High-performance permanent magnets have a wide range of applications in various fields of the information age. One distinct feature of permanent magnet materials is significant magnetic anisotropy, which is mainly affected by spin-orbit coupling (SOC). Focusing on materials containing $3d$ transition elements with specific Wyckoff positions, where certain partially occupied orbital multiplets can significantly enhance the effect of SOC, we perform a highly efficient search for permanent magnet materials in the inorganic crystal structure database. According to common standards of permanent magnets, we identify 19 potential permanent magnet materials. Among these candidates, 14 materials have already been discussed in previous studies, and we finally propose five new permanent magnet candidates. As examples, the detailed magnetic properties of two candidates among these five new proposed materials are presented. We believe that these potential permanent magnet materials deserve further experimental study.

An outstanding challenge in synthesis and theory is to develop molecular materials at ambient conditions that exhibit highly efficient energy transfer. Here we demonstrate the potential of a recently synthesized, highly conductive amorphous material—a nickel tetrathiafulvalene-tetrathiolate (NiTTFtt) polymer—to become an exciton condensate—a Bose-Einstein condensate of particle-hole pairs, known as excitons, that supports dissipationless flow of excitation energy. While exciton condensates have recently been realized in ordered materials, we show by advanced electronic structure calculations that this highly correlated phenomenon can potentially be realized in molecularly tailored, amorphous materials. In contrast to the Bechgaard salts that support superconductivity at compressed geometries requiring high pressures, we show that the recently synthesized, amorphous NiTTFtt polymer exhibits the computational signature of exciton condensation at experimentally realizable geometries, occurring at ambient pressures. Results suggest that superfluidity in this system and related systems—including van der Waals structures, molecular metals with extended-TTF dithiolate ligands, and Bechgaard salts—may occur via a nontraditional excitonic mechanism tuneable according to system composition, geometry, size, and charge. This study prompts further experimental investigation of the rational design of molecularly scaled exciton condensates with potential applications to efficient transport in technologically relevant materials.

Terrace-sized, single-orientation graphene can be grown on top of a carbon buffer layer on silicon carbide by thermal decomposition. Despite its homogeneous appearance, a surprisingly large variation in electron transport properties is observed. Here, we employ aberration-corrected low-energy electron microscopy to study a possible cause of this variability. We characterize the morphology of stacking domains between the graphene and the buffer layer of three different high-quality samples to capture the range of possible behavior. Similar to the case of twisted bilayer graphene, the lattice mismatch between the graphene layer and the buffer layer at the growth temperature causes a moiré pattern with domain boundaries between AB and BA stackings. We analyze this moiré pattern to characterize the relative strain and to count the number of edge dislocations. Furthermore, we show that epitaxial graphene on silicon carbide in general is close to a phase transition, causing intrinsic disorder in the form of the coexistence of anisotropic stripe domains and isotropic trigonal domains. Using adaptive geometric phase analysis, we determine the precise relative strain variation caused by these domains in different samples. We observe that the step edges of the SiC substrate influence the orientation of the domains and we discuss which aspects of the growth process influence these effects by comparing samples from different sources.

We present the growth and basic magnetic and transport properties of ${\mathrm{Cr}}_{1+x}{\mathrm{Pt}}_{5-x}\mathrm{P}$. We show that single crystals can readily be grown from a high-temperature solution created by adding dilute quantities of Cr to Pt-P based melts. Like other 1–5–1 compounds, ${\mathrm{Cr}}_{1+x}{\mathrm{Pt}}_{5-x}\mathrm{P}$ adopts a tetragonal P4/mmm structure composed face-sharing ${\mathrm{CrPt}}_3$ like slabs that are broken up along the $c$ axis by sheets of P atoms. EDS and x-ray diffraction measurements both suggest ${\mathrm{Cr}}_{1+x}{\mathrm{Pt}}_{5-x}\mathrm{P}$ has mixed occupancy between Cr and Pt atoms, similar to what is found in the closely related compound ${\mathrm{CrPt}}_3$, giving real compositions of ${\mathrm{Cr}}_{1.5}{\mathrm{Pt}}_{4.5}\mathrm{P}$ $(x=0.5)$. We report that ${\mathrm{Cr}}_{1.5}{\mathrm{Pt}}_{4.5}\mathrm{P}$ orders ferromagnetically at ${\mathit{T}}_C=464.5$ K with a saturated moment of $\approx 2.1{\mu }_{\mathit{B}}/\mathrm{Cr}$ at 1.8 K. Likely owing to the strong spin-orbit coupling associated with the large quantity of high Z, Pt atoms, ${\mathrm{Cr}}_{1.5}{\mathrm{Pt}}_{4.5}\mathrm{P}$ has exceptionally strong planar anisotropy with estimated anisotropy fields of 345 kOe and 220 kOe at 1.8 K and 300 K, respectively. The resistance of ${\mathrm{Cr}}_{1.5}{\mathrm{Pt}}_{4.5}\mathrm{P}$ has a metallic temperature dependence with relatively weak magnetoresistance. Electronic band structure calculations show that ${\mathrm{CrPt}}_5\mathrm{P}$ has a large peak in the density of states near the Fermi level, which is split into spin majority and minority bands in the ferromagnetic state. Furthermore, the calculations suggest substantial hybridization between $\mathrm{Cr}\text{−}3d$ and $\mathrm{Pt}\text{−}5d$ states near the Fermi level, in agreement with the experimentally measured anisotropy.

