Spin-spin Interaction Research Articles

Giant enhancement in coercivity of ferromagnetic α-Fe2O3 nanosheet grown on MoS2

To study the 2D materials, an interface interaction is very important to tune the physical properties because of the large specific surface area. When the antiferromagnetic α-Fe2O3 is grown in a single-crystalline form on a diamagnetic MoS2, enormous changes in magnetic properties are observed in the 2D composite system. Strong ferromagnetism with a giant coercivity of 1.8 T is observed in this single-crystalline α-Fe2O3/MoS2 heterostructure. It is noted that thinner sheets show better coercivity than the thicker sheets, and the coercivity decreases with the increase in temperature. This huge coercivity in larger and thinner single-crystalline α-Fe2O3 sheets grown on a MoS2 arises due to charge transfer from “S” to “Fe” and the surface pinning effect at the interface. A large negative magnetoresistance with a maximum value of 15% is achieved due to the spin-spin interaction, and a positive magnetoresistance is also observed at low field and high temperature as a result of the spin splitting effect.

Spin reorientation transition and spin dynamics study of perovskite orthoferrite TmFeO3 detected by electron paramagnetic resonance.

The temperature-dependent spin-reorientation transition (SRT) and spin interaction mechanism of bulk TmFeO3 were studied by the electron paramagnetic resonance (EPR) method. The combined experimental results of magnetic curves and EPR spectra confirmed that there is an antiferromagnetic transition at 85 K with a reentering ferromagnetic state due to the spin-reorientation behavior. In the high-temperature region of T > 90 K, there are three distinct resonance peaks in the EPR spectrum, which indicates the presence of multiple magnetic phases (canted antiferromagnetic, weak ferromagnetic, and paramagnetic phases). In the low-temperature region (T < 85 K), the temperature dependence of the EPR linewidth, effective g-factor, and intensity can be used to infer a strong spin-lattice correlation. Different magnetic interactions such as Fe3+-Fe3+, Fe3+-Tm3+, and Tm3+-Tm3+ lead to a paramagnetic-canted antiferromagnetic phase at T > 85 K, with SRT between 85-65 K and ferromagnetic interaction at the lower temperature, respectively. Above 90 K, we find that the spin relaxation mechanism is determined by the mixture of spin-spin and spin-lattice interactions. Below 85 K, the transverse relaxation rate increases with the decrease in temperature, which is consistent with the weakening of the fluctuating internal field in this temperature region. This EPR detection provides a new method to clarify the strong spin coupling in antiferromagnetic materials.

Synthesis, crystal structure, and magnetic properties of oxynitride perovskites SrMn0.2M0.8O2.6N0.4 (M = Nb, Ta).

Complex perovskites SrMn0.2Nb0.8O2.6N0.4 and SrMn0.2Ta0.8O2.6N0.4 were synthesized; these are rare examples of octahedral Mn2+ in oxynitride perovskites. Joint Rietveld refinement of neutron and X-ray data revealed that SrMn0.2Nb0.8O2.6N0.4 and SrMn0.2Ta0.8O2.6N0.4 had orthorhombic symmetries, in contrast with those of analogous perovskites SrM'0.2M0.8O3-xNx (M' = Li, Na, Mg; M = Nb, Ta), which are all tetragonal. Both SrMn0.2Nb0.8O2.6N0.4 and SrMn0.2Ta0.8O2.6N0.4 exhibited paramagnetic behavior with effective magnetic moments of 5.60μB and 5.94μB, respectively, consistent with a high-spin Mn2+ (d5, S = 5/2) state. The Weiss constants were -24.7 K for SrMn0.2Nb0.8O2.6N0.4 and -15.4 K for SrMn0.2Ta0.8O2.6N0.4, indicating the presence of weak antiferromagnetic spin-spin interactions. The band gaps of SrMn0.2Nb0.8O2.6N0.4 and SrMn0.2Ta0.8O2.6N0.4 were determined to be 1.75 eV and 2.2 eV, respectively, suggesting that the Mn 3d electrons were essentially localized.

