A systematic study of the evolution of the crystal structure and magnetic properties upon chromium substitution for iron atoms in the ${\mathrm{Fe}}_{3-x}{\mathrm{Cr}}_x{\mathrm{Se}}_4$ system is reported. According to neutron diffraction, Fe and Cr atoms are distributed unequally across the metal layers: with increasing $x$, substitution occurs predominantly in completely filled layers, and at $x>2$, substitution also proceeds in layers with vacancies. At low temperatures, the saturation magnetization exhibits a minimum near $x\approx 0.9$, which directly coincides with a maximum in the coercive field. Within a narrow concentration range ($0.75<x<1.25$), the ${\mathrm{Fe}}_{3-x}{\mathrm{Cr}}_x{\mathrm{Se}}_4$ compounds display a giant exchange bias (EB) effect that increases exponentially with decreasing temperature below 50 K. The observed EB effect is attributed to the clustering of Cr atoms, forming quasi-two-dimensional regions that induce unidirectional anisotropy at the boundaries with coexisting ferrimagnetic regions. At 2 K, the exchange bias field during switching of ferrimagnetic clusters in the compound with $x=0.9$ reaches a value of 15 kOe. These findings demonstrate that engineering the atomic-scale cation distribution is an effective strategy for controlling macroscopic exchange bias in bulk layered chalcogenides.

Predictive modeling of ultrashort-pulse laser ablation requires temperature-dependent material parameters derived from the electronic structure, namely the electronic thermal conductivity, electron-phonon coupling, and heat capacity. These parameters are well documented for elemental metals but remain sparsely documented for alloys, apart from application-relevant exceptions such as stainless steels. The technologically important titanium alloy Ti-6Al-4V is a prominent example, which is still modeled using elemental-titanium values. We compute the electronic transport of hcp Ti and Ti-6Al-4V from first principles, using the Kubo-Greenwood formalism within the Korringa-Kohn-Rostoker coherent-potential-approximation framework, treating chemical and thermal disorder on equal footing. For elemental Ti, the calculated electrical resistivity agrees with independent abinit electron-phonon calculations and experiment and also reproduces the high-temperature saturation near the Mott-Ioffe-Regel limit. Under electron-phonon nonequilibrium, the electronic thermal conductivity saturates and then decreases with electronic temperature, reaching a maximum of about $2.97\mathrm{k}\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ in Ti but only $0.47\mathrm{k}\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ in Ti-6Al-4V, a factor of 6.4 lower. In two-temperature-model simulations the alloy and elemental parameter sets yield peak lattice temperatures differing by only about 1.4%, because reduced electron-phonon coupling and thermal conductivity offset each other, consistent with reported experimental ablation thresholds that differ by about 3%, well within their measurement uncertainties. This compensation is strongest for subpicosecond pulses and weakens across the 1 to $10\mathrm{ps}$ crossover toward longer-pulse behavior. Replacing the first-principles thermal conductivity with the low-temperature Drude limit shifts the peak lattice temperature by up to 19%, showing that the functional form of the transport model is even more important than the elemental versus alloy distinction for predictive accuracy.

Recent experiments show a binary Ni-V face-centered cubic (FCC) solid solution alloy possessing superior strength and work hardenability exceeding extant multiprincipal element alloys with an FCC solid solution structure. The outstanding mechanical properties can be attributed to V solid solution strengthening, but the mechanistic effects of V solutes and short-range order (SRO) on deformation behavior remain unclear and perplexing. Here, we develop an extended modified embedded-atom method (XMEAM) interatomic potential for the binary Ni-V system to enable direct and accurate modeling of SRO and V-lattice defect interactions. The potential is fit to a broad range of lattice and defect properties from extant experiments and new density functional theory (DFT) calculations in multiple solid solution and intermetallic structures. Extensive benchmarks with molecular dynamics and Monte Carlo simulations show great accuracy and transferability of the developed potential in Ni-V solid solution alloys across a wide range of V concentrations as well as in intermetallic structures. In particular, the potential reproduces SRO, phase transitions, solute misfit volume and solute interaction with dislocations consistent with extant experiments and the Ni-rich side of the binary phase diagram. The new potential is also computationally efficient; its availability thus opens the essential path for large-scale, mechanistic modeling of plastic deformation and SRO effects in the Ni-V binary system with high fidelity and forms the foundation for developing other binary systems and extending to ternary systems.

