Spin States Research Articles

Switching Spin‐States: Spin Crossover vs. Coordination‐Induced Spin‐State Switching

AbstractSwitchable molecular materials have continued to attract the interest of chemists and physicists for decades. A prominent example are spin crossover complexes, where numerous textbooks, review articles, and special issues are available. A highly interesting alternative is the coordination‐induced spin‐state switching. In this concept, we will compare the two spin‐state switching mechanisms and discuss common aspects and differences. Additionally, a short overview of coordination‐induced spin state switching will be given.

Nutation-orbit resonances: The origin of the chaotic rotation of Hyperion and the barrel instability

While numerous planetary and asteroid satellites show evidence for non-trivial rotation states, none are as emblematic as Hyperion, which has long been held as the most striking example of chaotic spin-orbit evolution in the Solar System. Nevertheless, an analytically tractable theory of the full 3D spin-orbit dynamics of Hyperion has not been developed. We derive the Hamiltonian for a spinning axisymmetric satellite in the gravitational potential of a planet without assuming planar or principal axis rotation and without averaging over the spin period. Using this model, we demonstrate the emergence of resonances between the nutation and orbital frequencies that act as the primary drivers of the spin dynamics. This analysis reveals that, contrary to long-held belief, Hyperion is not tumbling chaotically. Instead, it lies near or in a nutation-orbit resonance that is first-order in eccentricity, allowing it to rotate quasi-regularly. The most reliable observations are consistent with either nonchaotic motion or chaos that is orders of magnitude smaller than originally claimed. A separate phenomenon, the so-called barrel instability, is shown to be related to a different set of nutation-orbit resonances that generalize the planar spin-orbit resonances. Finally, we show that changes in spin states over long timescales are best understood by considering chaotic diffusion of quasi-conserved quantities.

Application of partial wave analysis in multiphoton pair production

Electron-positron pair production is investigated in the multiphoton regime under polarized fields. Partial wave analysis can be applied to reveal the momentum spectral structure and identify the positions of valleys/peaks of the multiphoton rings by combining with CP conservation. Moreover, considering the spin states of created pairs in partial wave analysis, the particle orbital angular momentum associated with the valleys/peaks can also be identified from multiphoton rings. It is found that the approximate analytical treatments for angular distribution by using partial wave analysis are consistent with those of the numerical calculation using the Dirac-Heisenberg-Wigner formalism. The results are helpful for understanding the angular momentum information in momentum spectra, and they also have an implication for revealing the vortex structure near the valleys where the amplitude nearly vanishes. Published by the American Physical Society 2024

Unusual spin dynamics in the van der Waals antiferromagnet FeGa2S4

Spin dynamics in the van der Waals antiferromagnet FeGa2S4with triangular lattices are investigated using magnetometry, neutron scattering, and muon spin relaxation measurements. The characteristic spin relaxation time is thoroughly clarified over thirteen orders of magnitude. Although the temperature dependence of DC and AC susceptibilities recalls a conventional spin-glass transition, nonlinear susceptibilities showing no divergences at the anomalous temperature,T∗=16.87(7) K, deny that and instead hint at other mechanisms. Elastic neutron scattering together with previously measured muon results depict a slowly fluctuated (∼10-5 s) spin state aboveT∗. In juxtaposing the underlying simplest structure among frustrated magnets with an intricate hierarchy of time scales, FeGa2S4can be a playground for studying temporal spin correlations in the two-dimensional limit.

Facile Approach for the Fabrication of Vapor Sensitive Spin Transition Composite Nanofibers

In this work polymer nanofibers were functionalized by incorporation of the spin transition (ST) compound [Fe(H2btm)2(H2O)2]Cl2 (FeH2btm) (H2btm = di(1H‐tetrazol‐5‐yl)methane). FeH2btm is an interesting compound due to its ability to reversibly and sensitively switch between high spin (HS) and low spin (LS) state when exposed to common volatile compounds (VOC) like ammonia and methanol. By using polyvinylidene fluoride (PVDF) as the main compound, inhibiting interactions between the complex and polymer were minimized. By using UV‐Vis spectroscopy, the visible and reversible switching between HS and LS state when exposed to an ammonia or hydrochloric acid atmosphere was confirmed. Powder X‐Ray diffraction (PXRD), scanning electron microscopy (SEM) and energy dispersive X‐Ray spectroscopy (EDX) show a homogenous distribution of FeH2btm with no major crystalline accumulations and a mean fiber diameter of 106 ± 20 nm. The composite fiber has a similarly high thermal stability as the pure FeH2btm, as shown by thermogravimetric analysis (TGA). Mössbauer spectroscopy indicates an incomplete spin transition after exposition to ammonia. This could be due to low permeability of the VOC into the composite fiber.

