The combination of ferromagnetism and semiconducting behavior offers an avenue for realizing novel spintronics and spin-enhanced thermoelectrics. Here we demonstrate the synthesis of doped and nanocomposite half-Heusler ${\mathrm{Fe}}_{1+x}\mathrm{VSb}$ films by molecular beam epitaxy. For dilute excess Fe ($x<0.1$), we observe a decrease in the Hall electron concentration and no secondary phases in x-ray diffraction. Magnetotransport measurements suggest weak ferromagnetism that onsets at a temperature of $T_c\approx 5$ K. For higher Fe content ($x>0.1$), ferromagnetic Fe nanostructures precipitate from the semiconducting FeVSb matrix. The Fe/FeVSb interfaces are epitaxial, as observed by transmission electron microscopy and x-ray diffraction. Magnetotransport measurements suggest proximity-induced magnetism in the FeVSb from the Fe/FeVSb interfaces, or superparamagnetically coupled Fe-rich clusters, at an onset temperature of $T_c\approx 20$ K.

The lanthanide scandate materials are widely used substrates for thin film growth and the potential applications of the $Ln{\mathrm{ScO}}_3$ materials continue to grow with the recent ability to synthesize them as cuboidal faceted nanoparticles. A comprehensive understanding of the surface structure and chemistry of these oxides is essential for their informed application, either as single crystal or high surface area nanoparticle substrates. Here the $\left\{100\right\}$ pseudocubic surfaces of $Ln{\mathrm{ScO}}_3$ ($Ln=\mathrm{La}$, Nd, Sm, Gd) nanoparticles were examined with aberration-corrected electron microscopy and higher-level density functional theory to reveal ${\mathrm{ScO}}_x$ rich terminations across all investigated surfaces. Mixed terminations of single and double layer nature were observed, indicating the presence of multiple domains at the surface and introducing the possibility of synthetically controlling the surface reconstruction in the future.

Understanding and tailoring static and dynamic properties of magnetic insulator thin films is important for spintronic device applications. Here, we grow atomically flat epitaxial europium iron garnet (EuIG) thin films by pulsed laser deposition on (111)-oriented garnet substrates with a range of lattice parameters. By controlling the lattice mismatch between EuIG and the substrates, we tune the strain in EuIG films from the compressive to the tensile regime, which is characterized by x-ray diffraction. Using ferromagnetic resonance (FMR), we find that, in addition to the first-order perpendicular magnetic anisotropy which depends linearly on the strain, there is a significant second-order one that has a quadratic strain dependence. Inhomogeneous linewidth of the FMR increases notably with increasing strain, while the Gilbert damping parameter remains nearly constant $(\approx 2\times {10}^{\text{–}2})$. These results provide valuable insight into the spin dynamics in ferrimagnetic insulators and useful guidance for material synthesis and engineering of next-generation spintronics applications.

How thermally activated structural excitations quantitatively mediate transport and microplasticity in a model binary glass at the microsecond timescale is revealed using atomistic simulation. These local excitations, involving a stringlike sequence of atomic displacements, admit a far-field shear-stress signature and underlie the transport of free-volume and bond geometry. Such transport is found to correspond to the evolution of a disclination network describing the spatial connectivity of topologically distinct bonding environments, demonstrating the important role of geometrical frustration in both glass structure and its underlying dynamics.

The introduction of strain into semiconductors offers a well-known route to modify their band structure. Here, we show a single-step procedure for generating such strains smoothly and deterministically, over a very wide range, using a simple, easily available, highly scalable, ion implantation technique to control the degree of amorphization in and around single-crystal membranes. The amorphization controls the density of the material and thus the tension in the neighboring crystalline regions. We have demonstrated up to 3.1% biaxial tensile strain and 8.5% uniaxial strain in silicon, based on micro-Raman spectroscopy. This method achieves strain levels never previously reached in mesoscopic defect-free, crystalline silicon structures. The flexible, gently controllable, single-step process points toward very high mobility complementary metal-oxide-semiconductor devices and easy fabrication of direct-bandgap germanium for silicon-compatible optoelectronics.

