Spin Exchange Research Articles

Thermal one-point functions and their partial wave decomposition

In this work we address partial wave decompositions of thermal one-point functions in conformal field theories on S1 × Sd−1. With the help of Casimir differential equations we develop efficient algorithms to compute the relevant conformal blocks for an external field of arbitrary spin and with any spin exchange along the thermal circle, at least in three dimensions. This is achieved by identifying solutions to the Casimir equations with a special class of spherical functions in the harmonic analysis of the conformal group. The resulting blocks are then applied to study the decomposition of one-point functions of the scalar ϕ2 and the stress tensor T for a three-dimensional free scalar field ϕ. We are able to read off averaged OPE coefficients into exchanged fields of high weight and spin for a complete set of tensor structures. We also extract an asymptotic behaviour of conformal blocks and use it to analyse the density of heavy-heavy-light OPE coefficients for spinning operators, comparing it with semi-classical predictions, such as the dimensions of operators at large charge.

The Spin‐Selective Channels in Fully‐Exposed PtFe Clusters Enable Fast Cathodic Kinetics of Li‐O2 Batter y

In Li‐O2 batteries (LOBs), the electron transfer between triplet O2 and singlet Li2O2 possesses a spin‐dependent character but is still neglected, while the spin‐conserved electron transfer without losing phase information should guarantee fast kinetics and reduced energy barriers. Here, we provide a paradigm of spin‐selective catalysis for LOB that the ferromagnetic quantum spin exchange interactions between Pt and Fe atoms in fully‐exposed PtFe clusters filter directional e‐spins for spin‐conserved electron transfer at Fe‐Fe sites. The kinetics of O2/Li2O2 redox reaction is markedly accelerated as predicted by theoretical calculations, showing dramatically decreased relaxation time of the rate determining step for more than one order of magnitude, compared with the Fe clusters without spin‐selective behavior. In consequence, the assembled LOB provides ultrahigh energy conversion efficiency of 89.6% at 100 mA g‐1 under a discharge‐charge overpotential of only 0.32 V. This work provides new insights into the spin‐dependent mechanisms of O2/Li2O2 redox reaction, and the strategy of constructing spin catalysts at atomic level.

The Spin-Selective Channels in Fully-Exposed PtFe Clusters Enable Fast Cathodic Kinetics of Li-O2 Batter y.

In Li-O2 batteries (LOBs), the electron transfer between triplet O2 and singlet Li2O2 possesses a spin-dependent character but is still neglected, while the spin-conserved electron transfer without losing phase information should guarantee fast kinetics and reduced energy barriers. Here, we provide a paradigm of spin-selective catalysis for LOB that the ferromagnetic quantum spin exchange interactions between Pt and Fe atoms in fully-exposed PtFe clusters filter directional e-spins for spin-conserved electron transfer at Fe-Fe sites. The kinetics of O2/Li2O2 redox reaction is markedly accelerated as predicted by theoretical calculations, showing dramatically decreased relaxation time of the rate determining step for more than one order of magnitude, compared with the Fe clusters without spin-selective behavior. In consequence, the assembled LOB provides ultrahigh energy conversion efficiency of 89.6% at 100 mA g-1 under a discharge-charge overpotential of only 0.32 V. This work provides new insights into the spin-dependent mechanisms of O2/Li2O2 redox reaction, and the strategy of constructing spin catalysts at atomic level.

Topological magnon in exchange frustration driven incommensurate spin spiral of kagome-lattice YMn6Sn6

YMn6Sn6 consists of two types of Mn-based kagome planes stacked along the c-axis having a complex magnetic interaction. We report a spin reconstruction in YMn6Sn6 from ferromagnetic (FM) into a combination of two incommensurate spin spirals (SSs) originating from two different types of Mn kagome planes driven by frustrated magnetic exchanges along the c-axis with the inclusion of the Hubbard U. The pitch angle and wave vector of the incommensurate SSs are ∼89.3∘ and ∼ (0 0 0.248), respectively, which are in excellent agreement with the experiment. We employ an effective model Hamiltonian constructed out of exchange interactions to capture the experimentally observed nonequivalent nature of the two incommensurate SSs which also explain the FM-SS crossover due to antiferromagntic spin exchange with correlation. We further report the existence of a topological magnon with spin-orbit coupling in the incommensurate SS phase of YMn6Sn6 by calculating the topological invariants and Berry curvature profile. The location of the Dirac magnon in the energy landscape at 73 meV matches with another experimental report. We demonstrate the accuracy of our results by highlighting the experimental features in YMn6Sn6. Published by the American Physical Society 2024

