Intrachain Coupling Research Articles

Slow magnetic relaxation in rare μ2[sbnd]O-Bridged Holmium(III) and Erbium(III) chain compounds

Lanthanide chain compounds with slow relaxation of the magnetization (SRM) behavior have garnered wide attention due to their rich physical phenomena and wide applications. However, the study with non-Dy3+ ions are still rare, mainly due to the challenges in balancing single-ion magnetic anisotropy and intrachain exchange couplings. In this work, two new μ2O-bridged homospin chain compounds: [Ln(L)2(phen)(μ2OH)(μ2H2O)]n (Ln = Ho(1), Er(2), HL = 4-nitrobenzoic acid, phen = 1,10-phenanthroline), were synthesized under solvothermal conditions and fully characterized. Both compounds exhibit weak but effective intrachain couplings transmitted by single-O bridges, leading to Ising-like chain behavior. Dynamic magnetic measurements within the temperature range revealing this special chain behavior indicate that both compounds also exhibit SRM behavior. Such results suggest they could be categorized to the family of single-chain magnets, which are rarely reported for lanthanide compounds with non-radical ligands and non-Dy3+ systems.

Using Molecular Structure to Tune Intrachain and Interchain Charge Transport in Indacenodithiophene-Based Copolymers.

In this work, we compare two structurally near-amorphous rigid-rod polymers─poly(indacenodithiophene-co-benzothiadiazole), p(IDT-BT), and poly(indacenodithiophene-co-benzopyrollodione), p(IDT-BPD)─with orders of magnitude different mobilities to understand the effect charge carrier intrachain delocalization has on electronic transport. Quantum chemical calculations show that p(IDT-BPD) has a barrier to torsion that is significantly lower than that of p(IDT-BT) and is thus more likely to have reduced conjugation lengths. We utilize absorption and photoluminescence spectroscopy to characterize energetic disorder and show that p(IDT-BPD) has higher energetic disorder. Charge modulation spectroscopy (CMS) and model calculations are used to show that charge carriers are substantially delocalized in p(IDT-BT) and occupy near-uniform energetic environments. We find that mobility activated hopping barriers are similar in these two materials. Electronic structure calculations show that both intrachain and interchain couplings of monomer units are poor enough in p(IDT-BPD) that charge carriers collapse to single IDT units and transport via a through-space tunneling mechanism. This work highlights the remarkable charge transport properties of p(IDT-BT) by showing that high mobilities are achievable on device-relevant length scales with only 1D carrier delocalization.

Surfactant Composition Dependent Evolution of Electronic/Structural Properties of P3HT Nanoparticle Colloids Synthesized via Mini-Emulsion Technique

: This study investigates the influence of surfactant (sodium dodecyl sulfate, SDS) concentration on the size and optoelectronic properties of poly(3-hexylthiophene) (P3HT) nanoparticles (NPs) synthesized via the mini-emulsion technique. P3HT NPs were fabricated with varying SDS concentrations. The size dependent optoelectronic properties, including the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels, were analyzed through photoelectron spectroscopy in air, UV-Vis absorption spectroscopy and cyclic voltammetry. A clear trend of decreasing NP size with increasing SDS concentration was observed. Higher SDS levels resulted in smaller NPs with enhanced pi-pi stacking and shorter conjugation lengths. This structural change led to a noticeable shift in HOMO and LUMO levels, indicating a direct correlation between surfactant concentration and the electronic properties of the P3HT NPs. The absorption spectra revealed a decrease in the A0-0/A0-1 ratio with smaller NP size, suggesting a transition towards more pronounced H-aggregate characteristics. As the size of the P3HT NPs decreases, there is a notable increase in H-aggregate formation. This increase can be attributed to enhanced interchain interactions between the polymer chains. In smaller NPs, the surface area-to-volume ratio is higher, leading to more significant interactions between adjacent polymer chains. These interactions promote the formation of H-aggregates, characterized by their interchain pi-pi stacking, which differs from the intrachain coupling observed in J-aggregates.

Ferromagnetic Coupling in Quasi-One-Dimensional Hybrid Iron Chloride Hexagonal Perovskites.

We synthesize four novel quasi-one-dimensional organic-inorganic hybrid iron chloride compounds (CH3NH3FeCl3, CH(NH2)2FeCl3, C(NH2)3FeCl3, and C3H5N2FeCl3) and characterize their structural and magnetic properties. These materials crystallize in a hexagonal perovskite-type structure, constituting a triangular array of face-sharing iron chloride octahedra chains running along the c-axis, isolated from one another by the organic cation. Through magnetization and heat capacity measurements, we find that the intrachain coupling is weakly ferromagnetic for each variant. Importantly, this work underscores the utility of solid-state chemistry approaches in synthesizing new organic-inorganic hybrid materials.

