Prediction of Spin Orientations in Terms of HOMO-LUMO Interactions Using Spin-Orbit Coupling as Perturbation

The nanoscale explanation of metal cations differences in enhancing the Fe(III) coagulation performance

Coagulation is a widely applied and important process for water treatment, and the development of improved coagulation reagents continues to be a practical objective. However, mechanisms guiding the development of composite coagulants remain insufficiently understood. In addressing this deficiency, this study has investigated the enhancement of conventional Fe(III) coagulation by composite coagulants that incorporate an additional metal salt (Me: Ca²⁺, Al³⁺, Ti⁴⁺, Zr⁴⁺), focusing on the mechanistic roles that Me constituents play in Fe-based coagulation. The effectiveness of composite coagulants was assessed through floc size and the removal of organics and phosphates. Results demonstrated that Me constituents enhance coagulation performances to varying extents, with Al³⁺ and Zr⁴⁺ showing the most significant improvements. FT-ICR MS analysis at the molecular scale reveals that additional Me facilitates the removal of humic acid, hydrophobic macromolecules, and highly aromatic organics containing polycarboxyl and secondary carbon structures. EXAFS results indicate that co-hydrolysis of Fe³⁺ with Me disrupts the formation of conventional ferrihydrite at the nanoscale of flocs and promotes the development of Fe-phosphate clusters. Me effectively reduces the corner- and edge-sharing coordination between FeO₆ octahedra within clusters, resulting in a more dispersed arrangement of FeO₆ polymers with available binding sites for the PO4 tetrahedron. The shortened Fe-P bond indicates that Me promotes a more compact link between FeO₆ octahedra and PO₄ tetrahedra. By revealing how cations in composite coagulants change the nanoscale structure of Fe flocs to affect macroscopic coagulation, this study enhances the understanding of metal ion interactions during co-hydrolysis and co-precipitation in natural systems.

Crystal Structure and Low-Dimensional Magnetism in CsNiV2O6Cl

Single crystals of CsNiV2O6Cl were grown hydrothermally. Its crystal structure (space group I2̅/a) is based on vertex-sharing twisted chains of Ni2+O4Cl2 octahedra and edge-sharing chains of V5+O5 tetragonal pyramids. These chains running along the c- and a-axes, respectively, link, forming an open framework with Cs ions in the voids. At elevated temperatures, the temperature dependence of dc magnetic susceptibility evidences a Haldane-type behavior with estimated intrachain exchange interaction J = 267 ± 16.5 K followed by the strong upturn at lower temperatures. Both dc and ac magnetic susceptibilities exhibit a sharp peak at low temperatures; the latter is independent of frequency. The position of the peak in Fisher's specific heat d(χT)/dT coincides with that in specific heat Cp, which defines the Neel temperature TN = 5.6 ± 0.2 K. While the values of the calculated interchain exchange interaction J' and single-ion anisotropy D place this system into the Haldane sector of the Sakai-Takahashi phase diagram, the long-range antiferromagnetic order at low temperatures is induced by the defects/impurities.

Optimizing photocatalysis via electron spin control

Solar-driven photocatalytic technology holds significant potential for addressing energy crisis and mitigating global warming, yet is limited by light absorption, charge separation, and surface reaction kinetics. The past several years has witnessed remarkable progress in optimizing photocatalysis via electron spin control. This approach enhances light absorption through energy band tuning, promotes charge separation by spin polarization, and improves surface reaction kinetics via strengthening surface interaction and increasing product selectivity. Nevertheless, the lack of a comprehensive and critical review on this topic is noteworthy. Herein, we provide a summary of the fundamentals of electron spin control and the techniques employed to scrutinize the electron spin state of active sites in photocatalysts. Subsequently, we highlight advanced strategies for manipulating electron spin, including doping design, defect engineering, magnetic field regulation, metal coordination modulation, chiral-induced spin selectivity, and combined strategies. Additionally, we review electron spin control-optimized photocatalytic processes, including photocatalytic water splitting, CO2 reduction, pollutant degradation, and N2 fixation, providing specific examples and detailed discussion on underlying mechanisms. Finally, we outline perspectives on further enhancing photocatalytic activity through electron spin manipulation. This review seeks to offer valuable insights to guide future research on electron spin control for improving photocatalytic applications.

Lanthanide-Germanate Adelite, LnCo(GeO4)(OH) (Ln = La-Sm), with Edge-Sharing Octahedral Chains of Co2+ Ions: Spin Frustration Expected to Form Cycloids

A new series of P212121 adelite-type LnCo(GeO4)(OH) (Ln = La-Sm) single crystals were grown by a high-temperature, high-pressure hydrothermal method (650 °C and 100 MPa). Single-crystal diffraction refinements yielded chiral one-dimensional (1D) chains of Co2+ along the a axis with an average 2.98 Å separation between Co2+ centers in the [CoO2(OH)2]∞ ribbon chains. A three-dimensional (3D) superstructure is formed by a bridging lanthanide-germanium framework formed by two unique alternating 5.83 and 6.00 Å distances between interchain Co2+ centers along the a axis. Magnetic studies of the S = 3/2 Co2+ chains in LaCo(GeO4)(OH) revealed a highly anisotropic structure with a common Néel temperature of 32 K. Additionally, a spin-flip transition occurs at 2 K when a 7.3 T field is applied along the chain. Zero-field cooled susceptibility at this critical field resulted in a complex intermediate state consisting of three unique antiferromagnetic transitions at 3, 8, and 16 K. The spin exchanges of LaCo(GeO4)(OH) evaluated by density functional theory calculations show the presence of spin frustration in the 1D chains, which can lead to a cycloidal magnetic structure within the plane of [CoO2(OH)2]∞ chains. The observed magnetic properties are explained by considering the competition between the 1D intrachain and 3D-1D interchain antiferromagnetic interactions.

Ferro-Valleytricity with In-Plane Spin Magnetization

Ferro-valleytricity that manifests spin-orbit coupling (SOC)-induced spontaneous valley polarization is generally considered to occur in two-dimensional (2D) materials with out-of-plane spin magnetization. Here, we propose a mechanism to realize SOC-induced valley polarization and ferro-valleytricity in 2D materials with in-plane spin magnetization, wherein the physics correlates to non-collinear magnetism in triangular lattice. Our model analysis provides comprehensive ingredients that allow for ferro-valleytricity with in-plane spin magnetization, revealing that mirror symmetry favors remarkable valley polarization and time-reversal-mirror joint symmetry should be excluded. Through modulating the in-plane spin magnetization offset, the SOC-induced valley polarization could be reversed. Followed by first-principles, such a mechanism is demonstrated in a multiferroic triangular lattice of single-layer W3Cl8. We further show that the reversal of valley polarization could also be driven by applying an electric field that modulates ferroelectricity. Our findings greatly enrich valley physics research and significantly extend the scope for material classes of ferro-valleytricity.

