Intrachain Coupling Research Articles

Phase diagram of the frustrated spin ladder with the next nearest intrachain couplings

By the density matrix renormalization group method, the phase diagram of the frustrated spin-1/2 ladder with the next nearest intrachain and ferromagnetic interchain couplings is obtained. According to our results, the two-rung entanglement is shown to be more sensitive than order parameters for determining phase boundary in such a frustrated spin ladder model. Furthermore, the additional next nearest intrachain coupling is found to enhance the intermediate columnar dimerized phase evidently.

Synthesis, structural, thermal, and magnetic investigations of Co(II), Ni(II), and Mn(II) pyrophosphate chains

The reaction in water of cobalt(II), nickel(II) or manganese(II) chloride with 1,10-phenanthroline (phen) and sodium pyrophosphate (Na4P2O7) at low pH (∼2) afforded three isostructural pyrophosphate complexes of an unprecedented one-dimensional typology, namely, {[M(phen)(H2O)(H2P2O7)]·H2O}n with M=Co(1), Ni(2) and Mn(3). The di-hydrogen-pyrophosphate anion featured in these complexes adopts a rare bidentate/monodentate bridging mode leading to chain propagation. This unusual bridging pathway produces a metal–metal intra-chain separation of about 6.6–6.7Å for 1–3, values much larger than the metal–metal distance across the classic bis-bidentate PPi in the parent homodinuclear complexes {[Co(phen)2]2(μ-P2O7)}·6MeOH (1a), {[Ni(phen)2]2(H2O)(μ-P2O7)}·27H2O (2a) and {[Mn(phen)2]2(H2O)(μ-P2O7)}·13H2O (3a), corresponding to ca. 4.9, 5.0 and 4.7Å, respectively. Variable-temperature magnetic susceptibility measurements on polycrystalline samples of 1–3 revealed weak intrachain antiferromagnetic couplings [J=−0.93 (1), −1.88 (2) and −0.26cm−1 (3)], consistent with previous data on the dinuclear complexes 1a–3a.

Slow Relaxation of the Magnetization in a 4,2-Wavelike FeIII2CoII Heterobimetallic Chain

The reaction of the low-spin iron(III) complex [Fe(dmbpy)(CN)(4)](-) (1) with fully solvated cobalt(II) ions affords the cyanide-bridged heterobimetallic chain {[Fe(III)(dmbpy)(CN)(4)](2)Co(II)(H(2)O)(2)}(n) · 4nH(2)O (2), which exhibits intrachain ferromagnetic coupling and double slow relaxation of the magnetization.

FeIII(dmbpy)(CN)4]−: a new building block for designing single-chain magnets

We herein present the synthesis and magneto-structural study of a new family of heterobimetallic chains of general formula {[Fe(III)(dmbpy)(CN)(4)](2)M(II)(H(2)O)(2)}(n)·pnH(2)O [dmbpy = 4,4'-dimethyl-2,2'-bipyridine; M = Mn (2), Cu (3), Ni (4) and Co (5) with p = 4 (2), 3 (3), 9 (4) and 3.5 (5)] which were prepared by using the mononuclear PPh(4)[Fe(III)(dmbpy)(CN)(4)]·3H(2)O (1) building block (PPh(4)(+) = tetraphenylphosphonium) as a ligand toward fully solvated M(II) ions. The structure of 1 consists of discrete [Fe(III)(dmbpy)(CN)(4)](-) anions, tetraphenylphosphonium cations and noncoordinated water molecules. Complexes 2-5 are isostructural compounds whose structure consists of neutral 4,2-wave like heterobimetallic chains of formula {[Fe(III)(dmbpy)(CN)(4)](2)M(II)(H(2)O)(2)}(n) where the [Fe(III)(dmbpy)(CN)(4)](-) entity adopts a bis-monodentate coordination mode toward trans-[M(II)(H(2)O)(2)] units through two of its four cyanide groups in cis positions. 1 exhibits the magnetic behaviour of magnetically isolated six-coordinate low-spin Fe(III) complexes with an important orbital contribution. 2 behaves as ferrimagnetic Fe(III)(2)Mn(II) chains, whereas 3-5 exhibit intrachain ferromagnetic couplings between the low-spin Fe(III) and either Cu(II) (3), Ni (4) or Co(II) (5) as well as frequency-dependence of the out-of-phase ac susceptibility signals below 3.0 (3), 5.5 (4) and 5.0 K (5). The relaxation time and the energy to reverse the magnetization of 3-5 are related to the anisotropy of the M(II) center and to the intra- and interchain magnetic interactions. Unprecedentedly in the world of cyanide-bearing complexes, 5 exhibits a double slow relaxation of the magnetization.