Unusual Anomalous Hall Effect in Two-Dimensional Ferromagnetic Cr7Te8

Two-dimensional (2D) materials with inherent magnetism have attracted considerable attention in the fields of spintronics and condensed matter physics. The anomalous Hall effect (AHE) offers a theoretical foundation for understanding the origins of 2D ferromagnetism (2D-FM) and offers a valuable opportunity for applications in topological electronics. Here, we present uniform and large-size 2D Cr7Te8 nanosheets with varying thicknesses grown using the chemical vapor deposition (CVD) method. The 2D Cr7Te8 nanosheets with robust perpendicular magnetic anisotropy, even a few layers deep, exhibit a Curie temperature (TC) ranging from 180 to 270 K according to the varying thickness of Cr7Te8. Moreover, we observed a temperature-induced reversal in the sign of the anomalous Hall resistance, correlating with changes in the intrinsic Berry curvature. Additionally, the topological Hall effect (THE) observed at low temperatures suggests the presence of non-trivial spin chirality. Our findings about topologically non-trivial magnetic spin states in 2D ferromagnets provide a promising opportunity for new designs in magnetic memory spintronics.

Spin switching in Sm0.7Er0.3FeO3 triggered by terahertz magnetic-field pulses.

Driving spin systems to states far from equilibrium is indispensable in investigations of functional nonlinearities of antiferromagnets for spintronics. So far, it has been shown that electric-field pulses in the spectral region from the visible to the terahertz range can be used to induce ultrafast switching between different spin states. Here we demonstrate that a multicycle terahertz magnetic-field pulse can be used to induce non-thermal spin switching in antiferromagnets. When a strong pulse is applied to Sm0.7Er0.3FeO3, the magnetic order parameter is first driven away from the barrier between the two potential minima of this antiferromagnet and then, in the subsequent inertial motion towards the opposite direction, it crosses the barrier. Our analysis reveals that the initial motion is driven by a dynamical modification of the magnetic potential, and this modification is enhanced through coupling between the two magnon modes.

Redox-Neutral, Iron-Mediated Directed C-H Activation: General Principles and Mechanistic Insights.

Experimental and computational studies have been conducted and established the general principles for enabling redox-neutral C-H activation by iron(II) complexes. The idealized octahedral iron(II) dimethyl complex, (depe)2Fe(CH3)2 (depe = 1,2-bis(diethylphosphino)ethane) promoted the directed, regioselective ortho C(sp2)-H methylation of pivalophenone. The rate of the iron(II)-mediated C(sp2)-H functionalization depended on the lability of L-type phosphine ligands, the spin state of the iron center, and the size of the X-type ligands (halide, hydrocarbyl) in P4FeIIX2 complexes. The C(sp2)-H alkylation reaction proved general among multiple substrates with directing groups including carbonyl, imines and pyridines. Among these, ketones and aldehydes were identified as optimal and were compatible with various steric environments and presence of acidic α-hydrogens. With stronger nitrogen donors, higher barriers for product-forming reductive elimination were observed. The effect of orbital hybridization on the chemoselectivity of C-H activation through a σ-CAM pathway by dn>0 transition metals was also established by studying the stoichiometric reactivity of the differentially substituted (depe)2Fe(Me)R complexes (R = alkyl, aryl), where the Fe-R bond with greater s-character preferentially promoted selective C-H activation. Deuterium labeling and kinetic studies, coupled with computational analysis, supported a pathway involving phosphine dissociation and rate-determining C-H bond activation, leading to the observed products.