Theoretical investigation of temperature and frequency dependent ferroelectric properties in Rochelle salt (RS) crystal

By adding cubic-order and quartic-order phonon anharmonic interactions terms with spin-spin interactions terms, extra interaction term and external electric field has been considered in two-sublattice pseudospin lattice coupled mode (PLCM) model for phase transitions and dielectric properties of order-disorder Rochelle salt (RS) crystal. Using double-time temperature Green function method, we obtain the expression for Soft mode frequency, dielectric constant and tangent loss have been obtained for Rochelle salt crystal. Numerical calculations will be performed by fitting model values of various parameters in the above expressions for RS crystal. Present theoretical results agree well with experimental results of Sandy and Jones.

Copper(II) Hydrazone Complexes with Different Nuclearities and Geometries: Synthesis, Structural Characterization, Antioxidant Sod Activity and Antiproliferative Properties

New copper(II) hydrazone complexes with (Z)-2-(phenyl(2-(pyridin-2-yl)hydrazono)methyl)pyridine (L) were synthesized and characterized using various physicochemical methods. The geometry of complexes can be classified as mononuclear and binuclear. The complex 1 [Cu(L)Cl2] is mononuclear whereas solid-state structures of complex 2 contains a mixture of co-crystals of mono- and binuclear complexes 2a [Cu(L)(H2O)(SO4)] and 2b [(L)Cu-(SO4)2-Cu(L)]. The molecular structure of 2 contains two units of mononuclear complex 2a and two units of binuclear complex 2b. Copper contains in all mono- and binuclear complexes are in a distorted square pyramidal geometry. The present study indicates that complexes having different nuclearities and geometries can be achieved by changing synthetic conditions and methods. Variable temperature magnetic susceptibility measurements of the complexes have shown a weak anti-ferromagnetic interaction. The presence of weak anti-ferromagnetic interactions is mediated by intermolecular hydrogen bonding in 1 and by symmetric sulfate bridge in 2, respectively. The Epr spectra in polycrystalline state of 1 and 2 exhibited a broad signal at 2.149 due to the spin-spin interactions between two copper(II) ions. The cyclic voltammograms of complexes 1 and 2 in DMSO gave two irreversible redox waves. Density functional theory (DFT) calculations were evaluated in the study involved the molecular specification for the use of B3LYP/LANL2DZ formalism for copper atom and B3LYP/6-31G for the remaining atoms. Both complexes catalyzed the dismutation of superoxide ( 02). Furthermore, copper complexes and ligand were tested to explore the anticancer properties. Promising cytotoxicity of synthesized compounds was observed on the selected cancerous cell line of neuroblastoma, lung carcinoma, hepatocellular carcinoma and breast cancer.

Resonant microwave-mediated interactions between distant electron spins

Nonlocal qubit interactions are a hallmark of advanced quantum information technologies1-5. The ability to transfer quantum states and generate entanglement over distances much larger than qubit length scales greatly increases connectivity and is an important step towards maximal parallelism and the implementation of two-qubit gates on arbitrary pairs of qubits6. Qubit-coupling schemes based on cavity quantum electrodynamics2,7,8 also offer the possibility of using high-quality-factor resonators as quantum memories3,9. Extending qubit interactions beyond the nearest neighbour is particularly beneficial for spin-based quantum computing architectures, which are limited by short-range exchange interactions10. Despite the rapidly maturing device technology for silicon spin qubits11-16, experimental progress towards achieving long-range spin-spin coupling has so far been restricted to interactions between individual spins and microwave photons17-20. Here we demonstrate resonant microwave-mediated coupling between two electron spins that are physically separated by more than four millimetres. An enhanced vacuum Rabi splitting is observed when both spins are tuned into resonance with the cavity, indicating a coherent interaction between the two spins and a cavity photon. Our results imply that microwave-frequency photons may be used to generate long-range two-qubit gates between spatially separated spins.

Spin-Phonon Interfaces in Coupled Nanomechanical Cantilevers.