Chelating Schiff base assisted azide-bridged Mn(ii), Ni(ii) and Cu(ii) magnetic coordination polymers

Four new Mn(II), Ni(II) and Cu(II) coordination polymers [Mn2(L1)(μ(1,1)-N3)2(μ(1,3)-N3)2]n (1), [Ni(L2)2(μ(1,3)-N3)]n(ClO4)n (2), [Cu(L3)(μ(1,1)-N3)(N3)]n (3) and [Cu(L4)(μ(1,1)-N3)2]n (4) (L1 = N,N′-bis(2-pyridylmethylene)ethane-1,2-diamine, L2 = N-(2-pyridylmethylene)methylamine, L3 = N-(2-pyridylmethylene)-3-pyridylamine, L4 = N-(2-pyridylmethylene)-tbutylamine) have been synthesized and characterized by single-crystal X-ray analysis and magnetic measurements. Complex 1 indicates a stoichiometry-dependent structural change (based on Mn:L1:N3 = 2:1:4 molar ratio) and consists of two-dimensional (2-D) (4,4) net layers, in which Mn(II) centers are co-bridged by single end-to-end (EE), double end-on (EO) azide and chelate-bridging L1 ligands. Complex 2 shows a single EE azide-bridged one-dimensional (1-D) Ni(II) chain. Complexes 3 and 4 indicate single EO and double EO azide-bridged 1-D Cu(II) chains, respectively. Complex 1 exhibits weak ferromagnetism due to its intra-layer spin-canting with T(c) = 20 K. Complex 2 shows an unusual intra-chain ferromagnetic coupling and spin-canting behaviour. Both complexes 3 and 4 exhibit intra-chain antiferromagnetic interactions. Magneto-structural parameters for these related complexes were also discussed.

Slow magnetic relaxation in a 4,2-ribbon like FeIII2CoII heterobimetallic chain

The reaction of Co(NO(3))(2)·6H(2)O and 3-benzoylpyridine with the low-spin iron(III) complex, H[Fe(III)(phen)(CN)(4)], in methanol gives rise to a cyanide-bridged heterobimetallic chain [{Fe(III)(phen)(CN)(4)}(2)Co(II)(3-bpe)(2)] (1) that exhibits intrachain ferromagnetic coupling and slow double magnetic relaxation.

Constructing Single-Chain Magnets by Supramolecular π-π Stacking and Spin Canting: A Case Study on Manganese(III) Corroles

A single-chain magnet (SCM) was constructed from manganese(III) 5,10,15-tris(pentafluorophenyl)corrole complex [Mn(III) (tpfc)] through supramolecular π-π stacking without bridging ligands. In the crystal structures, [Mn(tpfc)] molecules crystallized from different solvents, such as methanol, ethyl acetate, and ethanol, exhibit different molecular orientations and intermolecular π-π interaction or weak Mn⋅⋅⋅O interaction to form a supramolecular one-dimensional motif or dimer. These three complexes show very different magnetic behaviors at low temperature. Methanol solvate 1 shows obvious frequency dependence of out-of-phase alternating-current magnetic susceptibility below 2 K and a magnetization hysteresis loop with a coercive field of 400 Oe at 0.5 K. It is the first example of spin-canted supramolecular single-chain magnet due to weak π-π stacking interaction. By fitting the susceptibility data χ(M) T (20-300 K) of 1 with the spin Hamiltonian expression H = -2J Σ(i=1)(n-1) S(Ai) S(Ai+1) + D Σ(i) S((iZ)(2)), the intrachain magnetic coupling parameter transmitted by π-π interaction of -0.31 cm(-1) and zero field splitting parameter D of -2.59 cm(-1) are obtained. Ethyl acetate solvate 2 behaves as an antiferromagnetic chain without ordering or slow magnetic relaxation down to 0.5 K. The magnetic susceptibility data χ(M) T (20-300 K) of 2 was fitted by assuming the spin Hamiltonian H = -2JΣ(i=1)(n-1) S(Ai) S(Ai+1), and the intrachain antiferromagnetic coupling constant of -0.07 cm(-1) is much weaker than that of 1. Ethanol solvate 3 with a dimer motif shows field-induced single-molecule magnet like behavior below 2.5 K. The exchange coupling constant J within the dimer propagated by π-π interaction is -0.14 cm(-1) by fitting the susceptibility data χ(M) T (20-300 K) with the spin Hamiltonian H = -2J S(A) S(B) + β(S((A)g(A)) + S((B)g(B)))H. The present studies open a new way to construct SCMs from anisotropic magnetic single-ion units through weak intermolecular interactions in the absence of bridging ligands.

