Recently, many interesting magnetic and electrical properties have been demonstrated in transition-metal intercalated $2\text{H-Nb}{\mathrm{S}}_2/\mathrm{Ta}{\mathrm{S}}_2$ layered single crystals. In this work, single crystals of Cr and Fe co-intercalated $2\text{H-Nb}{\mathrm{S}}_2$, with the compositions of ${\left({\mathrm{Cr}}_{1–x}{\mathrm{Fe}}_x\right)}_{1/3}\mathrm{Nb}{\mathrm{S}}_2 \left(x=0.0–1.0\right)$, are successfully grown and their magnetic and transport properties are systematically studied. With increasing Fe content, the magnetic transition temperature continually decreases from 117 to 37 K, and the magnetic coupling transforms from ferromagnetic to antiferromagnetic. Importantly, a rotation of the magnetic easy axis occurs in this process, with perpendicular magnetocrystalline anisotropy and considerable coercive field achieved in the $x=0.13–0.66$ compounds. Both $x=0.33$ and $x=0.50$ exhibit relatively low carrier concentration, stable anomalous Hall effect, and butterfly-shape magnetoresistance. Notably, large anomalous Hall conductivity is identified in $x=0.50$, whose origin is discussed from the calculated electronic structures. The realization of perpendicular anisotropy and large anomalous Hall conductivity in this two-dimensional ferromagnetic system can facilitate their future application in spintronic devices.

We study the creep behavior of a disordered brittle material (concrete) under successive loading steps, using acoustic emission and ultrasonic sensing to track internal damage. The primary creep rate is observed to follow a (Omori-type) power-law decay in the strain rate, the number of acoustic emission events, as well as the amplitudes of the ultrasonic beams, supporting a brittle-creep mechanism. The distribution of acoustic emission event energies is observed to have a scale-free power-law distribution instead of a truncated one expected for a system approaching a critical point at failure. The main outcome is, however, the discovery of unexpected history effects that make the material less prone to creep when it has been previously deformed and damaged under primary creep. With the help of a progressive damage model implementing thermal activation, we interpret this as an aging-under-stress phenomenon: During an initial creep step at relatively low applied stress, the easy-to-damage sites are exhausted first, depleting the excitation spectrum at low stress gap values. Consequently on reloading, although previously damaged, the primary creep restarts but the material creeps (and damages) less than it would under the same stress but without precreeping. Besides shedding a new light on the fundamental physics of creep of disordered brittle materials, this has important practical consequences in the interpretation of some experimental procedures, such as stress-stepping experiments.

Lamellar $\alpha \text{−}{\mathrm{MoO}}_3$ crystals were implanted with low fluence of radioactive ${}^{111\mathrm{m}}\mathrm{Cd}$ ions at ISOLDE-CERN. Subsequently, we have probed the interaction of the Cd impurity in the lattice with native point defects, such as oxygen vacancies, as a function of annealing temperature using the time differential perturbed angular correlations nanoscopic technique. The experimental data were complemented and interpreted by modeling different Cd-defect configurations in $\alpha \text{−}{\mathrm{MoO}}_3$ with first-principles density functional theory (DFT). The agreement between experiments and DFT simulations shows that only the interstitial Cd (${\mathrm{Cd}}_I$) prevails in the van der Waals gap, by inducing a polaron effect. Upon raising the annealing temperature, ${\mathrm{Cd}}_I$ is able to trap hole charge carriers resultant from the oxygen vacancies $V_{\mathrm{O}}$. Oxygen vacancies were found to form most commonly at two-fold coordinated (O2) atoms. According to comparison DFT results with the experimental electric field gradient values ($V_{zz}$ and $\eta$) and the calculated formation energies for different defect complexes, the configuration of ${\mathrm{Cd}}_I$ with two (O2) vacancies ($V_{\mathrm{O}2}$), located at different planes, is found to be more favorable and stable than the other defect configurations. The electron-polaron formation around the Cd impurity at an interstitial site is enhanced by inducing (O2) vacancies with the creation of hole polaron states.

