We have investigated the effect of Ge substitution on the magnetic ordering in the B20 itinerant chiral magnet MnSi prepared by melting and annealing under ambient pressure. From a metallurgical survey, the solubility limit of Ge was found to be $x=0.144\left(5\right)$ with annealing temperature $T_{\mathrm{an}}=1073$ K. Magnetization measurements on ${\mathrm{MnSi}}_{1-x}{\mathrm{Ge}}_x$ samples show that the helical ordering temperature $T_{\mathrm{c}}$ increases rapidly in the low-$x$ range, whereas it becomes saturated at higher concentration $x>0.1$. The Ge substitution also increases both the saturation magnetization $M_{\mathrm{s}}$ and the critical field to the fully polarized state $H_{\mathrm{c}2}$. In contrast to the saturation behavior of $T_{\mathrm{c}}$, those parameters increase linearly up to the highest Ge concentration investigated. In the temperature-magnetic field phase diagram, we found enlargement of the skyrmion phase region for large $x$ samples. We, furthermore, observed the nonlinear behavior of helical modulation vector $k$ as a function of Ge concentration, which can be described qualitatively using the mean field approximation.

We present the synthesis and a detailed investigation of structural and magnetic properties of polycrystalline $\mathrm{VO}{\left(\mathrm{HCOO}\right)}_2·\left({\mathrm{H}}_2\mathrm{O}\right)$ by means of x-ray diffraction, magnetic susceptibility, high-field magnetization, heat capacity, and electron-spin-resonance measurements. The compound crystallizes in an orthorhombic structure with space group $Pcca$. The crystal lattice features distorted ${\mathrm{VO}}_6$ octahedra connected via HCOO linkers (formate anions), forming a two-dimensional square lattice network with a bilayered structure. Analysis of magnetic susceptibility, high-field magnetization, and heat capacity data in terms of the frustrated square lattice model unambiguously establish the quasi-two-dimensional nature of the compound with nearest-neighbor interaction $J_1/k_{\mathrm{B}}\simeq 11.7\mathrm{K}$ and next-nearest-neighbor interaction $J_2/k_{\mathrm{B}}\simeq 0.02\mathrm{K}$. A Néel antiferromagnetic ordering sets in at $T_{\mathrm{N}}\simeq 1.1\mathrm{K}$. The ratio ${\theta }_{\mathrm{CW}}/T_{\mathrm{N}}\simeq 10.9$ reflects excellent two-dimensionality of the spin-lattice in the compound. A strong in-plane anisotropy is inferred from the linear increase of $T_{\mathrm{N}}$ with magnetic field, consistent with the structural data.

Spin-to-charge conversion at metal/oxide interfaces with stacked structures of permalloy/(Cu or Ag)/${\mathrm{Bi}}_2{\mathrm{O}}_3$ were systematically investigated by using the spin-pumping technique and cross-sectional transmission electron microscopy. Although the transport measurement reproduced the results in previous studies, the interfacial structure of (Cu or Ag)/${\mathrm{Bi}}_2{\mathrm{O}}_3$ was found to change depending on the crystalline orientation of the Cu or Ag underlayer. While the Ag/${\mathrm{Bi}}_2{\mathrm{O}}_3$ stacks with Ag(111) had steep interfaces, the formation of a nanometer-scale Cu-O layer can be found in the Cu/${\mathrm{Bi}}_2{\mathrm{O}}_3$ interface, which should be the main origin of the sign inversion of the conversion coefficients between Cu/${\mathrm{Bi}}_2{\mathrm{O}}_3$ and Ag/${\mathrm{Bi}}_2{\mathrm{O}}_3$. This study stresses the importance of nanostructure identification for discussing spin-to-charge conversions at metal/oxide interfaces.

Indium oxide is widely employed in applications ranging from optoelectronics and gas sensing to catalysis, as well as in thin-film heterostructures. To probe the fundamentals of phenomena at the heart of ${\text{In}}_2{\text{O}}_3$-based devices that are tied to the intrinsic surface and interface properties of the material, well-defined single-crystalline ${\text{In}}_2{\text{O}}_3$ surfaces are needed. We report on how to grow atomically flat ${\text{In}}_2{\text{O}}_3$(111) thin films on yttria-stabilized zirconia substrates by pulsed laser deposition. The films are largely relaxed and reproduce the atomic-scale details of the surfaces of single crystals, except for line defects originating from the antiphase domain boundaries that form because of the one-on-four lattice match between the surface unit cells of ${\text{In}}_2{\text{O}}_3$(111) and of the substrate. While optimizing the growth conditions, we observe that the morphology of the films is ruled by the oxygen chemical potential, which determines the nature and diffusivity of adspecies during growth.