First-principles calculation on the magnetic and electronic properties of iron sulfur compound

The magnetic structure and electronic properties of Ba 4Fe 2I 5S 4 have been studied by the full potential linearized augmented plane wave (FP-LAPW) method. We calculate non-magnetic, ferromagnetic, ferrimagnetic, and antiferromagnetic states of Ba 4Fe 2I 5S 4. Within GGA+U methods, Ba 4Fe 2I 5S 4 is ferrimagnetic with 2 μ B magnetic moment in the ground state. Two kinds of ferrimagnetic states have almost the same energy, which indicates interchain exchange coupling interaction is much weaker than intrachain exchange coupling interaction and the distance of Fe–Fe ion interchain is much larger than the distance intrachain. The electronic structure results show a half-metallic property in this kind of iron sulfur compound.

Unusual ferromagnetic superexchange in CdVO3: The role of Cd

A microscopic magnetic model of the low-pressure modification of CdVO3 is established, based on density functional theory (DFT) band-structure calculations, magnetization measurements, and quantum Monte-Carlo simulations. This compound is a rare example of a quasi-one-dimensional spin-1/2 system showing exclusively ferromagnetic exchange. The spin lattice of CdVO3 entails zigzag chains with an effective intrachain coupling J ~ -90 K and interchain couplings of Jc ~ -18 K and Ja ~ -3 K. Quantum fluctuations are partially suppressed by the sizable interchain coupling Jc that leads to an intermediate regime between one-dimensional and two-dimensional ferromagnetic systems. Apart from the peculiar spin model, CdVO3 features an unusual mechanism of ferromagnetic superexchange. The couplings largely originate from Cd 5s states mediating hoppings between half-filled and empty 3d states of V+4.

Magnetic properties of the low-dimensional spin-12magnetα-Cu2As2O7

In this work we study the interplay between the crystal structure and magnetism of the pyroarsenate \alpha-Cu_2As_2O_7 by means of magnetization, heat capacity, electron spin resonance and nuclear magnetic resonance measurements as well as density functional theory (DFT) calculations and quantum Monte Carlo (QMC) simulations. The data reveal that the magnetic Cu-O chains in the crystal structure represent a realization of a quasi-one dimensional (1D) coupled alternating spin-1/2 Heisenberg chain model with relevant pathways through non-magnetic AsO_4 tetrahedra. Owing to residual 3D interactions antiferromagnetic long range ordering at T_N\simeq10K takes place. Application of external magnetic field B along the magnetically easy axis induces the transition to a spin-flop phase at B_{SF}~1.7T (2K). The experimental data suggest that substantial quantum spin fluctuations take place at low magnetic fields in the ordered state. DFT calculations confirm the quasi-one-dimensional nature of the spin lattice, with the leading coupling J_1 within the structural dimers. QMC fits to the magnetic susceptibility evaluate J_1=164K, the weaker intrachain coupling J'_1/J_1 = 0.55, and the effective interchain coupling J_{ic1}/J_1 = 0.20.