We report a comprehensive and comparative study of structural, static, dynamic, and nonequilibrium magnetic properties on the polymorphs of $\mathrm{LiFeSn}{\mathrm{O}}_4$. It exhibits two polymorphs: (i) orthorhombic phase (HT) stabilized at high temperature and (ii) hexagonal phase (LT) obtained at lower synthetic temperature. The HT phase crystallizes in the orthorhombic structure (space group: Pmcn) and exhibits a site disordered, nonfrustrated zig-zag network of ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Sn}}^{4+}$ ions. On the other hand, the LT phase shows a disordered frustrated kagome network of ${\mathrm{Li}}^{1+}, {\mathrm{Fe}}^{3+}$, and ${\mathrm{Sn}}^{4+}$ ions crystallizing in the hexagonal structure (space group: $P{6}_{3}mc$). The low-temperature thermo-magnetic irreversibility and the absence of heat capacity anomaly in both polymorphs indicate the absence of long-range magnetic ordering and a possible glassy state. Zero-field-cooled and field-cooled magnetic memory effect and spin relaxation measurements stipulate the spin glass nature of the polymorphs. Further, spin glass behavior is confirmed by the AC susceptibility measurements. Interestingly, these polymorphs reveal different classes of spin glass states. The site disordered HT phase exhibits a single spin-flip time ${\tau }_0\sim 3\times {10}^{-13}$ sec, indicating a canonical spin glass state. In contrast, LT phase, which is disordered and geometrically frustrated, shows the spin-flip time of ${\tau }_0\sim 9\times {10}^{-10}$ sec, suggesting a cluster spin glass state. In addition, the exchange bias effect was observed due to magnetic inhomogeneity in both polymorphs.

The electromechanical properties of ferroelectrics are often strongly frequency-dependent, but the underlying structural kinetics are not well known or understood. Here, we use in situ stroboscopic neutron diffraction combined with a comprehensive structural refinement method to examine the frequency-dependent structural change in the commercial actuator material PIC 151 at realistic operating frequencies. A broad range of frequencies was measured and analyzed in detail. This work further underlines the crucial role of the field-induced phase transformation for explaining the kinetics in ferroelectric materials. Both the tetragonal majority phase and the rhombohedral minority phase contribute with different effects to the frequency dependence of the strain mechanisms. Even creep effects well beyond the probed frequencies can be explained with the observations.

${\mathrm{TiO}}_2$ is a technologically important material. In particular, its anatase polymorph plays a major role in photocatalysis, which can also accommodate charged and neutral vacancies. There is, however, scant theoretical work on the vacancy charge and associated diffusion from surface to subsurface and bulk in the literature. Here, we aim to understand +2 charge and neutral vacancy diffusion on anatase (101) surface using 72- and 216-atom surface slabs employing a semilocal density functional and the Hubbard model. The activation-relaxation technique nouveau coupled with quantum espresso is used to investigate the activated mechanisms responsible for the diffusion of oxygen vacancies. The small-slab model overstabilizes the +2 charged topmost surface vacancy, which is attributed to the strong Coulomb repulsion between vacancy and neighboring ${\mathrm{Ti}}^{+4}$ ions. The larger slab allows atoms to relax parallel to the surface, decreasing the +2 charged topmost surface vacancy stability. The calculated surface-to-subsurface barriers for the +2 charged vacancy and diffusion of the neutral vacancy on a slab of 216 atoms are 0.82 and 0.52 eV, respectively. Furthermore, the bulk vacancy prefers to migrate toward the subsurface with relatively low activation barriers 0.19 and 0.27 eV and the reverse process has to overcome 0.38- and 0.40-eV barriers for the +2 charged and the neutral vacancies. This explains the experimentally observed high concentration of vacancies at the subsurface sites rather than in the bulk, and the dynamic diffusion of vacancies from the bulk to the subsurface and from the subsurface to the bulk is highly likely on the surface of anatase (101). Finally, we provide a plausible explanation for the origin of recently observed subsurface-to-surface diffusion of oxygen vacancy from the calculated results.

