Antiferromagnetic Spin-exchange Interaction Research Articles

Interlayer-Coupling-Driven High-Temperature Superconductivity in La_{3}Ni_{2}O_{7} under Pressure.

The newly discovered high-temperature superconductivity in La_{3}Ni_{2}O_{7} under pressure has attracted a great deal of attention. The essential ingredient characterizing the electronic properties is the bilayer NiO_{2} planes coupled by the interlayer bonding of 3d_{z^{2}} orbitals through the intermediate oxygen atoms. In the strong coupling limit, the low-energy physics is described by an intralayer antiferromagnetic spin-exchange interaction J_{∥} between 3d_{x^{2}-y^{2}} orbitals and an interlayer one J_{⊥} between 3d_{z^{2}} orbitals. Taking into account Hund's rule on each site and integrating out the 3d_{z^{2}} spin degree of freedom, the system reduces to a single-orbital bilayer t-J model based on the 3d_{x^{2}-y^{2}} orbital. By employing the slave-boson approach, the self-consistent equations for the bonding and pairing order parameters are solved. Near the physically relevant 1/4-filling regime (doping δ=0.3∼0.5), the interlayer coupling J_{⊥} tunes the conventional single-layer d-wave superconducting state to the s-wave one. A strong J_{⊥} could enhance the interlayer superconducting order, leading to a dramatically increased T_{c}. Interestingly, there could exist a finite regime in which an s+id state emerges.

Theoretical study on the magnetic properties of cathode materials in the lithium-ion battery.

The layered LiMO2 (M = Co, Ni, and Mn) materials are commonly used as the cathode materials in the lithium-ion battery due to the distinctive layer structure for lithium extraction and insertion. Although their electrochemical properties have been extensively studied, the structural and magnetic properties of LiNiO2 are still under considerable debate, and the magnetic properties of monoclinic LiMnO2 are seldom reported. In this work, a detailed study of LiNiO2, LiMnO2, and a half-doped material LiNi0.5Mn0.5O2 is performed via both first-principles calculations and Monte Carlo simulations based on the effective spin Hamiltonian model. Through considering different structures, it is verified that a structure with a zigzag-type pattern is the most stable one of LiNiO2. Moreover, in order to figure out the magnetic properties, the spin exchange interactions are calculated, and then magnetic ground states are predicted in these three systems. The results show that LiNiO2 forms a spiral order that is caused by the competition from both the short-range and long-range spin exchange interactions, whereas the magnetic ground state of LiMnO2 is collinearly antiferromagnetic due to its nearest and next-nearest neighbor antiferromagnetic spin exchange interactions. However, LiNi0.5Mn0.5O2 is collinearly ferrimagnetic because of the ferromagnetic nearest neighbor Ni-Ni and Mn-Mn exchange interactions. Our work demonstrates the competition between the different exchange interactions in these cathode materials, which may be relevant to the performance of the lithium-ion battery.

Schrieffer-Wolff transformations for experiments: Dynamically suppressing virtual doublon-hole excitations in a Fermi-Hubbard simulator

In strongly interacting systems with a separation of energy scales, low-energy effective Hamiltonians help provide insights into the relevant physics at low temperatures. The emergent interactions in the effective model are mediated by virtual excitations of high-energy states: For example, virtual doublon-hole excitations in the Fermi-Hubbard model mediate antiferromagnetic spin-exchange interactions in the derived effective model, known as the $t-J-3s$ model. Formally this procedure is described by performing a unitary Schrieffer-Wolff basis transformation. In the context of quantum simulation, it can be advantageous to consider the effective model to interpret experimental results. However, virtual excitations such as doublon-hole pairs can obfuscate the measurement of physical observables. Here we show that quantum simulators allow one to access the effective model even more directly by performing measurements in a rotated basis. We propose a protocol to perform a Schrieffer-Wolff transformation on Fermi-Hubbard low-energy eigenstates (or thermal states) to dynamically prepare approximate $t-J-3s$ model states using fermionic atoms in an optical lattice. Our protocol involves performing a linear ramp of the optical lattice depth, which is slow enough to eliminate the virtual doublon-hole fluctuations but fast enough to freeze out the dynamics in the effective model. We perform a numerical study using exact diagonalization and find an optimal ramp speed for which the state after the lattice ramp has maximal overlap with the $t-J-3s$ model state. We compare our numerics to experimental data from our Lithium-6 fermionic quantum gas microscope and show a proof-of-principle demonstration of this protocol. More generally, this protocol can be beneficial to studies of effective models by enabling the suppression of virtual excitations in a wide range of quantum simulation experiments.