Heavy transition-metal tetraborides (e.g., tungsten tetraboride, molybdenum tetraboride, and molybdenum-doped tungsten tetraboride) exhibit superior mechanical properties, but solving their complex crystal structures has been a long-standing challenge. Recent experimental x-ray and neutron diffraction measurements combined with first-principles structural searches have identified a complex structure model for tungsten tetraboride that contains a boron trimer as an unusual structural unit with a stoichiometry of 1:4.2. In this paper, we expand the study to binary ${\mathrm{MoB}}_{4.2}$ and ternary ${\mathrm{W}}_{1-x}{\mathrm{Mo}}_x{\mathrm{B}}_{4.2}$ ($x=0.0–1.0$) compounds to assess their thermodynamic stability and mechanical properties using a tailor-designed crystal structure search method in conjunction with first-principles energetic calculations. Our results reveal that an orthorhombic ${\mathrm{MoB}}_{4.2}$ structure in $Cmcm$ symmetry matches well the experimental x-ray diffraction patterns. For the synthesized ternary Mo-doped tungsten tetraborides, a series of ${\mathrm{W}}_{1-x}{\mathrm{Mo}}_x{\mathrm{B}}_{4.2}$ structures are theoretically designed using a random substitution approach by replacing the W to Mo atoms in the $Cmcm$ binary crystal structure. This approach leads to the discovery of several ${\mathrm{W}}_{1-x}{\mathrm{Mo}}_x{\mathrm{B}}_{4.2}$ structures that are energetically superior and stable against decomposition into binary ${\mathrm{WB}}_{4.2}$ and ${\mathrm{MoB}}_{4.2}$. The structural and mechanical properties of these low-energy ${\mathrm{W}}_{1-x}{\mathrm{Mo}}_x{\mathrm{B}}_{4.2}$ structures largely follow the Vegard's law. Under changing composition parameter $x=0.0–1.0$, the superior mechanical properties of ${\mathrm{W}}_{1-x}{\mathrm{Mo}}_x{\mathrm{B}}_{4.2}$ stay in a narrow range. This unusual phenomenon stems from the strong covalent network with directional bonding configurations formed by boron atoms to resist elastic deformation. The findings offer insights into the fundamental structural and physical properties of ternary ${\mathrm{W}}_{1-x}{\mathrm{Mo}}_x{\mathrm{B}}_{4.2}$ in relation to the binary ${\mathrm{WB}}_{4.2}/{\mathrm{MoB}}_{4.2}$ compounds, which open a promising avenue for further rational optimization of the functional performance of transition-metal borides that can be synthesized under favorable experimental conditions for wide applications.

Low-dimensional magnetic materials have attracted much attention due to their novel properties and high potential for spintronic applications. In this work, we study the electronic structure and magnetic properties of the pseudo one-dimensional compound ${\mathrm{CrSbSe}}_3$, using density functional calculations, superexchange model analyses, and Monte Carlo simulations. We find that ${\mathrm{CrSbSe}}_3$ is a ferromagnetic (FM) semiconductor with a band gap of about 0.65 eV. The FM couplings within each zigzag spin chain are due to the Cr-Se-Cr superexchange with the near ${90}^{\circ }$ bonds, and the interchain FM couplings are one order of magnitude weaker. By inclusion of the spin-orbit coupling (SOC) effects, our calculations reproduce the experimental observation of the easy magnetization $a$ axis and the hard $b$ axis (the spin-chain direction), with the calculated moderate magnetic anisotropy of 0.19 meV/Cr. Moreover, we identify the nearly equal contributions from the single ion anisotropy of Cr, and from the exchange anisotropy due to the strong SOC of the heavy elements Sb and Se and their couplings with Cr. Using the parameters of the magnetic coupling and anisotropy from the above calculations, our Monte Carlo simulations yield the Curie temperature $T_{\mathrm{C}}$ of 108 K.

We performed ferromagnetic resonance measurements of a ${\left({\mathrm{La}}_{1-x}{\mathrm{Pr}}_x\right)}_{1-y}{\mathrm{Ca}}_y\mathrm{Mn}{\mathrm{O}}_{3-\delta }$ with $x=0.52\pm 0.05, y=0.23\pm 0.04$, and $\delta =0.14\pm 0.10$ thin single crystalline film which, in combination with micromagnetic simulations, reveal three temperature regions consistent with (i) a ferromagnetic-paramagnetic transition in which ferromagnetic domains nucleate and grow, (ii) followed by a filamentary fluidlike percolation of magnetic domains exhibiting dynamic processes and finally, iii) the existence of a blocking temperature below which the magnetism is a metastable glassy-like state with strong decoherence of the uniform resonance mode. Our results suggest a strain-liquid to strain-glass spin order transition in which the magnetism and fluidlike dynamics of the separated phases freeze at low temperatures. We show the magnetism dynamics depend strongly on the phase-separated state and morphology of the magnetic domains suggesting a route to control of phase separation and realization of spintronic and magnonic devices.