Magnetic skyrmions have captivated physicists due to their topological nature and novel physical properties. In addition, skyrmions hold significant promise for future information technologies. A key barrier to realizing skyrmion-based devices has been stabilizing these spin structures under ambient conditions. In this paper, we demonstrate that the tunable magnetic properties of amorphous Fe/Gd mulitlayers enable the formation of skyrmion lattices which are stable over a large temperature and magnetic field parameter space, including room temperature and zero magnetic field. These skyrmions, having a hybrid nature displaying both Bloch-type and Néel-type characteristics, are stabilized by dipolar interactions rather than Dzyaloshinskii-Moriya interactions, typically considered a requirement for the generation of skyrmions. Small angle neutron scattering (SANS) was used in combination with soft x-ray microscopy to provide a unique, multiscale probe of the local and long-range order of these structures. The hexagonal lattice seen in SANS results from the hybrid skyrmion picture obtained with micromagnetic simulations. These results identify a pathway to engineer controllable skyrmion phases in thin film geometries which are stable at ambient conditions.

The Pr-based cobaltate $\mathrm{P}{\mathrm{r}}_{0.5}\mathrm{C}{\mathrm{a}}_{0.5}\mathrm{Co}{\mathrm{O}}_3$ (PCCO) presents in bulk form a singular simultaneous valence and spin-state transition that turns the metallic state into insulator, and displays a large and ultrafast photoresponse in the insulating phase. Epitaxial thin films of PCCO have been grown by deposition on $\mathrm{LaAl}{\mathrm{O}}_3$(001) (LAO) substrate, chosen to minimize the mismatch with the film. The films grow epitaxially with two times the substrate periodicity $(2a_0\times 2a_0\times 2a_0)$ and the long perovskite axis perpendicular to the surface. We report a reduction of the structural symmetry from Pnma (bulk) to $P{2}_1{2}_1{2}_1$ (film). The $P{2}_1{2}_1{2}_1$ symmetry revealed by synchrotron x ray remains at low temperatures. These PCCO films are metallic, and ferromagnetic below $T_{\mathrm{C}}=170\mathrm{K}$, confirming the stabilization of excited $\mathrm{C}{\mathrm{o}}^{3+}$ spin states and the suppression of the concurrent Co spin-state, valence, and metal-insulator transitions. $Z$-contrast imaging and electron-energy-loss spectroscopy elemental maps reveal long-range ordered oxygen vacancy planes unexpectedly stacking parallel to the interface, in spite of the tensile character of the PCCO/LAO heterostructure. In contrast to the general tendency reported for strained $\mathrm{L}{\mathrm{a}}_{0.5}\mathrm{S}{\mathrm{r}}_{0.5}\mathrm{Co}{\mathrm{O}}_{3-\delta }$ (LSCO) films, we show that a nominal tensile strain can be also compatible with the presence of alternating O vacancy planes parallel to the interface, instead of perpendicular to it. That occurs thanks to the double cell of the film and the formation of the (1/2, 1/2, 1/2) superstructure studied in this work. These results expand the possibilities of controlling interfacial physical properties via engineering of ordered oxygen-defect structures in strongly correlated oxides.

The influence of film orientation, strain relaxation, and flexoelectric fields on the stability of the spin cycloid in (110)-oriented $\mathrm{BiFe}{\mathrm{O}}_3$ epitaxial films grown on $\mathrm{LaAl}{\mathrm{O}}_3$ substrates is investigated. By means of advanced x-ray-diffraction techniques, we show that thinner films have very large strain gradients which give rise to high flexoelectric fields. Using low-energy Raman spectroscopy and conversion electron Mössbauer spectroscopy (CEMS) we show that films up to 53 nm thick possess collinear antiferromagnetic order, with no cycloidal modulation. This suppression of the cycloid is proposed to be from strain and strain-gradient-induced flexoelectric fields. On the other hand, films thicker than 90 nm show a complex spin texture consistent with two separate cycloids, likely with different propagation directions. Interestingly, CEMS analysis suggests that the two cycloids have the same spin rotation plane. The multiple cycloids are suggested to arise from different ferroelastic domains (in turn influenced by twinning in the substrate) with different strain relaxation behaviors. These results offer insight into the factors that influence cycloid stability in the less common (110) film orientation and have implications for future magnonic devices.