Collective excitations in cigar-shaped spin-orbit-coupled spin-1 Bose-Einstein condensates

We study theoretically the collective excitations of a spin-orbit-coupled spin-1 Bose-Einstein condensate with antiferromagnetic spin-exchange interactions in a cigar-shaped trapping potential at zero and finite temperatures using the Hartree-Fock-Bogoliubov theory with Popov approximation. The collective modes at zero temperature are corroborated by real-time evolution of the ground state subjected to a perturbation suitable to excite a density or a spin mode. We also calculate a few low-lying modes analytically and find very good agreement with the numerical results. We confirm the presence of excitations belonging to two broad categories, namely, density and spin excitations, based on the calculation of dispersion. The degeneracy between a pair of spin modes is broken by the spin-orbit coupling. At finite temperature, spin and density excitations show qualitatively different behavior as a function of temperature.

Interaction of pseudohalides copper(II) complexes of hydrazide ligand with DNA: synthesis, spectral characterization, molecular docking simulations and superoxide dismutase activity

A new class of mono- and binuclear complexes [Cu(L)(ClO4)(H2O)] 1, [(Cu)(L)(N3)]2 2, [(Cu)(L)(OCN)]2 3, and [(Cu)(L)(CNS)]2 4, have been synthesized (where HL = (E)-N′-(phenyl(pyridin-2-yl)methylene)thiophene-2-carbohydrazide). All complexes have been characterized by elemental analysis and spectroscopic techniques. The crystalline nature of complexes was investigated by powder X-ray diffraction techniques. Polycrystalline Epr spectra with a well-defined half-field signal of complexes 2–4 suggested the intra exchanged-coupled systems. The electrochemical nature of all complexes was examined using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The room temperature magnetic moment (μeff = 1.47–1.63 BM) for binuclear complexes reveals the presence of weak antiferromagnetic spin-exchange interactions between copper(II) ions. The geometrical structural index (τ5) suggests that the geometries around copper(II) ion remains distorted square pyramidal in each copper. All synthesized complexes and DNA were simulated by molecular docking to understand the binding of complexes with DNA. The superoxide dismutase activity (SOD) of all complexes was investigated.

Tetra-MnIII-Containing 30-Tungsto-4-phosphate, [MnIII4(H2O)2(P2W15O56)2]12-: Synthesis, Structure, XPS, Magnetism, and Electrochemical Study.

Reaction of the mixed-valent Mn12-acetato complex [MnIII8MnIV4O12(CH3COO)16(H2O)4] with the trilacunary Wells-Dawson-type heteropolytungstate [P2W15O56]12- in acidic acetate solution (pH 1.1) resulted in the tetra-MnIII-containing polyanion [MnIII4(H2O)2(P2W15O56)2]12- (1). Single-crystal XRD on Na12[MnIII4(H2O)2(P2W15O56)2]·84H2O (1a) revealed that four MnIII ions form a rhombic Mn4O16 core encapsulated by two [P2W15O56]12- units. X-ray photoelectron spectroscopy (XPS) data confirm the +3 oxidation state of the four manganese ions in 1. Magnetic measurements from 1.8-300 K in a 100 Oe magnetic field allowed for the extraction of full fitting parameters from the susceptibility data for 1. The negative Ja value (Ja = -2.16 ± 0.08 K, Jb = 3.24 ± 1.73 K, g = 2.35 ± 0.040, and ρ = 0.34 ± 0.03) suggests a dominant antiferromagnetic spin exchange interaction between the four MnIII ions, with the positive Jb being an accompanying result of Ja. Electrochemical studies revealed a reversible MnIV/MnIII redox couple in 1 at the +0.80 to +1.1 V potential region with E1/2 = +0.907 V.

