ABSTRACT
We combine synchrotron-based infrared absorption and Raman scattering spectroscopies with diamond anvil cell techniques and first-principles calculations to explore the properties of hafnia under compression. We find that pressure drives HfO[Formula: see text]:7%Y from the mixed monoclinic ([Formula: see text]) [Formula: see text] antipolar orthorhombic ([Formula: see text]) phase to pure antipolar orthorhombic ([Formula: see text]) phase at approximately 6.3 GPa. This transformation is irreversible, meaning that upon release, the material is kinetically trapped in the [Formula: see text] metastable state at 300 K. Compression also drives polar orthorhombic ([Formula: see text]) hafnia into the tetragonal ([Formula: see text]) phase, although the latter is not metastable upon release. These results are unified by an analysis of the energy landscape. The fact that pressure allows us to stabilize targeted metastable structures with less Y stabilizer is important to preserving the flat phonon band physics of pure HfO[Formula: see text].
ABSTRACT
Electronic structure calculations indicate that the Sr2FeSbO6 double perovskite has a flat-band set just above the Fermi level that includes contributions from ordinary subbands with weak kinetic electron hopping plus a flat subband that can be attributed to the lattice geometry and orbital interference. To place the Fermi energy in that flat band, electron-doped samples with formulas Sr2-xLaxFeSbO6 (0 ≤ x ≤ 0.3) were synthesized, and their magnetism and ambient temperature crystal structures were determined by high-resolution synchrotron X-ray powder diffraction. All materials appear to display an antiferromagnetic-like maximum in the magnetic susceptibility, but the dominant spin coupling evolves from antiferromagnetic to ferromagnetic on electron doping. Which of the three subbands or combinations is responsible for the behavior has not been determined.
ABSTRACT
We synthesize four novel quasi-one-dimensional organic-inorganic hybrid iron chloride compounds (CH3NH3FeCl3, CH(NH2)2FeCl3, C(NH2)3FeCl3, and C3H5N2FeCl3) and characterize their structural and magnetic properties. These materials crystallize in a hexagonal perovskite-type structure, constituting a triangular array of face-sharing iron chloride octahedra chains running along the c-axis, isolated from one another by the organic cation. Through magnetization and heat capacity measurements, we find that the intrachain coupling is weakly ferromagnetic for each variant. Importantly, this work underscores the utility of solid-state chemistry approaches in synthesizing new organic-inorganic hybrid materials.
ABSTRACT
We report the high-pressure synthesis (6 GPa, 1200 °C) and ambient-pressure characterization of hexagonal HP-BaCoO3. The material (with a 2H crystal structure) has a short intrachain Co-Co distance of about 2.07 Å. Our magnetization investigation revealed robust diamagnetic behavior below approximately 130 K when the material was exposed to weak applied magnetic fields (10 Oe) and a distinct "half-levitation" phenomenon below that temperature, as is often observed for superconductors. Its field-dependent magnetization profile, however, unveils the characteristics of ferromagnetism, marked by a substantial magnetic retentivity of 0.22(1) µB/Co at a temperature of 2 K. Electrical resistivity measurements indicate that HP-BaCoO3 is a ferromagnetic insulator, not a superconductor.
ABSTRACT
Unlike what happens in conventional ferroics, the ferrorotational (FR) domain manipulation and visualization in FR materials are nontrivial as they are invariant under both space-inversion and time-reversal operations. FR domains have recently been observed by using the linear electrogyration (EG) effect and X-ray diffraction (XRD) diffraction mapping. However, ferrorotational selectivity, such as the selective processing of the FR domains and direct visualization of the FR domains, e.g., under an optical microscope, would be the next step to study the FR domains and their possible applications in technology. Unexpectedly, we discovered that the microscopic FR structural distortions in ilmenite crystals can be directly coupled with macroscopic mechanical rotations in such a way that FR domains can be visualized under an optical microscope after innovative rotational polishing, a combined ion milling with a specific rotational polishing, or a twisting-induced fracturing process. Thus, the FR domains could be a unique medium to register the memory of a rotational mechanical process due to a novel selective coupling between its microscopic structural rotations and an external macroscopic rotation. Analogous to the important enantioselectivity in modern chemistry and the pharmaceutical industry, this newly discovered ferrorotational selectivity opens up opportunities for FR manipulation and new FR functionality-based applications.