Contrasting Magnetic Structures in the Quaternary Sulfides Ba2FeMS5 (M = Sb, Bi)

Ba2FeSbS5 and Ba2FeBiS5 are two isostructural quaternary sulfides that crystallize in the Pnma space group with four formula units per unit cell. Ba2FeSbS5 has lattice parameters a = 12.08609(3) Å, b = 8.83426(2) Å, and c = 8.89114(2) Å, and Ba2FeBiS5 has a = 12.09610(3) Å, b = 8.89281(2) Å, and c = 8.82437(2) Å at room temperature. They comprise infinite [FeMS5]4- (M = Sb, Bi) chains, where Fe3+ is present in FeS4 tetrahedra and M3+ ions reside in edge-sharing MS6 distorted octahedra, each of which shares an edge with an FeS4 tetrahedron. Powder neutron diffraction measurements confirm the presence of long-range antiferromagnetic order of the Fe3+ moments in both materials, where Fe-S···S-Fe super-superexchange interactions which act along the direction of the [FeMS5]4- (M = Sb, Bi) chains are the driving force for this antiferromagnetic order. The magnetic Bragg reflections reside on a k-vector with k = (1/2 0 1/2), and the relative orientations of the moments are similar in the two cases One significant difference is that the moments are aligned along the crystallographic b-axis in Ba2FeSbS5, whereas in Ba2FeBiS5 they lie along the longer crystallographic a-axis, reflecting the weak directional preference of the Fe3+ moments. Furthermore, an additional incommensurately modulated ordering of the Fe3+ moments is suggested for Ba2FeSbS5 (but not Ba2FeBiS5) by the appearance of small additional magnetic Bragg peaks in the neutron diffraction data, which may be a consequence of greater magnetic frustration in Ba2FeSbS5.

Spin-Electrochemistry of Transition Metal Oxides for Energy Storage: Concepts, Advances and Perspectives

Developing high-capacity and cyclically stable transition metal (TM)-based electrode materials for energy storage devices, such as aqueous ion energy storage systems, is crucial for addressing the growing issue of energy scarcity. The spin state, or spin configuration of the d-electrons, plays a vital role in the electrochemical energy storage performance of these materials. However, there has been a lack of systematic descriptions regarding the role of spin configurations in electrochemical energy storage to date. This review aims to elucidate the advantages of controlling the spin states of metal centers to enhance energy storage performance and highlights recent progress in employing spin state regulation in electrochemical energy storage. Additionally, it covers the various characterization techniques used to determine spin states. Finally, we discuss the future prospects and challenges within this emerging field, with the aim of accelerating the development of spin-based electrochemical energy storage technologies. This review also seeks to provide clear and reliable directions for the design and preparation of novel energy storage materials.

Prediction of the two-dimensional ferromagnetic semiconductor Janus 2H-ZrTeI monolayer with large valley and piezoelectric polarizations

Two-dimensional room-temperature Janus ferrovalley semiconductors with valley polarization and piezoelectric polarization offer new perspectives for designing multifunctional nanodevices. Herein, using first-principles calculations, we predict that the Janus 2H-ZrTeI monolayer is an intrinsic ferromagnetic semiconductor with in-plane magnetic anisotropy and a Curie temperature of 111 K. The Janus ZrTeI monolayer possesses a significant valley polarization of 141 meV due to time-reversal and inversion symmetry breaking. Based on the valley-contrasting Berry curvature, the anomalous valley Hall effect can be observed under an in-plane electric field. Meanwhile, the breaking of the inversion symmetry and mirror symmetry results in large longitudinal and transverse piezoelectric coefficients. By applying biaxial strain, the Janus 2H-ZrTeI monolayer can also be transformed into a Weyl nodal line semimetal. Furthermore, bilayers of ZrTeI with AB and BA stacking configurations allow the coexistence of valley polarization and ferroelectricity, enabling the manipulation of magnetism, ferroelectric polarization, and valley polarization through interlayer sliding. Our work provides a platform for studying valley polarization, piezoelectricity, and multiferroic coupling, which is significant for the application of multifunctional devices.

Observation of Haldane magnetism in organically templated vanadium phosphate (enH2)0.5VPO4OH

We prepared an organically templated magnet, (enH2)0.5VPO4OH (enH2 = diprotonated ethylenediamine), hydrothermally and characterized its crystal structure by powder X-ray diffraction and Fourier-transform infrared spectroscopy, and its physical properties by magnetization, specific heat and nuclear magnetic resonance measurements and density functional theory calculations. (enH2)0.5VPO4OH consists of uniform chains of V3+ (d2, S = 1) ions and exhibits Haldane magnetism with spin gap Δ = 59.3 K from the magnetic susceptibility χ(T) at μ0H = 0.1 T, which is reduced to 48.4 K at μ0H = 9 T according to the 31P shift. The NMR data evidence the formation of a spin-glass state of unpaired S = 1/2 spins at TS-G ≈ 3 K and indicate that the Haldane S = 1 spin chain segments are much longer in the organically templated magnet (enH2)0.5VPO4OH than in the ammonium counterpart NH4VPO4OH. The single-ion anisotropy D and the interchain exchange J' in (enH2)0.5VPO4OH and NH4VPO4OH were estimated in density functional calculations to find them very weak compared to the intrachain exchange J.

Large valley polarization and the valley-dependent Hall effect in a Janus TiTeBr monolayer

Ferrovalley materials hold great promise for implementation of logic and memory devices in valleytronics. However, there have so far been limited ferrovalley materials exhibiting significant valley polarization and high Curie temperature (TC). Using first-principles calculations, we predict that the TiTeBr monolayer is a promising ferrovalley candidate. It exhibits intrinsic ferromagnetism with TC as high as 220 K. It is indicated that an out-of-plane alignment of magnetization demonstrates a valley polarization up to 113 meV in the topmost valence band, as further verified by perturbation theory considering both the spin polarization and spin-orbit coupling. Under an in-plane electric field, the valley-dependent Berry curvature results in the anomalous valley Hall effect (AVHE). Moreover, under a suitable in-plane biaxial strain, the TiTeBr monolayer transforms into a Chern insulator with a nonzero Chern number, yet retains its ferrovalley characters and thus the emergent quantum anomalous valley Hall effect (QAVHE). Our study indicates that the TiTeBr monolayer is a promising ferrovalley material, and it provides a platform for investigating the valley-dependent Hall effect.

Negative-carbon recycling of copper from waste as secondary resources using deep eutectic solvents

Copper plays a crucial role in the low-carbon transformation of global communities with prevalent use of electric vehicles. This study proposed an environmentally friendly approach that utilizes a deep eutectic solvent (DES), choline chloride-ethylene glycol (ChCl-EG), as green solvent for the selective extraction of copper from scrap materials. With hydrogen peroxide as an oxidizing agent, the copper species from the printed circuit boards (PCBs) scraps were efficiently leached by the DES through oxidation-complexation reactions (conditions: 25 min, 20 °C, and 5 wt% H2O2). Molecular dynamics and density functional theory were performed to simulate the intricate cascade of interactions between copper species and hydrogen bond donors/acceptors of DES, providing insights into the mechanistic processes involved. Copper was selectively recovered from the DES leachate containing impurities (e.g., Pb2+, Sn2+, and Al3+) through electrodeposition via a diffusion-controlled reaction under a constant potential mode. A comprehensive life cycle assessment of the process demonstrated that the utilisation of DES in the extraction of copper from waste PCBs could result in significant reduction in carbon dioxide emissions (-93.6 kg CO2 eq of 1000 kg waste PCBs), thus mitigating the carbon footprint of global copper use through the proposed solvometallurgical recycling process of secondary resources.

