the active diffusion paths along all crystallographic directions. We find that both $\mathrm{Ga}{}_{\text{i}}^{3+}$ and $\mathrm{V}{}_{\text{Ga}}^{3-}$ diffusion are fastest along the $c$ axis, due to three-split defects that bridge neighboring unit cells along the $c$ axis and enable diffusing species to circumvent pathways with high-energy migration barriers. Although isolated $\mathrm{Ga}{}_{\text{i}}^{3+}$ diffuse faster than isolated $\mathrm{V}{}_{\text{Ga}}^{3-}$, self-diffusion of Ga is predominantly mediated by ${\mathrm{V}}_{\text{Ga}}^{3-}$ due to the higher ${\mathrm{V}}_{\text{Ga}}^{3-}$ defect concentration under most thermodynamic environments.

In recent years, surface segregation of doping elements in layered oxide positive electrode (cathode) materials for metal-ion batteries has drawn considerable attention. It was repeatedly shown that an increase of surface concentration of a particular element can have either detrimental or beneficial impact on the stability of the electrochemically active surface, manifesting declined or improved electrochemical performance. However, the physical and chemical reasons for segregation remain poorly understood. To explain the behavior of commercially important doping elements, such as Mg, Al, Ti, V, Cr, Mn, Fe, and Ni, we performed a density functional theory study of their segregation at the (104) low-energy surface of ${\mathrm{LiCoO}}_2$. By careful control of local oxidation states and magnetic moments of surface atoms, we find their most stable configurations. We discover that all elements, except Al and Cr, are prone to segregation that is primarily driven by the surface energies' difference between the host and solute lattices, which is explained through crystal-field stabilization energies. An additional contribution to segregation is caused by the elastic energy penalty to the ionic size mismatch effect. Finally, we rationalize the available experimental results and provide several predictions of highly segregating and nonsegregating dopants.

Low-dimensional materials, in which the electronic and transport properties are drastically modified in comparison to those of three-dimensional bulk materials, yield a key class of thermoelectric materials with high conversion efficiency. Among such materials, the organic compounds may serve peculiar properties owing to their unique molecular-based low-dimensional structures with highly anisotropic molecular orbitals. Here we present the thermoelectric transport properties of the quasi-one-dimensional dimer-Mott insulator ${\beta }^{\prime }$-(BEDT-${\mathrm{TTF})}_2{\mathrm{ICl}}_2$, where BEDT-TTF stands for bis(ethylenedithio)-tetrathiafulvalene. We find that the thermopower exhibits typical activation-type temperature variation expected for insulators but its absolute value is anomalously large compared to the expected value from the activation-type temperature dependence of the electrical resistivity. Successively, the Jonker-plot analysis, in which the thermopower is usually scaled by the logarithm of the resistivity, shows an unusual relation among such transport quantities. We discuss a role of the low dimensionality for the enhanced thermopower along with recent observations of such a large thermopower in several low-dimensional materials.

The prediction of glass forming ability (GFA) and various properties in bulk metallic glasses (BMGs) pose a challenge due to the unique disordered atomic structure in this type of material. Machine learning shows the potential ability to find a way out. However, the training set from the experimental data of BMGs faces the issue of data imbalance, including the distribution of data related to elements, the range of performance data, and the distribution of sparse and dense data area in each specific system. In this work, the origin of the data imbalance and its impact on the GFA prediction ability of machine-learning models are analyzed. We propose the solutions by training the model using the pruned dataset to mitigate the imbalance and by performing an active experimental iterative learning to compensate for the information loss resulting from data reduction. The strategy is proved in Zr-Al-Cu system, and the automated workflow has been established. It effectively avoids the prediction results from trapping into the intensive training-data area or from inducing by the data distribution of similar element systems. This approach will expedite the development of BMGs compositions, especially for unexplored systems.

