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.

Halide perovskites exhibit giant photostriction, that is, volume or shape changes upon illumination. However, the microscopic origin of this phenomenon remains unclear and there are experimental reports of both light-induced lattice expansion and contraction. In this Letter, we establish a general method, based on first-principles calculations and molecular orbital theory, which provides a microscopic picture of photostriction in insulators based on the orbital characters of their electronic bands near the Fermi level. For lead-halide perovskites, we find that different valence states have different bonding characters, leading to opposing strengthening or weakening of bonds depending on the photoexcitation energy. The overall trend is that light induces lattice contraction at low excitation energies, while giant lattice expansion occurs at high excitation energies, rationalizing experimental reports.

Lithium-rich garnets such as ${\mathrm{Li}}_7{\mathrm{La}}_3{\mathrm{Zr}}_2{\mathrm{O}}_{12}$ (LLZO) are promising solid electrolytes with potential application in all-solid-state batteries that use lithium-metal anodes. The practical use of garnet electrolytes is limited by pervasive lithium-dendrite growth, which leads to short-circuiting and cell failure. One proposed mechanism of lithium-dendrite growth is the direct reduction of lithium ions to lithium metal within the electrolyte, and lithium garnets have been suggested to be particularly susceptible to this dendrite-growth mechanism due to high electronic conductivities relative to other solid electrolytes. The electronic conductivities of LLZO and other lithium-garnet solid electrolytes, however, are not yet well characterized. Here, we present a general scheme for calculating the intrinsic electronic conductivity of a nominally insulating material under variable synthesis conditions from first principles, and apply this to the prototypical lithium-garnet LLZO. Our model predicts that under typical battery operating conditions, electron and hole mobilities are low ($<1{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$), and bulk electron and hole carrier concentrations are negligible, irrespective of initial synthesis conditions or dopant levels. These results suggest that the bulk electronic conductivity of LLZO is not sufficiently high to cause bulk lithium-dendrite growth during cell operation, and that any non-negligible electronic conductivity in lithium garnet samples is likely due to extended defects or surface contributions.

Ytterbium doping in all-inorganic lead-halide perovskites $\left[\mathrm{CsPb}{\left({\mathrm{Cl}}_{1-x}{\mathrm{Br}}_x\right)}_3\right]$ generates interesting properties including quantum cutting and narrow line emission, making these materials attractive spectral down converters for solar photovoltaics. The relationship between this optical efficiency and the defect structure(s) associated with ${\mathrm{Yb}}^{3+}$ dopants within perovskites is not well understood. Various charge-neutral doping motifs have previously been proposed and studied computationally, including clusters involving two substitutional ${\mathrm{Yb}}^{3+}$ ions charge compensated by a single local ${\mathrm{Pb}}^{2+}$ vacancy. Near-band-edge defect states associated with such motifs are believed to play an important mechanistic role in quantum cutting itself. Here, we report the results of x-ray absorption and x-ray total-scattering measurements on ytterbium-doped $\mathrm{CsPb}{\mathrm{Cl}}_3$. XANES shows that the dopant oxidation state is exclusively ${\mathrm{Yb}}^{3+}$, and a combination of $\mathrm{Yb}{L}_3$ and $\mathrm{Pb}{L}_3$ extended x-ray absorption fine structure (EXAFS) shows that this ${\mathrm{Yb}}^{3+}$ substitutes exclusively at ${\mathrm{Pb}}^{2+}$ sites, where it adopts a pseudo-octahedral ${\left[\mathrm{Yb}{\mathrm{Cl}}_6\right]}^{3-}$ coordination environment. Shell-by-shell fits to the data show a short Yb-Cl bond distance of 2.58 Å compared to the Pb-Cl bond distance of 2.83 Å. We confirm this finding by x-ray pair distribution function analysis, which also shows evidence of additional ${\mathrm{Pb}}^{2+}$ vacancy formation induced by ${\mathrm{Yb}}^{3+}$ doping. We evaluate whether this is the primary mechanism of charge compensation using simulated EXAFS and pair distribution function data for several computed defect structures. Together, these results resolve the local dopant structures and charge-compensation mechanisms in lanthanide-doped all-inorganic lead-halide perovskites, and, as such, significantly advance the understanding of structure-function relationships in this important class of materials.

We report the deposition and characterization of a set of high-quality ${\left({\mathrm{SrNiO}}_3\right)}_1/{\left({\mathrm{SrTiO}}_3\right)}_n$ superlattices using oxide molecular beam epitaxy. We demonstrate that one unit cell of ${\mathrm{SrNiO}}_3$ can be stabilized as a perovskite in these structures and that there is no charge transfer across the heterointerface. Detailed spectroscopy data analysis indicates that holes are confined to the ${\mathrm{SrNiO}}_3$ unit cells, resulting in a Ni valence between 3 and 4. Hole hopping conductivity is observed in the $n=1$ superlattice but is strongly suppressed along the $c$-axis direction for $n=3$ and 5, resulting in the insulating behavior in the latter. Our study will inspire the epitaxial synthesis of ${\left({\mathrm{SrNiO}}_3\right)}_1/{\left(R\mathrm{Ni}{\mathrm{O}}_3\right)}_n$ superlattices, as measurements of their properties could open a platform for studying nickelate-based superconductors.