The interaction between point defects and dislocations plays a crucial role in governing material properties and microstructural evolutions under external stimuli, such as mechanical deformation and irradiation. Here, we present an atomistic study of the interactions between point defects and dislocations in concentrated solid-solution alloys (CSAs). Using molecular statics and kinetic Monte Carlo methods, we demonstrate that the strain energy and stress field distribution induced by a dislocation in CSAs are highly inhomogeneous along the dislocation line, which leads to heterogeneity of defect-dislocation interactions. Specifically, the interactions are spatially different and screened by the random arrangement of different elemental species. Such localization of defect-dislocation interaction indicates that the “dislocation-bias” mechanism that is a driving force for radiation-induced void swelling can be suppressed in concentrated alloys.

The microstructural evolution of metals and alloys is governed by the diffusion of defects over complex energy landscapes. Whenever metastability occurs in atomistic simulations, well-separated timescales emerge making it necessary to implement event-based kinetic models at larger scales. The crucial task then involves characterizing the important events contributing to mass transport. We herein describe fast first-passage algorithms based on the theory of absorbing Markov chains assuming that defects undergo reversible diffusion. We show that the absorbing transition rate matrix can be transformed into a symmetric definite-positive matrix enabling us to implement direct and iterative sparse solvers. The efficiency of the approach is demonstrated with direct computations of elastodiffusion properties around a cavity in aluminum and Monte Carlo computations of cluster diffusivity in low-alloyed manganese steels.

We observe a ferroelectric (FE) order in an unexplored ${\mathrm{CuCr}}_2{\mathrm{O}}_4$ with a reasonably high value of the FE Curie temperature $\left(T_{\mathrm{FE}}\right)$ at 170 K, which is also much higher than the magnetic ordering temperature. The systematic substitution of Jahn-Teller (J-T) active divalent Cu ion by a non-Jahn-Teller active divalent Co ion causes a systematic shift of $T_{\mathrm{FE}}$ from 170 K for $x=0$ to 146 K for $x=0.8$ in ${\mathrm{Cu}}_{1-x}{\mathrm{Co}}_x{\mathrm{Cr}}_2{\mathrm{O}}_4$. The values of electric polarization vary from 0.0665 $\mu {\mathrm{C}\mathrm{cm}}^{-2}$ to 0.1704 $\mu {\mathrm{C}\mathrm{cm}}^{-2}$, which is maximum for $x=0.6$, associated with the highest value of the coercivity. The synchrotron diffraction studies of the compounds with $x=0.2$ and 0.8 confirm that a structural transition to a polar $Ima2$ space group from the tetragonally distorted $I{4}_1/amd$ structure gives rise to the ferroelectricity. In all the members of ${\mathrm{Cu}}_{1-x}{\mathrm{Co}}_x{\mathrm{Cr}}_2{\mathrm{O}}_4$ series, the $T_{\mathrm{FE}}$ is observed at much higher temperature than the corresponding magnetic ordering temperatures $\left(T_N\right)$. These results are in contrast to that of the reported results of $T_{\mathrm{FE}}<T_N$ for the end member with $x=1$ or ${\mathrm{CoCr}}_2{\mathrm{O}}_4$, where the J-T active ${\mathrm{Cu}}^{2+}$ is absent. We propose that the J-T distortion in the entire series with $0\le x\le 0.8$ holds the key, where interplay between the J-T distortion driven orbital order and the structural distortion correlates tuning of the $T_{\mathrm{FE}}$ in ${\mathrm{Cu}}_{1-x}{\mathrm{Co}}_x{\mathrm{Cr}}_2{\mathrm{O}}_4$.

The Materials Genome Initiative calls for a dramatic increase in the rate of materials discovery and development. High-throughput (HT) calculations can advance this goal by efficiently screening a large search space for candidate materials to study in more depth. Thermoelectric materials (TEs) are prime candidates for such HT calculations: The properties required to achieve good performance are known, but systematic ways of improving these properties are scarce. Furthermore, known HT methods for TEs only address bulk crystals—screening realistic multicomponent alloys for their TE properties has yet to be accomplished. In this paper, we use a density functional theory driven HT screening-and-sorting procedure to search for new multicomponent bulk-nanostructured thermoelectric materials. We make maximum use of minimal calculations to obtain eight descriptors of the thermodynamics and TE performance of five-element semiconductor alloy systems from combinations of ternary additions in binary compounds. We use these descriptors to reduce a search space of 29 700 five-element systems to a set of 130 candidates. We screen these candidates using TE descriptors to identify several existing high-performance thermoelectrics as well as promising new material systems awaiting further experimental verification.