Solute segregation is a crucial means of stabilizing nanostructured alloys, and at very small grain sizes, this requires consideration of triple junctions (TJs), which attain a meaningful volume fraction and thus become relevant for bulk material behavior. Here, the solute segregation spectra for grain boundary (GB) and TJ sites are calculated for a large number of dilute Al-based binary systems with available interatomic potentials. A defect-identifying algorithm is applied to quantify the average GB thickness and classify the intergranular site spectra into GB and junction subspectra. The algorithm is also applied to a hybrid electronic-level database for GB segregation of various solutes in Al, yielding polycrystalline TJ solute segregation spectra from first principles. The results suggest that TJ segregation is alloy or interatomic potential dependent and can exhibit either boundary or junction preference. With these spectra as inputs, the spectral GB segregation model gives quantitative predictions of segregation as a function of grain size, temperature, and total solute concentration, suitable for alloy screening and design.

Tellurium is a gyrotropic, $p$-type Weyl semiconductor with remarkable electronic, optical, and transport properties. It has been argued that some of these properties might stem from Weyl nodes at crossing points in the band structure and their nontrivial topological textures. However, Weyl nodes in time-reversal invariant semiconductors are split up in energy, rather than in momentum, and located deep below (far above) the top (bottom) of the valence (conduction) band, challenging such an interpretation. Here, instead, we use a four-band$\mathbf{k}·\mathbf{p}$ Hamiltonian for $p$-type tellurium to show how the k-dependent spin-orbit interaction mixes up the top two (Weyl node free) and bottom two (Weyl-node-containing) valence bands, generating a 3D hedgehog orbital magnetic texture at the uppermost valence band, already accessible to transport at the lowest doping. Hedgehog textures are important signatures of Weyl fermion physics, in general, and in the context of condensed matter physics arise form the carriers' wave packet rotation being locked to their propagation wave vector. For spatially dispersive media, such an induced hedgehog texture/carrier rotation stabilizes two nonreciprocal and antisymmetric components to the Hall transport within different weak-localization (antilocalization) relaxation regimes: the anomalous and planar Hall effects, usually forbidden by time-reversal symmetry. Our AC magnetotransport measurements on Sn-doped tellurium confirm the theoretical predictions and our paper demonstrates how Weyl signatures generally appear in transport on enantiomorphic materials with natural optical activity.

Nanotube encapsulation is a powerful technique for coaxing solids into unconventional configurations. By synthesizing materials within the interior confines of hollow nanotubes, lower dimensional morphologies, such as one-dimensional chains or nanoribbons, are favored. We have used carbon nanotube encapsulation to realize ultranarrow, atomically precise $\mathrm{Hf}{\mathrm{Te}}_2$ nanoribbons. A local, electron-beam-stimulated transition from the metallic 1T phase to the previously unreported semiconducting 1H phase is observed. We study computationally how charging can drive the phase transition and the stability of the different atomic configurations.

Broadband ferromagnetic resonance is measured in single crystalline Fe films of varying thickness sandwiched between MgO layers. An exhaustive magnetic characterization of the films (exchange constant, cubic, uniaxial and surface anisotropies) is enabled by the study of the uniform and the first perpendicular standing spin wave modes as a function of applied magnetic field and film thickness. Additional measurements of nonreciprocal spin-wave propagation allow us to separate each of the two interface contributions to the total surface anisotropy. The results are consistent with the model of a quasi-bulk film interior and two magnetically different top and bottom interfaces, a difference ascribed to different oxidation states.