The search for new ferromagnetic compounds is often targeted at known structure families, particularly those containing iron, cobalt, and manganese. We propose a method to expand this search to lesser-known structure types, using a database of experimental Curie and Néel temperatures. This study, in particular, illustrates the case of compounds containing the element cobalt, and we demonstrate how the use of such a database can lead to the discovery of ferromagnetic materials that had previously been overlooked. We report statistics from a literature survey of the magnetic properties of Co-based compounds with more than 33 at. % Co. We classify more than 13 000 compounds by structure type, cobalt content, and magnetic ground state. From these data, compounds $\mathrm{Ta}{\mathrm{Co}}_2\mathrm{Ga}$, ${\mathrm{La}}_6{\mathrm{Co}}_{13}\mathrm{Bi}$, and ${\mathrm{Nd}}_2{\mathrm{Co}}_3$ were identified as potential ferromagnets, and we confirm their ferromagnetic ordering theoretically via first-principles calculations and experimentally via synthesis and characterization measurements. In addition, the analysis is focused on the collection of data trends and discovery of ferromagnetic materials with easy-axis magnetic anisotropy. Both known ferromagnetic materials with unknown magnetic anisotropy, and unstudied compounds were considered. From the subset of known ferromagnets with unknown anisotropy, the compound ${\mathrm{Co}}_2\mathrm{Mg}$ was synthesized, characterized, and determined to have easy-axis magnetic anisotropy at room temperature.

Spintronic phenomena exhibiting a longitudinal resistance change under magnetization reversal are a quite novel feature in nanoscience, which has been intensively studied in hopes of realizing all-electrical magnetization direction detection devices, where no reference ferromagnetic layer is required. However, cryogenic temperatures and/or high magnetic fields have been required to achieve noticeable effects. Here, the high heat-to-charge conversion efficiency of the Heusler alloy Weyl semimetal ${\mathrm{Co}}_2\mathrm{MnGa}$ is exploited in single layer nanoscaled wires at room temperature to produce at least two orders of magnitude enhancement of the resistance change ratio, when compared with conventional ferromagnets. Such resistance change under magnetization reversal is consistently explained through temperature distribution simulations and direct thermoelectric measurements of the large anomalous Nernst effect (ANE) in this topologically nontrivial material. Although many reports consider ANE signals as perturbations or undesired artifacts, we demonstrate that they are dominant in this system and can be seized for nonvolatile memory readout, as shown in a prototype device. These results open up new horizons of using enhanced thermoelectric voltages in novel materials for magnetization direction detection in any system where significant temperature gradients exist.

In the field of van der Waals heterostructures, the twist angle between stacked two-dimensional layers has been identified to be of utmost importance for the properties of the heterostructures. In this context, we previously reported the growth of a single layer of unconventionally oriented epitaxial graphene that forms in a surfactant atmosphere [F. C. Bocquet et al., Phys. Rev. Lett. 125, 106102 (2020)]. The resulting G-$R{0}^{\circ }$ layer is aligned with the SiC lattice, and hence represents an important milestone towards high-quality twisted bilayer graphene, a frequently investigated model system in this field. Here, we focus on the surface structures obtained in the same surfactant atmosphere, but at lower preparation temperatures at which a boron nitride template layer forms on SiC(0001). In a comprehensive study based on complementary experimental and theoretical techniques, we find—in contrast to the literature—that this template layer is a hexagonal ${\mathrm{B}}_x{\mathrm{N}}_y$ layer, but not high-quality hBN. It is aligned with the SiC lattice and gradually replaced by low-quality graphene in the $0^{\circ }$ orientation of the ${\mathrm{B}}_x{\mathrm{N}}_y$ template layer upon annealing.

Two-dimensional magnetic materials have recently attracted great interest due to their unique functions as the electric field control of a magnetic phase and the anomalous spin Hall effect. For such remarkable functions, a spin-orbit coupling (SOC) serves as an essential ingredient. Here we report a giant positive magnetoresistance in a layered magnetic semiconductor ${\mathrm{AgCrSe}}_2$, which is a manifestation of the subtle combination of the SOC and Zeeman-type spin splitting. When the carrier concentration, $n$, approaches the critical value of $2.5\times {10}^{18}\mathrm{c}{\mathrm{m}}^{\text{–}3}$, a sizable positive magnetoresistance of $\sim 400\%$ emerges upon the application of magnetic fields normal to the conducting layers. Based on the magneto-Seebeck effect and the first-principles calculations, the unconventional magnetoresistance is ascribable to the enhancement of effective carrier mass in the SOC-induced $J=3/2$ state, which is tuned to the Fermi level through the Zeeman splitting enhanced by the $p\text{−}d$ coupling. This study demonstrates an aspect of the SOC-derived magnetotransport in two-dimensional magnetic semiconductors, paving the way to spintronic functions.

Dielectric capacitors hold an enormous advantage for energy storage that requires a fast charging/discharging rate; but relatively low energy capacity is a key limitation for conventional dielectric materials. Recently, design strategies by tuning the ferroelectric ${\mathrm{BiFeO}}_3$ (BFO) to an antiferroelectric or relaxor have shown great promise, especially owing to the large polarization at high electric field. Here, using a first-principles-based method, it is predicted that rare-earth substitution of varied elements and composition can systematically tune the stability of the antiferroelectric phase, leading to further enhanced energy densities and high efficiencies, for instance, reaching 239 J ${\mathrm{cm}}^{-3}$ in thulium substituted BFO and generally beyond 80%, respectively. The storage performance is further interpreted based on a simple model, pointing to the importance of transition fields, polarization of the ferroelectric state, and dielectric constant.