Quark spin effects in e+e− annihilation: A Monte Carlo event generator study

Quark spin effects in e+e− annihilation to pseudoscalar and vector mesons are implemented for the first time in the Monte Carlo event generator. The spin-dependent fragmentation of the string stretched between the produced quark-antiquark pair with correlated spin states is described by the string+P30 model implemented in the string fragmentation routine of by using the package. The simulated events are used to study the model predictions for the Collins asymmetries of mesons produced back-to-back in the e+e− center of mass system by using both the thrust axis method and the hadronic plane method. The obtained asymmetries are compared to the available data from the BELLE and experiments and the underlying Collins analyzing power from the string+P30 model is compared with phenomenological extractions. Published by the American Physical Society 2024

Cavity-magnon-polariton spectroscopy of strongly hybridized electro-nuclear spin excitations in LiHoF4

We first present a formalism that incorporates the input-output formalism and the linear response theory to employ cavity-magnon-polariton coupling as a spectroscopic tool for investigating strongly hybridized electro-nuclear spin excitations. A microscopic relation between the generalized susceptibility and the scattering parameter |S11|\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$|S_{11}|$$\\end{document} in strongly hybridized cavity-magnon-polariton systems has been derived without resorting to semi-classical approximations. The formalism is then applied to both analyze and simulate a specific systems comprising a model quantum Ising magnet (LiHoF4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {LiHoF}_4$$\\end{document}) and a high-finesse 3D re-entrant cavity resonator. Quantitative information on the electro-nuclear spin states in LiHoF4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {LiHoF}_4$$\\end{document} is extracted, and the experimental observations across a broad parameter range were numerically reproduced, including an external magnetic field traversing a quantum critical point. The method potentially opens a new avenue not only for further studies on the quantum phase transition in LiHoF4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {LiHoF}_4$$\\end{document} but also for a wide range of complex magnetic systems.

Spin-bearing molecules as optically addressable platforms for quantum technologies

Abstract Efforts to harness quantum hardware relying on quantum mechanical principles have been steadily progressing. The search for novel material platforms that could spur the progress by providing new functionalities for solving the outstanding technological problems is however still active. Any physical property presenting two distinct energy states that can be found in a long-lived superposition state can serve as a quantum bit (qubit), the basic information processing unit in quantum technologies. Molecular systems that can feature electron and/or nuclear spin states together with optical transitions are one of the material platforms that can serve as optically addressable qubits. The attractiveness of molecular systems for quantum technologies relies on the fact that molecular structures of atomically defined nature can be obtained in endless diversity of chemical compositions. Crucially, by harnessing the molecular design protocols, the optical and spin (electronic and nuclear) properties of molecules can be tailored, aiding the design of optically addressable spin qubits and quantum sensors. In this contribution, we present a concise and collective discussion of optically addressable spin-bearing molecules – namely, organic molecules, transition metal (TM) and rare-earth ion (REI) complexes – and highlight recent results such as chemical tuning of optical and electron spin quantum coherence, optical spin initialization and readout, intramolecular quantum teleportation, optical coherent storage, and photonic-enhanced optical addressing. We envision that optically addressable spin-carrying molecules could become a scalable building block of quantum hardware for applications in the fields of quantum sensing, quantum communication and quantum computing.

Incommensurate Order with Translationally Invariant Projected Entangled-Pair States: Spiral States and Quantum Spin Liquid on the Anisotropic Triangular Lattice

Incommensurate Order with Translationally Invariant Projected Entangled-Pair States: Spiral States and Quantum Spin Liquid on the Anisotropic Triangular Lattice

Hydrogen-Bond-Assisted Catalysis: Hydroxylation of Paclitaxel by Human CYP2C8.

Paclitaxel (PTX, or Taxol), a chemotherapeutic agent widely employed in the treatment of various cancers, undergoes metabolic transformations through the cytochrome P450 enzymes CYP3A4 and CYP2C8. CYP3A4 catalyzes the aromatic hydroxylation reaction of PTX, whereas CYP2C8 demonstrates a distinct reactivity pattern, producing 6α-hydroxypaclitaxel via alkane hydroxylation. Despite the significant impact of PTX metabolism on its anticancer efficacy, the detailed mechanisms underlying these transformations have remained largely unclear. In this study, we employed hybrid quantum mechanics and molecular mechanics (QM/MM) calculations to elucidate the mechanism of PTX metabolism by human CYP2C8. Our QM/MM results reveal that the hydroxylation of PTX by CYP2C8 follows an atypical rebound mechanism. Either of the two hydrogen atoms at the C6 position of PTX can be abstracted, leading to a common radical intermediate. Although the subsequent rebound barrier is unusually high, stereochemical scrambling is unlikely, as the rebound barrier for the formation of the 6α-hydroxylated PTX─the actual product─is significantly lower than that for the 6β-hydroxylated metabolite. Thus, product selectivity is determined by the non-rate-determining rebound step. Furthermore, the hydroxyl group at the C7 position of PTX plays a catalytic role by facilitating the hydrogen abstraction and rebound steps. Our study also confirms a pronounced stability of the transition state in the high-spin sextet spin state, enabled by the enzyme's specific substrate positioning.