We present a method to locate and characterize grain boundaries in polycrystalline materials from the real-space coordinates of their constituent particles. The method is robust against imperfections such as thermal noise and vacancies. We apply the algorithm to experimentally found real-space coordinates to explicitly measure local misorientations and structure at grain boundaries. We consider particle coordinates obtained from an epitaxially templated colloidal $\mathrm{\Sigma }17$ bicrystal, finding that, even though the bicrystal is predominantly $\mathrm{\Sigma }17$ and face-centered cubic, small volumes of hexagonally closed-packed structure generate a mosaic of grain boundaries, increasing the complexity of the templated grain boundary. We also consider a homogeneously nucleated colloidal polycrystal and apply our method with no prior knowledge of grain boundary structure. Accordingly, we reveal detailed misorientation distributions and grain boundary structures. The method may be applied to any set of coordinates of atoms or particles in a polycrystalline system.

Spin-polarized currents play a key role in spintronics. Recently, it has been found that antiferromagnets with a non-spin-degenerate band structure can efficiently spin-polarize electric currents, even though their net magnetization is zero. Among the antiferromagnetic metals with magnetic space group symmetry supporting this functionality, the noncollinear antiferromagnetic antiperovskites $A\mathrm{N}{\mathrm{Mn}}_3$ ($A=\mathrm{Ga}$, Ni, Sn, or Pt) are especially promising. This is due to their high Néel temperatures and a good lattice match to perovskite oxide substrates, offering possibilities of high structural quality heterostructures based on these materials. Here, we investigate the spin polarization of antiferromagnetic $A\mathrm{N}{\mathrm{Mn}}_3$ metals using first-principles density functional theory calculations. We find that the spin polarization of the longitudinal currents in these materials is comparable with that in widely used ferromagnetic metals and thus can be exploited in magnetic tunnel junctions and spin transfer torque devices. Moreover, for certain film growth directions, out-of-plane transverse spin currents with a giant charge-to-spin conversion efficiency can be achieved, implying that the $A\mathrm{N}{\mathrm{Mn}}_3$ antiperovskites can be used as efficient spin sources. These properties make $A\mathrm{N}{\mathrm{Mn}}_3$ compounds promising for application in spintronics.

We report a giant thermoelectric figure of merit $ZT$ (up to six at 1100 K) in $n$-doped lanthanum oxysulphate LaSO. Thermoelectric coefficients are computed from ab initio bands within Bloch-Boltzmann theory in an energy-, chemical potential-, and temperature-dependent relaxation time approximation. The lattice thermal conductivity is estimated from a model employing the ab initio phonon and Grüneisen-parameter spectrum. The main source of the large $ZT$ is the significant power factor which correlates with a large band complexity factor. We also suggest a possible $n$-type dopant for the material based on ab initio calculations.

Demonstrating both the intrinsic and extrinsic nature of the giant piezoelectric effect (GPE) in complex solid solutions, near the morphotropic phase boundary, has been extremely challenging until now, because such materials exhibit multiple phases on the order of tens of microns across, meaning important information is lost due to averaging when using established high resolution diffraction techniques to extract three dimensional structural information. We have used a different approach proposed by Nisbet et al. [Acta Crystallogr. Sect. A 71, 20 (2015)], which has been adapted to differentiate between spatially adjacent phases and simultaneously track the evolution of those phases in response to electric fields. As a result, we have identified three environment specific GPEs. The first of these is a GPE which is an order of magnitude greater than previously reported for a given change in field. This is observed during a tetragonal-monoclinic transition in a multiphasic environment. A secondary, large GPE is observed in the neighboring, nontransitioning, monoclinic phase due to stress biasing, and a more typical GPE is observed when the system becomes monophasic. Our results demonstrate the simultaneous and complex interplay of intrinsic and extrinsic factors contributing to the GPE which is likely to have implications for device manufacture and miniaturization.

Solute diffusion through solid-solid interfaces is paramount to many physical processes. From a modeling point of view, the discontinuities in the energy landscape at a sharp interface represent difficulties in predicting solute diffusion that, to date, have not been solved in a consistent manner across length scales. Using an explicit finite volume method, this work is the first to derive numerical solutions to the diffusion equations at a continuum level while including discrete variations in the energy landscape at a bicrystal interface. An atomic jump equation consistent with atomistic descriptions is derived and scaled up into a compendium of model interfaces: monolayer energy barriers, monolayer interfacial traps, multilayered traps, and heterogeneous interfaces. These can track solute segregation behavior and long-range diffusion effects. We perform simulations with data for hydrogen diffusion in structural metals, of relevance to the assessment of the hydrogen embrittlement phenomenon, and point defects in electronic devices. The approach developed represents an advancement in the mathematical treatment of solute diffusion through solid-solid interfaces and an important bridge between the atomistic and macroscopic modeling of diffusion, with potential applications in a variety of fields in materials science and physics.