ABSTRACT
A series of garnets of formula Er3+xGa5-xO12 are described, for which we report the crystal structures for both polycrystalline and single-crystal samples. The x limit in the garnet phase is between 0.5 and 0.6 under our conditions, with the Er fully occupying the dodecahedral (24c) garnet site plus some of the octahedral site (16a) in place of the Ga normally present. Long-range antiferromagnetic order with spin-ice-like frustration is suggested by the transition temperature (TN ≈ 0.8 K) being lower than the Curie-Weiss theta. The magnetic ordering temperature does not depend on the Er excess, but there is increasing residual entropy as the Er excess is increased, highlighting the potential for unusual magnetic behavior in this system. The field-dependent magnetic entropy trend is consistent with the reported behavior for frustrated triangular magnetic systems: an increasing transition temperature with a broader hump as the applied field increases [Xing, J.; Phys. Rev. Mater. 2019, 3(11), 114413;Filippi, J.; Solid State Commun. 1977, 23(9), 613-616; Bloxsom, J. A. Thermal and Magnetic Studies of Spin Ice Compounds. University College London, 2016].
ABSTRACT
BaSnO3 exhibits the highest carrier mobility among perovskite oxides, making it ideal for oxide electronics. Collective charge carrier oscillations known as plasmons are expected to arise in this material, thus providing a tool to control the nanoscale optical field for optoelectronics applications. Here, the existence of relatively long-lived plasmons supported by high-mobility charge carriers in La-doped BaSnO3 (BLSO) is demonstrated. By exploiting the high spatial and energy resolution of electron energy-loss spectroscopy with a focused beam in a scanning transmission electron microscope, the dispersion, confinement ratio, and damping of infrared localized surface plasmons (LSPs) in BLSO nanoparticles are systematically investigated. It is found that LSPs in BLSO exhibit a high degree of spatial confinement compared to those sustained by noble metals and have relatively low losses and high quality factors with respect to other doped oxides. Further analysis clarifies the relation between plasmon damping and carrier mobility in BLSO. The results support the use of nanostructured degenerate semiconductors for plasmonic applications in the infrared region and establish a solid alternative to more traditional plasmonic materials.
ABSTRACT
HfO2, a simple binary oxide, exhibits ultra-scalable ferroelectricity integrable into silicon technology. This material has a polymorphic nature, with the polar orthorhombic (Pbc21) form in ultrathin films regarded as the plausible cause of ferroelectricity but thought not to be attainable in bulk crystals. Here, using a state-of-the-art laser-diode-heated floating zone technique, we report the Pbc21 phase and ferroelectricity in bulk single-crystalline HfO2:Y as well as the presence of the antipolar Pbca phase at different Y concentrations. Neutron diffraction and atomic imaging demonstrate (anti)polar crystallographic signatures and abundant 90°/180° ferroelectric domains in addition to switchable polarization with negligible wake-up effects. Density-functional-theory calculations indicate that the yttrium doping and rapid cooling are the key factors for stabilization of the desired phase in bulk. Our observations provide insights into the polymorphic nature and phase control of HfO2, remove the upper size limit for ferroelectricity and suggest directions towards next-generation ferroelectric devices.
ABSTRACT
Terahertz vortex beams with different superposition of the orbital angular momentum l=±1, ±2, ±3, and ±4 and spin angular momentum σ=±1 were used to study antiferromagnetic (AFM) resonances in TbFe_{3}(BO_{3})_{4} and Ni_{3}TeO_{6} single crystals. In both materials we observed a strong vortex beam dichroism for the AFM resonances that are split in external magnetic field. The magnitude of the vortex dichroism is comparable to that for conventional circular dichroism due to σ. The selection rules at the AFM resonances are governed by the total angular momentum of the vortex beam: j=σ+l. In particular, for l=±2, ±3, and ±4 the sign of l is shown to dominate over that for conventional circular polarization σ.
ABSTRACT
Hafnia (HfO_{2})-based thin films have promising applications in nanoscale electronic devices due to their robust ferroelectricity and integration with silicon. Identifying and stabilizing the ferroelectric phases of HfO_{2} have attracted intensive research interest in recent years. In this work, first-principles calculations on (111)-oriented HfO_{2} are used to discover that imposing an in-plane shear strain on the metastable tetragonal phase drives it to a polar phase. This in-plane-shear-induced polar phase is shown to be an epitaxial-strain-induced distortion of a previously proposed metastable ferroelectric Pnm2_{1} phase of HfO_{2}. This ferroelectric Pnm2_{1} phase can account for the recently observed ferroelectricity in (111)-oriented HfO_{2}-based thin films on a SrTiO_{3} (STO) (001) substrate [Nat. Mater. 17, 1095 (2018)NMAACR1476-112210.1038/s41563-018-0196-0]. Further investigation of this alternative ferroelectric phase of HfO_{2} could potentially improve the performances of HfO_{2}-based films in logic and memory devices.