Tunable valley polarization effect and second-order topological state in monolayer FeClSH

In two-dimensional (2D) materials, breaking the inversion symmetry plays an important role in valleytronics. Ferrovalley (FV) materials can achieve spontaneous valley polarization (VP) without additional modulation due to the magnetic exchange interaction and strong spin-orbit coupling. Using first-principles calculations, we predict a new 2D material, Janus FeClSH, which exhibits a large spontaneous VP. This monolayer is a perfect FV material, where the valence band maximum and conduction band minimum are located at the K/K' point. A large VP of 102.95 meV is spontaneously generated for the case of out-of-plane magnetization. Additionally, we propose that the irradiating circularly polarized light can be used to realize VP for the case of in-plane magnetization. Remarkably, a triangular nanoflake of FeClSH with armchair edges can show nontrivial corner states, exhibiting a second-order topological insulator (SOTI) state. The VP effect and SOTI state are tunable with the Hubbard U parameter, making the FeClSH monolayer promising for the study of the coupling between VP and SOTI.

Hidden Valley Polarization, Piezoelectricity, and Dzyaloshinskii-Moriya Interactions of Janus Vanadium Dichalcogenides

Due to the lack of inversion symmetry and the discovery of room-temperature ferromagnetism, two-dimensional semiconducting vanadium-based van der Waals transition-metal dichalcogenides (V-TMDs) are drawing attention for their possible application in spintronics and valleytronics. Here, we show the functional properties enriched by the broken inversion, out-of-plane mirror, and time-reversal symmetries of Janus H-VXY TMDs (X, Y = S, Se, Te). By first-principles calculations, we reveal the intrinsic xy easy-plane magnetism of the Janus vanadium-based TMD monolayers and systematically study their hidden valley polarization and giant magneto band structure. Their strong nearest-neighbor exchange strengths lead to near-room-temperature magnetic phase transitions. The Janus H-VXY system also exhibits piezoelectricity with nonzero e31 and e21. Interestingly, it is found that the right-handed Dzyaloshinskii-Moriya interaction has nonzero in-plane components in our Janus system, with fluctuating magnitudes determined by competence between relaxed bond-angle and atomic index of ligands.

Piezoelectricity and valley polarization in a semilithiated 2H-TiTe2 monolayer with near room-temperature ferromagnetism

Two-dimensional ferromagnetic semiconductors with coupled valley physics and piezoelectric responses offer unprecedented opportunities to miniaturize low-power multifunctional integrated devices. Prompted by epitaxial fabrication of nonmagnetic 2H-TiTe2 monolayer on the Au(111) substrate, we predict through both density functional theory and Monte Carlo simulations that the semilithiated 2H-TiTe2 monolayer (Li@2H-TiTe2) is a stable near room-temperature semiconducting ferromagnet. Under an out-of-plane magnetization, Li@2H-TiTe2 exhibits a clean valley polarization up to 160 meV in its conduction band and a valley-contrasting Berry curvature due to the broken inversion and time-reversal symmetries, in favor of achievable anomalous valley Hall effect. Alternatively, the simultaneous charge, spin, valley Hall currents can be realized as well in the ferromagnetic system with circularly polarized light. Furthermore, the missing mirror symmetry generates a scarce vertical piezoelectricity as large as 0.89 pm V-1. These findings indicate that asymmetric surface functionalization by Li deposition on the 2H-TiTe2 monolayer opens up a vital avenue to predesign superior and tailored multifunctional materials.

Effect of MnxOy Nanoparticles Stabilized with Methionine on Germination of Barley Seeds (Hordeum vulgare L.)

The aim of this research was to study the effect of Mn_xO_y nanoparticles stabilized with L-methionine on the morphofunctional characteristics of the barley (Hordeum vulgare L.) crop. Mn_xO_y nanoparticles stabilized with L-methionine were synthesized using potassium permanganate and L-methionine. We established that Mn_xO_y nanoparticles have a diameter of 15 to 30 nm. According to quantum chemical modeling and IR spectroscopy, it is shown that the interaction of Mn_xO_y nanoparticles with L-methionine occurs through the amino group. It is found that Mn_xO_y nanoparticles stabilized with L-methionine have positive effects on the roots and seedling length, as well as the seed germination energy. The effect of Mn_xO_y nanoparticles on Hordeum vulgare L. seeds is nonlinear. At a concentration of 0.05 mg/mL, there was a statistically significant increase in the length of seedlings by 68% compared to the control group. We found that the root lengths of samples treated with Mn_xO_y nanoparticle sols with a concentration of 0.05 mg/mL were 62.8%, 32.7%, and 158.9% higher compared to samples treated with L-methionine, KMnO₄, and the control sample, respectively. We have shown that at a concentration of 0.05 mg/mL, the germination energy of seeds increases by 50.0% compared to the control sample, by 10.0% compared to the samples treated with L-methionine, and by 13.8% compared to the samples treated with KMnO₄.

Enhanced Intrinsic Anomalous Valley Hall Effect Induced by Spin-Orbit Coupling in MXene Monolayer M3N2O2 (M = Y, La)

The limitation of suitable anomalous valley Hall effect (AVHE) materials has seriously hindered the booming development and the widespread application of valleytronics. Here, through the first-principles calculations, we propose a MXene monolayer Y₃N₂O₂ with spontaneous valley polarization (VP) of 21.3 meV, which induces intrinsic AVHE. The VP can be modulated linearly, which provides a route of effective control of the valley signals. Importantly, VP can be enhanced by adjusting up the spin-orbit coupling (SOC) based on a SOC Hamiltonian model and the first-principles calculations. From this physics underlying, we substitute the Y atom with the La atom and further propose the monolayer La₃N₂O₂, in which the heavy atom La will provide stronger SOC than Y atom. The spontaneous VP in La₃N₂O₂ is enhanced to 100.4 meV, so AVHE can be easily achieved. Our work not only provides compelling candidates for AVHE materials but also offers a novel mindset for finding suitable valleytronic devices.

Spontaneous Valley Polarization in a Ferromagnetic Fe(OH)2 Monolayer

At present, creating sizable spontaneous valley polarization is at the center of the study of valleytronics, which, however, is still a huge challenge. In this work, we determined that the ferromagnetic Fe(OH)₂ monolayer of the hexagonal lattice is a highly appealing candidate for valleytronics by using first-principles calculations in conjunction with tight-binding model analysis. In light of the simultaneous inversion symmetry breaking and time-reversal symmetry breaking, we illustrated that the strong spin-orbit coupling and robust ferromagnetic exchange interaction cause a spontaneous valley polarization as large as 67 meV for Fe(OH)₂, indicative of room-temperature application. In addition, the physics of valley-selective circular dichroism, spin/valley Hall effects, and topological phase transition were also discussed.

