The advancement of machine learning technologies has revolutionized the search and optimization of material properties. These algorithms often rely on theoretical calculations, such as density functional theory (DFT), for data inputs and validation, which are not always effective for uranium-based materials due to their strong electron correlations. This study presents a computationally inexpensive machine learning approach, specifically a random forest classifier, to predict the magnetic ground states of uranium compounds using only structural inputs. Our model, trained on a curated dataset of experimentally verified magnetic orders, achieves a mean accuracy of $60.2\%$, significantly outperforming random chance. Through a purely structural descriptor, our method offers a reliable alternative for discovering new materials with desirable magnetic properties, addressing the challenges posed by strong correlations in quantum materials.

We use micromagnetic simulations in this study to investigate the magnetic properties of a pellet of agglomerated ${\mathrm{Co}}_2\mathrm{C}$ nanoparticles (NPs). The magnetic structure in the NP pellet is modeled as a bilayer interface comprising a ferromagnetic (FM) block adjacent to a monolayer of frozen, uncompensated, disordered spin (DS) configuration characterized by a net magnetization. Introducing an exchange-coupling constant $\left(A_{\mathrm{int}}\right)$ at the FM/DS interface reveals an asymmetric hysteresis loop and an exchange bias (EB) effect above a critical $A_{\mathrm{int}}$ threshold of $3\times {10}^{-15}\mathrm{J}{\mathrm{m}}^{-1}$. Our simulations reproduce the experimentally determined values of the EB field $\left(H_{\mathrm{EB}}\right)$ and coercive field $\left(H_{\mathrm{C}}\right)$ and also provide an estimate of the FM/DS interfacial exchange-coupling energy $\left(J_{\mathrm{int}}\right)$ of $9.4\times {10}^{-4}\mathrm{J}{\mathrm{m}}^{-2}$ and the average uncompensated spin moments of $\langle M_{\mathrm{DS}}\rangle \sim 0.04$ (normalized units) for our pellet. Additionally, the temperature $\left(T\right)$ dependence of $H_{\mathrm{EB}}$ suggests the presence of thermally activated features in $J_{\mathrm{int}}\left(T\right)$. Furthermore, the simulations highlight the significance of domain-wall pinning effects at the FM-DS interface, affecting the FM layer's anisotropy and coercivity. We propose a comprehensive model that emphasizes the impact of interfacial exchange-coupling energy and domain-wall pinning effects on the FM layer's anisotropy; it attributes the EB effect in a ${\mathrm{Co}}_2\mathrm{C}$ NP pellet to the interaction of uncompensated spins in the DS layer with the FM layer, which propagates deep into the FM layer and also affects its coercivity.

The rare-earth nitrides are the only series of intrinsic ferromagnetic semiconductors where the interplay of spin and unquenched orbital angular momentum provides access to a range of magnetic behavior. Furthermore, the magnetic properties can be finely tuned through the combination of multiple lanthanide ions in the nitride. Here, we present a combined computational and experimental study on the electronic and magnetic properties of ${\mathrm{Gd}}_x{\mathrm{Sm}}_{1-x}\mathrm{N}$ and discuss the effect of cation substitution on the internal exchange field and band structure. We find that as the coercive field of ${\mathrm{Gd}}_x{\mathrm{Sm}}_{1-x}\mathrm{N}$ changes over orders of magnitude via cation substitution, the internal exchange field changes by $\sim 20\%$. Control of these material properties is vital in the field of superconducting spintronics. Finally, motivated by an enhanced concentration of nitrogen vacancies in films with higher Sm content, we investigate computationally the formation of nitrogen vacancy defects in ${\mathrm{Gd}}_x{\mathrm{Sm}}_{1-x}\mathrm{N}$, finding that the formation energy is significantly reduced for vacancy sites adjacent to Sm ions rather than Gd ions.