We demonstrate an approach for calculating temperature-dependent quantum and anharmonic effects with beyond density-functional theory accuracy. By combining machine-learned potentials and the stochastic self-consistent harmonic approximation, we investigate the cubic to tetragonal transition in strontium titanate and show that the paraelectric phase is stabilized by anharmonic quantum fluctuations. We find that a quantitative understanding of the quantum paraelectric behavior requires a higher-level treatment of electronic correlation effects via the random phase approximation. This approach enables detailed studies of emergent properties in strongly anharmonic materials beyond density-functional theory.

We report the magnetic, thermodynamic, and electrical properties of ${\mathrm{EuRh}}_2{\mathrm{Al}}_8$, a Eu-based heavy fermion member in the ${\mathrm{RT}}_2{\mathrm{X}}_8$ families with an orthorhombic $Pbam$ structure. Magnetization studies reveal multiple phase transitions in the single crystals, including two successive antiferromagnetic transitions at $T_{N1}\sim 12.5\mathrm{K}$ and $T_{N2}\sim 8.2\mathrm{K}$. These two transitions are closely related to competing magnetic interactions in the Shastry-Sutherland lattice, which further give rise to another in-plane spin-flop transition at 1/3 of the full magnetization below 5 K when the applied magnetic field is higher than 6 T within the $ab$ plane. In addition to these, specific heat measurements in ${\mathrm{EuRh}}_2{\mathrm{Al}}_8$ demonstrate a heavy fermion state with a large Sommerfeld coefficient $\gamma =393\mathrm{mJ}·{\mathrm{mol}}^{-1}·{\mathrm{K}}^{-2}$. Electrical transport measurement shows that its resistivity exhibits a $T^2$-dependence below $T_{N2}$ and a robust linear $T$-dependence above $T_{N1}$, which is also typical of a heavy fermion metal. Our work provides fundamental physical properties of ${\mathrm{EuRh}}_2{\mathrm{Al}}_8$ and promotes understanding of the complex magnetic interactions and unusual spin correlations in the ${\mathrm{RT}}_2{\mathrm{X}}_8$ families.

Creep is defined as time-dependent deformation and rupture processes taking place within a material subjected to constant applied stress smaller than its athermal, time-independent strength. This time dependence is classically attributed to the thermal activation of local deformation events. The phenomenology of creep is characterized by several ubiquitous but empirical rheological and scaling laws. We focus here on primary creep following the onset of loading, for which a power law decay of the strain rate is observed, $\dot{\varepsilon }\sim t^{-p}$, with the exponent $p$ varying between $\simeq 0.4$ and 1, this upper bound defining the so-called logarithmic creep. Although this phenomenology is known for more than a century, the physical origin of Andrade-like $(p<1)$ creep remains unclear and debated. Here we show that $p<1$ values arise from the interplay between thermal activation and elastic stress redistribution. The latter stimulates creep dynamics from a shortening of waiting times between successive events, is associated to material damage and, possibly, at high temperature and/or stresses, gives rise to avalanches of deformation events.

Thermal diodes, which allow heat transfer in a preferential direction while being blocked in a reverse direction, have numerous applications in thermal management, information processing, energy harvesting, etc. Typical materials of thermal diodes in previous works include phase-change and magneto-optical materials. However, such thermal diodes depend highly on specific working temperatures or external magnetic fields. In this work, we propose a near-field radiative thermal diode (NFRTD) based on two Weyl semimetal (WSM) nanoparticles (NPs) mediated by a WSM planar substrate, which works without an external magnetic field and with flexible temperatures. Numerical results show that the maximum rectification ratio of NFRTD can be up to 2673 when the emitter is 200 K and receiver is 180 K, which exceeds the maximum value reported in some previous works by more than 10 times. The underlying physical mechanism is the strong coupling of the localized plasmon modes in the NPs and nonreciprocal surface plasmon polaritons in the substrate. In addition, we calculate the distribution of the Green's function and reflection coefficient to investigate nonreciprocal energy transfer in NFRTDs. Finally, we discuss the effects of momentum separation on the rectification performance of the NFRTD. This work demonstrates the great potential of WSMs in thermal rectification and paves a path for designing high-performance NFRTDs.