Synthesis and Magnetic Properties of the Ternary Oxofluoride Fe3Sb4O6F6

The new compound Fe3Sb4O6F6 was prepared by hydrothermal synthesis and its crystal structure was determined from single‐crystal X‐ray diffraction data. The synthesis was made under slightly basic conditions to prevent oxidation of Fe2+ to Fe3+. The compound crystallizes in the cubic space group I‐43m with separate crystallographic sites for Fe2+ and Sb3+. Fe3Sb4O6F6 is isostructural with M3Sb4O6F6 (M = Co, Ni, Zn). The crystal structure is comprising distorted [FeO2F4] octahedra connected via corner sharing at F‐atoms and [SbO3] trigonal pyramids that form [Sb4O6] units that connect via O‐atoms to the Fe‐atoms. Mössbauer spectroscopy measurements on the hydrothermal synthesis products prove the majority phase contains Fe in the oxidation state +2. Powder X‐ray diffraction suggests that an additional phase of the Mössbauer sample containing Fe3+ can be attributed to FeSbO2F2 as secondary phase. Fe3Sb4O6F6 exhibits antiferromagnetic order below ca. 72 K succeeded by a second magnetic phase transition at ca. 30 K. Strong antiferromagnetic spin‐exchange interaction is attributed to 180° Fe–F–Fe superexchange pathways identified in the crystal structure.

Spin excitations in dipolar spin-1 condensates

We investigate the low-lying spin excitation of a trapped dipolar spin-1 condensate with antiferromagnetic spin-exchange interactions by numerically solving the Bogoliubov--de Gennes equations. We explore the behavior of the excited modes with different dipolar interaction strength and in different trap geometries. We also discuss the origin of the Nambu-Goldstone (NG) zero modes in different phases by analyzing the broken continuous symmetries of the ground-state wave function. In particular, we find a quasi-NG mode in the antiferromagnetic phase. These studies lead to the discovery of an unusual quantum phase and the exact critical trap aspect ratio for one of the phase transitions.

Inverse scattering transform and soliton solutions for square matrix nonlinear Schrödinger equations with non-zero boundary conditions

The inverse scattering transform (IST) with non-zero boundary conditions at infinity is developed for an m×m matrix nonlinear Schrödinger-type equation which, in the case m=2, has been proposed as a model to describe hyperfine spin F=1 spinor Bose–Einstein condensates with either repulsive interatomic interactions and anti-ferromagnetic spin-exchange interactions (self-defocusing case), or attractive interatomic interactions and ferromagnetic spin-exchange interactions (self-focusing case). The IST for this system was first presented by Ieda et al. (2007) , using a different approach. In our formulation, both the direct and the inverse problems are posed in terms of a suitable uniformization variable which allows to develop the IST on the standard complex plane, instead of a two-sheeted Riemann surface or the cut plane with discontinuities along the cuts. Analyticity of the scattering eigenfunctions and scattering data, symmetries, properties of the discrete spectrum, and asymptotics are derived. The inverse problem is posed as a Riemann–Hilbert problem for the eigenfunctions, and the reconstruction formula of the potential in terms of eigenfunctions and scattering data is provided. In addition, the general behavior of the soliton solutions is analyzed in detail in the 2 × 2 self-focusing case, including some special solutions not previously discussed in the literature.

Synthesis, characterization, and magnetochemical properties of two Mn4 clusters derived from 2-pyridinecarboxaldehyde Schiff base ligands

Two tetranuclear manganese complexes, [Mn4(L1)6](ClO4)2⋅2.75H2O (1) [HL1 = 4-methyl-2-((pyridin-2-ylmethylene)amino)phenol] and [Mn4(L2)4(NO3)3(OH)]⋅pz⋅3H2O (2) [HL2 = (1H-pyrazol-1-yl)(pyridin-2-yl)methanol, pz = pyrazole], have been synthesized and characterized by IR spectroscopy, elemental analysis, single-crystal X-ray diffraction, and magnetic measurements. The structural analysis revealed that the central manganese ion is linked with three apical manganese ions through six phenoxo-bridges creating a Mn4O6 core for 1; 2 has a cubane-like topology with the Mn(II) ions and the deprotonated oxygens from L2 alternatively occupying vertices. The magnetic studies indicated a weak ferromagnetic coupling interaction (J = 0.48 ± 0.087 cm−1, g = 2.00, θ = −0.78 K) for 1 and a weak antiferromagnetic spin-exchange interaction (J1 = −0.50 ± 0.075 cm−1, J2 = −0.13 ± 0.082 cm−1, g = 1.98) between Mn(II) ions for 2. The magnetostructural correlations of the two Mn4 clusters have been discussed tentatively.