Bandwidth compensation for ultra-high-sensitivity SERF magnetometers in magnetocardiac sensing

The trade-off between sensitivity and bandwidth has limited the clinical application of spin exchange relaxation-free (SERF) atomic magnetometers in magnetocardiac measurements. This research addresses the issue by modeling the SERF magnetometer as a first-order inertial link and proposing a method that integrates transient response with tracking signals. The tracking-differential link enables the simultaneous acquisition of both transient and tracking signals, leading to effective noise suppression. Empirical mode decomposition is employed to extract features and filter out noise, ensuring high signal quality. This method extends the bandwidth of dual-beam magnetometers from 9.77 Hz to 240 Hz and single-beam magnetometers from 139 Hz to 289 Hz, while preserving sensitivities of 1 fT/Hz1/2 and 10 fT/Hz1/2, respectively. This research enables high-bandwidth measurements with sub-femtotesla magnetic field sensitivity, presenting promising application opportunities.

Magnetization Plateaus by the Field-Induced Partitioning of Spin Lattices

To search for a conceptual picture describing the magnetization plateau phenomenon, we surveyed the crystal structures and the spin lattices of those magnets exhibiting plateaus in their magnetization vs. magnetic field curves by probing the three questions: (a) why only certain magnets exhibit magnetization plateaus, (b) why there occur several different types of magnetization plateaus, and (c) what controls the widths of magnetization plateaus. We show that the answers to these questions lie in how the magnets under field absorb Zeeman energy, hence changing their magnetic structures. The magnetic structure of a magnet insulator is commonly described in terms of its spin lattice, which requires the determination of the spin exchanges’ nonnegligible strengths between the magnetic ions. Our work strongly suggests that a magnet under the magnetic field partitions its spin lattice into antiferromagnetic (AFM) or ferrimagnetic fragments by breaking its weak magnetic bonds. Our supposition of the field-induced partitioning of spin lattices into magnetic fragments is supported by the anisotropic magnetization plateaus of Ising magnets and by the highly anisotropic width of the 1/3-magnetization plateau in azurite. The answers to the three questions (a)–(c) emerge naturally by analyzing how these fragments are formed under the magnetic field.

A non-thermal method to maintain alkali vapor density of anti-relaxation coating cell in spin exchange relaxation-free magnetometer

The long-term stability of alkali metal vapor cell density is crucial for the performance of Spin Exchange Relaxation-Free (SERF) magnetometers. This paper addresses the issue of atomic density consistency commonly encountered with OTS and paraffin coatings in current quantum magnetometers. For the first time, the LIAD non-thermal method is applied to SERF magnetometers to maintain the long-term stability of alkali metal density. The study identifies the critical roles of desorption light luminous flux and integrating sphere uniformity in enhancing LIAD effectiveness. A new model based on the absorption spectrum of 85Rb and 87Rb was developed, achieving an R-square value of 0.989 and revealing a rubidium isotopic abundance ratio of 2.8:1, with OTS-coated cells showing the highest density retention. These findings contribute to the advancement of cryogenic SERF magnetometers by providing a deeper understanding of LIAD mechanisms and offering a viable alternative to thermal density control methods.

Single-Step Synthesis of An Ideal Chain Antiferromagnet [H2(4,4'-bipyridyl)](H3O)2Fe2F10 with Spin S=5/2.

One-dimensional (1D) magnets are of great interest owing to their intriguing quantum phenomena and potential application in quantum computing. We successfully synthesized an ideal antiferromagnetic spin S=5/2 chain compound [H2(4,4'-bpy)](H3O)2Fe2F10 (4,4'-bpy=4,4'-bipyridyl) 1, using a single-step low-temperature hydrothermal method under conditions that favors the protonation of the bulky bidentate ligand 4,4'-bpy. Compound 1 consists of well-separated (Fe3+-F-)∞ chains with a large Fe-F-Fe angle of 174.8°. Both magnetic susceptibility and specific heat measurements show that 1 does not undergo a magnetic long-range ordering down to 0.5 K, despite the strong Fe-F-Fe intrachain spin exchange J with J/kB=-16.2(1) K. This indicates a negligibly weak interchain spin exchange J'. The J'/J value estimated for 1 is extremely small (<2.8×10-6), smaller than those reported for all other S=5/2 chain magnets. Our hydrothermal synthesis incorporates both [H2(4,4'-bpy)]2+ and (H3O)+ cations into the crystal lattice with numerous hydrogen bonds, hence effectively separating the (Fe3+-F-)∞ spin chains. This single-step hydrothermal synthesis under conditions favoring the protonation of bulky bidentate ligands offers an effective synthetic strategy to prepare well-separated 1D spin chain systems of magnetic ions with various spin values.