End-to-End Azide-Bridged Manganese(III) Chain Compounds: Field-Induced Magnetic Phase Transitions and Variation of TC to 38 K Depending on the Side Groups of the Schiff Bases

Three one-dimensional coordination polymers [Mn(L)(N(3))](n) [L = L1 (1), L2 (2), L3 (3); L1H(2) = N,N'-bis(5-chlorosalicylideneiminato)-1,3-diaminopentane, L2H(2) = N,N'-bis(5-bromosalicylideneiminato)-1,3-diaminopentane, L3H(2) = N,N'-bis(5-bromosalicylideneiminato)-1,3-diamino-2-dimethylpropane] bridged by end-to-end azides were prepared. The crystal systems differ according to the Schiff bases used. Each Mn atom adopts a typical Jahn-Teller distortion. The helicity of the chains occurs in a racemic manner only for 2. No noncovalent forces are relevant in 2, while π-π contacts are visible in 1 and 3. Magnetic measurements show the presence of apparent spin canting. Complexes 1 and 3 exhibit a field-induced metamagnetic transition from an antiferromagnetic state to a weak ferromagnetic phase, whereas 2 embraces a field-induced two-step magnetic phase transition. The critical temperature is observed at 38 K for 2, which is relatively higher than those for 1 (11 K) and 3 (10 K). The pronounced long-range order may contribute from intrachain exchange couplings and through-space dipolar interactions between adjacent chains.

Magnetic properties of the antiferromagnetic spin-12chain systemβ-TeVO4

The magnetic susceptibility and magnetization of high quality single crystal beta-TeVO4 are reported. We show that this compound, made of weakly coupled infinite chains of VO5 pyramids sharing corners, behaves as a S = 1/2 one-dimensional Heisenberg antiferromagnet. From magnetic experiments we deduce the intrachain antiferromagnetic coupling constant J/kB = 21.4 $\pm$ 0.2 K. Below 5 K a series of three phase transitions at 2.26, 3.28 and 4.65 K is observed.

Single-chain magnet features in 1D [MnR4TPP][TCNE] compounds

Molecular chains of antiferrimagnetically coupled MnIII-ion (S = 2) and TCNE (tetracyanoethylene) radical moments (s = ½) show different behaviour depending on group R substituted to TPP (tetraphenylporphyrin) and on the substitution site. The compound with R = F in Ortho position is a Single-Chain Magnet (SCM) with blocking temperature Tb = 6.6K, while that with R = F in Meta position shows both blocking (Tb = 5.4 K) and magnetic ordering transition (Tc = 10 K). For bulky groups R = OCnH2n+1, the magnetically ordered phase is observed (Tc ≈ 22 K), which does not however prevent slow relaxation at T <8 K. Magnetic hysteresis with coercive field Hc of 2 T at 2.3 K is like that of SCM. The frequency dependent AC susceptibility in the superimposed DC field reveals common features of all systems. The energy of intrachain ferromagnetic coupling between effective spin units 3/2, relevant at low temperatures, is determined for all compounds and the interchain dipolar coupling is estimated. It is concluded that slow relaxation is inherent for all quasi one-dimensional compounds and for the magnetically ordered ones shows up in the high enough magnetic field.

Structural and Electronic Modulation of Magnetic Properties in a Family of Chiral Iron Coordination Polymers

The complexes FeL(2) [L = bidentate Schiff base ligands obtained from (R)-(+)-α-phenylethanamine and 4-substituted salicylaldehydes, substituent R = H, (t)Bu, NO(2), OMe, CN, OH] react with ditopic proligands 1,4-pyrazine (pz) or 4,4'-bipyridine (bpy), to give a family of optically pure Fe(II) polymeric chain complexes of formula {FeL(2)(μ-pz)}(∞) and {FeL(2)(μ-bpy)}(∞). Crystallographic studies show that a range of structures are formed including unidirectional and bidirectional linear polymers and canted zigzag chains. Interchain interactions via π-contacts and hydrogen bonding are also observed. SQuID magnetometry studies on all of the complexes reveal antiferromagnetic interactions, the magnitudes of which are rationalized on the basis of substituent electronic properties and bridging ligand identity. For complexes with bridging pz, the antiferromangnetic interaction is enhanced by electron-releasing substituents on the Fe units, and this is accompanied by a contraction in the intrachain distance. For complexes bridged with the longer bpy the intrachain antiferromagnetic couplings are much weaker as a result of the longer intrachain distance. The magnetic data for this series of chain complexes follow a Bonner-Fisher 1D chain model, alongside a zero field splitting (ZFS) model for Fe(II) (S = 2) as appropriate. The intrachain antiferromagnetic coupling J values, g-factors, and the axial ZFS parameter D were obtained.