The advancement of technologies relies on the discovery of new materials with emerging physical properties that are determined by their crystal structures. Ruddlesden-Popper (R-P) phases with a formula of $A_{n+1}{B}_n{X}_{3n+1}$ ($n=1,2,3,...,\infty$) are among one of the most widely studied classes of materials due to their electrical, optical, magnetic, and thermal properties as well as their combined multifunctional properties. In R-P phases, intergrowth is well known in the short range; however, no existing compounds have been reported to have different $n$ mixed in bulk single crystals. Here we design a hybrid R-P nickelate $\mathrm{L}{\mathrm{a}}_2\mathrm{Ni}{\mathrm{O}}_4·\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$ by alternatively stacking bilayers, which is the active structural motif in the $\text{high-}{T}_{\mathrm{c}}$ superconductor $\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$ and single layers of the antiferromagnetic insulator $\mathrm{L}{\mathrm{a}}_2\mathrm{Ni}{\mathrm{O}}_4$. We report the successful synthesis of $\mathrm{L}{\mathrm{a}}_2\mathrm{Ni}{\mathrm{O}}_4·\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$ single crystals, and x-ray diffraction and real-space imaging via scanning transmission electron microscopy (STEM) show that the crystal structure consists of single layers and bilayers of $\mathrm{Ni}{\mathrm{O}}_6$ octahedral stacking alternatively perpendicular to the $ab$ plane, characterized by the orthorhombic Immm (No. 71) space group. Resistivity measurements indicate a metallic ground state and a peculiar resistivity maximum around 140 K. Density functional theory (DFT+$U$) calculations corroborate this finding and reveal that both the bilayer and the single layer are metallic and that the single layer becomes paramagnetic metallic due to the charge transfer via LaO layers. The discovery of $\mathrm{L}{\mathrm{a}}_2\mathrm{Ni}{\mathrm{O}}_4·\mathrm{L}{\mathrm{a}}_3\mathrm{N}{\mathrm{i}}_2{\mathrm{O}}_7$ opens a door to access a family of three-dimensional hybrid R-P phases with the formula of $A_{n+1}{B}_n{X}_{3n+1}·A_{m+1}^{\prime }{B}_m^{\prime }{X}_{3m+1}^{\prime }$ ($n\ne m$), which potentially host a plethora of emerging physical properties for various applications.

In the last decade, studies of magnetoresistance in heterostructures of topological insulator (TI) and ferromagnetic (FM) insulators have indicated the existence of induced magnetization at TI surfaces. However, the magnetic proximity effect in heterostructures of TIs and FM metals has been less explored. Here, we report a spin-valve-like magnetoresistance (MR) switching observed in a bilayer device of ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ and a Co/Pt multilayer ([Co/Pt]), where the [Co/Pt] is a FM metal with a perpendicular magnetic anisotropy. This MR switching happens at temperatures below 1 K and for magnetic field sweeps along all in-plane and out-of-plane directions, at values much lower than the magnetization switching fields of the top FM layer. The in-plane field sweeps at various angles also reveal a threefold symmetry of the switching fields, matching the symmetry of the TI crystal structure. We suggest that the large MR switching rises from the interplay between the magnetization of the top FM metal layer and the induced magnetization at the TI surface.

Infrared photoionization and intracenter cross sections as well as oscillator strengths of intracenter transitions in silicon doped with single-electron, shallow donors are determined in research-grade crystals and compared with the corresponding values calculated by various theoretical models. The float-zone grown crystals were doped with substitutional group-V, interstitial group IA lithium and lithium-oxygen complex at concentrations of ${10}^{12}–{10}^{17}\mathrm{atoms}/\mathrm{c}{\mathrm{m}}^3$. The concentrations of electrically active impurity centers in the samples were determined from resistivity measurements. Experimentally integrated cross sections were obtained from low-temperature absorption spectra of impurities. For an isocoric substitutional donor, the oscillator strengths for intracenter transitions into the lowest odd-parity states were compared for two main crystal growth and doping methods: the float-zone and the Czochralski techniques. The applicability of the obtained calibration coefficients for various ranges of impurity concentrations is discussed. Recommendations are given for the optimal selection of optical transitions for quantifying the density of shallow donors in silicon along with experimental values for each shallow center. The oscillator strengths of transitions of shallow impurities were estimated for almost all observed donor transitions, including those into high excited, Rydberg-like atomic states, as well as for the intracenter transitions into several even-parity excited states.