Hydrogen is a key player in global strategies to reduce greenhouse gas emissions. In order to make hydrogen a widely used fuel, we require more efficient methods of storing it than the current standard of pressurized cylinders. An alternative method is to adsorb ${\mathrm{H}}_2$ in a material and avoid the use of high pressures. Among many potential materials, layered materials such as graphene present a practical advantage as they are lightweight. However, graphene and other 2D materials typically bind ${\mathrm{H}}_2$ too weakly to store it at the typical operating conditions of a hydrogen fuel cell, meaning that high pressure would still be required. Modifying the material, for example by decorating graphene with adatoms, can strengthen the adsorption energy of ${\mathrm{H}}_2$ molecules, but the underlying mechanisms are still not well understood. In this work, we systematically screen alkali and alkaline-earth metal decorated graphene sheets for the static thermodynamic adsorption of hydrogen gas from first principles and focus on the mechanisms of binding. We show that there are three mechanisms of adsorption on metal decorated graphene and each leads to distinctly different hydrogen adsorption structures. The three mechanisms can be described as weak van der Waals physisorption, metal adatom facilitated polarization, and Kubas adsorption. Among these mechanisms, we find that Kubas adsorption is easily perturbed by an external electric field, providing a way to tune ${\mathrm{H}}_2$ adsorption. This work is foundational and builds our understanding of ${\mathrm{H}}_2$ adsorption under idealized conditions.

The recent discovery of nematic liquid crystals with polar order (ferroelectric) has created immense interest. Despite intensive research, several physical properties of this liquid crystal are yet to be investigated and understood. Here, we report experimental studies on the surface alignment, birefringence, and flexoelectric coefficient of a polar nematic $\left(N_{\mathrm{F}}\right)$ liquid crystal. Our experiments directly reveal that the splay fluctuations influence the birefringence several degrees above the nonpolar $\left(N\right)$ to polar nematic $\left(N_{\mathrm{F}}\right)$ phase transition temperature, and the heat capacity exponent obtained from the tilt angle fluctuations is close to the value reported in adiabatic scanning calorimetry measurements. The flexoelectric coefficient of the nonpolar nematic phase shows a power-law dependence on temperature. It demonstrates a strong polar coupling of pretransitional ferroelectric fluctuations with the field. These results are important for applications as well as for understanding all pretransitional effects in ferroelectric nematic liquid crystals.

There are intensive efforts to search for mechanisms that lead to spin-orbit torque with unusual spin orientation, particularly out-of-plane spin orientation which can efficiently switch perpendicular magnetizations. Such a phenomenon has been observed in materials with low structural symmetry, ferromagnetic materials, and antiferromagnets with noncollinear spin structures. Here, we demonstrate the observation of, in addition to out-of-plane spin orientation, spin orientation along the charge current direction in ${\mathrm{Mn}}_3\mathrm{Sn}$, a noncollinear antiferromagnet and Weyl semimetal. The mechanism arises from noncollinear spin structure with spin-orbit coupling and it can be viewed as spin rotation around the octupole moment, the lowest order of cluster multipole moment pertaining to the ${\mathrm{Mn}}_3\mathrm{Sn}$ crystal group.

The transition between necking-mediated tensile failure of glasses, at elevated temperatures and/or low strain rates, and shear-banding-mediated tensile failure, at low temperatures and/or high strain rates, is investigated using tensile experiments on metallic glasses and atomistic simulations. We experimentally and simulationally show that this transition occurs through a sequence of macroscopic failure patterns, parametrized by the ultimate tensile strength. Quantitatively analyzing the spatiotemporal dynamics preceding failure, using large scale atomistic simulations corroborated by experimental fractography, reveals how the collective evolution and mutual interaction of shear-driven plasticity and dilation-driven void formation (cavitation) control the various macroscopic failure modes. In particular, we find that, at global failure, the size of the largest cavity in the loading direction exhibits a nonmonotonic dependence on the temperature at a fixed strain rate, which is rationalized in terms of the interplay between shear- and dilation-driven plasticity. We also find that the size of the largest cavity scales with the cross-sectional area of the undeformed sample. Our results shed light on tensile failure of glasses and highlight the need to develop elastoplastic constitutive models of glasses incorporating both shear- and dilation-driven irreversible processes.