Understanding the Role of Spin State in Cobalt Oxyhydroxides for Water Oxidation

AbstractAlthough the electronic state of catalysts is strongly corrected with their oxygen evolution reaction (OER) performances, understanding the role of spin state in dynamic electronic structure evolution during OER process is still challenging. Herein, we developed a spin state regulation strategy to boost the OER performance of CoOOH through elemental doping (CoMOOH, M=V, Cr, Mn, Co and Cu). Experimental results including magnetic characterization, in situ X‐ray absorption spectroscopy, in situ Raman and density functional theory calculations unveil that Mn doping could successfully increase the Co sites from low spin state to intermediate spin state, leading to the largest lattice distortion and smallest energy gap between dxy and dz2 orbitals among the obtained CoMOOH electrocatalysts. Benefiting from the promoted electron transfer from dxy to dz2 orbital, facilitated formation of active high‐valent *O−Co(IV) species at applied potential, and reduced energy barrier of rate‐determining step, the CoMnOOH exhibits the highest OER performance. Our work provides significant insight into the correction between dynamic electronic structure evolution and OER performance by understanding the role of spin state regulation in metal oxyhydroxides, paving a new avenue for rational design of high‐activity electrocatalysts.

Regulating the Spin‐State of Cobalt in Three‐Dimensional Covalent Organic Frameworks for High‐Performance Sodium‐Iodine Rechargeable Batteries

Although the catalytic activity is heavily reliant on the electronic structure of the catalyst, understanding the impact of electron spin regulation on electrocatalytic performance is still rarely investigated. This work presents a novel approach involving the single‐atom coordination of cobalt (Co) within metalloporphyrin‐based three‐dimensional covalent organic frameworks (3D‐COFs) to facilitate the catalytic conversion for sodium‐iodine batteries. The spin state of Co is modulated by altering the oxidation state of the porphyrin‐centered Co, achieving optimal catalysis for iodine reduction. Experimental results demonstrate that CoII and CoIII are incorporated into the 3D‐COFs, exhibiting spin ground states of S = 1/2 and S = 0, respectively. The low spin state of CoIII is favorable to hybridize with the sp 3d orbitals of I3‐, thus facilitating the conversion of I3‐ to I‐. Density‐functional theory (DFT) calculations further reveal that the presence of CoIII enhances iodide adsorption and accelerates the formation of NaI in 3D‐COFs‐CoIII, thereby promoting its rapid kinetic behaviors. Notably, the I2@3D‐COFs‐CoIII cathode achieves a high reversible capacity of 227.7 mAh g‐1 after 200 cycles at 0.5 C and demonstrates exceptional cyclic stability, exceeding 2000 cycles at 10 C with a minor capacity fading rate of less than one 0.01% per cycle.

Regulating the Spin-State of Cobalt in Three-Dimensional Covalent Organic Frameworks for High-Performance Sodium-Iodine Rechargeable Batteries.

Although the catalytic activity is heavily reliant on the electronic structure of the catalyst, understanding the impact of electron spin regulation on electrocatalytic performance is still rarely investigated. This work presents a novel approach involving the single-atom coordination of cobalt (Co) within metalloporphyrin-based three-dimensional covalent organic frameworks (3D-COFs) to facilitate the catalytic conversion for sodium-iodine batteries. The spin state of Co is modulated by altering the oxidation state of the porphyrin-centered Co, achieving optimal catalysis for iodine reduction. Experimental results demonstrate that CoII and CoIII are incorporated into the 3D-COFs, exhibiting spin ground states of S = 1/2 and S = 0, respectively. The low spin state of CoIII is favorable to hybridize with the sp 3d orbitals of I3-, thus facilitating the conversion of I3- to I-. Density-functional theory (DFT) calculations further reveal that the presence of CoIII enhances iodide adsorption and accelerates the formation of NaI in 3D-COFs-CoIII, thereby promoting its rapid kinetic behaviors. Notably, the I2@3D-COFs-CoIII cathode achieves a high reversible capacity of 227.7 mAh g-1 after 200 cycles at 0.5 C and demonstrates exceptional cyclic stability, exceeding 2000 cycles at 10 C with a minor capacity fading rate of less than one 0.01% per cycle.