Single‐Step Synthesis of An Ideal Chain Antiferromagnet [H2(4,4′‐bipyridyl)](H3O)2Fe2F10 with Spin S=5/2

AbstractOne‐dimensional (1D) magnets are of great interest owing to their intriguing quantum phenomena and potential application in quantum computing. We successfully synthesized an ideal antiferromagnetic spin S=5/2 chain compound [H2(4,4′‐bpy)](H3O)2Fe2F10 (4,4′‐bpy=4,4′‐bipyridyl) 1, using a single‐step low‐temperature hydrothermal method under conditions that favors the protonation of the bulky bidentate ligand 4,4′‐bpy. Compound 1 consists of well‐separated (Fe3+−F−)∞ chains with a large Fe−F−Fe angle of 174.8°. Both magnetic susceptibility and specific heat measurements show that 1 does not undergo a magnetic long‐range ordering down to 0.5 K, despite the strong Fe−F−Fe intrachain spin exchange J with J/kB=−16.2(1) K. This indicates a negligibly weak interchain spin exchange J′. The J′/J value estimated for 1 is extremely small (&lt;2.8×10−6), smaller than those reported for all other S=5/2 chain magnets. Our hydrothermal synthesis incorporates both [H2(4,4′‐bpy)]2+ and (H3O)+ cations into the crystal lattice with numerous hydrogen bonds, hence effectively separating the (Fe3+−F−)∞ spin chains. This single‐step hydrothermal synthesis under conditions favoring the protonation of bulky bidentate ligands offers an effective synthetic strategy to prepare well‐separated 1D spin chain systems of magnetic ions with various spin values.

Quantum Spin Exchange Interactions Trigger O p Band Broadening for Enhanced Aqueous Zinc-Ion Battery Performance.

The pressing demand for large-scale energy storage solutions has propelled the development of advanced battery technologies, among which zinc-ion batteries (ZIBs) are prominent due to their resource abundance, high capacity, and safety in aqueous environments. However, the use of manganese oxide cathodes in ZIBs is challenged by their poor electrical conductivity and structural stability, stemming from the intrinsic properties of MnO2 and the destabilizing effects of ion intercalation. To overcome these limitations, our research delves into atomic-level engineering, emphasizing quantum spin exchange interactions (QSEI). These essential for modifying electronic characteristics, can significantly influence material efficiency and functionality. We demonstrate through density functional theory (DFT) calculations that enhanced QSEI in manganese oxides broadens the O p band, narrows the band gap, and optimizes both proton adsorption and electron transport. Empirical evidence is provided through the synthesis of Ru-MnO2 nanosheets, which display a marked increase in energy storage capacity, achieving 314.4 mAh g-1 at 0.2 A g-1 and maintaining high capacity after 2000 cycles. Our findings underscore the potential of QSEI to enhance the performance of TMO cathodes in ZIBs, pointing to new avenues for advancing battery technology.

SWAP algorithm for lattice spin models.

We adapted the SWAP molecular dynamics algorithm for use in lattice Ising spin models. We dressed the spins with a randomly distributed length and we alternated long-range spin exchanges with conventional single spin flip Monte Carlo updates, both accepted with a stochastic rule which respects detailed balance. We show that this algorithm, when applied to the bidimensional Edwards-Anderson model, speeds up significantly the relaxation at low temperatures and manages to find ground states with high efficiency and little computational cost. The exploration of spin models should help in understanding why SWAP accelerates the evolution of particle systems and sheds light on relations between dynamics and free-energy landscapes.

Analysis and measurement of magnetic noise for tesla shielding based on superconducting coils applied to SERF magnetometer

Tesla Shielding (TS) is closed superconducting coils composed of superconducting tape, designed to resist changing magnetic fields, thereby achieving magnetic shielding. TS, optically transparent, is suitable for integration with spin exchange relaxation-Free (SERF) magnetometers, thereby improving the sensitivity of SERF magnetometers. However, no prior research has been conducted on the magnetic noise of TS. Noise source identification was conducted on the superconducting tapes used in the TS. We modeled the magnetic noise of superconducting coils, analyzed the the relationship between geometric parameters and magnetic noise of coils, and proposed methods to suppress magnetic noise. Finally, we established a measurement system to measure the magnetic noise of superconducting coils. The results confirm the feasibility of the magnetic noise calculation model and the effectiveness of the methods for suppressing magnetic noise. This study can guide the design of TS, which is important for improving the sensitivity of SERF magnetometers.