We use spin-polarized low-energy electron microscopy to investigate domain pattern transfer in a multiferroic heterostructure consisting of a (111)-oriented ${\mathrm{BaTiO}}_3$ substrate and an epitaxial Ni film. After in situ thick-film deposition and annealing through the ferroelectric phase transition, interfacial strain transfer from ferroelastic domains in the substrate and inverse magnetostriction in the magnetic thick film introduce a uniaxial in-plane magnetic anisotropy that rotates by ${60}^{\circ }$ between alternating stripe regions. We show that two types of magnetic domain wall can be initialized in principle. Combining experimental results with micromagnetic simulations, we show that a competition between the exchange and magnetostatic energies in these domain walls has a strong influence on the magnetic domain configuration.

Cuprous halides ($\mathrm{Cu}X$, $X=\mathrm{Cl}$, Br, or I) have been extensively investigated in the literature, but there still exist debates on whether the ground-state structures of $\mathrm{Cu}X$ are zinc blende. By performing molecular dynamics simulations at finite temperatures with a newly developed accurate deep-learning potential for CuCl, we find that, in the absence of accurate exchange interactions, there exist collective off-center displacements of Cu, leading to the formation of large complex Cu cluster structures. However, these cluster structures are unstable once exchange interactions are properly included. Nevertheless, due to strong anharmonicity, thermal fluctuations could also lead to sizable off-center Cu displacements, resulting in instantaneous small Cu clusters. Still, these cluster configurations are not stable or metastable in the ground state. We thus unambiguously demonstrate that, although anharmonic off-center displacements of Cu are present in CuCl at finite temperatures, zinc blende is still the thermodynamically most favorable phase. These insights are critical to the understanding of liquidlike anharmonic behavior of Cu atoms in various Cu-containing compounds, which impacts a number of important properties such as thermal conductivity, ferroelectricity, and superconductivity.

Diffusion of Zn in (001)- and $\left(\overline{2}01\right)$-oriented $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ was studied using secondary-ion mass spectrometry and first-principles calculations based on hybrid and semilocal functionals. The $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ samples were sealed in quartz ampules together with a piece of metallic Zn and heated to temperatures of 900–1100 ${}^{\circ }\mathrm{C}$ for 1 h. The Zn concentration profiles as a function of depth were simulated by employing the trap-limited diffusion model. From this model the migration barrier for Zn diffusion was found to be $E_m=2.2\pm 0.2$ and $2.1\pm 0.1\mathrm{eV}$ in the (001) and ($\overline{2}01$) orientations of $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$, respectively, with corresponding dissociation energies of $E_d$ = 3.5 $\pm 1.1$ and $3.2\pm 0.6\mathrm{eV}$. Results from the first-principles calculations predict an interstitialcy mechanism for the Zn diffusion when it is not in its trapped state. Using the nudged elastic band method, we obtain a barrier of 1.6 eV for migration of Zn split interstitials $\left({\mathrm{Zn}}_i\right)$ in both the [001] and $\left[\overline{2}01\right]$ directions, in accordance with the results obtained from the trap-limited diffusion model. Interestingly, the Ga vacancy is found to be able to trap two Zn atoms forming a shallow donor complex labeled ${\mathrm{Zn}}_i{\mathrm{Zn}}_{\mathrm{Ga}}$. The energy needed for ${\mathrm{Zn}}_i$ to dissociate from this donor complex is estimated to be 2.99 eV, in reasonable agreement with the trap dissociation energies extracted from the diffusion model.