Direct Evidence of Breakdown of Spin Statistics in Ion-Atom Charge Exchange Collisions

Direct Evidence of Breakdown of Spin Statistics in Ion-Atom Charge Exchange Collisions

Homogeneous Catalysts for Hydrogenative PHIP Used in Biomedical Applications

AbstractAt present, two competing hyperpolarization (HP) techniques, dissolution dynamic nuclear polarization (DNP) and parahydrogen (para‐H2) induced polarization (PHIP), can generate sufficiently high liquid state 13C signal enhancement for in vivo studies. PHIP utilizes the singlet spin state of para‐H2 to create non‐equilibrium spin populations. In hydrogenative PHIP, para‐H2 is irreversibly added to unsaturated precursors, typically in the presence of a homogeneous catalyst. The hydrogenation catalyst plays a crucial role in converting the singlet spin order of para‐H2 into detectable nuclear polarization. Currently, rhodium(I) bisphosphine complexes are the most widely employed catalysts for PHIP, capable of catalyzing the addition of para‐H2 to unsaturated precursors in organic solvents or aqueous media, depending on the ligand. Chiral catalysts enable the stereoselective production of hyperpolarized substrates. Ruthenium(II) piano stool complexes are capable of trans addition and are used to generate hyperpolarized fumarate. However, these catalysts systems are not optimal, and the greatest source of nuclear spin polarization loss is attributed to the mixing of singlet and triplet states of the protons derived from the para‐H2 during the hydrogenation process. Hence, future efforts should focus on enhancing the efficiency and kinetics of these catalysts.

Optical manipulation of spin states in ultracold magnetic atoms via an inner-shell hz transition

Lanthanides, like erbium and dysprosium, have emerged as powerful platforms for quantum-gas research due to their diverse properties, including a significant large spin manifold in their absolute ground state. However, effectively exploiting the spin richness necessitates precise manipulation of spin populations, a challenge yet to be fully addressed in this class of atomic species. In this work, we present an all-optical method for deterministically controlling the spin composition of a dipolar bosonic erbium gas, based on a clocklike transition in the telecom window at 1299nm. The atoms can be prepared in just a few tens of microseconds in any spin-state composition using a sequence of Rabi-pulse pairs, selectively coupling Zeeman sublevels of the ground state with those of the long-lived clocklike state. Finally, we demonstrate that this transition can also be used to create spin-selective light shifts, thus fully suppressing spin-exchange collisions. These experimental results unlock exciting possibilities for implementing advanced spin models in isolated, clean, and fully controllable lattice systems. Published by the American Physical Society 2024

Chromium Complex of Macrocyclic Ligands as Precursor for Nitric Oxide Release: A Theoretical Study.

Our research on the chromium complex of macrocyclic ligands as a precursor for nitric oxide release makes a significant contribution. We detailed the analysis of nitrito chromium complexes, specifically trans-[M(III)L1-5(ONO)2]+, M=Cr(III) and L1-L5represent different ligands: L1=1,4,8,11-tetraazacyclotetradecane, L2= (5,7-dimethyl-6-benzylcyclam), L3=(5,7-dimethyl-6-anthracylcyclam), L4= (5,7-dimethyl-6-(p-hydroxymethylbenzyl)-1,4, 8,11-cyclam) and L5= (5,7-dimethyl-6-(1¢-methyl-4´-(1"-carboxymethylpyrene) benzyl)-1,4,8,11-tetraazacyclotetradecane). Our objective is to comprehensively understand the mechanism of NO release and identify the key factors influencing NO delivery. The optimized structure of the complexes at spin states S = 1/2 or 3/2 indicates a decrease in the Cr(III)-O bond length (1.669-1.671 Å) along with an increase in the Cr(III)O-NO bond length (2.735 - 2.741 Å), which facilitates the release of NO. Furthermore, there is a significant change in the bond angle (Cr-O-NO), from 120.4° to 116.9°, with respect to S=3/2, thus enlarging theO-NO bond and supporting the β-cleavage of NO from the complex. The calculated activation energy for the complexes reflects the energy difference between the low-spin doublet and high-spin quartet state due to spin crossover (SCO). Moreover, the Natural Transition Orbitals (NTOs) confirm the involvement of a hole-particle in the excitation. Additionally, TD-DFT reveals the pendant chromophore's role in generating NO, as the chromophore antenna effectively enhances light absorption.