Electronic structures, elastic behaviors and magnetic properties of monolayer [formula omitted] and [formula omitted] Ni[formula omitted]I[formula omitted]

This study investigates the electronic structures, elastic behaviors, and magnetic properties of monolayer Ni2I2 in two novel phases, P3̄m1 and P4/nmm, using first-principles calculations and Monte Carlo simulations. The electronic structures of P3̄m1 and P4/nmm phases show half-metallic properties with spin magnetic moments of 0.85 and 0.82 μB respectively. Both phases exhibit mechanical and dynamic stability. The P3̄m1 phase has isotropic elastic properties and good ductility, while the P4/nmm phase shows significant crystallographic anisotropy. The spin exchange coupling constants between the nearest and the next-nearest neighbor Ni ions in the P4/nmm phase are nearly an order of magnitude higher than those in the P3̄m1 phase, with the former having a Curie temperature close to room temperature at 296 K, significantly higher than the 27 K of the latter. The strain modulation range for structural and magnetic phase transitions between the P3̄m1 and P4/nmm phases is provided theoretically.

Synchronous achievement of laser frequency stabilization and tunability via modulation transfer spectroscopy on the rubidium D1 line

In the Spin Exchange Relaxation Free (SERF) magnetometer, the laser frequency must be stabilized at the alkali D1 line and tunable within a range of several gigahertz (GHz). We theoretically and experimentally analyzed the modulated sideband and resonant frequencies on the D1 transition line of rubidium (Rb) atoms using a modulation transfer spectroscopy (MTS) frequency stabilization system. The laser's self-estimated frequency stability shows the Allan deviation of 1.5 × 10−12/τ for resonance peak stabilization and 1.4 × 10−12/τ for sideband stabilization. The spectrum of the modulated laser interacting with the rubidium D1 line exhibits several absorption peaks and MTS signals across a 6 GHz scanning frequency range, which can be used to lock and tune the laser. This method enhances the application of distributed feedback semiconductor lasers in Rb atom-based magnetometers.

Enhancing Magnetic Ordering in Two-Dimensional Metal-Organic Frameworks via Frontier Molecular Orbital Engineering.

Two-dimensional (2D) metal-organic frameworks (MOFs) have promise for use in lightweight permanent magnets in contrast to inorganic solid- or molecule-based magnets, but the realization of 2D MOF magnets with a high ordering temperature is limited by the typically weak spin exchange interactions. Here, we have proposed a frontier molecular orbital engineering strategy for modulating magnetism in 2D MOFs. It shows that the magnetic ground state can be mediated by two intra-atomic spin exchange pathways in organic ligands, akin to the Bloch and Heisenberg models, depending on the shape of the frontier orbitals of the organic ligands. By engineering the shape of the lowest unoccupied molecular orbital (LUMO) via chemical hydrogenation, we achieved a nearly 11-fold increase in the ordering temperature. In particular, a quantitative analysis shows that the ordering temperature increases linearly with the orbital delocalization index of the ligands' LUMO. This work suggests a general frontier orbital engineering approach for modulating the spin exchange interaction in 2D MOF magnets.

Unlocking Lattice Oxygen on Selenide-Derived NiCoOOH for Amine Electrooxidation and Efficient Hydrogen Production.

In pursuit of advancing the electrooxidation of amines, which is typically encumbered by the inertness of C(sp3)-H/N(sp3)-H bonds, our study introduces a high-performance electrocatalyst that significantly enhances the production efficiency of vital chemicals and fuels. We propose a novel electrocatalytic strategy employing a uniquely designed (NixCo1-x)Se2-R electrocatalyst, which is activated through Se-O exchange and electron orbital spin manipulation. This catalyst efficiently generates M4+ species, thus enabling the activation of lattice oxygen and streamlining the electrooxidation of amines. Empirical evidence from isotope labeling, molecular probes, and computational analyses indicates that the electrocatalyst fosters the formation of energetically favorable peroxy radical intermediates, which substantially expedite the reaction kinetics. The refined electrocatalyst achieves an exceptional current density of 20 mA cm-2 at a potential of 1.315 V, with selectivity surpassing 99% for propionitrile, while demonstrating remarkable stability over 560 h. This work emphasizes the criticality of deciphering the fundamental mechanisms of amine electrooxidation and charts a more sustainable pathway for the nitrile and hydrogen production, marking a substantial advancement in the field of electrocatalysis.