ABSTRACT
X-type hexaferrites have been receiving considerable attention due to their promising applications in many magnetic-electronic fields. However, the growth of single-crystal X-type hexaferrite is still a challenge. Herein we reported, for the first time, the preparation of single crystal X-type hexaferrite Sr2Co2Fe28O46 (Sr2Co2X) with high-quality and large size using floating-zone method with laser as the heating source. The crystals show rhombohedral symmetry with space group of R-3m (No. 166, a = 5.8935(1) Å and c = 83.7438(17) Å). Co2+ and Fe3+ oxidation states were confirmed by the X-ray absorption near-edge spectroscopy. The prepared Sr2Co2X exhibits a spin reorientation transition from easy-cone to easy-axis at T2 of 343 K and a ferrimagnetism-paramagnetism transition at Curie temperature (TC) of â¼743 K. The spin reorientation transition was accompanied by magnetocaloric effect (MCE). Both conventional and inverse MCEs were observed near T2 with a magnetic field applied along the c-axis. The maximum value of the magnetic entropy change along the c-axis was evaluated to be 1.1 J/kg·K for a magnetic field change of 5 T.
ABSTRACT
Directional non-reciprocity refers to the phenomenon where the motion in one direction differs from the motion in the opposite direction. This behavior is observed across various systems, such as one-way traffic and materials displaying electronic/optical directional dichroism, characterized by the symmetry of velocity vectors. Magnetic toroidal moments (MTMs), which typically arise from rotational spin arrangements, also possess the symmetry of velocity vectors, making them inherently directionally non-reciprocal. In this paper, we examine magnetic point groups (MPGs) that exhibit MTMs, subsequently leading to off-diagonal linear magnetoelectricity. Our focus is on the induction of MTMs through electric fields, magnetic fields, or shear stress, while enumerating the relevant MPGs. The findings of our study will serve as valuable guidance for future investigations on directional non-reciprocity, MTMs, and off-diagonal linear magnetoelectric effects.
ABSTRACT
A layered rhombohedral polymorph of indium(III) triiodide is synthesized at high pressure and temperature. The unit cell symmetry and approximate dimensions are determined by single crystal X-ray diffraction. Its R3Ì crystal structure, with a = 7.214 Å, and c = 20.47 Å, is refined by the Rietveld method on powder X-ray diffraction data. The crystal structure is based on InI6 octahedra sharing edges to form honeycomb lattice layers, though with considerable stacking defects. Different from ambient pressure InI3, which has a monoclinic molecular structure and a light-yellow color, high pressure InI3 is layered and has an orange color. The band gaps of both the monoclinic and rhombohedral variants of InI3 are estimated from diffuse reflectance measurements.
ABSTRACT
Superconducting states onsetting at moderately high temperatures have been observed in epitaxially stabilized RENiO2-based thin films. However, recently, it has also been reported that superconductivity at high temperatures is observed in bulk La3Ni2O7-δ at high pressure, opening further possibilities for study. Here we report the reduction profile of La3Ni2O7 in a stream of 5% H2/Ar gas and the isolation of the metastable intermediate phase La3Ni2O6.45, which is based on Ni2+. Although this reduced phase does not superconduct at ambient or high pressures, it offers insights into the Ni-327 system and encourages future study of nickelates as a function of oxygen content.
ABSTRACT
The spin Hall effect (SHE) allows efficient generation of spin polarization or spin current through charge current and plays a crucial role in the development of spintronics. While SHE typically occurs in non-magnetic materials and is time-reversal even, exploring time-reversal-odd (T-odd) SHE, which couples SHE to magnetization in ferromagnetic materials, offers a new charge-spin conversion mechanism with new functionalities. Here, we report the observation of giant T-odd SHE in Fe3GeTe2/MoTe2 van der Waals heterostructure, representing a previously unidentified interfacial magnetic spin Hall effect (interfacial-MSHE). Through rigorous symmetry analysis and theoretical calculations, we attribute the interfacial-MSHE to a symmetry-breaking induced spin current dipole at the vdW interface. Furthermore, we show that this linear effect can be used for implementing multiply-accumulate operations and binary convolutional neural networks with cascaded multi-terminal devices. Our findings uncover an interfacial T-odd charge-spin conversion mechanism with promising potential for energy-efficient in-memory computing.
ABSTRACT
Nonreciprocal quantum transport effect is mainly governed by the symmetry breaking of the material systems and is gaining extensive attention in condensed matter physics. Realizing electrical switching of the polarity of the nonreciprocal transport without external magnetic field is essential to the development of nonreciprocal quantum devices. However, electrical switching of superconducting nonreciprocity remains yet to be achieved. Here, we report the observation of field-free electrical switching of nonreciprocal Ising superconductivity in Fe3GeTe2/NbSe2 van der Waals (vdW) heterostructure. By taking advantage of this electrically switchable superconducting nonreciprocity, we demonstrate a proof-of-concept nonreciprocal quantum neuronal transistor, which allows for implementing the XOR logic gate and faithfully emulating biological functionality of a cortical neuron in the brain. Our work provides a promising pathway to realize field-free and electrically switchable nonreciprocity of quantum transport and demonstrate its potential in exploring neuromorphic quantum devices with both functionality and performance beyond the traditional devices.