Erbium oxide ($\mathrm{E}{\mathrm{r}}_2{\mathrm{O}}_3$) is a rare earth sesquioxide with possible applications in CMOS as a gate dielectric, in photovoltaics, and in scalable optical quantum computing technology. Further, erbium exhibits photoluminescence in the telecom $C$ band at $1540\mathrm{nm}$, whose fine structure depends on the crystal structure. Crystal field symmetry of the erbium site in $\mathrm{E}{\mathrm{r}}_2{\mathrm{O}}_3$ governs the Stark-split states and phonon-assisted excitations in $\mathrm{E}{\mathrm{r}}^{3+}$. The ground state of $\mathrm{E}{\mathrm{r}}_2{\mathrm{O}}_3$ is a cubic (bixbyite) phase, but it undergoes a phase transition to monoclinic and hexagonal phases at high temperatures and pressures. In this work, we explore the electronic structure, formation energy, phonon dispersion, and Raman scattering in the three phases of $\mathrm{E}{\mathrm{r}}_2{\mathrm{O}}_3$ using density functional theory. We then investigate temperature- and pressure-induced phase transitions between the three phases of $\mathrm{E}{\mathrm{r}}_2{\mathrm{O}}_3$. We compare our results with existing experiments and find good agreement.

Monolayer ${\mathrm{NiI}}_2$ garners large research interest because of its multiferroic behavior stemming from the interplay between its noncollinear magnetic order and the spin-orbit coupling. This prompts an investigation into the stability of the magnetic order in ${\mathrm{NiI}}_2$ and similar materials under external stimuli. In this paper, we report the effect of biaxial and uniaxial strain on the magnetic ground state, the critical temperature, and the magnonic properties of the ${\mathrm{Ni}\mathit{X}}_2$ ($X$ = I, Br, Cl) monolayers. For all three materials, we reveal intricate strain-dependent phase diagrams, including ferromagnetic, helimagnetic, and skyrmionic phases. Moreover, we discuss the necessity of considering the biquadratic exchange interaction in the latter analysis. We reveal that the biquadratic exchange significantly alters both the magnetic ground state and the critical temperature of the magnetic order, and we demonstrate that its importance becomes even more explicit when monolayer Ni-dihalides are strained. Finally, we calculate the magnonic dispersion for the predicted magnetic states, showing that the skyrmionic phase functions as a magnonic crystal, and demonstrate the presence of strain-tunable soft magnon modes at finite wavevectors in the helimagnetic phase.

Hexagonal $ABC$ intermetallics are predicted to have tunable ferroelectric, topological, and magnetic properties as a function of the polar buckling of $BC$ atomic planes. We report the impact of isovalent lanthanide substitution on the buckling, structural phase transitions, and electronic and magnetic properties of ${\mathrm{Gd}}_x{\mathrm{La}}_{1-x}\mathrm{PtSb}$ films grown by molecular beam epitaxy (MBE) on $c$ plane sapphire substrates. The ${\mathrm{Gd}}_x{\mathrm{La}}_{1-x}\mathrm{PtSb}$ films form a solid solution from $x=0$ to $x=1$ and retain the polar hexagonal structure ($P{6}_{3}mc$) out to $x\le 0.95$. With increasing $x$, the PtSb buckling increases and the out-of-plane lattice constant $c$ decreases due to the lanthanide contraction. While hexagonal LaPtSb is a highly conductive polar metal, the carrier density decreases with $x$ until an abrupt phase transition to a zero band overlap semimetal is found for cubic GdPtSb at $x=1$. The magnetic susceptibility peaks at small but finite $x$, which we attribute to Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling between localized $4f$ moments, whose concentration increases with $x$, and free carriers that decrease with $x$. Samples with $x\ge 0.3$ show antiferromagnetic Curie-Weiss behavior and a Neel temperature that increases with $x$. The ${\mathrm{Gd}}_x{\mathrm{La}}_{1-x}\mathrm{PtSb}$ system provides opportunities to dramatically alter the polar buckling and concentration of local $4f$ moments.

Antiperovskite nitrides are potential candidates for applications harvesting solar light. With a comprehensive state-of-the-art approach combining hybrid density-functional theory, many-body perturbation theory, the Wannier-Mott model, density-functional perturbation theory, and the Feynman polaron model, we explore excitonic and polaronic effects in ${\mathit{X}}_3\mathrm{N}A$ ($X$ = Mg, Ca, Sr, Ba; $A$ = Sb, As). For all, we uncover a significant influence of the ionic dielectric screening on the static dielectric constant. Small exciton binding energies, weak electron-phonon coupling, and high charge-carrier mobilities facilitate enhanced charge transport in ${\mathrm{Mg}}_3\mathrm{NSb}$, ${\mathrm{Ca}}_3\mathrm{NSb}$, ${\mathrm{Sr}}_3\mathrm{NSb}$, and ${\mathrm{Ba}}_3\mathrm{NSb}$. Our results highlight the potential of these nitrides as optimal candidates for efficient photovoltaic absorbers.