Based on free-energy functionals, phase-field modeling enables the simulation of microstructural pattern formation and dynamics while providing spatially resolved information on the underlying local thermodynamics. In the same spirit, free-energy functionals for atomic systems can be used for analogous purposes at atomic resolution; we refer to this approach as atomic-scale phase-field modeling. However, previous attempts have been limited to classical pairwise interatomic potentials because of the high computational cost and limited scalability associated with evaluating free-energy functionals involving many-body interactions. In this work, we generalize the atomic-scale phase-field methodology to many-body systems, whose efficient evaluation is facilitated by modifying the stochastic self-consistent harmonic approximation (order-$N$ SSCHA) and by machine-learning potentials. We apply this method to bulk Cu and Si in the NPT ensemble, where the predicted equilibrium lattice constants show agreement with molecular-dynamics simulations, validating the theoretical framework for these relatively simple systems. Furthermore, we apply the method to the $\mathrm{\Sigma }5\left(310\right)\left[001\right]$ grain boundary in Cu using a simulation cell containing several hundred atoms, yielding atomically resolved maps of local free-energy distributions. The results reveal a pronounced concentration of free energy at the grain-boundary core, suggesting a possible coupling between tensile stress and entropy. We then applied the developed methodology to more complex materials, namely, the thermal expansion of ${\mathrm{SrTiO}}_3$ and the polarization-dependent free-energy surfaces of ${\mathrm{PbTiO}}_3$. For these systems, the agreement with other methods was less satisfactory than for the simpler benchmarks, revealing the current limitations of the framework and identifying directions for further development. This study represents a step toward the accurate free-energy functionals applicable to large-scale atomic systems, thereby advancing the atomic-scale phase-field concept.

The interplay of oxygen deficiency and vanadium multiple valency in the candidate multiferroic V-doped $Pca{2}_1$ hafnia ${\mathrm{HfO}}_2$ is studied by first-principles calculations. Low-lying V majority gap states accept electrons from oxygen-vacancy donors, reducing their formation energy, and converting nominal ${\mathrm{V}}^{4+}$ centers into ${\mathrm{V}}^{3+}$. The resulting local magnetization and screening changes are reflected in the calculated V core-level shifts, which are consistent with the experimentally observed x-ray photoelectron spectroscopy signatures. The calculated ${\mathrm{V}}^{3+}/{\mathrm{V}}^{4+}$ population ratio determined by oxygen vacancies only matches experiment in reducing conditions, suggesting that additional electron reservoirs may contribute under atomic-layer-deposition growth conditions. A similar scenario also seems to apply to the recently observed multiferroicity in Cr-doped hafnia, where oxygen deficiency is expected from the synthesis route.

Cumulative geometric frustration can drive self-limited assembly and morphology selection through size-dependent energetic costs. However, the slenderness of quasi-one-dimensional systems generally suppresses the formation of long-range longitudinal gradients. We show that the suppression of longitudinal gradients can be overcome by tuning the ratio between the longitudinal and transverse (shear) moduli. We demonstrate the recovery of cumulative frustration across distinct quasi-one-dimensional systems, each frustrated through a different mechanism, by the introduction of a soft response mode. The resulting saturation length scale is universal and is dictated by the local constitutive information of the system.

We present a fully analytical description for the stationary vapor-solid (VS) distributions of III-V ternary epilayers and nanomaterials of different types in the most complex case of ternaries with two highly volatile group V elements. The approach is based on the minimum free energy principle and a self-consistent determination of the total growth rate of a ternary structure. This enables one to circumvent the uncertainty in the unmeasurable concentrations of group V atoms in a mother phase. The analytic VS distribution is a combination of the kinetic Langmuir-McLean distribution and the equilibrium distribution, whose weights are regulated by the effective III/V ratio. The model fits well the whole set of data on the stationary compositions of epilayers and catalyst-free and vapor-liquid-solid nanowires in the four material systems $\mathrm{AlS}{\mathrm{b}}_x{\mathrm{As}}_{1-x}, \mathrm{InS}{\mathrm{b}}_x{\mathrm{As}}_{1-x}, \mathrm{In}{\mathrm{P}}_x{\mathrm{As}}_{1-x}$ and $\mathrm{Ga}{\mathrm{P}}_x{\mathrm{As}}_{1-x}$ and provides a method for controlling the compositions of III-V ternary nanomaterials by the growth parameter tuning.