2D electrene LaH2monolayer: an ideal ferrovalley direct semiconductor with room-temperature ferromagnetic stability

In developing nonvolatile valleytronic devices, ferromagnetic (FM) ferrovalley semiconductors are critically needed due to the existence of spontaneous valley polarization. At present, however, the known real materials have various drawbacks towards practical applications, including the in-plane FM ground state, low Curie temperature (TC), small valley polarization, narrow energy window with clean polarized valley, and indirect bandgap. From first-principles calculations, here we predict anideal ferrovalley semiconductor, honeycomb LaH₂monolayer (ML), whose intrinsic properties can overcome all these shortcomings. We demonstrate that LaH₂ML, having satisfied structural stability, is a FM half-semiconducting electrene (La3+2H-⋅e-) with its magnetic moments localized at the lattice interstitial sites rather than La atoms. At the same time, LaH₂ML holds the following desired attributes: a robust out-of-plane FM ground state with a highTC(334 K), a sizable valley polarization (166 meV), a wide energy window (137 meV) harboring clean single-valley carriers, and a direct bandgap. These results identify a much needed ideal ferrovalley semiconductor candidate, holding the promising application potential in valleytronics and spintronics devices.

Spontaneous Valley Polarization and Electrical Control of Valley Physics in Single-Layer TcIrGe2S6

The modulation of valley polarization in one single system is of important fundamental and practical importance in quantum information technology. Here, through the first-principles calculations, we identify single-layer TcIrGe₂S₆ as a tantalizing candidate for realizing the modulation of valley polarization. Arising from the combination of inversion symmetry breaking and intrinsic magnetic exchange interaction, single-layer TcIrGe₂S₆ exhibits spontaneous valley polarization. The value of valley polarization in the conduction band is 161 meV, favorable for achieving the intriguing anomalous valley Hall effect. Furthermore, single-layer TcIrGe₂S₆ possesses ferroelectric order. More remarkably, its ferroelectric and valley physics can be strongly coupled, namely, the valley properties can be switched off and on electrically. These findings not only provide a compelling candidate for two-dimensional valleytronic research but also open a new avenue for modulating valley physics.

Skin-Deep Aspect of Thermopower in Bi2Q3, PbQ, and BiCuQO (Q = Se, Te): Hidden One-Dimensional Character of Their Band Edges Leading to High Thermopower

ConspectusThermoelectric (TE) materials have received much attention because of their ability to convert heat energy to electrical energy. At a given temperature T, the efficiency of a TE material for this energy conversion is measured by the figure of merit zT, which is related to the thermopower (or Seebeck coefficient) S, the thermal conductivity κ, and the electrical conductivity σ of the TE material as zT = (S²σT)/κ. Bi₂Q₃ and PbQ (Q = Se, Te) are efficient TE materials with high zT, although they are not ecofriendly and their stability is poor at high temperature. In principle, a TE material can have a high zT if it has a low thermal conductivity and a high electrical conductivity, but the latter condition is hardly met in a real material because the parameters S, σ and κ have a conflicting dependence on material properties. The difficulty in searching for TE materials of high zT is even more exasperated because the relationship between the thermopower S and the carrier density n (hereafter, the S-vs-n relationship) for the well-known hole-doped samples of BiCuSeO showed that the hole carriers responsible for their thermopower are associated largely with the electronic states lying within ∼0.5 eV of its valence band maximum (VBM). Thus, the states governing the TE properties lie in the "skin-deep" region from the VBM. For electron-doped TE systems, the electron carriers responsible for their thermopower should also be associated with the electronic states lying within ∼0.5 eV of the conduction band minimum (CBM). This makes it difficult to predict TE materials of high zT. One faces a similar skin-deep phenomenon in searching for superconductors of high transition temperature because the transition from a normal metallic to a superconducting state involves the normal metallic states in the vicinity of the Fermi level E_F. Other skin-deep phenomena in metallic compounds include the formation of charge density wave (CDW), which involves the electronic states in the vicinity of their Fermi levels. For magnetic materials of transition-metal ions, the preferred orientation of their spin moments is a skin-deep phenomenon because it is governed by the interaction between the highest-occupied and the lowest unoccupied d-states of these ions. In the present work we probe the issues concerning how to find the possible range of thermopower expected for a given TE material and hence how to recognize what experimental values of thermopower are expected or unusual. For these purposes, we analyze the accumulated S and n data on the three well-studied TE materials, Bi₂Q₃, PbQ, and BiCuQO (Q = Se, Te), as representative examples, in terms of the ideal theoretical S-vs-n relationships, which we determine for their defect-free Bi₂Q₃, PbQ, and BiCuQO structures using density functional theory (DFT) calculations under the rigid band approximation. We find that the general trends in the experimental S-vs-n relationships are reasonably well explained by the calculated S-vs-n relationships, and the carrier densities covering these relationships are associated with the states lying within ∼0.5 eV from their band edges confirming the skin-deep nature of their thermoelectric properties. Despite the fact that these TE materials are not one-dimensional (1D) in structure, they mostly possess sharp density-of-state peaks around their band edges because their band dispersions have a hidden 1D character so their thermopower is generally high in magnitude.

Spin-Orbital States and Strong Antiferromagnetism of Layered Eu2SrFe2O6 and Sr3Fe2O4Cl2

The insulating iron compounds Eu₂SrFe₂O₆ and Sr₃Fe₂O₄Cl₂ have high-temperature antiferromagnetic (AF) order despite their different layered structures. Here, we carry out density functional calculations and Monte Carlo simulations to study their electronic structures and magnetic properties aided with analyses of the crystal field, magnetic anisotropy, and superexchange. We find that both compounds are Mott insulators and in the high-spin (HS) Fe²⁺ state (S = 2) accompanied by the weakened crystal field. Although they have different local coordination and crystal fields, the Fe²⁺ ions have the same level sequence and ground-state configuration (3z²-r²)²(xz, yz)²(xy)¹(x²-y²)¹. Then, the multiorbital superexchange produces strong AF couplings, and the (3z²-r²)/(xz, yz) mixing via the spin-orbit coupling (SOC) yields a small in-plane orbital moment and anisotropy. Indeed, by tracing a set of different spin-orbital states, our density functional calculations confirm the strong AF couplings and the easy planar magnetization for both compounds. Moreover, using the derived magnetic parameters, our Monte Carlo simulations give the Néel temperature T_N = 420 K (372 K) for the former (the latter), which well reproduce the experimental results. Therefore, the present study provides a unified picture for Eu₂SrFe₂O₆ and Sr₃Fe₂O₄Cl₂ concerning their electronic and magnetic properties.