Coupled micro- and nanomechanical oscillators are of fundamental and technical interest for emerging quantum technologies. Upon interfacing with long-lived solid-state spins, the coherent manipulation of the quantum hybrid system becomes possible even at ambient conditions. Although the ability of these systems to act as a quantum bus inducing long-range spin-spin interactions has been known, the possibility to coherently couple electron/nuclear spins to the common modes of multiple oscillators and map their mechanical motion to spin-polarization has not been experimentally demonstrated. We here report experiments on interfacing spins to the common modes of a coupled cantilever system and show their correlation by translating ultralow forces induced by radiation from one oscillator to a distant spin. Further, we analyze the coherent spin-spin coupling induced by the common modes and estimate the entanglement generation among distant spins.

Microwave properties of Mg–Zn ferrite deposited by the thermal evaporation technique

Spinel ferrite samples of Mg0.6Zn0.4Fe2O4 were fabricated using the sol-gel technique. Thermal evaporation in the vacuum technique was used to deposit an (850, 350) ± 30 nm thick layer of this ferrite powder on the glass substrates. The results of XRD, SEM, and AFM showed that the prepared thin films are polycrystalline and nano-sized, with homogeneous particle size and good distribution. The porosity of the films was small, and the occurrence of microstrain on the crystals was observed because of the sintering temperature.Ferrite's thin-film thickness effect on the microwave properties was studied using the Vector Network Analyzer (VNA) in the X-band frequency range of 8–12.5 GHz.The microwave properties increased with increasing film thickness due to the spin-spin interaction process between the incidence waves and the spin-wave. High stability of the reflection, absorption and very high proportions for the two thicknesses is obtained. The resonance peaks for the thin films of spinel ferrite appeared at frequencies of 8.2, 8.4, 8.6, 9.2, 9.8, 10.0, 10.2, 11.2, 11.4, 12.01, and 12.2 GHz.

Robust scalable architecture for a hybrid spin-mechanical quantum entanglement system

Practical quantum information technique requires a large scalable quantum network. We proposed a hybrid system for deterministic scalable spin entanglement network based on nitrogen-vacancy (NV) centers in diamond coupling with carbon nanotube. The fault-tolerant entangled gate between two remote NV centers can be realized with vibrating nanotube assisted spin-spin interaction with current experimental technology. This interaction can be directly generalized to multi-NV-center entanglement architecture. Moreover, the effects of the single spin dephasing (SSD) and spin cross relaxation (SCR) on this state generation process were analyzed in detail. We found that the decay rate scales as ${N}^{2}$, corresponding to the number of independent decoherence channels. However, by employing dressed state protection and independent tunable interaction method, SSD and SCR can be mitigated efficiently and the decay rate of the generated multi-NV-center entanglement scales as $N$, which boosts the size of the entanglement network up to hundreds of qubits. Such a hybrid quantum system compatible with current topological protection provides a useful platform for the investigation of quantum computation.

Description of mass spectrum of Bc-meson family

Purpose. Calculation of the spectrum of masses of system ¯ bc consisting of two heavy b and c quarks ( B c mesons family) within the potential models of heavy quarkonium. In particular, to calculate the spin-dependent splitting of the energy S and P levels of a given of heavy mesons family. Investigate the dependence of the energy splitting magnitude on the parameters of the interaction potential between the quarks. Methods. The spin-dependent splittings of the S and P energy levels caused by spin-spin, spin-orbital and tensor interactions in the framework of the Breit-Fermi quasi-relativistic approximation with the screened quark interaction potential are calculated. Wave functions and matrix elements of spin-spin, spin-orbital and tensor interactions were calculated numerically. Results. It is found that the energies of the S and P levels and the magnitude of the «fine» and «hyperfine» splitting depend essentially on the mixing constant λ of scalar and vector long-range screening potential and the constant of the strong interaction α s (whose value is almost unchanged within the B c meson family). Increasing the contribution of the Lorentz vector potential to operators of spin-orbital, spin-spin and tensor interactions leads to increase of the magnitude of the corresponding splittings of energy levels. The obtained value of the mixing constant λ = 0 . 3 indicates that the confined screened potential has a predominantly scalar Lorentz nature (about 70 %), and the Coulomb-like potential of one-gluon exchange is purely a Lorentz vector. Conclusions. The calculated energy levels of the system ¯ bc can be used for experimental search for B c mesons.