The Hume-Rothery rules have been successfully used for the design of new alloys, including solid solutions, intermetallics, and a few commonly known icosahedral quasicrystals. Yet when the alloys become more chemically complex and consist of more than four principal elements, it remains an open question whether the Hume-Rothery rules are still valid for designing chemically complex icosahedral quasicrystals, or high-entropy icosahedral quasicrystals. In this work, quaternary and quinary alloys were systematically designed to possess electron per atom (e/a) ratios and average atomic radii $\left(R_a\right)$ comparable to those of the stable Al-Cu-Fe icosahedral quasicrystal, by alloying with Co and Ni. Icosahedral quasicrystals were identified in the quaternary alloys Al-Cu-Fe-Co and Al-Cu-Fe-Ni but with significantly reduced volume fractions compared to Al-Cu-Fe. Notably, the icosahedral quasicrystal was absent in the quinary alloy Al-Cu-Fe-Co-Ni. The 6D quasilattice constant (${\mathrm{a}}_{6\mathrm{D}}$) of the icosahedral quasicrystal decreased upon alloying, with Co inducing a larger reduction than Ni. Compositional analyses revealed Al-O, Fe-Co, Cu-Ni, and Fe-Ni substitutions within the icosahedral quasicrystal, with Ni partitioning approximately equally between Cu and Fe. Our findings show the limitations of applying the Hume-Rothery rules as a predictive guideline for icosahedral quasicrystals Al-Cu-Fe containing Co or Ni. Furthermore, the simulated electronic structure of the 3/2 icosahedral approximant demonstrated the formation of a pseudogap, clarified the mechanism of Fe-Co substitution, and reinforced the importance of the critical e/a ratio. Crystal Orbital Hamilton Population (COHP) analysis revealed that Al acted as the primary stabilizer of the icosahedral structure, whereas Cu could be replaced for enhanced phase stability.

${\mathrm{ScV}}_6{\mathrm{Sn}}_6$ is a V-based kagome-lattice material similar to the ${\mathrm{AV}}_3{\mathrm{Sb}}_5$ (A = Cs, Rb, K) family. Unlike ${\mathrm{AV}}_3{\mathrm{Sb}}_5$, ${\mathrm{ScV}}_6{\mathrm{Sn}}_6$ exhibits a three-dimensional charge density wave (CDW) order and yet no superconductivity transition has been observed at low temperature. In this work, we confirm the $\sqrt{3}\times \sqrt{3}\times 3$ CDW via NMR and detect NMR signatures of the $\sqrt{3}\times \sqrt{3}\times 2$ short-range order. Above the CDW transition temperature $T_{\mathrm{CDW}}=88\mathrm{K}$, full width at half maximum of the NMR spectra reveals sensitivity to short-range order. Below $T_{\mathrm{CDW}}$, the NMR spectra corresponding to $[m=-7/2$ ↔ $-5/2]$ satellite transition of V split into two peaks, with an intensity ratio of 2:1. Detailed analyses show that a $\sqrt{3}\times \sqrt{3}\times 3$ charge density wave order in ${\mathrm{ScV}}_6{\mathrm{Sn}}_6$ is consistent with our experimental results.

We report a family of two-dimensional (2D) rectangular $\gamma \text{−}X$ ($X$=N, P, As, Sb, Bi) materials that simultaneously exhibit topologically nontrivial properties and ultra-large, strain-sensitive negative Poisson's ratios (NPRs). According to first-principles calculations, the $\gamma \text{−}X$ single layers (SLs) exhibit excellent mechanical, dynamic, and thermodynamic stability, with strongly anisotropic electronic structures and mechanical properties. At equilibrium, $\gamma$-Bi SL is a 2D topological insulator (TI), which has a PBE band gap of 0.06 eV and a HSE06 energy gap of 0.13 eV. Though $\gamma$-N, P, As, and Sb SLs are trivial insulators, biaxial tensile strain can trigger a topological phase transition, transforming them into 2D TIs. Mechanically, $\gamma$-P, As, Sb, and Bi SLs exhibit NPRs ranging from $-0.002$ to $-0.066$, and all the SLs, including $\gamma$-N SL, show strongly strain-dependent in-plane and out-of-plane NPRs. Remarkably, the uniaxial compression along the armchair direction induces a giant out-of-plane NPR of $-2.864$ in $\gamma$-P SL, far exceeding the NPR values in previously reported auxetic materials. Moreover, these SLs can withstand ultimate tensile strains along the zigzag direction ranging from $2\%$ to $52\%$. The van der Waals layered 3D counterparts of $\gamma \text{−}X$ also exhibit strong anisotropy and NPRs, with maximum magnitudes between $-0.052$ and $-1.290$.