Structures and Magnetic Ordering in Layered Cr Oxide Arsenides Sr2CrO2Cr2OAs2 and Sr2CrO3CrAs

Two novel chromium oxide arsenide materials have been synthesized, Sr₂CrO₂Cr₂OAs₂ (i.e., Sr₂Cr₃As₂O₃) and Sr₂CrO₃CrAs (i.e., Sr₂Cr₂AsO₃), both of which contain chromium ions in two distinct layers. Sr₂CrO₂Cr₂OAs₂ was targeted following electron microscopy measurements on a related phase. It crystallizes in the space group P4/mmm and accommodates distorted CrO₄As₂ octahedra containing Cr²⁺ and distorted CrO₂As₄ octahedra containing Cr³⁺. In contrast, Sr₂CrO₃CrAs incorporates Cr³⁺ in CrO₅ square-pyramidal coordination in [Sr₂CrO₃]⁺ layers and Cr²⁺ ions in CrAs₄ tetrahedra in [CrAs]⁻ layers and crystallizes in the space group P4/nmm. Powder neutron diffraction data reveal antiferromagnetic ordering in both compounds. In Sr₂CrO₃CrAs the Cr²⁺ moments in the [CrAs]⁻ layers exhibit long-range ordering, while the Cr³⁺ moments in the [Sr₂CrO₃]⁺ layers only exhibit short-range ordering. However, in Sr₂CrO₂Cr₂OAs₂, both the Cr²⁺ moments in the CrO₄As₂ environments and the Cr³⁺ moments in the CrO₂As₄ polyhedra are long-range-ordered below 530(10) K. Above this temperature, only the Cr³⁺ moments are ordered with a Néel temperature slightly in excess of 600 K. A subtle structural change is evident in Sr₂CrO₂Cr₂OAs₂ below the magnetic ordering transitions.

Sr₂CrO₂Cr₂OAs₂ and Sr₂CrO₃CrAs are both mixed-anion materials containing chromium ions in two unique layers. In Sr₂CrO₂Cr₂OAs₂, Cr³⁺ ions in CrO₂As₄ environments order antiferromagnetically at around 600 K and Cr²⁺ ions in CrO₄As₂ environments also order antiferromagnetically at a lower temperature of 530(10) K. In contrast, only the Cr²⁺ moments in the [CrAs]⁻ layers exhibit long-range ordering in Sr₂CrO₃CrAs as the Cr³⁺ moments in the [Sr₂CrO₃]⁺ layers only exhibit short-range ordering.

Tunable Cr4+ Molecular Color Centers

The inherent atomistic precision of synthetic chemistry enables bottom-up structural control over quantum bits, or qubits, for quantum technologies. Tuning paramagnetic molecular qubits that feature optical-spin initialization and readout is a crucial step toward designing bespoke qubits for applications in quantum sensing, networking, and computing. Here, we demonstrate that the electronic structure that enables optical-spin initialization and readout for S = 1, Cr(aryl)₄, where aryl = 2,4-dimethylphenyl (1), o-tolyl (2), and 2,3-dimethylphenyl (3), is readily translated into Cr(alkyl)₄ compounds, where alkyl = 2,2,2-triphenylethyl (4), (trimethylsilyl)methyl (5), and cyclohexyl (6). The small ground state zero field splitting values (<5 GHz) for 1-6 allowed for coherent spin manipulation at X-band microwave frequency, enabling temperature-, concentration-, and orientation-dependent investigations of the spin dynamics. Electronic absorption and emission spectroscopy confirmed the desired electronic structures for 4-6, which exhibit photoluminescence from 897 to 923 nm, while theoretical calculations elucidated the varied bonding interactions of the aryl and alkyl Cr⁴⁺ compounds. The combined experimental and theoretical comparison of Cr(aryl)₄ and Cr(alkyl)₄ systems illustrates the impact of the ligand field on both the ground state spin structure and excited state manifold, laying the groundwork for the design of structurally precise optically addressable molecular qubits.

Unusual Spin Exchanges Mediated by the Molecular Anion P2S64-: Theoretical Analyses of the Magnetic Ground States, Magnetic Anisotropy and Spin Exchanges of MPS3 (M = Mn, Fe, Co, Ni)

We examined the magnetic ground states, the preferred spin orientations and the spin exchanges of four layered phases MPS3 (M = Mn, Fe, Co, Ni) by first principles density functional theory plus onsite repulsion (DFT + U) calculations. The magnetic ground states predicted for MPS3 by DFT + U calculations using their optimized crystal structures are in agreement with experiment for M = Mn, Co and Ni, but not for FePS3. DFT + U calculations including spin-orbit coupling correctly predict the observed spin orientations for FePS3, CoPS3 and NiPS3, but not for MnPS3. Further analyses suggest that the ||z spin direction observed for the Mn2+ ions of MnPS3 is caused by the magnetic dipole-dipole interaction in its magnetic ground state. Noting that the spin exchanges are determined by the ligand p-orbital tails of magnetic orbitals, we formulated qualitative rules governing spin exchanges as the guidelines for discussing and estimating the spin exchanges of magnetic solids. Use of these rules allowed us to recognize several unusual exchanges of MPS3, which are mediated by the symmetry-adapted group orbitals of P2S64- and exhibit unusual features unknown from other types of spin exchanges.

COSMO-RS Analysis of CO2 Solubility in N-Methyldiethanolamine, Sulfolane, and 1-Butyl-3-methyl-imidazolium Acetate Activated by 2-Methylpiperazine for Postcombustion Carbon Capture

Novel aqueous (aq) blends of N-methyldiethanolamine (MDEA), sulfolane (TMSO₂), and 1-butyl-3-methyl-imidazolium acetate ([bmim][Ac]) with amine activator 2-methylpiperazine (2-MPZ) are analyzed through conductor-like screening model for real solvents (COSMO-RS) for possible application in the chemisorption of CO₂. The molecules associated are analyzed for their ground-state energy, σ potential, and σ surface. Thermodynamic and physicochemical properties have been assessed and paralleled with the experimental data. Vapor pressure of the blended systems and pure component density and viscosity have been compared successfully with the experimental data. Important binary interaction parameters for the aqueous blends over a wide temperature, pressure, and concentration range have been estimated for NRTL, WILSON, and UNIQUAC 4 models. The COSMO-RS theory is further applied in calculating the expected CO₂ solubility over a pressure range of 1.0-3.0 bar and temperature range of 303.15-323.15 K. Henry's constant and free energy of solvation to realize the physical absorption through intermolecular interaction offered by the proposed solvents. Perceptive molecular learning from the behavior of chemical constituents involved indicated that the best suitable solvent is aq (MDEA + 2-MPZ).

Orbital Magnetic Moments of the High-Spin Co2+ Ions at Axially-Elongated Octahedral Sites: Unquenched as Reported from Experiment or Quenched as Predicted by Theory?