Quantum information processing with closely-spaced diamond color centers in strain and magnetic fields [Invited

Electron and nuclear spins of diamond nitrogen-vacancy (NV) centers are good candidates for quantum information processing as they have long coherence time and can be initialized and read out optically. However, creating a large number of coherently coupled and individually addressable NV centers for quantum computing has been a big challenge. Here we propose methods to use high-density diamond NV centers coupled by spin-spin interaction with an average separation on the order of 10 nm for quantum computing. We propose to use a strain gradient to encode the position information of each NV center in the energy level of its excited electron orbital state, which causes a shift of its optical transition frequency. With such strain encoding, more than 100 closely-packed NV centers below optical diffraction limit can be read out individually by resonant optical excitation. A magnetic gradient will be used to shift the electron spin resonant (ESR) frequencies of NV centers. Therefore, the spin state of each NV center can be individually manipulated and different NV centers can be selectively coupled. A universal set of quantum operations for two-qubit and three-qubit system is introduced by careful design of external drives. Moreover, entangled states with multiple qubits can be created by this protocol, which is a major step towards quantum information processing with solid-state spins.

Hidden-charm and hidden-bottom molecular pentaquarks in chiral effective field theory

The newly observed Pc(4312), Pc(4440) and Pc(4457) at the LHCb experiment are very close to the {varSigma}_coverline{D} and {varSigma}_c{overline{D}}^{ast } thresholds. In this work, we perform a systematic study and give a complete picture on the interactions between the {varSigma}_c^{left(ast right)} and {overline{D}}^{left(ast right)} systems in the framework of heavy hadron chiral effective field theory, where the short-range contact interaction, long-range one-pion-exchange contribution, and intermediate-range two-pion-exchange loop diagrams are all considered. We first investigate the three Pc states without and with considering the Λc contribution in the loop diagrams. It is difficult to simultaneously reproduce the three Pcs unless the Λc is included. The coupling between the {varSigma}_c^{left(ast right)}{overline{D}}^{left(ast right)} and {Lambda}_c{overline{D}}^{left(ast right)} channels is crucial for the formation of these Pcs. Our calculation supports the Pc(4312), Pc(4440) and Pc(4457) to be the S-wave hidden-charm {left[{varSigma}_coverline{D}right]}_{J=1/2}^{I=1/2},{left[{varSigma}_c{overline{D}}^{ast}right]}_{J=1/2}^{I=1/2} and {left[{varSigma}_c{overline{D}}^{ast}right]}_{J=3/2}^{I=1/2} molecular pentaquarks, respectively. Our calculation disfavors the spin assignment {J}^P=frac{1^{-}}{2} for Pc(4457) and {J}^P=frac{3^{-}}{2} for Pc(4440), because the excessively enhanced spin-spin interaction is unreasonable in the present case. We obtain the complete mass spectra of the {left[{varSigma}_c^{left(ast right)}{overline{D}}^{left(ast right)}right]}_J systems with the fixed low energy constants. Our result indicates the existence of the {left[{varSigma}_c^{ast }{overline{D}}^{ast}right]}_Jleft(J=frac{1}{2},frac{3}{2},frac{5}{2}right) hadronic molecules. The previously reported Pc(4380) might be a deeper bound one. Additionally, we also study the hidden-bottom {varSigma}_b^{left(ast right)}{B}^{left(ast right)} systems, and predict seven bound molecular states, which could serve as a guidance for future experiments. Furthermore, we also examine the heavy quark symmetry breaking effect in the hidden-charm and hidden-bottom systems by taking into account the mass splittings in the propagators of the intermediate states. As expected, the heavy quark symmetry in the bottom cases is better than that in the charmed sectors. We notice that the heavy quark symmetry in the {varSigma}_coverline{D} and {varSigma}_c^{ast}overline{D} systems is much worse for some fortuitous reasons. The heavy quark symmetry breaking effect is nonnegligible in predicting the effective potentials between the charmed hadrons.