ABSTRACT
X-ray circular dichroism, arising from the contrast in X-ray absorption between opposite photon helicities, serves as a spectroscopic tool to measure the magnetization of ferromagnetic materials and identify the handedness of chiral crystals. Antiferromagnets with crystallographic chirality typically lack X-ray magnetic circular dichroism because of time-reversal symmetry, yet exhibit weak X-ray natural circular dichroism. Here, the observation of giant natural circular dichroism in the Ni L3-edge X-ray absorption of Ni3TeO6 is reported, a polar and chiral antiferromagnet with effective time-reversal symmetry. To unravel this intriguing phenomenon, a phenomenological model is proposed that classifies the movement of photons in a chiral crystal within the same symmetry class as that of a magnetic field. The coupling of X-ray polarization with the induced magnetization yields giant X-ray natural circular dichroism, revealing typical ferromagnetic behaviors allowed by the symmetry in an antiferromagnet, i.e., the altermagnetism of Ni3TeO6. The findings provide evidence for the interplay between magnetism and crystal chirality in natural optical activity. Additionally, the first example of a new class of magnetic materials exhibiting circular dichroism is established with time-reversal symmetry.
ABSTRACT
Magnetic toroidicity is an uncommon type of magnetic structure in solid-state materials. Here, we experimentally demonstrate that collinear spins in a material with R-3 lattice symmetry can host a significant magnetic toroidicity, even parallel to the ordered spins. Taking advantage of a single crystal sample of CoTe6O13 with an R-3 space group and a Co2+ triangular sublattice, temperature-dependent magnetic, thermodynamic, and neutron diffraction results reveal A-type antiferromagnetic order below 19.5 K, with magnetic point group -3' and k = (0,0,0). Our symmetry analysis suggests that the missing mirror symmetry in the lattice could lead to the local spin canting for a toroidal moment along the c axis. Experimentally, we observe a large off-diagonal magnetoelectric coefficient of 41.2 ps/m that evidences the magnetic toroidicity. In addition, the paramagnetic state exhibits a large effective moment per Co2+, indicating that the magnetic moment in CoTe6O13 has a significant orbital contribution. CoTe6O13 embodies an excellent opportunity for the study of next-generation functional magnetoelectric materials.
ABSTRACT
We employ synchrotron-based near-field infrared spectroscopy to image the phononic properties of ferroelectric domain walls in hexagonal (h) Lu0.6Sc0.4FeO3, and we compare our findings with a detailed symmetry analysis, lattice dynamics calculations, and prior models of domain-wall structure. Rather than metallic and atomically thin as observed in the rare-earth manganites, ferroelectric walls in h-Lu0.6Sc0.4FeO3 are broad and semiconducting, a finding that we attribute to the presence of an A-site substitution-induced intermediate phase that reduces strain and renders the interior of the domain wall nonpolar. Mixed Lu/Sc occupation on the A site also provides compositional heterogeneity over micron-sized length scales, and we leverage the fact that Lu and Sc cluster in different ratios to demonstrate that the spectral characteristics at the wall are robust even in different compositional regimes. This work opens the door to broadband imaging of physical and chemical heterogeneity in ferroics and represents an important step toward revealing the rich properties of these flexible defect states.
ABSTRACT
Layered Li2 SrNb2 O7 , an inorganic oxide in its bulk single-crystalline form, is experimentally demonstrated to exhibit multiple structural facets such as ferroelasticity, ferroelectricity, and antiferroelectricity. The transition from a room temperature (RT) centrosymmetric structure to a low-temperature out-of-plane ferroelectric and in-plane antiferroelectric structure and the low-temperature (LT) ferroelectric domain configuration are unveiled in TEM, piezoresponse force microscopy, and polarization loop studies. Li2 SrNb2 O7 also exhibits highly tunable ferroelasticity and excellent Li+ in-plane conduction, which leads to a giant in-plane memristor behavior and an in-plane electronic conductivity increase by three orders of magnitude by electric poling at room RT). The accumulation of Li+ vacancies at the crystal-electrode interface is visualized using in situ optical microscopy. The Li-ionic biased state shows a clear in-plane rectification effect combined with a significant relaxation upon time at RT. Relaxation can be fully suppressed at LTs such as 200 K, and utilizing an electric field cooling, a stable rectification can be achieved at 200 K. The results shed light on the selective control of multifunctionalities such as ferroelasticity, ferroelectricity, and ionic-migration-mediated effects (a memristor effect and rectification) in a single-phase bulk material utilizing, for example, different directions, temperatures, frequencies, and magnitudes of electric field.