Recently, the two-dimensional (2D) material germanium selenide (GeSe) was shown to possess extraordinary physicochemical properties as well as great potential for electrical and optical applications, whereas its thermal radiative properties remain elusive. Here, we present a comprehensive study of the near-field thermal radiation (NFTR) of monolayer GeSe by means of fluctuational electrodynamics theory. It is shown that, at a small vacuum gap, such a 2D semiconductor not only supports a giant heat flux that surpasses the black-body limit by four orders of magnitude but is also far ahead of graphene with the same electron density. This extraordinary thermal radiation is attributed to the strong quasi-elliptic surface plasmon polaritons supported by the monolayer GeSe at near- and midinfrared frequency regions. In addition, we show how electron density affects the NFTR of monolayer GeSe, where the effect can be switched from suppression to enhancement by elevating the vacuum gap. Furthermore, we investigate the possibility of using mechanical rotation to modulate the NFTR. We find that, at a lower electron density, the NFTR of the monolayer GeSe could be more effectively modulated through mechanical rotation. Finally, we investigate the interference effect of the dielectric substrate on the NFTR, pointing out the nonmonotonic dependency between its thermal radiation and the dielectric constant of substrate. All in all, in this paper, we provide a fundamental understanding of the NFTR in GeSe single layer and offer guidance for further research and modulation in emerging energy conversion and thermal management.

As the first intrinsic antiferromagnetic topological insulator, ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ has provided a platform to investigate the interplay of band topology and magnetism as well as the emergent phenomena arising from such an interplay. Here we report the chemical-vapor-transport (CVT) growth and characterization of ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$, as well as the observation of the field-induced quantized Hall conductance in 6-layer devices. Through comparative studies between our CVT-grown and flux-grown ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ via magnetic, transport, scanning tunneling microscopy, and angle-resolved photoemission spectroscopy measurements, we find that CVT-grown ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ is marked with higher Mn occupancy on the Mn site, slightly higher ${\mathrm{Mn}}_{\mathrm{Bi}}$ antisites, smaller carrier concentration, and a Fermi level closer to the Dirac point. Furthermore, a 6-layer device made from the CVT-grown sample shows by far the highest mobility of 2500 ${\mathrm{cm}}^2\mathrm{V}\mathrm{s}$ in ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ devices with the quantized Hall conductance appearing at 1.8 K and 8 T. Our study provides a route to obtain high-quality single crystals of ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ that are promising to make superior devices and realize emergent phenomena, such as the layer Hall effect and quantized anomalous Hall effect, etc.

The ferroaxial order, which is characterized by a rotational structural distortion in a crystal, has been recently proposed as one of ferroic orders. Though the domain formation is a characteristic feature in ferroic materials, there has been little study done concerning that for the ferroaxial order. Here, we investigate ferroaxial domains that are formed through a ferroaxial transition in two representative ferroaxial materials, ${\mathrm{NiTiO}}_3$ and $\mathrm{RbFe}{\left(\mathrm{Mo}{\mathrm{O}}_4\right)}_2$. We spatially resolve their domain structures using an optical method based on electric-field-induced optical rotation, that is, electrogyration (EG). In ${\mathrm{NiTiO}}_3$, multidomains are constructed when crystals undergo a ferroaxial transition and the domain size depends on the cooling rate around the transition temperature. Furthermore, the ferroaxial domain structure obtained by the EG measurement is well matched with that by scanning x-ray diffraction. $\mathrm{RbFe}{\left(\mathrm{Mo}{\mathrm{O}}_4\right)}_2$ also exhibits multidomain states in which domain patterns are different each time a crystal undergoes a ferroaxial transition. In addition, the temperature dependence of the EG signal well obeys that of the order parameter of a first-order phase transition. These results ensure the effectiveness of the EG effect to elucidate the nature of ferroaxial order.