A puckered sheet is a freestanding crystalline membrane with an embedded array of bistable buckled units. Recent work has shown that the bistable units behave like spins in a two-dimensional compressible Ising antiferromagnet with, however, a coupling to flexural phonons. At finite temperature, this purely mechanical system displays Ising-like phase transitions, which drive anomalous thermal expansion. Here, we show that geometry can be used to control phase behavior: curvature produces a radius-dependent “external field” that encourages alignment between neighboring “spins,” disrupting the ordered checkerboard ground state of antialigned neighbors. The effective field strength scales as the inverse of the radius of curvature. We identify this effective field theoretically with both a discrete real space model and a nonlinear continuum elastic model. We then present molecular dynamics simulations of puckered sheets in cylindrical geometries at zero and finite temperature, probing the influence of curvature on the stability of configurations and phase transitions. Our work demonstrates how curvature and temperature can be used to design and operate a responsive and tunable metamaterial at either the macroscale or nanoscale.

Herein, we report the discovery of a novel Gd-based magnetic compound ${\mathrm{GdPt}}_2\mathrm{B}$ with a chiral crystal structure. X-ray diffraction and chemical composition analyses reveal a ${\mathrm{CePt}}_2\mathrm{B}$-type crystal structure (space group $P{6}_{4}22$) for ${\mathrm{GdPt}}_2\mathrm{B}$. Moreover, we successfully grew single crystals of ${\mathrm{GdPt}}_2\mathrm{B}$ using the Czochralski method. Magnetization measurements and the Curie-Weiss analysis demonstrate that the ferromagnetic interaction is dominant in ${\mathrm{GdPt}}_2\mathrm{B}$. A clear transition is observed in the temperature dependence of electrical resistivity, magnetic susceptibility, and specific heat at $T_{\mathrm{O}}$ = 87 K. The magnetic phase diagram of ${\mathrm{GdPt}}_2\mathrm{B}$, which consists of a field-polarized ferromagnetic region and a magnetically ordered region, resembles those of known chiral helimagnets. Furthermore, magnetic susceptibility measurements reveal a possible spin reorientation within the magnetically ordered phase in magnetic fields perpendicular to the screw axis. The results demonstrate that ${\mathrm{GdPt}}_2\mathrm{B}$ is a suitable platform for investigating the competing effects of ferromagnetic and antisymmetric exchange interactions in rare-earth-based chiral compounds.

We show how transient electron scavengers can be utilized to control the carrier concentration at polar/nonpolar perovskite interfaces. By combining quantitative synchrotron x-ray-based interface structure determination with ab initio modeling, we demonstrate that Nd vacancy formation and the resulting formation of Nd adatoms, stabilized by oxygen scavengers at the growth front, can quantitatively account for the decreased carrier concentration at the $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3/n \mathrm{Nd}\mathrm{Ti}{\mathrm{O}}_3/\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3\left(001\right)$ heterojunction for $n=1$ unit cell. This study yields insight into growth mechanisms and the effect of transient species and defects on the electronic properties of oxide heterojunctions.

Resistive random-access memories are promising for nonvolatile memory and brain-inspired computing applications. High variability and low yield of these devices are key drawbacks hindering reliable training of physical neural networks. In this paper, we show that doping an oxide electrolyte, ${\mathrm{Al}}_2{\mathrm{O}}_3$, with electronegative metals makes resistive switching significantly more reproducible, surpassing the reproducibility requirements for obtaining reliable hardware neuromorphic circuits. Based on density functional theory calculations, the underlying mechanism is hypothesized to be the ease of creating oxygen vacancies in the vicinity of electronegative dopants due to the capture of the associated electrons by dopant midgap states and the weakening of Al-O bonds. These oxygen vacancies and vacancy clusters also bind significantly to the dopant, thereby serving as preferential sites and building blocks in the formation of conducting paths. We validate this theory experimentally by implanting different dopants over a range of electronegativities in devices made of multiple alternating layers of ${\mathrm{Al}}_2{\mathrm{O}}_3$ and WN and find superior repeatability and yield with highly electronegative metals, Au, Pt, and Pd. These devices also exhibit a gradual SET transition, enabling multibit switching that is desirable for analog computing.