QED model of resonance phenomena in quasionedimensional multichain qubit systems

The analytical solution of the task of the interaction of quantized EM-field with axially symmetric quasi-1D multichain qubit system by taking into account both the intrachain and interchain qubit coupling has been obtained for the first time. The appearance in stationary optical spectra of complementary lines, which is consequence of quantum nature of EM-field, leading to Rabi wave packets’ formation, is predicted for all quasi-1D systems with strong electron–photon interaction. The model proposed is considered on the example of perfect carbon quasi-1D zigzag shaped nanotubes, for which a new quasi-1D model, which is qualitatively different from well-known 2D-model, is proposed.

Spin-Peierls transition in theS=12compound TiPO4featuring large intrachain coupling

We investigated the magnetic and structural properties of the quasi-one-dimensional 3${d}^{1}$ quantum chain system TiPO${}_{4}$ ($J~$ 965 K) by magnetic susceptibility, heat capacity, electron spin resonance, x-ray diffraction, and nuclear magnetic resonance (NMR) measurements, and by density functional theory (DFT) calculations. TiPO${}_{4}$ undergoes two magnetostructural phase transitions, one at 111 K and the other at 74 K. Below 74 K, NMR detects two different $^{31}\mathrm{P}$ signals and the magnetic susceptibility vanishes, while DFT calculations evidence a bond alternation of the Ti-Ti distances within each chain. Thus, the 74 K phase transition is a spin-Peierls transition which evolves from an incommensurate phase existing between 111 and 74 K.

DFT study of structure–properties correlations in [MnTPP][TCNE] quasi-one-dimensional molecular magnets

We report the first band structure calculations of the quasi-one-dimensional [MnTPP][TCNE] compounds (TPP = meso-tetraphenylporphyrinato, TCNE = tetracyanoethylene), based on Density Functional Theory (DFT) methods, in order to interpret the magnetic ordering in these prototypic systems. We compare and contrast the results of broken-symmetry DFT calculations for extended systems, with periodic boundary conditions, and for finite systems, magnetic dimers modeling the actual molecular magnets. By varying systematically the main angles, we are able to determine the geometry dependence of the exchange interaction. Structure–properties correlations in these charge-transfer salts reveal the determinant role of the Mn-(N≡C)TCNE bond angle on the strength of the ferrimagnetic coupling between the S1 = 2 spin located on the MnIII-porphyrin donor and the S2 = 1/2 spin positioned on the cyanocarbon acceptor. When the Mn-(N≡C)TCNE angle is decreased, the intrachain magnetic coupling strengthens, correlated with the increase in the \( d_{{z^{2} }} - \pi * \) orbital overlap. The exchange coupling constants resulting from DFT calculations of extended systems, with periodic boundary conditions, were found to be consistent with those obtained for the dimers, but systematically smaller. The exchange constants vary strongly with the functional used, hybrid functionals such as B3LYP leading to results that better correlate with the experimental mean-field critical temperatures. The coupling constant varies significantly with the type of broken-symmetry approach, depending on the overlap between magnetic orbitals, but weakly on the basis set once polarization effects are included. The electronic structure calculations for the extended systems provide a density of states consistent with the energy spectrum of the corresponding dimer, allowing for an intuitive explanation of the intrachain ferrimagnetic ordering.

Slow relaxation of the magnetization in Oximato-bridged heterobimetallic Copper(II)-Manganese(III) chains

The use of the oximato-containing copper(II) complexes, [Cu(Hdeg)2] (H2deg = diethylglyoxime), [Cu(Hmeg)2] (H2meg = methylethylglyoxime) and [Cu(Hdmg)2] (H2dmg = dimethylglyoxime), as ligands toward manganese(II) acetate in methanol afforded the heterobimetallic compounds of formula [MnCu(deg)2(CH3COO)(H2O)2] (1), [MnCu(meg)2(CH3COO)(H2O)2] (2) and [MnCu(dmg)2(CH3COO)(H2O)2] (3) where the starting manganese(II) ion was oxidized to manganese(III) by air. In the lack of single crystals suitable for X-ray diffraction analysis, X-ray absorption techniques (EXAFS and XANES) at 40 K were used for the structural characterization of 1-3. The analysis of the X-ray absorption data reveals that 1-3 are oximato-bridged CuII-MnIII bimetallic chains with elongated octahedral CuN4O2 and MnO6 surroundings. The study of the magnetic properties of 1-3 reveals a metamagnetic-like behavior due to the coexistence of strong intrachain ferromagnetic couplings [J = +52.5 (1), +49.1 (2) and +52.1 cm-1 (3)] and weak interchain antiferromagnetic interactions [j = -0.070 (1), -0.075 (2) and -0.078 cm-1 (3)]. The strict orthogonality between the magnetic orbital of the copper(II) ion and those of the manganese(III) center, together with the well known ability of the oximato group to mediate magnetic interactions when acting as a bridge between two metal ions, account for the relatively strong intrachain ferromagnetic coupling in 1-3. Alternating current susceptibility measurements for 1-3 in the low temperature range under zero dc magnetic field reveal a frequency-dependence of the out-of-phase ac signal as expected for single chain magnets