Magnetic properties of Cu[C6H2(COO)4][H3N–(CH2)2–NH3]·3H2O - A quasi-two-dimensional S = 1/2 antiferromagnet on rectangular lattice

The analysis of specific heat, magnetic susceptibility and magnetization identified the studied compound Cu[C6H2(COO)4][H3N–(CH2)2–NH3]·3H2O as a quasi-two-dimensional S = 1/2 Heisenberg antiferromagnet on the rectangular lattice with the intrachain coupling J1/kB≈ 7.39 K and the interaction ratio R ≈ 0.44. A phase transition to a magnetically ordered state was observed in zero magnetic field at TN = 1.28 K. The analysis of magnetic specific heat in non-zero magnetic fields revealed features characteristic of the field-induced Berezinskii-Kosterlitz-Thouless phase transition theoretically predicted for ideal two-dimensional magnets. The electron paramagnetic resonance studies of Cu[C6H2(COO)4][H3N–(CH2)2–NH3]·3H2O revealed the increase of gx and gy and decrease of gz below 25 K due to the presence of dipolar coupling and the exchange anisotropy. The upturn of linewidth appearing below 30 K can be ascribed to the development of intralayer magnetic correlations.

Simultaneous Force and Fluorescence Spectroscopy on Single Chains of Polyfluorene: Effect of Intra-Chain Aggregate Coupling

Conjugated polymer chains in compact conformations or in films exhibit spectral features that can be attributed to interactions between individual conjugated segments of the chain, including formation of aggregates or excimers. Here, we use atomic force microscopy (AFM) on single chains of the conjugated polymer polyfluorene (PFO) to control the intersegment interactions by mechanically unfolding the chain. Simultaneously with the force spectroscopy we monitor fluorescence from the single PFO chains using a fluorescence microscope. We found that mechanical stretching of the chain causes disappearance of the green emission band. This observation provides evidence that the green emission originates from an intrachain aggregated state on the self-folded chain, which is decoupled by the stretching. In addition, the stretching upon laser irradiation leads to the appearance of additional features in the force spectra, small force peaks in the initial stages of the unfolding. These features are attributed to a combination of excitonic and van der Waals coupling of a ground-state intrachain aggregate.

Influence of Cr-ion substitution on the magnetization and dielectric properties of the frustrated Ca3CoMnO6 compound

The Cr-doped Ca3CoMn1-xCrxO6 (x=0, 0.05, 0.1, 0.15) polycrystalline samples were prepared using a modified sol-gel method. The structural, magnetic and dielectric properties were systemically investigated. With increasing Cr3+-doping level, the partial Co2+ ions change to Co3+, leading to a decreased lattice volume. Correspondingly, the length of the short-range magnetic correlation is inhibited and a faster dynamic behavior in time dependent magnetization is found. At the benefit of the magnetic structural changes with the introduction of Cr3+ ions, the relaxor degree of the ferroelectric transition that induced by the exchange striction becomes lower, while the activation energy of the frozen polar-nanoregions increases. The replacement of Mn4+ by Cr3+ also leads to a reduced intra-chain antiferromagnetic coupling and the emergence of Co3+-Co3+ ferromagnetic interaction. As consequence, the Curie-Weiss temperature (θ) increases monotonously. The variation in dielectric permittivity with magnetic field confirms the existence of large magnetodielectric coupling in the Ca3CoMn1-xCrxO6 (0 ​≤ ​x ​≤ ​0.15) samples. Especially for the x ​= ​0.15 sample, the permittivity changes by about 7% under the magnetic field of H=4 ​T.

Tunable Magnetic Transition Temperatures in Organic–Inorganic Hybrid Cobalt Chloride Hexagonal Perovskites

Magnetically active atomic distances may impact the magnetic ordering in a given system both directly and indirectly. We synthesize three novel quasi-one-dimensional organic–inorganic hybrid cobalt chloride chain compounds (CH3NH3CoCl3, CH(NH2)2CoCl3, and C(NH2)3CoCl3) and characterize their magnetic and thermodynamic properties. These materials crystallize in a hexagonal perovskite-type structure consisting of chains of face-sharing Co–Cl octahedra separated by the respective organic cation. Temperature- and field-dependent magnetic susceptibility analyses reveal that each compound possesses antiferromagnetic intrachain coupling and that the strength of the correlations is comparable across the three materials. Moreover, the interchain Co–Co distance, which depends on the size of the organic cation, is directly related to the temperature at which long-range magnetic ordering occurs.