X-ray characterization and magnetic properties of dioxygen-bridged Cu(II) and Mn(III) Schiff base complexes.

The coordination chemistry of multinuclear metal compounds is important because of their relevance to the multi-metal active sites of various metalloproteins and metalloenzymes. Multinuclear Cu(II) and Mn(III) compounds are of interest due to their various properties in the fields of coordination chemistry, inorganic biochemistry, catalysis, and optical and magnetic materials. Oxygen-bridged binuclear Mn(III) complexes generally exhibit antiferromagnetic interactions and a few examples of ferromagnetic interactions have also been reported. Binuclear Cu(II) complexes are important due to the fact that they provide examples of the simplest case of magnetic interaction involving only two unpaired electrons. Two novel dioxygen-bridged copper(II) and manganese(III) Schiff base complexes, namely bis(μ-4-bromo-2-{[(3-oxidopropyl)imino]methyl}phenolato)dicopper(II), [Cu2(C10H10BrNO2)2], (1), and bis(diaqua{4,4'-dichloro-2,2'-[(1,1-dimethylethane-1,2-diyl)bis(nitrilomethanylylidene)]diphenolato}manganese(III)) bis{μ-4,4'-dichloro-2,2'-[(1,1-dimethylethane-1,2-diyl)bis(nitrilomethanylylidene)]diphenolato}bis[aquamanganese(III)] tetrakis(perchlorate) ethanol disolvate, [Mn(C18H16Cl2N2O2)(H2O)2]2[Mn2(C18H16Cl2N2O2)2(H2O)2](ClO4)4·2C2H5OH, (2), have been synthesized and single-crystal X-ray diffraction has been used to analyze their crystal structures. The structure analyses of (1) and (2) show that each Cu(II) atom is four-coordinated, with long weak Cu...O interactions of 2.8631 (13) Å linking the dinuclear halves of the centrosymmetric tetranucelar molecules, while each Mn(III) atom is six-coordinated. The shortest intra- and intermolecular nonbonding Mn...Mn separations are 3.3277 (16) and 5.1763 (19) Å for (2), while the Cu...Cu separations are 3.0237 (3) and 3.4846 (3) Å for (1). The magnetic susceptibilities of (1) and (2) in the solid state were measured in the temperature range 2-300 K and reveal the presence of antiferromagnetic spin-exchange interactions between the transition metal ions.

Synthesis, crystal structure and magnetic properties of a new copper oxo-antimony sulphate CuSb6O8(SO4)2.

The new copper oxo-antimony sulphate CuSb6O8(SO4)2 crystallizes in the triclinic space group P1[combining macron] with the unit cell parameters a = 5.5342(4) Å, b = 7.6706(6) Å, c = 9.2374(7) Å, α = 96.505(5)°, β = 93.818(4)°, γ = 109.733(4)° and Z = 1. The crystal structure is made up of layers stacking along [001]. The layers are charge neutral and are connected to each other by only weak interactions. The copper atoms adopt a square planar [CuO4] coordination and such units are well separated from each other by corner and edge sharing to [SbO4] building blocks. The latter polymerize to form sheets with the formula [Sb3O8]∞. Sulphate groups connect to the antimony oxide sheets by corner sharing and are located at the interface of the layers. Above ∼10 K the magnetic susceptibility follows very well a Curie-Weiss law whereas below 10 K increasing deviations indicate the onset of antiferromagnetic correlations. Fitting the data in the range 10-50 K yields a Curie-Weiss temperature θ of -2.25(5) K. A sharp anomaly centered at TC = 0.67 K in the heat capacity data indicates long-range magnetic ordering. Short range antiferromagnetic correlations well above TC are seen in the magnetic contribution to the heat capacity and the magnetic susceptibility. These can be well described by the magnetism of a spin S = 1/2 Heisenberg chain with the nearest neighbor antiferromagnetic spin exchange interaction of Jintra = ∼2.8 K.