Magnetic anisotropy and geometrical frustration in the Ising spin-chain system Sr5Rh4O12

A structural and thermodynamic study of the newly synthesized single crystal Sr5Rh4O12 is reported. Sr5Rh4O12 consists of a triangular lattice of spin-chains running along the c-axis. It is antiferromagnetically ordered below 23 K with the intrachain and interchain coupling being ferromagnetic (FM) and antiferromagnetic (AFM), respectively. There is strong evidence for an Ising character in the interaction and geometrical frustration that causes incomplete long-range AFM order. The isothermal magnetization exhibits two steplike transitions leading to a ferrimagnetic state at 2.4 T and a FM state at 4.8 T, respectively. Sr5Rh4O12 is a unique frustrated spin-chain system ever found in 4d and 5d-based materials without a presence of an incomplete 3d-electron shell.

Synthesis, Crystal Structures and Magnetic Properties of MIICuII Chains (M=Mn and Co) with Sterically Hindered Alkyl‐Substituted Phenyloxamate Bridging Ligands

A series of neutral oxamato-bridged heterobimetallic chains of general formula [MCu(L(x)2 (S)2] · p S · q H2O [p = 0-1, q = 0-2.5; L1 = N-2,6-dimethylphenyloxamate, S = DMF with M = Mn (1a) and Co (1b); L2 = N-2,6-diethylphenyloxamate, S = DMF with M = Mn (2a) and Co (2b) or S = DMSO with M = Mn (2c) and Co (2 d); L3 = N-2,6-diisopropylphenyloxamate, S = DMF with M = Mn (3a) and Co (3b) or S = DMSO with M = Mn (3c) and Co (3d)] were prepared by treating the corresponding anionic oxamatocopper(II) complexes [Cu(L(x))(2)]2- (x = 1-3) with M(2+) cations (M = Mn and Co) in DMF or DMSO as the solvent. The single-crystal X-ray structures of 2a and 3a reveal the occurrence of well-isolated, zigzag, oxamato-bridged manganese(II)-copper(II) chains. The intrachain Cu···Mn distances across the oxamato bridge are 5.3761(7) and 5.4002(17) Å for 2a and 3a, respectively, whereas the shortest interchain Mn···Mn distances are 9.4475(16) and 8.1649(14) Å for 2a and 3 a, respectively. All of these M(II) Cu(II) chains (M = Mn and Co) exhibit 1D ferrimagnetic behaviour with moderately strong intrachain antiferromagnetic coupling between the square-planar Cu(II) and octahedral high-spin M(II) ions across the oxamato bridge [-J=31.4-35.2 and 33.4-44.8 cm(-1) , respectively; H = ∑(i)-JS(M,i) (S(Cu,i) +S(Cu,i-1))]. Only the Co(II) Cu(II) chains show slow magnetic relaxation effects characteristic of single-chain magnets (SCMs). Analysis of the magnetic relaxation dynamics of 3d shows a thermally activated mechanism (Arrhenius law dependence) with values of the pre-exponential factor (τ(0) = 2.6 × 10(-9) s) and activation energy (E(a) =7.7 cm(-1) ) that are typical of SCMs. In contrast, two relaxation regimes are observed for 2d in different temperature regions (τ(0) = 3.2 × 10(-10) s and E(a) = 24.7 cm(-1) for T < 4.5K and τ(0) = 3.2 × 10(-14) s and E(a) = 37.5 cm(-1) for T>4.5K).