Neutron diffraction studies on magnetic solids composed of axially elongated CoO₄X₂ (X = Cl, Br, S, Se) octahedra show that the ordered magnetic moments of their high-spin Co²⁺ (d⁷, S = ³/₂) ions are greater than 3 μ_B, i.e., the spin moment expected for S = ³/₂ ions, and increase almost linearly from 3.22 to 4.45 μ_B as the bond-length ratio r_Co-X/r_Co-O increases from 1.347 to 1.659 where r_Co-X and r_Co-O are the Co-X and Co-O bond lengths, respectively. These observations imply that the orbital moments of the Co²⁺ ions increase linearly from 0.22 to 1.45 μ_B with increasing the r_Co-X/r_Co-O ratio from 1.347 to 1.659. We probed this implication by examining the condition for unquenched orbital moment and also by evaluating the magnetic moments of the Co²⁺ ions based on DFT+U+SOC calculations for those systems of the CoO₄X₂ octahedra. Our work shows that the orbital moments of the Co²⁺ ions are essentially quenched and, hence, that the observations of the neutron diffraction studies are not explained by the current theory of magnetic moments. This discrepancy between experiment and theory urges one to check the foundations of the current theory of magnetic moments as well as the current method of neutron diffraction refinements for ordered magnetic structures.

Trigonal Bipyramidal V3+ Complex as an Optically Addressable Molecular Qubit Candidate

Synthetic chemistry enables a bottom-up approach to quantum information science, where atoms can be deterministically positioned in a quantum bit or qubit. Two key requirements to realize quantum technologies are qubit initialization and read-out. By imbuing molecular spins with optical initialization and readout mechanisms, analogous to solid-state defects, molecules could be integrated into existing quantum infrastructure. To mimic the electronic structure of optically addressable defect sites, we designed the spin-triplet, V3+ complex, (C6F5)3trenVCNtBu (1). We measured the static spin properties as well as the spin coherence time of 1 demonstrating coherent control of this spin qubit with a 240 GHz electron paramagnetic resonance spectrometer powered by a free electron laser. We found that 1 exhibited narrow, near-infrared photoluminescence (PL) from a spin-singlet excited state. Using variable magnetic field PL spectroscopy, we resolved emission into each of the ground-state spin sublevels, a crucial component for spin-selective optical initialization and readout. This work demonstrates that trigonally symmetric, heteroleptic V3+ complexes are candidates for optical spin addressability.

Magnetic Ordering in the Layered Cr(II) Oxide Arsenides Sr2CrO2Cr2As2 and Ba2CrO2Cr2As2

Sr₂CrO₂Cr₂As₂ and Ba₂CrO₂Cr₂As₂ with Cr²⁺ ions in CrO₂ sheets and in CrAs layers crystallize with the Sr₂Mn₃Sb₂O₂ structure (space group I4/mmm, Z = 2) and lattice parameters a = 4.00800(2) Å, c = 18.8214(1) Å (Sr₂CrO₂Cr₂As₂) and a = 4.05506(2) Å, c = 20.5637(1) Å (Ba₂CrO₂Cr₂As₂) at room temperature. Powder neutron diffraction reveals checkerboard-type antiferromagnetic ordering of the Cr²⁺ ions in the arsenide layers below T_{N1_Sr}, of 600(10) K (Sr₂CrO₂Cr₂As₂) and T_{N1_Ba} 465(5) K (Ba₂CrO₂Cr₂As₂) with the moments initially directed perpendicular to the layers in both compounds. Checkerboard-type antiferromagnetic ordering of the Cr²⁺ ions in the oxide layer below 230(5) K for Ba₂CrO₂Cr₂As₂ occurs with these moments also perpendicular to the layers, consistent with the orientation preferences of d⁴ moments in the two layers. In contrast, below 330(5) K in Sr₂CrO₂Cr₂As₂, the oxide layer Cr²⁺ moments are initially oriented in the CrO₂ plane; but on further cooling, these moments rotate to become perpendicular to the CrO₂ planes, while the moments in the arsenide layers rotate by 90° with the moments on the two sublattices remaining orthogonal throughout [behavior recently reported independently by Liu et al. [Liu et al. Phys. Rev. B 2018, 98, 134416]]. In Sr₂CrO₂Cr₂As₂, electron diffraction and high resolution powder X-ray diffraction data show no evidence for a structural distortion that would allow the two Cr²⁺ sublattices to couple, but high resolution neutron powder diffraction data suggest a small incommensurability between the magnetic structure and the crystal structure, which may account for the coupling of the two sublattices and the observed spin reorientation. The saturation values of the Cr²⁺ moments in the CrO₂ layers (3.34(1) μ_B (for Sr₂CrO₂Cr₂As₂) and 3.30(1) μ_B (for Ba₂CrO₂Cr₂As₂)) are larger than those in the CrAs layers (2.68(1) μ_B for Sr₂CrO₂Cr₂As₂ and 2.298(8) μ_B for Ba₂CrO₂Cr₂As₂) reflecting greater covalency in the arsenide layers.

Hydride-Reduced Eu2SrFe2O6: A T-to-T' Conversion Enabling Fe2+ in Square-Planar Coordination

Low-temperature reaction of A-site-ordered layered perovskite Eu₂SrFe₂O₇ (T structure) with CaH₂ induces a shift in the Eu₂O₂ slabs to form Eu₂SrFe₂O₆ with a T' structure (I4/mmm space group) in which only the Fe cation is reduced. Contrary to the previously reported T' structures with Jahn-Teller-active d⁹ cations (Cu²⁺ and Ni⁺), stabilization of Eu₂SrFe₂O₆ with the Fe²⁺ (d⁶) cation reflects the stability of the FeO₄ square-planar unit. The stability of T'-type Eu₂SrFe₂O₆ over a T-type polymorph is confirmed by density functional theory calculations, revealing the d_z² occupancy for the T' structure. Eu₂SrFe₂O₆ has a bilayer magnetic framework with an Fe-O-Fe superexchange J_∥ and an Fe-Fe direct exchange J_⊥ (where J_∥ > J_⊥), which broadly explains the observed T_N of 390-404 K. Interestingly, the magnetic moments of Eu₂SrFe₂O₆ lie in the ab plane, in contrast to the structurally similar Sr₃Fe₂O₄Cl₂ having an out-of-plane spin alignment.

Spontaneous Rotation of Ferrimagnetism Driven by Antiferromagnetic Spin Canting

Spin-reorientation phase transitions that involve the rotation of a crystal's magnetization have been well characterized in distorted-perovskite oxides such as orthoferrites. In these systems spin reorientation occurs due to competing rare-earth and transition metal anisotropies coupled via f-d exchange. Here, we demonstrate an alternative paradigm for spin reorientation in distorted perovskites. We show that the R_{2}CuMnMn_{4}O_{12} (R=Y or Dy) triple A-site columnar-ordered quadruple perovskites have three ordered magnetic phases and up to two spin-reorientation phase transitions. Unlike the spin-reorientation phenomena in other distorted perovskites, these transitions are independent of rare-earth magnetism, but are instead driven by an instability towards antiferromagnetic spin canting likely originating in frustrated Heisenberg exchange interactions, and the competition between Dzyaloshinskii-Moriya and single-ion anisotropies.