Van der Waals (vdW) heterostructures are attracting enormous attention due to their remarkable physical properties governed by moiré superlattices (MSLs) directly controlled by interlayer twist angles or a lattice mismatch. We investigated surface properties of moiré heterostructures made up of commercially available chemical vapor deposited (CVD) graphene and exfoliated ${\mathrm{MoS}}_2$ layers on silicon oxide, by means of spectroscopy, microscopy, and diffraction. High resolution Auger elemental maps and spectra revealed composition inhomogeneity due to thickness variations in CVD graphene and signatures of oxidation of bare ${\mathrm{MoS}}_2$ surface exposed to the ambient atmosphere. Low-energy electron microscopy and diffraction disclosed local stacking and crystallographic information in the graphene-${\mathrm{MoS}}_2$ moiré heterostructure, including evidence for small-angle twisted bilayer MSL regions in CVD monolayer graphene. This systematic study helps us to understand the overall configuration of the vdW heterostructures and correlate their structure and performance in transport experiments.

We perform a 40–250 GHz electron spin resonance (ESR) study of the spin-chain quantum magnet ${\mathrm{Cs}}_2{\mathrm{CoCl}}_4$ in a paramagnetic phase. A continuous crossover from spin-3/2 to pseudospin-1/2 ESR was found when lowering the temperature from 15 to 3 K. This observation provides direct spectroscopic confirmation of a concept of pseudospins-1/2 used in the literature for a description of the low-temperature correlated state of this quantum magnet.

We use density functional theory with a Hubbard correction to investigate Ti-centered electron polarons at neutral PbO-centered ${180}^{\circ }$ domain walls in tetragonal ${\text{PbTiO}}_3$. The Hubbard parameter for Ti $3d$ states is determined using the finite-size-corrected polaronic energy-level alignment procedure, yielding stable electron-polaron formation in bulk ${\mathrm{PbTiO}}_3$ with a trapping energy of $-0.06\mathrm{eV}$. In the domain-wall supercell, the excess electron localizes on a Ti site and forms a ${\mathrm{Ti}}^{3+}$ center with an occupied in-gap $d_{xy}$ state. Comparison of bulk-like and near-wall Ti sites shows that their trapping energies differ by only about 0.01 eV, indicating that this neutral domain wall does not provide a significant thermodynamic driving force for electron-polaron segregation. While the Ising-like reversal of the out-of-plane polarization is preserved, the localized electron induces a finite transverse polarization component normal to the wall, enhancing a local Néel-like distortion that is strongest when the polaron is located at the wall. These results show that neutral ${180}^{\circ }$ domain walls in ${\mathrm{PbTiO}}_3$ do not substantially alter the stability of Ti-centered electron polarons, but they can couple to the polaron-induced lattice distortion through a localized transverse polarization response.

We systematically investigate the magnetic properties of the triangular-lattice quantum magnet ${\mathrm{K}}_2\mathrm{CsYb}{\left(\mathrm{P}{\mathrm{O}}_4\right)}_2$. The results reveal no evidence of long-range magnetic order down to 2 K. The Curie-Weiss temperatures obtained from low-temperature fits of magnetic susceptibility, ${\theta }_{\mathrm{CW},ab}=-0.014\mathrm{K}$ and ${\theta }_{\mathrm{CW},c}=-0.557\mathrm{K}$, indicate the presence of weak anisotropic antiferromagnetic exchange interactions. The crystal-field analysis yields an energy gap of 30.19 meV between the ground state and the first excited Kramers doublet, confirming that the low-temperature physics is well described by the spin-orbit entangled $J_{\text{eff}}=1/2$ state, which is also supported by the first-principles calculations. Furthermore, the frequency-field ($v\text{−}H$) relationship in the electron-spin-resonance spectra exhibits a distinct zero-field intercept, significantly deviating from the noninteracting paramagnetic behavior. This deviation, arising from the internal field caused by spin correlations at low temperatures, allows us to extract the anisotropic exchange interaction: $J_{\pm }/k_{\mathrm{B}}=-0.007\mathrm{K}$ and $J_{zz}/k_{\mathrm{B}}=-0.025\mathrm{K}$.