Three-dimensional (3D) topological insulators (TIs) with large spin Hall conductivity have emerged as potential candidates for spintronic applications. Here, we report spin to charge conversion in bilayers of amorphous ferromagnet (FM) ${\mathrm{Fe}}_{78}{\mathrm{Ga}}_{13}{\mathrm{B}}_9$ (FeGaB) and 3D TI ${\mathrm{Bi}}_{85}{\mathrm{Sb}}_{15}$ (BiSb) activated by two complementary techniques: spin pumping and ultrafast spin-current injection. DC magnetization measurements establish the soft magnetic character of FeGaB films, which remains unaltered in the heterostructures of FeGaB-BiSb. Broadband ferromagnetic resonance (FMR) studies reveal enhanced damping of precessing magnetization and large value of spin mixing conductance $(5.03\times {10}^{19}{\mathrm{m}}^{\text{–}2})$ as the spin angular momentum leaks into the TI layer. Magnetic field controlled bipolar DC voltage generated across the TI layer by inverse spin Hall effect is analyzed to extract the values of spin Hall angle and spin diffusion length of BiSb. The spin pumping parameters derived from the measurements of the femtosecond light-pulse-induced terahertz emission are consistent with the result of FMR. The Kubo-Bastin formula and tight-binding model calculations shed light on the thickness-dependent spin-Hall conductivity of the TI films, with predictions that are in remarkable agreement with the experimental data. Our results suggest that room temperature deposited amorphous and polycrystalline heterostructures provide a promising platform for creating novel spin orbit torque devices.

Plasticity of body-centered cubic tantalum with preexisting dislocations is investigated under $\left[001\right]$ uniaxial compression/tension loading using a molecular dynamic simulation method. At low temperature or high strain rate, twinning is the main deformation mechanism under both $\left[001\right]$ compression and tension. However, the twinning mechanism under compression is different from the conventional twinning mechanism under tension, which is formed by $1/6\left[1\overline{1}1\right]$ twinning dislocations moving on adjacent $\left(\overline{1}12\right)$ planes along the twinning direction. The twin nucleates from six-layer dissociation of a $1/2\left[111\right]$ screw dislocation and grows by the glide of disconnections that step the twin boundary by two $\left(\overline{1}12\right)$ planes. Further study shows that this type of twinning mode generates a finite antitwinning shear strain, the magnitude of which is one-half of that generated by the conventional deformation twinning. Finally, the two twinning mechanisms are discussed in terms of the energy landscape.

Two-dimensional semiconductor phosphorene has attracted extensive research interests for potential applications in optoelectronics, spintronics, catalysis, sensors, and energy conversion. To harness phosphorene's potential requires a better understanding of how intrinsic defects control carrier concentration, character, and mobility. Using density functional theory and a charge correction scheme to account for the appropriate boundary conditions, we conduct a comprehensive study of the effect of structure on the formation energy, electronic structure, and charge transition level of the charged vacancy point defects in phosphorene. We predict that the neutral vacancy exhibits a 9-5 ring structure with a formation energy of 1.7 eV and transitions to a negatively charged state at a Fermi level 1.04 eV above the valence band maximum. The corresponding optical charge transitions display sizable Frank-Condon shifts with a large Stokes shift of 0.3 eV. Phosphorene vacancies should become negatively charged in $n$-doped phosphorene, which would passivate the dopants and reduce the charge carrier concentration and mobility.

Varying thickness in ferroelectric heterostructures systematically changes both the strain and the electrical boundary conditions and thus the polarization screening. This has a direct result on the observed ferroelectric nanotopologies, from polar vortices, skyrmions, and bubbles to Kittel type stripe/labyrinthine domains. Here, a control of the topological defect transitions is reported in epitaxial (001)-oriented $\mathrm{Pb}{\mathrm{Zr}}_{0.4}{\mathrm{Ti}}_{0.6}{\mathrm{O}}_3/\mathrm{SrTi}{\mathrm{O}}_3/\mathrm{Pb}{\mathrm{Zr}}_{0.4}{\mathrm{Ti}}_{0.6}{\mathrm{O}}_3$ (PZT/STO/PZT) heterostructures. Piezoresponse force microscopy is exploited to capture various topological defect states, such as merons, skyrmions, dislocations, bimerons, and three- or fourfold junctions and hence to understand their transition pathways. The thickness of the dielectric spacer and/or ferroelectric layer is tuned during growth to manipulate the strength of the residual depolarization field; this consequently leads to a range of the abovementioned topological defect structures. This is further corroborated by effective Hamiltonian-based Monte Carlo simulations that provide insight into why and how altering the thickness of ferroelectric or dielectric layers triggers topological phase transitions. This controlled design of nanoscale ferroic topologies opens possibilities of engineering emergent transitions.