Effect of Nonmagnetic Ion Deficiency on Magnetic Structure: Density Functional Study of Sr2MnO2Cu2-xTe2, Sr2MO2Cu2Te2 (M = Co, Mn), and the Oxide-Hydrides Sr2VO3H, Sr3V2O5H2, and SrVO2H

Two seemingly puzzling observations on two magnetic systems were analyzed. For the oxide-hydrides Sr₂VO₃H, Sr₃V₂O₅H₂, and SrVO₂H, made up of VO₄H₂ octahedra, the spin orientations of the V³⁺ (d², S = 1) ions were reported to be different, namely, perpendicular to the H-V-H bond in Sr₂VO₃H but parallel to the H-V-H bond in Sr₃V₂O₅H₂ and SrVO₂H, despite that the d-state split patterns of the VO₄H₂ octahedra are similar in the three oxide-hydrides. Another puzzling observation is the contrasting magnetic structures of Sr₂CoO₂Cu₂Te₂ and Sr₂MnO₂Cu_1.58Te₂, consisting of the layers made up of corner-sharing MO₄Te₂ (M = Co, Mn) octahedra. The Co²⁺ spins in each CoO₂Te₂ layer are antiferromagnetically coupled with spins perpendicular to the Te-Co-Te bond, whereas the Mn³⁺/Mn²⁺ ions of each MnO₂Te₂ layer are ferromagnetically coupled with spins parallel to the Te-Mn-Te bonds. We investigated the cause for these observations by performing first-principles density functional theory (DFT) calculations for stoichiometric phases Sr₂VO₃H, Sr₃V₂O₅H₂, SrVO₂H, Sr₂CoO₂Cu₂Te₂, and Sr₂MnO₂Cu₂Te₂, as well as nonstoichiometric phase Sr₂MnO₂Cu_1.5Te₂. Our study reveals that the V³⁺ ions in all three oxide-hydrides should have the spin orientation parallel to the H-V-H bond. The unusual magnetic structure of the MnO₂Te₂ layers of Sr₂MnO₂Cu_1.52Te₂ arises from the preference of a Mn³⁺ spin to be parallel to the Te-Mn-Te bond, the ferromagnetic spin exchange between adjacent Mn³⁺ and Mn²⁺ ions, and the nearly equal numbers of Mn³⁺ and Mn²⁺ ions in each MnO₂Te₂ layer. We show that the spin orientation of the magnetic ions in an antiferromagnetically coupled perovskite layer, expected in the absence of nonmagnetic ion vacancies, cannot be altered by the magnetic ions of higher oxidation that result from trace vacancies at the nonmagnetic ion sites.

Electronic and Structural Factors Controlling the Spin Orientations of Magnetic Ions

Magnetic ions M in discrete molecules and extended solids form ML_n complexes with their first-coordinate ligand atoms L. The spin moment of M in a complex ML_n prefers a certain direction in coordinate space because of spin-orbit coupling (SOC). In this minireview, we examine the structural and electronic factors governing the preferred spin orientations. Elaborate experimental measurements and/or sophisticated computational efforts are required to find the preferred spin orientations of magnetic ions, largely because the energy scale of SOC is very small. The latter is also the very reason why one can readily predict the preferred spin orientation of M by analyzing the SOC-induced highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) interactions of the ML_n complexes in terms of qualitative perturbation theory. The strength of this HOMO-LUMO interaction depends on the spin orientation, which is governed by the selection rules based on the minimum |ΔL_z| value (i.e., the minimum difference in the magnetic quantum numbers) between the HOMO and LUMO. With the local z axis of ML_n chosen as its n-fold rotational axis, the preferred spin orientation is parallel to the z axis (∥z) when |ΔL_z| = 0 but perpendicular to the z axis (⊥z) when |ΔL_z| = 1.

High-Pressure Synthesis of A2 NiO2 Ag2 Se2 (A=Sr, Ba) with a High-Spin Ni2+ in Square-Planar Coordination

Square-planar coordinate Ni2+ ions in oxides are exclusively limited to a low-spin state (S=0) owing to extensive crystal field splitting. Layered oxychalcogenides A2 NiII O2 Ag2 Se2 (A=Sr, Ba) with the S=1 NiO2 square lattice are now reported. The structural analysis revealed that the Ni2+ ion is under-bonded by a significant tensile strain from neighboring Ag2 Se2 layers, leading to the reduction in crystal field splitting. Ba2 NiO2 Ag2 Se2 exhibits a G-type spin order at 130 K, indicating fairly strong in-plane interactions. The high-pressure synthesis employed here possibly assists the expansion of NiO2 square lattice by taking the advantage of the difference in compressibility in oxide and selenide layers.

Progress towards creating optically addressable molecular qubits

The emerging field of quantum information science promises to transform a diverse range of scientific fields, ranging from computation to sensing and metrology. The interdisciplinary scientific community laid the groundwork for the next generation of quantum technologies through key advances in understanding the fundamental unit of quantum information science, the qubit. Electronic spin is a promising platform for qubits, demonstrating suitably long coherence times, optical initialization, and single spin addressability. Herein, we discuss recent accomplishments and future progress from our group targeted at imbuing transition metal complexes with the aforementioned properties, creating a pathway to fusing spatial precision with long coherence times. A strong emphasis of this feature article is progressing towards single spin measurements via a chemical approach for imbuing molecular qubits with an optically-induced spin polarization mechanism.

Intrinsic Quantum Anomalous Hall Effect with In-Plane Magnetization: Searching Rule and Material Prediction

So far, most theoretically predicted and experimentally confirmed quantum anomalous Hall effects (QAHEs) are limited in two-dimensional (2D) materials with out-of-plane magnetization. In this Letter, starting from 2D nodal-line semimetal, a general rule for searching QAHE with in-plane magnetization is mapped out. Because of spin-orbital coupling, we found that the magnetization will prefer an in-plane orientation if the orbital of degenerate nodal-line states at the Fermi level have the same absolute value of magnetic quantum number. Moreover, depending on the broken or conserved mirror symmetry, either a QAHE or 2D semimetal can be realized. Based on first principles calculations, we further predict a real material of monolayer LaCl to be an intrinsic QAHE with in-plane magnetization. By tuning the directions of in-plane magnetization, the QAHE in LaCl demonstrates a threefold rotational symmetry with a Chern number of either +1 or -1, and the transition point is characterized by a 2D semimetal phase. All these features are quantitatively reproduced by tight-binding model calculations, revealing the underlying physics clearly. Our results greatly extend the scope for material classes of QAHE and hence stimulate immediate experimental interest.