Growth, structure and thermal stability of quasicrystalline Al–Pd–Mn–Ga thin films

Growth of Al–Pd–Mn–Ga quasicrystalline thin film is hindered by the low melting temperature of Ga (30 °C) and the formation of residual binary phases. In this study, a stable icosahedral film with a composition near Al67.5Pd19Mn7.5Ga5.7 has been achieved using the co-sputtering of Al64.9Pd20.7Mn8.4Ga6 and Al materials followed by ex-situ annealing. The increase in the 6d lattice parameter from 6.45 to 6.48 Å of icosahedral phases suggested that Ga (+1) successfully replaced Al(+3) in the composition. The temperature-dependent XRD study (from RT to 700 °C) reveals that the icosahedral phase found only in a narrow temperature window of 350 – 450 °C. Interestingly, Al63Pd18Mn7.5Ga6 quasicrystalline thin film exhibits cluster spin glass behaviour due to spin-spin interaction of localized Mn ions. These stable icosahedral thin films with crack-free well-defined surfaces can be useful for potential surface-related applications.

Evolution of two-time correlations in dissipative quantum spin systems: Aging and hierarchical dynamics

We consider the evolution of two-time correlations in the quantum XXZ spin-chain in contact with an environment causing dephasing. Extending quasi-exact time-dependent matrix product state techniques to consider the dynamics of two-time correlations within dissipative systems, we uncover the full quantum behavior for these correlations along all spin directions. Together with insights from adiabatic elimination and kinetic Monte Carlo, we identify three dynamical regimes. For initial times, their evolution is dominated by the system unitary dynamics and depends on the initial state and the Hamiltonian parameters. For weak spin-spin interaction anisotropy, after this initial dynamical regime, two-time correlations enter an algebraic scaling regime signaling the breakdown of time-translation invariance and the emergence of aging. For stronger interaction anisotropy, these correlations first go through a stretched exponential regime before entering the algebraic one. Such complex relaxation arises due to the competition between the proliferation dynamics of energetically costly excitations and their motion. As a result, dissipative heating dynamics of spin systems can be used to probe the entire spectrum of the underlying Hamiltonian.

Ferromagnetic ordering in cobalt doped methylammonium lead bromide: An ab-initio study

Ferromagnetic ordering has been theoretically observed in Co-doped methylammonium lead bromide (MAPbBr3) using first principles approach for the first time. The methylammonium lead bromide system with Co-doping at Pb-site along with Pb-vacancy becomes a p-type semiconductor with significantly large magnetic moment. The spin polarized total and partial density of states (DOS) have been analysed to find out the source of the induced magnetic moment. Spin-spin interaction investigation reveals that the magnetism in Co-doped MAPbBr3 system favours ferromagnetic spin-ordering. This direct band gap Co-doped MAPbBr3 could be a suitable material for spintronics application.

Synthesis and structure of fluorinated tetraphenylantimony β-diketonates

The reactions of pentaphenylantimony with fluorinated β-diketones have been studied. The structure of the obtained compounds has been determined by the X-ray diffraction method and confirmed by IR, 1H, 13C and 19F NMR spectroscopy. According to X-ray diffraction analysis data, the reaction products are tetraphenylantimony 1,1,1-trifluoropentane-2,4-dionate (3а), 1,1,1-trifluoro-5,5-dimethylhexane-2,4-dionate (3b) and 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyloctane-3,5-dionate (3c): Ph4Sb[OC(R)CHC(R')O] (R = CH3 (3a), Bu-t (3b, 3c); R' = CF3 (3a, 3b), C3F7 (3c)), the antimony atoms in the molecules have a distorted octahedral coordination. The CSbC angles equal 158.26(14)°, 157.90(9)°, 157.75(15)° (3 a‒c), the CSbO angles are 164.70(12)°, 168.05(12)° (3a); 165.47(9)°, 167.37(7)° (3b); 164.96(14)°, 169.66(13)° (3c). The Sb–C bond lengths vary in the ranges of 2.142(4)–2.164(4) Å, 2.144(2)–2.160(2) Å, 2.142(4)–2.160(4) Å (3 a‒c), the Sb–O distances are 2.358(3), 2.333(3) Å (3a); 2.306(2), 2.339(2) Å (3b); 2.376(3), 2.289(3) Å (3c). The 3a and 3b13C NMR spectra contain short spin-spin interactions between carbon and fluorine atoms with a large direct spin-spin coupling constant, 1JCF ≈ 286.0 Hz, which are characteristic for fluorinated compounds.