Dinuclear manganese(II) complexes of hexaazamacrocycles bearing N-benzoylated pendant separated by aromatic spacers: Antibacterial, DNA interaction, cytotoxic and molecular docking studies

Three new homodinuclear manganese(II) complexes of the type [Mn2L1–3(ClO4)(H2O)](ClO4)3 (1–3) have been synthesized via cyclocondensation of terephthalaldehyde with three different benzoylated pendants in the presence of manganese(II) perchlorate and characterized by spectroscopic methods. Cyclic voltammetric investigation of complexes (1–3) depict two quasi-reversible one electron reduction processes in the cathodic potential region (E1pc=–0.73 to–0.83V, E2pc=–1.31 to −1.40V) and two quasi-reversible one electron oxidation processes in the anodic potential region (E1pa=1.03 to 1.10V, E2pa=1.69 to 1.77V). Electronic absorption spectra of the complexes suggested tetrahedral geometry around the central metal ion. The observed low magnetic moment values (μeff, 5.60–5.68 B.M.) of the complexes indicate the presence of an antiferromagnetic spin–exchange interaction between two metal centers, which was also supported by the broad EPR signal. All the compounds were tested for antibacterial activity against Gram (–ve) and Gram (+ve) bacterial strains. The binding studies of complexes with CT-DNA suggested minor-groove mode of interaction. Molecular docking studies were carried out in order to find the binding affinity of complexes with DNA and protein EGFR Kinase. The complexes are stabilized by additional electrostatic and van der Waals interaction with the DNA, and support minor groove mode of binding. The cleavage activity of complexes on pBR322 plasmid DNA displays efficient activity through a mechanistic pathway involving hydroxyl radicals. The cytotoxicity of complexes 2 and 3 have been tested against human liver adenocarcinoma (HepG2) cell line. Nuclear-chromatin cleavage has also been observed with propidium iodide (PI) staining and alkaline single-cell gel electrophoresis (comet assay) techniques.

Azido bridge mediated catecholase activity, electrochemistry and magnetic behavior of a dinuclear copper(II) complex of a phenol based “end-off” compartmental ligand

A dinuclear Cu(II) species [Cu2L2(H2O)2(N3)](NO3)2 (L=2,6-bis(N-ethylpyrrolidine-iminomethyl)-4-methyl-phenolato) where two Cu centers are bridged by phenoxido and μ1,1-azido bridges with Cu–Cu separation of ∼3Å have been synthesized with the view to explore the role of azido bridge on catecholase activity and electrochemical property and the roles of both the bridging groups on magnetic coupling of two copper centers. The complex exhibits excellent catecholase activity in acetonitrile as well as in DMSO medium not only by oxidizing 3,5-di-tert-butylcatechol (3,5-DTBC) but also tetrachlorocatechol (TCC), a catechol which is very thorny to oxidize, under aerobic conditions and becomes the first example of its own kind. CV study reveals three quasi-reversible reductive couples which are tentatively assigned as Cu2II to CuIICuI and CuICuI reduction followed by reduction of CuICuI complex to Cu0Cu0 species. Variable temperature magnetic study suggests the presence of an antiferromagnetic spin–exchange interaction between Cu(II) ions in the dimer via double bridge where the antiferromagnetic contribution of phenoxido bridge predominates over the ferromagnetic interaction of azido bridge.