Two-dimensional multiferroic materials are ideal systems for exploring new coupling mechanisms between different ferroic orders and producing novel quantum phenomena with potential applications. We employ first-principles density functional theory calculations to discover intrinsic ferroelectric and antiferroelectric phases of $\mathrm{Cr}\mathrm{P}{\mathrm{Se}}_3$, which show ferromagnetic order and compete with the centrosymmetric phase with an antiferromagnetic order. Our analysis shows that the electrical dipoles of such type-I multiferroic phases come from the out-of-plane displacements of phosphorus ions due to the stereochemically active lone pairs. The coupling between polar and magnetic orders creates the opportunity for tuning the magnetic ground state by switching from the centrosymmetric to the ferroelectric phase using an out-of-plane electric field. In ferroelectric and antiferroelectric phases, the combination of easy-plane anisotropy and Dzyaloshinskii-Moriya interactions indicates that they can host topological magnetic vortices such as meron pairs.

We demonstrate that nature has produced a close-packed helical twisted filamentous material in the biomineralization of the mollusk. In liquid crystals, twist–bend nematics have been predicted and observed. We present and analyze evidence that the helical biomineral microstructure of mollusk shells may be formed from such a liquid-crystal precursor.

The Stoner criterion allows only three single elements possessing room-temperature (RT) ferromagnetism: cobalt (Co), nickel (Ni), and iron (Fe). Although these three elements have played central roles in magnetism-based materials, their large work function ($4.5\sim 5.2\mathrm{eV}$) is becoming a non-negligible obstacle for realization of spin devices using nonmetallic materials with finite energy gaps, because injection of electron spins into these nonmetallic materials is strongly hampered due to the large Schottky barrier height. Hence, a novel ferromagnetic or ferrimagnetic material simultaneously possessing RT ferromagnetism or ferrimagnetism and high Fermi energy is strongly required. Here, we show that an Fe-based alloy, iron-gadolinium (FeGd), allows circumvention of the obstacle. Surprisingly, only 20% of Gd incorporation in Fe dramatically modulates the Fermi energy from −4.8 to −3.0 eV, which is the largest modulation in all metallic alloys reported thus far. The coexistence of ferrimagnetism and nonzero spin polarization at RT of FeGd supports its abundant potential for future applications in low-carrier-density materials such as monolayer, organic, and nondegenerate inorganic semiconductors.

We have investigated hybridized magnon-phonon excitation (magnon polarons) in spin Seebeck effects (SSEs) in ${\mathrm{Bi}}_x{\mathrm{Y}}_{3-x}{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ (${\mathrm{Bi}}_x{\mathrm{Y}}_{3-x}\mathrm{IG}$; $x=0$, 0.5, and 0.9) films with Pt contact. We observed sharp peak structures in the magnetic field $H$ dependence of the longitudinal SSE (LSSE) voltages, which appear when the phonon dispersions are tangential to the magnon dispersion curve in ${\mathrm{Bi}}_x{\mathrm{Y}}_{3-x}\mathrm{IG}$. By increasing the Bi amount $x$, the peak fields in the LSSE shift toward lower $H$ values due to the reduction of the sound velocities in ${\mathrm{Bi}}_x{\mathrm{Y}}_{3-x}\mathrm{IG}$. We also measured the SSE in a nonlocal configuration and found that magnon-polaron anomalies appear with different signs and intensities. Our result shows composition-tunability of magnon-polaron anomalies and provides a clue to further unravel the physics of magnon-polaron SSEs.

Using depth- and element-resolved characterization, we report insights into antiferromagnetic coupling in ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}/\mathrm{permalloy}$ (YIG/Py) and ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}/\mathrm{Co}$ (YIG/Co) thin-film heterostructures grown on $\mathrm{Si}/{\mathrm{SiO}}_2$ and ${\mathrm{Gd}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ substrates. We build on recent work demonstrating antiferromagnetic coupling in polycrystalline YIG/metallic-ferromagnetic systems by characterizing differences in the structural and magnetic properties which depend on the choice of ferromagnet (Py vs Co), seed layer (with and without Pt), and substrate $(\mathrm{Si}/{\mathrm{SiO}}_2 \mathrm{vs} {\mathrm{Gd}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12})$. These differences in the sample structure manifest as notable changes in interface coupling sign, magnetic reversal mechanisms, magnetic depth profiles, and domain structure. Through a combination of magnetometry, polarized neutron reflectometry, and x-ray photoemission electron microscopy, a comprehensive picture of the magnetic interactions is realized, with lateral- and depth resolution at submicrometer and nanometer scales, respectively. These results confirm that both Co and Py share a preference to align antiparallel to polycrystalline YIG grown on some substrates $(\mathrm{Si}/{\mathrm{SiO}}_2$ and $\mathrm{Si}/{\mathrm{SiO}}_2/\mathrm{Pt})$, while coupling ferromagnetically with highly oriented YIG on (111) ${\mathrm{Gd}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ and (110) ${\mathrm{Gd}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}/\mathrm{Pt}$ substrates. The complex interplay among magnetic interactions at the YIG/ferromagnetic interface has important implications for spintronic and magnonic devices based on this platform.