Coupling Constants, High Spin, and Broken Symmetry States of Organic Radicals: an Assessment of the Molecules-in-Molecules Fragmentation-Based Method.

We extend the application of our multilayer molecules-in-molecules (MIM) fragmentation-based method to the study of open-shell systems, particularly organic radicals. A test set of organic mono-, di- and polyradicals with a wide range in size, containing up to 360 atoms, was investigated. Total energies computed with MIM using density functional theory (DFT) were compared with full, unfragmented energies to assess the performance of MIM and to develop a systematic protocol for the treatment of large radical systems. More specifically, a two-layer (MIM2) model with a fragmentation scheme along the backbone involving covalently bonded dimers, trimers, or tetramers was considered, with DFT at a smaller basis set serving as the low level of theory. The MIM method was evaluated on the high-spin state and several possible broken-symmetry (BS) states for di- and polyradicals. When relevant spin-spin interactions were considered, the errors in total energies were less than 1 kcal mol-1. In addition, the applicability of MIM2 was extended to predict the intersite magnetic exchange coupling constants (J), which were compared with reference values. Further, since the energy levels derived from Hamiltonian diagonalization are physically more meaningful, the calculated J values estimated from the BS-DFT methodology were used to obtain the lower spin state energies of the polyradicals. The difference in calculated total energies of the lower spin state between full and MIM2 lie within 1 kcal mol-1 in the majority of these cases. Our rigorous, quantum chemical study demonstrates that MIM can be successfully applied to the study of large organic radicals reliably and accurately within the framework of BS-DFT.

Long-distance entangling gates between quantum dot spins mediated by a superconducting resonator

Recent experiments with silicon qubits demonstrated strong coupling of a microwave resonator to the spin of a single electron in a double quantum dot, opening up the possibility of long-range spin-spin interactions. We present our theoretical calculation of effective interactions between distant quantum dot spins coupled by a resonator, and propose a protocol for fast, high-fidelity two-qubit gates consistent with experimentally demonstrated capabilities. Our simulations show that, in the presence of noise, spin-spin entangling gates significantly outperform cavity-mediated gates on charge qubits.

Collective modes in pumped unconventional superconductors with competing ground states

Motivated by the recent development of terahertz pump-probe experiments, we investigate the short-time dynamics in superconductors with multiple attractive pairing channels. Studying a single-band square lattice model with spin-spin interaction as an example, we find the signatures of collective excitations of the pairing symmetries (known as Bardasis-Schrieffer modes) as well as the order parameter amplitude (Higgs mode) in the short-time dynamics of the spectral gap and quasiparticle distribution after an excitation by a pump pulse. We show that the polarization and intensity of the pulse can be used to control the symmetry of the non-equilibrium state as well as frequencies and relative intensities of the contributions of different collective modes. We find particularly strong signatures of the Bardasis-Schrieffer mode in the dynamics of the quasiparticle distribution function. Our work shows the potential of modern ultrafast experiments to address the collective excitations in unconventional superconductors and highlights the importance of sub-dominant interactions for the non-equilibrium dynamics in these systems.

Weak coupling magnetism of the ionic Kondo lattice model

We consider a one-dimensional ionic Kondo lattice model, which consists of a hopping term, a local spin-spin interaction, and an alternating one-particle potential. With this model, which is feasible with cold atom setups, we show that it is possible to obtain a quasi-long-range magnetic order for small local couplings, using the density matrix renormalization group method. We found a quasi-long-range antiferromagnetic phase, which is absent in the original model but common for Kondo lattice materials. For weak local couplings and potentials of great strength, we found a quasi-long-range ferromagnetic-antiferromagnetic ground state crossover when the global commensurate density increases.