Structure and Magnetic Properties of Pseudo-1D Chromium Thiolate Coordination Polymers

The synthesis, structure, and magnetic properties of two novel, pseudo-one-dimensional (1D) chromium thiolate coordination polymers (CPs), CrBTT and Cr2BDT3, are reported. The structures of these materials were determined using X-ray powder diffraction revealing highly symmetric 1D chains embedded within a CP framework. The magnetic coupling of this chain system was measured by SQUID magnetometry, revealing a switch from antiferromagnetic to ferromagnetic behavior dictated by the angular geometrical constraints within the CP scaffold consistent with the Goodenough-Kanamori-Anderson rules. Intrachain magnetic coupling constants JNN of -32.0 and +5.7 K were found for CrBTT and Cr2BDT3, respectively, using the 1D Bonner-Fisher model of magnetism. The band structure of these materials has also been examined by optical spectroscopy and density functional theory calculations revealing semiconducting behavior. Our findings here demonstrate how CP scaffolds can support idealized low-dimensional structural motifs and dictate magnetic interactions through tuning of geometry and inter-spin couplings.

Ferromagnetically coupled single-chain magnets exhibiting a magnetic hysteresis of 0.42 Tesla in cyano-bridged FeIII2MII (M = Ni, Fe) coordination polymers.

The synthesis, single-crystal structures and magnetic properties of two new double-zigzag-chain cyano-bridged heterobimetallic {[MII(Py-NOH)2][FeIII(Tp*)(CN)3]2}·H2O ([FeIII2MII]) (Py-NOH = 4-pyridinealdoxime, Tp* = tris(3,5-dimethylpyrazol-1-yl)borohydride, M = Ni (1), Fe (2)) compounds are reported. The crystal structures of both compounds were determined by single-crystal X-ray diffraction. Complexes 1 and 2 are isostructural, with the crystal structure comprising neutral double-zigzag (4,2-ribbon-like) bimetallic chains. The FeIII ion is coordinated by three cyanide carbon atoms and three nitrogen atoms of Tp* anions. However, the MII ion is surrounded by four cyanide nitrogen atoms and two nitrogen atoms from two Py-NOH ligands. The crystal structures and magnetic studies demonstrate that both complexes behave as single-chain magnetics (SCMs) with intrachain ferromagnetic coupling. Furthermore, [FeIII2NiII] exhibits an excellent coercive field of 0.42 T at 1.8 K, among cyano-bridged 3d transition-metal-based SCMs reported thus far. Preliminary theoretical calculations provide a deep understanding of the magnetic properties of [FeIII2NiII].

Synthesis, structure, and magnetism in the ferromagnet La3MnAs5 : Well-separated spin chains coupled via itinerant electrons

In this work, we systematically report the synthesis, structure, and magnetism of a compound of filled anti-${\mathrm{Mn}}_{3}{\mathrm{Si}}_{5}$ type ${\mathrm{La}}_{3}{\mathrm{MnAs}}_{5}$. It crystallizes in a hexagonal structure with the space group of $P{6}_{3}/mcm$ (193). The structure consists of face-sharing ${\mathrm{MnAs}}_{6}$ octahedral chains along the $c$ axis, which are well separated by a large distance of 8.$9913\phantom{\rule{0.28em}{0ex}}\AA{}$, demonstrating a strong one-dimensional (1D) structural character. Physical property measurements indicate that ${\mathrm{La}}_{3}{\mathrm{MnAs}}_{5}$ is a ferromagnetic metal with ${T}_{\mathrm{C}}\ensuremath{\sim}112\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Due to the short-range intrachain spin coupling, the susceptibility deviates from the Curie-Weiss behavior in a wide temperature window and the magnetic entropy corresponding to the ferromagnetic transition is significantly lower than that expected from the fully saturated state. The magnetic critical behavior studies show that ${\mathrm{La}}_{3}{\mathrm{MnAs}}_{5}$ can be described by the three-dimensional Heisenberg model. The orbital hybridization between the 1D ${\mathrm{MnAs}}_{6}$ chain and intermediate La atom near the Fermi level reveals that the itinerant electrons play a key role in transmitting spin interaction among the ${\mathrm{MnAs}}_{6}$ spin chains. Our results indicate that ${\mathrm{La}}_{3}{\mathrm{MnAs}}_{5}$ is a rare ferromagnetic metal with well-separated spin chains, which provides a good opportunity to study the mechanism of interchain spin coupling via itinerant electrons.