Capillary-driven mass transport in solids is typically understood in terms of surface-diffusion limited kinetics, leading to conventional solid-state dewetting of thin films. However, another mass transport mechanism, so-called surface-attachment/detachment limited kinetics, is possible. It can shrink a solid film, preserving its original topology without breaking it in isolated islands, and leads to faster dynamics for smaller film curvature in contrast with the opposite behavior observed for surface-diffusion limited kinetics. In this work, we present a rimless dewetting regime for Si, which is ascribed to effective attachment-limited kinetics mediated by the coexistence of crystalline and amorphous Si phases. Phase-field numerical simulations quantitatively reproduce the experimental observations, assessing the main mass transport mechanism at play. The process can be exploited to obtain in a deterministic fashion monocrystalline islands (with $95\%$ probability) pinned at $\approx 500$ nm from a hole milled within closed patches.

We have studied low-energy configurations in two-dimensional arrays consisting of Ising-type dipolar coupled nanomagnets lithographically defined onto a two-dimensional Cairo lattice, thus dubbed the dipolar Cairo lattice. Employing synchrotron-based photoemission electron microscopy (PEEM), we perform real-space imaging of moment configurations achieved after thermal annealing. These states are then characterized in terms of vertex populations, spin- and emergent magnetic charge correlations, and a topology-enforced emergent ice rule. The results reveal a strong dominance of short-range correlations and the absence of long-range order, reflecting the high degree of geometrical spin frustration present in this example of an artificial frustrated spin system.

Superconductivity in materials whose crystal structure lacks inversion symmetry is a prime candidate for unconventional superconductivity. A new noncentrosymmetric compound ${\mathrm{Zr}}_3\mathrm{Ir}$ crystallizes in a tetragonal $\alpha -{\mathrm{V}}_3\mathrm{S}$ structure. The magnetization, specific heat, and muon spin rotation confirm s-wave superconductivity, having a transition temperature $T_c=2.3$ K. Muon spin relaxation confirms the preservation of time reversal symmetry in the superconducting ground state.

The cubic intermetallic compound $\mathrm{B}{\mathrm{a}}_{10}\mathrm{T}{\mathrm{i}}_{24}\mathrm{B}{\mathrm{i}}_{39}$ has a $\mathrm{B}{\mathrm{a}}_6\mathrm{B}{\mathrm{i}}_{16}$ polyhedral cage with a Bi guest atom encapsulated inside. The compound can be formulated as $\mathrm{B}{\mathrm{a}}_5\mathrm{T}{\mathrm{i}}_{12}\mathrm{B}{\mathrm{i}}_{19+x}$ when $x$ signifies the extra Bi atoms filling cages. It crystallizes in a complex noncentrosymmetric cubic structure in space group $P\text{−}43m$ with cell parameter $a=12.6787\left(4\right)\AA$. The guest Bi atoms distribute diffusely in the cages and seem to play a role in stabilizing the crystal structure. The magnetic susceptibility of this compound shows a weak temperature dependence with a positive slope coefficient. The charge transport properties as a function of temperature exhibit two competing components which are in charge of positive and negative magnetoresistances. Electronic band-structure calculations reveal the complex multiband hybridization of Ti/Bi orbitals near the Fermi surface, which may play a role in the enormous electron-electron scattering in this material evidenced by the large Kadowaki-Woods ratio.

Eumelanin is regarded to be an attractive candidate material for biomedical applications. Despite many theoretical studies exploring the structure of eumelanin, an exact mapping of the energetic landscape of the very large phase space of eumelanin is still elusive. In this work, we implement a piecewise Ising model to predict formation enthalpies of eumelanin single and double tetramers, and demonstrate its superior predictive and generalizable capabilities. We believe this model will prove very useful in theoretically characterizing the many unique properties attributed to its disorder. The modular nature of the predictive Ising model built up in this work is well-suited for analysis and characterization of a larger phase space of eumelanin polymers, including hexamers and octomers, as well as larger stacked structures, such as potential triple and quadruple eumelanin tetramers. Absorbance data can be incorporated with populationwide predictions of polymer abundance to produce weighted-average predictions of broadband absorbance of bulk eumelanin.