Nonequivalent Spin Exchanges of the Hexagonal Spin Lattice Affecting the Low-Temperature Magnetic Properties of RInO3 (R = Gd, Tb, Dy): Importance of Spin-Orbit Coupling for Spin Exchanges between Rare-Earth Cations with Nonzero Orbital Moments

Rare-earth indium oxides RInO₃ (R = Gd, Tb, Dy) consist of spin-frustrated hexagonal spin lattices made up of rare-earth ions R³⁺, where R³⁺ = Gd³⁺ (f⁷, L = 0), Tb³⁺ (f⁸, L = 3), and Dy³⁺ (f⁹, L = 5). We carried out DFT calculations for RInO₃, including on-site repulsion U with/without spin-orbit coupling (SOC), to explore if their low-temperature magnetic properties are related to the two nonequivalent nearest-neighbor (NN) spin exchanges of their hexagonal spin lattices. Our DFT + U + SOC calculations predict that the orbital moments of the Tb³⁺ and Dy³⁺ ions are smaller than their free-ion values by ∼2μ_B while the Tb³⁺ spins have an in-plane magnetic anisotropy, in agreement with the experiments. This suggests that the f orbitals of each R³⁺ (R = Tb, Dy) ion are engaged, though weakly, in bonding with the surrounding ligand atoms. The magnetic properties of GdInO₃ with the zero orbital moment are adequately described by the spin exchanges extracted by DFT + U calculations. In describing the magnetic properties of TbInO₃ and DyInO₃ with nonzero orbital moments, however, the spin exchanges extracted by DFT + U + SOC calculations are necessary. The spin exchanges of RInO₃ (R = Gd, Tb, Dy) are dominated by the two NN spin exchanges J₁ and J₂ of their hexagonal spin lattice, in which the honeycomb lattice of J₂ forms spin-frustrated ( J₁, J₁, J₂) triangles. The J₂/ J₁ ratios are calculated to be ∼3, ∼1.7, and ∼1 for GdInO₃, TbInO₃, and DyInO₃, respectively. This suggests that the antiferromagnetic (AFM) ordering of GdInO₃ below 1.8 K is most likely an AFM ordering of its honeycomb spin lattice and that TbInO₃ would exhibit low-temperature magnetic properties similar to those of GdInO₃ while DyInO₃ would not.

Enhancement of magnetic anisotropy in a Mn-Bi heterobimetallic complex

A novel Mn²⁺Bi³⁺ heterobimetallic complex, featuring the closest MnBi interaction for a paramagnetic molecular species, exhibits unusually large axial zero-field splitting. We attribute this enhancement to the proximity of Mn²⁺ to a heavy main group element, namely, bismuth.

Single-Domain Ferromagnet of Noncentrosymmetric Uniaxial Magnetic Ions and Magnetoelectric Interaction

The feasibility of a single-domain ferromagnet based on uniaxial magnetic ions was examined. For a noncentrosymmetric uniaxial magnetic ion of magnetic moment μ at a site of local electric dipole moment p, it is unknown to date whether μ prefers to be parallel or antiparallel to μ. The nature of this magnetoelectric interaction was probed in terms of analogical reasoning based on the Rashba effect and density functional theory (DFT) calculations. We show that μ and p prefer an antiparallel arrangement, predict that Fe-doped CaZnOS is a single-domain ferromagnet like a bar magnet, and find the probable cause for the ferromagnetism and weak magnetization hysteresis in Fe-doped hexagonal ZnO and ZnS at very low dopant concentrations.

Spin orientations of the spin-half Ir(4+) ions in Sr3NiIrO6, Sr2IrO4, and Na2IrO3: Density functional, perturbation theory, and Madelung potential analyses

The spins of the low-spin Ir(4+) (S = 1/2, d(5)) ions at the octahedral sites of the oxides Sr3NiIrO6, Sr2IrO4, and Na2IrO3 exhibit preferred orientations with respect to their IrO6 octahedra. We evaluated the magnetic anisotropies of these S = 1/2 ions on the basis of density functional theory (DFT) calculations including spin-orbit coupling (SOC), and probed their origin by performing perturbation theory analyses with SOC as perturbation within the LS coupling scheme. The observed spin orientations of Sr3NiIrO6 and Sr2IrO4 are correctly predicted by DFT calculations, and are accounted for by the perturbation theory analysis. As for the spin orientation of Na2IrO3, both experimental studies and DFT calculations have not been unequivocal. Our analysis reveals that the Ir(4+) spin orientation of Na2IrO3 should have nonzero components along the c- and a-axis directions. The spin orientations determined by DFT calculations are sensitive to the accuracy of the crystal structures employed, which is explained by perturbation theory analyses when interactions between adjacent Ir(4+) ions are taken into consideration. There are indications implying that the 5d electrons of Na2IrO3 are less strongly localized compared with those of Sr3NiIrO6 and Sr2IrO4. This implication was confirmed by showing that the Madelung potentials of the Ir(4+) ions are less negative in Na2IrO3 than in Sr3NiIrO6 and Sr2IrO4. Most transition-metal S = 1/2 ions do have magnetic anisotropies because the SOC induces interactions among their crystal-field split d-states, and the associated mixing of the states modifies only the orbital parts of the states. This finding cannot be mimicked by a spin Hamiltonian because this model Hamiltonian lacks the orbital degree of freedom, thereby leading to the spin-half syndrome. The spin-orbital entanglement for the 5d spin-half ions Ir(4+) is not as strong as has been assumed.

Transformation of the coordination complex [Co(C3S5)2]2- from a molecular magnet to a potential qubit

We employ ac susceptibility as a probe of small changes of transverse zero-field splitting, revealing that these subtle changes transform [Co(C₃S₅)₂]^2– from a molecular magnet to a candidate qubit.

Mononuclear transition metal complexes demonstrate significant potential in the divergent applications of spintronics and quantum information processing. The facile tunability of these complexes enables structure function correlations for a plethora of relevant magnetic quantities. We present a series of pseudotetrahedral [Co(C₃S₅)₂]^2– complexes with varying deviations from D_2d symmetry to investigate the influence of structural distortions on spin relaxation dynamics and qubit viability, as tuned by the variable transverse magnetic anisotropy, E. To overcome the traditional challenge of measuring E in species where D ≫ E, we employed a different approach of harnessing ac magnetic susceptibility to probe the emergence of quantum tunneling of magnetization as a proxy for E. Across the range of values for E in the series, we observe magnetic hysteresis for the smallest value of E. The hysteresis disappears with increasing E, concomitant with the appearance of an observable, low frequency (L-band) electron paramagnetic resonance (EPR) signal, indicating the potential to controllably shift the molecule's utilization from classical to quantum information processing applications. The development of design principles for molecular magnet information processing requires separate design principles for classical versus quantum regimes. Here we show for the first time how subtle structural changes can switch the utility of a complex between these two types of applications.

Magnetic structure of (C5H12N)CuBr3: origin of the uniform Heisenberg chain behavior and the magnetic anisotropy of the Cu2+(S = 1/2) ions

The AFM chain behavior observed for (pipH)CuBr₃is not caused by the CuBr₃chains, but by the interchain exchanges leading to two-leg spin ladders. The Cu²⁺ions have easy-axis anisotropy, and this arises largely from the SOC of the Br⁻ligands.