We report a detailed study of the magnetic, transport, and thermodynamic properties of ${\mathrm{Ce}}_2{\mathrm{Te}}_5$ single crystals, a layered $f$-electron van der Waals magnet. Four consecutive transitions at $\sim 5.2$, 2.1, 0.9, and 0.4 K were observed in the ac-plane electrical resistivity $\rho \left(T\right)$, which were further confirmed in specific heat $C_{\text{p}}\left(T\right)$ measurements. Analysis of the magnetic susceptibility $\chi \left(T\right)$, the magnetic-field variation of $\rho \left(T\right)$, and the increase of the first transition temperature ($T_{\text{c}}\sim 5.2\mathrm{K}$) with applied magnetic field indicates ferromagnetic order, while the decrease of the other transitions with field suggests different states with dominant antiferromagnetic interactions below $T_2\sim 2.1\mathrm{K}$, $T_3\sim 0.9\mathrm{K}$, and $T_4=0.4\mathrm{K}$. Critical behavior analysis around $T_{\text{c}}$ that gives critical exponents $\beta =0.31\left(2\right)$, $\gamma =0.99\left(2\right)$, $\delta =4.46\left(1\right)$, and $T_{\text{c}}=5.32\left(1\right)\mathrm{K}$ indicates that ${\mathrm{Ce}}_2{\mathrm{Te}}_5$ shows a three-dimensional magnetic critical behavior. Moreover, the Hall resistivity ${\rho }_{\text{xy}}$ indicates that ${\mathrm{Ce}}_2{\mathrm{Te}}_5$ is a multiband system with a relatively high electron mobility $\sim 2900{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ near $T_{\text{c}}$, providing further opportunities for future device applications.

Antiferromagnetically (AFM) coupled skyrmions offer potential advantages for spintronic devices, including reduced dipolar fields that may enable smaller skyrmion sizes and a reduction of the skyrmion Hall effect. However, the topological stability of AFM-coupled skyrmions subjected to dramatic spin deformation through low-temperature cycling has not been investigated. Here we report the discovery of a topological spin memory effect for AFM-coupled skyrmion pairs in [Co/Gd/${\mathrm{Pt]}}_{10}$ multilayered films. Photoemission electron microscopy imaging shows that bubble skyrmions in the multilayer that are stable at room temperature evolve into complex in-plane spin textures as the temperature is lowered and reform completely when the sample is warmed back up. Simulations demonstrate that Dzyaloshinskii-Moriya interactions play a key role in this spin memory effect, and furthermore reveal that the topological charge is preserved throughout the dramatic spin texture rearrangement and recovery. These results highlight a key aspect of topological protection—the preservation of the topological properties under continuous deformation—and also provide a promising avenue for information encryption and recovery.

We derive and motivate a Laplacian-level, orbital-free meta-generalized-gradient approximation (LL-MGGA) for the exchange-correlation energy, targeting accurate ground-state properties of $sp$ and $sd$ metallic condensed matter, in which the density functional for the exchange-correlation energy is only weakly nonlocal due to perfect long-range screening. Our model for the orbital-free kinetic energy density restores the fourth-order gradient expansion for exchange to the ${\mathrm{r}}^2\mathrm{SCAN}$ meta-GGA [Furness et al., J. Phys. Chem. Lett. 11, 8208 (2020)], yielding a LL-MGGA we call OFR2. OFR2 matches the accuracy of SCAN for prediction of common lattice constants and improves the equilibrium properties of alkali metals, transition metals, and intermetallics that were degraded relative to the PBE GGA values by both SCAN and ${\mathrm{r}}^2\mathrm{SCAN}$. We compare OFR2 to the ${\mathrm{r}}^2\mathrm{SCAN}$-L LL-MGGA [Mejia-Rodriguez and Trickey, Phys. Rev. B 102, 121109(R) (2020)] and show that OFR2 tends to outperform ${\mathrm{r}}^2\mathrm{SCAN}$-L for the equilibrium properties of solids, but ${\mathrm{r}}^2\mathrm{SCAN}$-L much better describes the atomization energies of molecules than OFR2 does. For best accuracy in molecules and nonmetallic condensed matter, we continue to recommend SCAN and ${\mathrm{r}}^2\mathrm{SCAN}$ . Numerical performance is discussed in detail, and our paper provides an outlook to machine learning.