Electronic phase separation is crucial for the fascinating macroscopic properties of the ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ (LAO/STO) paradigm oxide interface, including the coexistence of superconductivity and ferromagnetism. We investigate this phenomenon using angle-resolved photoelectron spectroscopy (ARPES) in the soft-x-ray energy range, where the enhanced probing depth combined with resonant photoexcitation allow us access to fundamental electronic structure characteristics – momentum-resolved spectral function, dispersions and ordering of energy bands, Fermi surface – of buried interfaces. Our experiment uses x-ray irradiation of the LAO/STO interface to tune its oxygen deficiency, building up a dichotomic system where mobile weakly correlated $\mathrm{Ti}{t}_{2\mathrm{g}}$ electrons coexist with localized strongly correlated $\mathrm{Ti}{e}_{\mathrm{g}}$ ones. The ARPES spectra dynamics under x-ray irradiation shows a gradual intensity increase under constant Luttinger count of the Fermi surface. This fact identifies electronic phase separation (EPS) where the mobile electrons accumulate in conducting puddles with fixed electronic structure embedded in an insulating host phase, and allows us to estimate the lateral fraction of these puddles. We discuss the physics of EPS invoking a theoretical picture of oxygen-vacancy clustering, promoted by the magnetism of the localized $\mathrm{Ti}{e}_{\mathrm{g}}$ electrons, and repelling of the mobile $t_{2\mathrm{g}}$ electrons from these clusters. Our results on the irradiation-tuned EPS elucidate the intrinsic one taking place at the stoichiometric LAO/STO interfaces.

The deposition of a thin oxide layer at metal/semiconductor interfaces has been previously reported as a means of reducing contact resistance in two-dimensional (2D) electronics. Using x-ray photoelectron spectroscopy with in situ Ti deposition, we fabricate $\mathrm{Au}/\mathrm{Ti}/\mathrm{Ti}{\mathrm{O}}_x/\mathrm{Mo}{\mathrm{S}}_2$ samples as well as $\mathrm{Au}/\mathrm{Ti}/\mathrm{Mo}{\mathrm{S}}_2$ and $\mathrm{Au}/\mathrm{Ti}{\mathrm{O}}_x/\mathrm{Mo}{\mathrm{S}}_2$ for comparison. Elemental titanium reacts strongly with $\mathrm{Mo}{\mathrm{S}}_2$ whereas no interface reactions are observed in the two types of samples containing $\mathrm{Ti}{\mathrm{O}}_x/\mathrm{Mo}{\mathrm{S}}_2$ interfaces. Using time-domain thermoreflectance for measurements of thermal boundary conductance, we find that samples contacted with Ti and a thin $\mathrm{Ti}{\mathrm{O}}_x$ layer at the interface (∼1.5 nm) exhibit the same behavior as samples contacted solely with pure Ti. The $\mathrm{Au}/\mathrm{Ti}{\mathrm{O}}_x/\mathrm{Mo}{\mathrm{S}}_2$ samples exhibit ∼20% lower thermal boundary conductance, despite having the same $\mathrm{Mo}{\mathrm{S}}_2$ interface chemistry as the samples with thin oxide at the Ti/$\mathrm{Mo}{\mathrm{S}}_2$ interface. We identify the mechanism for this phenomenon, attributing it to the different interfaces with the top Au contact. Our work demonstrates that the use of thin interfacial oxide layers to reduce electrical contact resistance does not compromise heat flow in 2D electronic devices. We note that the thicknesses of the Ti and $\mathrm{Ti}{\mathrm{O}}_x$ layers must be considered for optimal thermal transport.

Samarium sulfide (SmS) is a nonmagnetic narrow-gap (0.06 eV) semiconductor that undergoes a transition to a metallic intermediate valence state at 6.5 kbar. Europium sulfide (EuS) is a ferromagnetic semiconductor with a Curie temperature of 16 K and a gap of 1.6 eV. Here we present a study of the lattice constant, magnetic susceptibility, and resistivity of the substitution series $\mathrm{S}{\mathrm{m}}_{1-x}\mathrm{E}{\mathrm{u}}_x\mathrm{S}$ for $0<x<1$. We observe a smooth interpolation of magnetic and transport behavior across the series, consistent with a virtual crystal scenario and Vegard's law. Surprisingly, however, the lattice constant deviates below Vegard's law in a manner that suggests parametric control of the Sm-Sm distance by the Eu moment in the manner of a magnetic polaron.