$\mathrm{Eu}{\mathrm{Cd}}_2{\mathrm{As}}_2$ is an antiferromagnetic semimetal that can host nontrivial topological properties, depending upon its magnetic state and excitations. Here, we report the synthesis and characterization of $\mathrm{Eu}{\left({\mathrm{Cd}}_{1-x}{\mathrm{Ag}}_x\right)}_2{\mathrm{As}}_2$ and ${\mathrm{Eu}}_{1-y}{\mathrm{Na}}_y{\mathrm{Cd}}_2{\mathrm{As}}_2$, and we study the evolution and nature of magnetic order with doping. Temperature-substitution phase diagrams are constructed from the electrical resistance and magnetic susceptibility data. We observe a splitting of the magnetic transition into two different transitions, and the gradual increase in one of the transition temperatures with Ag and Na substitution. The other transition remains more or less independent of doping. We further show that a magnetic state with a net ferromagnetic moment is stabilized by both Ag and Na doping and this can be explained by considering the changes in band filling due to substitution as suggested by density functional theory (DFT) calculations. We thus show that chemical substitution and the subsequent changes in band filling could be a pathway to tune the magnetic ground state and to stabilize a ferromagnetic phase in $\mathrm{Eu}{\mathrm{Cd}}_2{\mathrm{As}}_2$.

The interplay between metallic glasses (MGs) mechanical properties, fracture energy $\left(G\right)$, and glass-forming ability (GFA) and their dependence on alloy composition remain poorly understood. Here, we perform molecular dynamics simulations to investigate the intrinsic composition dependence of $G$ in ${\mathrm{Cu}}_x{\mathrm{Zr}}_{100-x}\mathrm{MGs}$ $(x=20,30,40,50,64)$. The results indicate that the value of $G$ increases with Cu content. In addition, it is revealed that MGs with higher $G$ values display higher Poisson's ratio (ν) and GFA, suggesting a close correlation between fracture toughness, mechanical properties, and GFA. This correlation between G, ν, and GFA can be understood based on the fragility ($m$) of supercooled liquids, which is directly related to the structural heterogeneity in MGs. Larger $m$ values are related to dynamic slowdown and supercooled liquid stabilization, which enhance GFA and the formation of pronounced structural heterogeneity, comprised of loosely packed regions that favor β relaxation and the activation of shear transformation zones. Those concurrently promote the expansion of the plastic zone at the crack tip, enhancing the observed value of $G$. These simulation results shed light on the intrinsic relationship between fracture toughness, mechanical properties, and alloy composition in MGs.

The rare-earth perovskite ${\mathrm{TbScO}}_3$ has been widely used as a substrate for the growth of epitaxial ferroelectric and multiferroic thin films, while its detailed low-temperature magnetic properties were rarely reported. In this paper, we performed detailed magnetization, specific heat, and single crystal neutron scattering measurements, along with the crystalline electric field calculations to study the low-temperature magnetic properties of ${\mathrm{TbScO}}_3$. All our results suggest the magnetic ${\mathrm{Tb}}^{3+}$ has an Ising-like pseudo-doublet ground state at low temperatures. Due to the constrain of local point symmetry, these ${\mathrm{Tb}}^{3+}$ Ising moments are confined in the $ab$ plane with a tilt angle of $\phi =\pm {48}^{\mathrm{o}}$ to the $a$ axis. In zero field, the system undergoes an antiferromagnetic phase transition at $T_{\mathrm{N}}=2.53$ K, and forms a $G_x{A}_y$ noncollinear magnetic structure below $T_{\mathrm{N}}$. We find the dipole-dipole interactions play an important role to determine the magnetic ground state, which are also responsible for the quasi-one-dimensional magnetism in ${\mathrm{TbScO}}_3$. The significant anisotropic diffuse scatterings further confirm the quasi-one-dimensional magnetism along the $c$ axis. The magnetic phase diagram with the field along the easy $b$ axis is well established. In addition to the $G_x{A}_y$ antiferromagnetic state, there is an exotic field-induced phase emerged near the critical field $B_{\mathrm{c}}\simeq 0.7$ T, where three-dimensional magnetic order is suppressed but strong one-dimensional correlations may still exist.