Above-room-temperature intrinsic ferromagnetism in ultrathin van der Waals crystal Fe3+xGaTe2

Two-dimensional (2D) van der Waals (vdW) magnets are crucial for ultra-compact spintronics. However, so far, no vdW crystal has exhibited tunable above-room-temperature intrinsic ferromagnetism in the 2D ultrathin regime. Here, we report the tunable above-room-temperature intrinsic ferromagnetism in ultrathin vdW crystal Fe3+xGaTe2 (x = 0 and 0.3). By increasing the Fe content, the Curie temperature (TC) and room-temperature saturation magnetization of bulk Fe3+xGaTe2 crystals are enhanced from 354 to 376 K and 43.9 to 50.4 emu·g−1, respectively. Remarkably, the robust anomalous Hall effect in 3-nm Fe3.3GaTe2 indicates a record-high TC of 340 K and a large room-temperature perpendicular magnetic anisotropy energy of 6.6 × 105 J m−3, superior to other ultrathin vdW ferromagnets. First-principles calculations reveal the asymmetric density of states and an additional large spin exchange interaction in ultrathin Fe3+xGaTe2 responsible for robust intrinsic ferromagnetism and higher TC. This work opens a window for above-room-temperature ultrathin 2D magnets in vdW-integrated spintronics.

A comparison of pulse and CW EPR [formula omitted]-relaxation measurements of an inhomogeneously broadened nitroxide spin probe undergoing Heisenberg spin exchange 2. The intercept discrepancy

Experimental confirmation of a theoretical prediction of a non-linear broadening of the spin packets of nitroxide free radicals due to Heisenberg spin exchange at low concentrations, C, is presented. A recent demonstration that spectra with resolved proton hyperfine structure may be analyzed efficiently and accurately was utilized to confirm the theory. As C→0, a plot of the spin-packet line width (SPW) curves downward due to the presence of proton hyperfine couplings that increase the number of distinguishable quantum spin states. At higher C, the broadening is linear with C and the results for the spin exchange rate constant determined from the slope of the broadening of the average spin-packet line width and electron spin echo measurements are in agreement. It is shown that applying modest digital smoothing does not change the values of the SPW. An example of a practical application of these methods to published work is presented, allowing an enigma to be resolved.

Nature of electrically detected magnetic resonance in highly nitrogen-doped 6H -SiC single crystals

This work focuses on unraveling electron paramagnetic resonance (EPR) and electrically detected magnetic resonance (EDMR) properties of n-type 6H silicon carbide (SiC) single crystals with high concentrations of uncompensated nitrogen (N) donors, which is essential for fundamental understanding of spin-related phenomena, developing spin-based devices, optimizing materials and devices, and advancing research in quantum information and spintronics. Utilizing low-temperature multifrequency EPR spectroscopy (9.4–395.12 GHz), we identified two intense signals labeled as S line and S1 line in the 6H-SiC crystals with ND–NA≈8×1018 and 4×1019cm−3. In addition, in 6H-SiC crystals with ND–NA≈8×1018cm−3, a low-intensity triplet from N donors substituting the quasicubic “k2” nonequivalent position (Nk2) was observed. The S line [g⊥=2.0029(2),g∥=2.0038(2)] was assigned to the exchange interaction of conduction electrons and Nk2, while the S1 line [g⊥=2.0030(2),g∥=2.0040(2)] is caused by the exchange spin coupling of localized N donors at the “k1” and “k2” positions. The S1 line was observed in high-frequency EDMR spectra of 6H-SiC with ND–NA≈8×1018cm−3, and its emergence was explained by an enhancement of the hopping conductivity due to the EPR-induced temperature increase mechanism. No EDMR spectra were found to occur in the 6H-SiC crystals with ND–NA≈4×1019cm−3, which is close to the critical donor concentration value for a semiconductor-metal transition. Thus it can be concluded that this N donor concentration is too high for the appearance of spin-dependent scattering and too low for the emergence of EPR-induced hopping mechanisms in 6H-SiC. Published by the American Physical Society 2024

Hole Spin Coherence in InAs/InAlGaAs Self‐Assembled Quantum Dots Emitting at Telecom Wavelengths

Measurements of the longitudinal and transverse spin relaxation times of holes in an ensemble of vertically tunnel‐coupled self‐assembled InAs/InAlGaAs quantum dots (QDs), emitting in the telecom spectral range, are reported. The spin coherence is determined using the spin mode‐locking method in the inhomogeneous ensemble of QDs. Modeling the signal allows us to extract the hole spin coherence time to be in the range of μs. The longitudinal spin relaxation time μs is measured using the spin inertia method. The parameters investigated allow us to suggest that the main relaxation mechanism at low magnetic fields is related to the electron–hole spin exchange.