Since the discovery of intrinsic ferromagnetism in ${\mathrm{CrI}}_3$ and ${\mathrm{Cr}}_2{\mathrm{Ge}}_2{\mathrm{Te}}_6$, research has been initiated to explore diverse new van der Waals (vdW) magnetic materials. In this study, we successfully synthesized high-quality single crystals of the vdW material ${\mathrm{TaNi}}_2{\mathrm{Te}}_2$ using the chemical vapor transport method. Subsequently, we mechanically exfoliated the crystals into thin layers and investigated their physical properties. Our results reveal the presence of a rare canted antiferromagnetic behavior in ${\mathrm{TaNi}}_2{\mathrm{Te}}_2$, which is accompanied by remarkable metallic characteristics and elevated carrier mobility of $1.05{\mathrm{cm}}^2$/Vs. This study offers a approach to achieving canted antiferromagnetism in two-dimensional vdW systems, and provides intriguing possibilities in spintronics and electronic devices.

We leverage quantum graph theory to quickly and accurately characterize acoustic metamaterials comprising networks of interconnected pipes. Anisotropic bond lengths are incorporated in the model that correspond to space-coiled acoustic structures to exhibit dispersion spectra reminiscent of hyperbolic metamaterials. We construct two metasurfaces with embedded graph structure and, motivated by the graph theory, infer and fine-tune their dispersive properties to engineer nonresonant negative refraction of acoustic surface waves at their interface. Agreement between the graph model, full-wave simulations, and experiments bolsters quantum graph theory as a new paradigm for metamaterial design.

Recent high-throughput computational searches have predicted many novel ternary nitride compounds providing new opportunities for materials discovery in underexplored phase spaces. Nevertheless, there are hardly any predictions and/or syntheses that incorporate only transition metals into new ternary nitrides. Here, we report on the synthesis, structure, and properties of ${\mathrm{MnCoN}}_2$, a new ternary nitride material comprising only transition metals and N. We find that crystalline ${\mathrm{MnCoN}}_2$ can be stabilized over its competing binaries, and over a tendency of this system to become amorphous, by controlling growth temperature within a narrow window slightly above ambient condition. We find that single-phase ${\mathrm{MnCoN}}_2$ thin films form in a cation-disordered rocksalt crystal structure. X-ray photoelectron spectroscopy analysis suggests that ${\mathrm{MnCoN}}_2$ is sensitive to oxygen through various oxides and hydroxides binding to cobalt on the surface. X-ray absorption spectroscopy is used to verify that ${\mathrm{Mn}}^{3+}$ and ${\mathrm{Co}}^{3+}$ cations exist in an octahedrally coordinated environment, which is distinct from a combination of CoN and MnN binaries and in agreement with the rocksalt-based crystal structure prediction. Magnetic measurements suggest that ${\mathrm{MnCoN}}_2$ has a canted antiferromagnetic ground state below 10 K. We extract a Weiss temperature of $\theta =-49.7\mathrm{K}$, highlighting the antiferromagnetic correlations in ${\mathrm{MnCoN}}_2$.

Surface modification of nanochannels via binding polymers is important in cutting-edge research disciplines such as the design of functional ion channels or ${\mathrm{CO}}_2$ capture and conversion. Capturing surface modifications of nanochannels remains a great challenge due to the barrier-limited binding kinetics of polymers on the inner surfaces of nanochannels. By using our newly developed integral of first passage times (IFS), we show that the barrier-limited surface modifications of nanochannels highly depend on the bending magnitudes of inner surfaces. The highly curved surfaces can absorb less polymers than those on the weakly curved surface. In particular, we show that the final polymer densities on the inner surfaces of nanochannels and nanospheres are closer to each other at the same radius but with different mean curvatures. The findings clarify that the protracted surface modifications of the nanochannels are primarily dictated by the channel radius, providing useful guidelines for designing functional nanochannels in different applications.