Tetranuclear Nickel and Cobalt Complexes with an Incomplete Double‐Cubane Structure – Homo‐ and Heterometallic Complexes and Their 1D Coordination Polymers

AbstractThe reactions of M(OAc)2·4H2O (M = Ni, Co) with three unsymmetrical amine‐diol ligands RN(CH2CH2OH)(CH2CH2CH2OH) (H2Ln: n = 1, R = benzyl; n = 2, R = 4‐methylbenzyl; n = 3, R = 2‐naphthalenylmethyl) in the presence of NEt3 or pyridine in MeOH or BnOH gave the tetranuclear complexes [M4(HLn)2(OAc)6(MeOH)2] {M = Ni, n = 1 (1a), 2 (1b), 3 (1c); M = Co, n = 1 (4a), 2 (4b), 3 (4c)} and [M4(HLn)2(OAc)6(BnOH)2] {M = Ni, n = 1 (2a), 2 (2b), 3 (2c); M = Co, n = 1 (5a), 2 (5b), 3 (5c)}. When p‐xylene‐α,α′‐diol was used instead of monoalcohols, the tetranuclear {M4O6} units were linked by p‐xylene‐α,α′‐diol to form the 1D coordination polymers [M4(HLn)2(OAc)6(p‐HOCH2C6H4CH2OH)]m {M = Ni, n = 1 (3a), 2 (3b); M = Co, n = 1 (6a), 2 (6b)}. The structures of 1–6 were determined by X‐ray crystallography and consist of centrosymmetrical tetranuclear {M4O6} face‐shared defective double‐cubane cores supported by two monodeprotonated (HLn)– ligands. The mixed‐metal tetranuclear complexes [Ni2.2Co1.8(HL1)2(OAc)6(MeOH)2] (7) and [Mn1.7Ni2.3(HL1)2(OAc)5(OMe)2] (8) were also synthesized by using equimolar amounts of Ni2+ and M2+ (M = Co, Mn) ions. X‐ray crystallographic and fluorescent analyses revealed that 7 is isomorphous with 1a and 4a and contains nonstoichiometric amounts of disordered Ni2+ and Co2+ ions in an average ratio of 2.2:1.8 with different occupancies for the two crystallographically independent metal centers. In contrast, 8 consists of a C2‐symmetrical face‐shared defective double‐cubane {MII3MnIIIO6} core with a Ni/Mn ratio of 2.3:1.7; the amounts of Ni2+ and Mn2+ ions vary depending on the metal sites, and one of the C2 axial positions is exclusively occupied by Mn3+ ions. Detailed magnetostructural analyses on the nickel (1a, 2a, 3a) and cobalt (4a) complexes with appropriate spin‐Hamiltonian models showed that both ferro‐ and antiferromagnetic spin exchange interactions were involved within the tetranuclear units, and their extent depends on the combination of the metal ions and the ligand systems in a delicate fashion.

Strongly correlated one-dimensional magnetic behavior ofNiTa2O6

The magnetic properties of NiTa$_2$O$_6$ were investigated by magnetic susceptibility, specific heat, electron paramagnetic resonance, neutron powder diffraction and pulse field magnetization measurements. Accompanying \textit{ab initio} DFT calculations of the spin-exchange constants complemented and supported our experimental findings that NiTa$_2$O$_6$ must be described as a quasi-1D Heisenberg $S$ = 1 spin chain system with a nearest-neighbor only anti-ferromagnetic spin-exchange interaction of 18.92(2) K. Inter-chain coupling is by about two orders of magnitude smaller. Electron paramagnetic resonance measurements on Mg$_{1-x}$Ni$_x$Ta$_2$O$_6$ ($x \approx$ $1\%$) polycrystalline samples enabled us to estimate the single-ion zero-field splitting of the $S$ = 1 states which amounts to less than $4\%$ of the nearest-neighbor spin-exchange interaction. At 0 T NiTa$_2$O$_6$ undergoes long-range anti-ferromagnetic ordering at 10.3(1) K evidenced by a $\lambda$-type anomaly in the specific heat capacity. On application of a magnetic field the specific heat anomaly is smeared out. We confirmed the magnetic structure by neutron powder diffraction measurements and at 2.00(1) K refined a magnetic moment of 1.93(5) $\mu_{\rm{B}}$ per Ni$^{2+}$ ion. Additionally, we followed the magnetic order parameter as a function of temperature. Lastly we found saturation of the magnetic moment at 55.5(5) T with a $g$-factor of 2.14(1), with an additional high field phase above 12.8(1) T. The onset of the new high field phase is not greatly effected by temperature, but rather smears out as one approaches the long-range ordering temperature.