The formation and study of oxygen vacancies are critical for the development of enhanced functional oxides; in the oxygen evolution reaction (OER), oxygen vacancies are proposed to influence the activity and degradation of electrocatalysts. We use thin films of state-of-the-art OER catalyst $\mathrm{SrIr}{\mathrm{O}}_3$ deposited on crystal substrates with varied lattice parameters to demonstrate the effect of epitaxial strain on oxygen vacancy formation. Through in situ x-ray diffraction under elevated temperatures and reducing conditions of 3% ${\mathrm{H}}_2$/balance ${\mathrm{N}}_2$, we show that tensile epitaxial strain makes oxygen vacancy formation more favorable, whereas compressive epitaxial strain has no significant effect compared with an unstrained film. We further use in situ and ex situ x-ray absorption spectroscopy to reveal the effect of strain on the favorability of full reduction of Ir species within $\mathrm{SrIr}{\mathrm{O}}_3$ films from $\mathrm{I}{\mathrm{r}}^{4+}$ to $\mathrm{I}{\mathrm{r}}^0$ and on the energy levels of unoccupied electronic states in the out-of-plane direction, respectively. This study adds experimental evidence for the link between strain and oxygen vacancy formation in $5d$ thin film perovskites, for which the discussion has been dominated by theory-based approaches.

Strontium titanate ($\mathrm{SrTi}{\mathrm{O}}_3$) can exhibit multiple orders, including superconductivity, an antiferrodistortive instability, and ferroelectricity. The cooperation or competition between these orders in samples that undergo all three transitions is of great fundamental interest. Here, we report scanning transmission electron microscopy imaging of the antiferrodistortive and ferroelectric structural distortions in a compressively strained $\mathrm{SrTi}{\mathrm{O}}_3$ film that was previously shown to become superconducting at ∼410 mK. The experiments are complemented by first-principles simulations. Unlike the polar ferroelectric phase, which is suppressed by dopants, the antiferrodistortive order is insensitive to the presence of the free carriers. The single-domain nature of the antiferrodistortive phase excludes any role of antiferrodistortive domain walls in the superconductivity. A previously reported low-temperature resistance anomaly is associated with the ferroelectric transition, not the antiferrodistortive transition.

Nickel-based superalloys are an exceptional class of materials that are indispensable for high-temperature applications in the aerospace and power sector industries worldwide. The prolonged application of these materials in a demanding environment is hindered by the increased oxidation rates and deformation due to mass gain at high temperatures and the presence of corrosive agents. Calculating the oxidation properties using experimental techniques is laborious and highly cost/time intensive, which presents a considerable challenge to reducing the oxidation in these materials. In this work, we establish an extensive database consisting of the specific mass gain due to oxidation ($\mathrm{\Delta }m$) and the parabolic oxidation rates (${\mathrm{k}}_{\mathrm{p}}$) of nickel-based superalloys spanning all the superalloy generations. Highly accurate machine learning (ML) models are developed to predict ($\mathrm{\Delta }m$) using artificial neural networks and tree-based XGBoost. The ML models are extended by unsupervised $k$ means clustering to improve the accuracy of the models and generate insights on the composition-property linkages. Additionally, the ML model for ${\mathrm{k}}_{\mathrm{p}}$ developed utilizing XGBoost yields unprecedented results with errors of 0.04. The ML model is analyzed using the SHapely Additive exPlanations parameters to determine the effect of individual features on the model. Further, we employ a genetic algorithm-based approach utilizing the developed ML models to minimize the ${\mathrm{k}}_{\mathrm{p}}$ to improve the performance of the superalloys at high temperatures. The genetic algorithm-assisted optimization successfully yields several compositions for new Ni superalloys with up to 20% reduction in the ${\mathrm{k}}_{\mathrm{p}}$. This work presents essential advances for accelerating the targeted discovery of new materials for highly specialized and demanding applications.