Van der Waals semiconductors have provided a new platform to extend the physics and applications of cavity exciton polaritons, thanks to their flexibility of integration, large oscillator strength, and novel moiré physics. However, the inhomogeneous broadening of excitons, originating from strain, defect, or interface fluctuation, has been an obstacle to further exploring coherent quantum phenomena and devices in this community. In this work, we show that the contribution of exciton inhomogeneous broadening to polariton linewidth can be fully suppressed by increasing Rabi splitting. The results can be well reproduced theoretically- by modeling the excitonphoton coupling using a non-Hermitian Hamiltonian. Our findings not only shed light on the development of coherent Van der Waals polariton devices but also demonstrate a general conclusion on the correlation between the inhomogeneous broadening of a solid-state oscillator and the linewidth of its corresponding light-matter hybrids.

Current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) devices are promising for next-generation magnetic read heads in hard disk drives due to their low resistance area product compared to tunnel magnetoresistive devices. While $\mathrm{C}{\mathrm{o}}_2\mathrm{FeG}{\mathrm{a}}_{0.5}\mathrm{G}{\mathrm{e}}_{0.5}$ (CFGG) and $\mathrm{C}{\mathrm{o}}_2\mathrm{M}{\mathrm{n}}_{0.5}\mathrm{F}{\mathrm{e}}_{0.5}\mathrm{Si}$ (CMFS) are representative half-metallic Co-based Heusler alloys with experimentally observed high magnetoresistance (MR) in CPP-GMR with an Ag spacer, there is no understanding of the origin of the different band matching with the Ag spacer for the evaluation of ferromagnetic electrodes. In this study, first-principles calculations of the ballistic conductance in (001)-CFGG/Ag/CFGG and CMFS/Ag/CMFS were performed to clarify an origin of the difference in the spin-dependent conductance. We found that the majority-spin conductance of the CFGG/Ag(001) at its maximum was about 45% higher than that of the CMFS/Ag(001) over all interfacial terminations, indicating the advantageous potential of CFGG for achieving a larger MR ratio in CPP-GMR. The Fermi surface analysis revealed that a hybridization between the $d$ states of the CFGG electrode and the $p$ states of the Ag spacer around the Brillouin zone edge plays an important role in the Fermi surface matching at the interface. In addition, the calculated exchange stiffness constant revealed that CFGG/Ag(001) interfaces exhibit higher stability to thermal fluctuations of the spin-moment than CMFS/Ag(001) interfaces, indicating suppression of the decrease of the MR ratios at finite temperatures. All these findings provide important insights for the selection of materials for high-performance spintronic devices.

Superparamagnetic colloidal beads present fascinating assembly dynamics and propulsion in time-varying magnetic fields. However, little is known about the mechanisms governing their magnetization dynamics. We measure the beads' magnetic relaxation time from the effective interaction potential in dimers under rotating magnetic fields. Remarkably, our results indicate the presence of magnetic relaxation mechanisms much slower than that of the constituent magnetic elements, resembling a feature of glassy systems. These findings gain further insight into the magnetization and dynamics of composite colloids in complex magnetic fields.

Transition metal dichalcogenides (TMDs) are the base materials for diverse technological devices such as photovoltaics, lithium-ion batteries, hydrogen-evolution catalysis, transistors, photodetectors, DNA detection, memory devices, and nanotribological systems. Their flexible ${\mathrm{MX}}_2$ stoichiometry enables the fine-tuning of their properties via cation or anion substitution, thus allowing heterostructures with diverse functionalities to be engineered at the nanoscale. In this respect, we perform first-principles simulations to individuate possible novel structures derived from monolayer and bilayer ${\mathrm{MoS}}_2$ and ${\mathrm{WS}}_2$ alloyed with various metal and nonmetal dopants at different concentrations. We evaluate the relative stability and characterize the mechanisms responsible for their formation through electronic descriptors. Specifically, we identify bond covalency and orbital polarization as collective indicators for favorable electronic distributions, while the electronic structure of the isolated atom may be used for the selection of suitable dopants. The proposed methodology constitutes a general protocol, which can easily be extended to van der Waals heterostructures beyond those based on TMDs. Finally, the methodology can be used to help machine learning algorithms screen material databases for high-throughput discovery of new van der Waals–based alloys.