Density-functional theory for the spin-1 bosons in a one-dimensional harmonic trap

We propose the density-functional theory for one-dimensional harmonically trapped spin-1 bosons in the ground state with repulsive density-density interaction and anti-ferromagnetic spin-exchange interaction. The density distributions of spin singlet paired bosons and polarized bosons with different total polarization for various interaction parameters are obtained by solving the Kohn-Sham equations which are derived based on the local density approximation and the Bethe ansatz exact results for homogeneous system. Non-monotonicity of the central densities is attributed to the competition between the density interaction and spin-exchange. The results reveal the phase separation of the paired and polarized bosons, the density profiles of which respectively approach the Tonks-Girardeau gases of Bose-Bose pairs and scalar bosons in the case of strong interaction. We give the R-P phase diagram at strong interaction and find the critical polarization, which paves the way to direct observe the exotic singlet pairing in spinor gas experimentally.

Crystal structure and magnetic properties of Cr3Te5O13Cl3

A new chromium tellurite oxochloride, Cr3Te5O13Cl3, has been prepared by solid-state reaction and the crystal structure was determined by single crystal X-ray diffraction. The compound crystallizes in the non-centrosymmetric space group P2(1)2(1)2(1) with the unit cell a = 4.90180(10) Å, b = 17.3394(2) Å, c = 17.5405(2) Å, Z = 4, R1 = 0.0282. The Cr(3+) ions have octahedral [CrO6] oxygen coordination, the Te(4+) ions have one sided [TeO3] and [TeO3Cl] coordinations. The [CrO6] octahedra are edge sharing and form chains extending along [100]. These are connected by corner sharing [TeO3] and [TeO3Cl] groups to form layers parallel to (110). The layers are connected by weak interactions in between Te(4+) in the layers and Cl(-) ions located in between. The compound undergoes antiferromagnetic ordering at ~34 K with a Weiss constant of -230 K. Isothermal magnetization measurements reveal a critical field of about 0.25 T above which the magnetization versus field changes from linear to a Brillouin-like saturation behaviour. The frustration ratio amounts to ~6.8 indicative of sizable competing antiferromagnetic spin-exchange interaction. The dielectric constant ε (6 kHz) amounts to ~7.9 and decreases by about 1% on cooling from 50 K to liquid helium temperatures.

Synthesis, structural analysis and magnetic properties of two novel doubly oxygen bridged binuclear manganese(III) and copper(II) complexes with ONO tridentate ligands

Two novel binuclear Mn(III) [C22H26Cl4Mn2N2O6] (1) and Cu(II) [C26H14Cl4Cu2N2O4] (2) Schiff base complexes have been synthesized and their crystal structures have been determined by single crystal X-ray diffraction analysis. Structural analysis of (1) and (2) shows that the Schiff base ligand of dimers coordinates toward one metal atom in a tridentate mode and each Mn atom is six-coordinated while each Cu atom is four-coordinated. The two halves of the dimers are related by a crystallographic inversion center. The intramolecular non-bonding Mn⋯Mn separation is 2.994Å for complex (1) and Cu⋯Cu separation is 2.994Å for complex (2). Magnetic susceptibilities for (1) and (2) in the solid state have been measured over the temperature range 2–350K as a function of temperature and the magnetic parameters have been determined with fitting procedure. Magnetic measurements on (1) and (2) reveal the presence of antiferromagnetic spin–exchange interactions between the transition metal ions.

Quantum criticality of spin-1 bosons in a one-dimensional harmonic trap

We investigate universal thermodynamics and quantum criticality of spin-1 bosons with strongly repulsive density-density and antiferromagnetic spin-exchange interactions in a one-dimensional harmonic trap. From the equation of state, we find that a partially-polarized core is surrounded by two wings composed of either spin-singlet pairs or a fully spin-aligned Tonks-Girardeau gas depending on the polarization. We describe how the scaling behaviour of density profiles can reveal the universal nature of quantum criticality and map out the quantum phase diagram. We further show that at quantum criticality the dynamical critical exponent $z = 2$ and correlation length exponent $\nu=1/2$. This reveals a subtle resemblance to the physics of the spin-1/2 attractive Fermi gas.