We investigate the relation between lattice, vibrational, and electrical changes in Ru/ Re-doped M-type barium hexaferrite, ${\mathrm{BaFe}}_{11.9}{(\mathrm{Ru},\mathrm{Re})}_{0.1}{\mathrm{O}}_{19}$. Temperature-dependent x-ray diffraction shows only a few weak extra reflections associated with the minor $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$ phase, with no temperature-induced change in the BaM crystal structure. However, the lattice parameters and unit-cell volume change their thermal-expansion behavior between 390 and 420 K. Raman spectroscopy shows a complementary local response, with two selected Fe-O modes, assigned to mixed ${\mathrm{FeO}}_6$ octahedral vibrations and ${\mathrm{FeO}}_5$ bipyramidal vibrations, displaying shallow nonmonotonic shifts near 380–400 K. At higher temperatures, the electrical measurements reveal a systematic change in charge dynamics. The phase map obtained from the loss tangent changes from a capacitivelike response toward a stronger resistive contribution, while the real part of the ac conductivity, ${\sigma }_{\mathrm{ac}}^{\prime }\left(T\right)$, develops a clearer frequency dependence above about 480 K. Effective Arrhenius fits in the 293–483 K interval yield frequency-dependent activation energies and preexponential factors that follow a Meyer-Neldel-like relation, with $E_{\mathrm{MN}}=(41.0\pm 0.5)\mathrm{meV}$ and $T_{\mathrm{MN}}=(476\pm 6)\mathrm{K}$. The value of $E_{\mathrm{MN}}$ is close to the phonon energy of the Raman mode near $335{\mathrm{cm}}^{-1}, E_{\mathrm{ph}}\approx 41.5\mathrm{meV}$, associated with mixed ${\mathrm{FeO}}_6$ octahedral vibrations. The structural, vibrational, and electrical results therefore indicate that the previously reported semiconductor-to-metal crossover is accompanied by small changes in the local Fe-O environment. The comparable vibrational and Meyer-Neldel energy scales are consistent with a possible contribution of phonon-assisted hopping involving the ${\mathrm{FeO}}_6$ octahedral network.

Identifying high-performance thermoelectrics in chemically related two-dimensional materials requires understanding how different sublattices separately regulate electronic transport, phonon softening, and anharmonic heat conduction. Here, we use $\mathrm{Mg}{A}_2{Z}_4$ monolayers as a model material family to establish such a chemically resolved design principle. By combining first-principles stability analysis, carrier-transport calculations, and lattice thermal conductivity calculations including both three- and four-phonon scattering, we systematically investigate 30 $\mathrm{Mg}{A}_2{Z}_4$ monolayers with $A=\mathrm{Sc}$, Y, Al-In and $Z=\mathrm{S}$-Te, Cl-I. The dynamically stable semiconducting members are mainly concentrated in the Al-, Ga-, and In-based chalcogenides, defining a selective thermoelectric stability window rather than a random set of candidates. We find that the $A$-site cation primarily controls the electronic transport through band-edge dispersion and valley convergence, whereas the $Z$-site anion predominantly governs lattice heat conduction by tuning phonon softening, group velocity, and higher-order anharmonic scattering. This chemical partitioning leads to a favorable balance in $\mathrm{Mg}{\mathrm{Al}}_2\mathrm{T}{\mathrm{e}}_4$, which reaches a peak $\mathit{ZT}$ of 2.75 at 900 K. More importantly, explicit four-phonon calculations show that conventional three-phonon treatments systematically overestimate the lattice thermal conductivity of representative high-performance members by 37–53%, demonstrating that four-phonon scattering is not a minor correction but a necessary criterion for reliable thermoelectric assessment in this family. These results identify $\mathrm{Mg}{\mathrm{Al}}_2\mathrm{S}{\mathrm{e}}_4, \mathrm{Mg}{\mathrm{Al}}_2\mathrm{T}{\mathrm{e}}_4, \mathrm{MgG}{\mathrm{a}}_2\mathrm{T}{\mathrm{e}}_4$, and $\mathrm{MgI}{\mathrm{n}}_2\mathrm{T}{\mathrm{e}}_4$ as the high-performance region of the $\mathrm{Mg}{A}_2{Z}_4$ family and establish a transferable materials-physics framework linking sublattice chemistry, electronic transport, and four-phonon-limited heat conduction in two-dimensional thermoelectrics.