Low-energy spin excitations of the frustrated ferromagnetic J1−J2 chain material linarite PbCuSO4(OH)2 in applied magnetic fields parallel to the b axis

We report a study of the spin dynamics of the frustrated ferromagnetic $J_1$-$J_2$ chain compound linarite, PbCuSO$_4$(OH)$_2$, in applied magnetic fields up to field polarization. By means of an extreme-environment inelastic neutron scattering experiment, we have measured the low-energy spin excitations of linarite in fields up to 8.8 T for $\mathbf{H} \parallel b$ axis. We have recorded the spin excitation spectra along $h$, $k$ and $l$ for the field-induced magnetic phases IV, V and the field polarized state close to saturation. By employing first-principles calculations, we estimate the leading magnetic exchanges out of the $bc$ plane and model the dispersion relations using linear spin-wave theory. In this way, we find evidence for a (very weak) residual magnetic exchange coupling out of the $bc$ plane. Together with the previously established dominant intrachain couplings $J_1$ and $J_2$ and the interchain coupling $J_3$, we derive an effective set of exchange couplings for a microscopic description of linarite. Further, we find that the peculiar character of phase V manifests itself in the measured spin dynamics.

Vibrations Responsible for Luminescence from HJ-Aggregates of Conjugated Polymers Identified by Cryogenic Spectroscopy of Single Nanoparticles.

A single polymer chain can be thought of as a covalently bound J-aggregate, where the microscopic transition-dipole moments line up to emit in phase. Packing polymer chains into a bulk film can result in the opposite effect, inducing H-type coupling between chains. Cofacial transition-dipole moments oscillate out of phase, canceling each other out, so that the lowest-energy excited state turns dark. H-aggregates of conjugated polymers can, in principle, be coaxed into emitting light by mixing purely electronic and vibronic transitions. However, it is challenging to characterize this electron-phonon coupling experimentally. In a bulk film, many different conformations exist with varying degrees of intrachain J-type and interchain H-type coupling strengths, giving rise to broad and featureless aggregate absorption and emission spectra. Even if single nanoparticles consisting of only a few single chains are grown in a controlled fashion, the luminescence spectra remain broad, owing to the underlying molecular dynamics and structural heterogeneity at room temperature. At cryogenic temperatures, emission from H-type aggregates should be suppressed because, in the absence of thermal energy, internal conversion drives the aggregate to the lowest-energy dark state. At the same time, electronic and vibronic transitions narrow substantially, facilitating the attribution of spectral signatures to distinct vibrational modes. We demonstrate how to distinguish signatures of interchain H-type aggregate species from those of intramolecular J-type coupling. Whereas all dominant vibronic modes revealed in the photoluminescence (PL) and surface-enhanced resonance Raman scattering spectra of a single chromophore within a single polymer chain are identified in the J-type aggregate luminescence spectra, they are not all present at once in the H-type spectra. Universal spectral features are found for the luminescence from strongly HJ-coupled chains, clearly resolving the vibrations responsible for the nonadiabatic excited-state molecular dynamics that enable light emission. We discuss the possible combinations of vibrational modes responsible for H-type aggregate PL and demonstrate that only one, mainly the lowest energy one, of the three dominant vibrational modes contributes to the 0-1 transition, whereas combinations of all three are found in the 0-2 transition. From this analysis, we can distinguish between energy shifts due to either J-type intrachain coupling or H-type interchain interactions, offering a means to directly discriminate between structural and energetic disorder.

Field-temperature induced dimensionality crossover in Ca3Co2O6 spin system

Quasi-one dimensional spin chain compound, Ca3Co2O6, undergoes field and temperature induced dimensionality crossover at about 25 K from one-dimension to three-dimensionally correlated state. It is shown that interplay of intrachain and interchain couplings with thermal energy in this infinite spin chain system is responsible for this phenomenon. It is established from the measurement of temperature dependent magnetic susceptibility and field dependence of magnetization along different crystallographic axes of the single crystal. Further, the effect of chain truncation on dimensionality crossover has been studied to substantiate the role of these interactions in this phenomenon. Reduction of chain length causes decrease of the effective intrachain coupling strength without affecting the interaction of neighbouring chains significantly. As a result, the propensity of dimensional crossover is found to be weaker in the broken chain compared to the longer chain.

Exchange coupling in a thiocyanato-bridged copper(II) chain: Computational approach to magnetostructural correlations

In this article we report the synthesis and magneto-structural characterization of two new copper(II) compounds with thiocyanato and methyl(2-pyridil) ketone oxime (mpkOH), namely [Cu(NCS)(mpkO)(mpkOH)] (1) and [Cu(µ-NCS)(NCS)(mpkOH)]n (2). Compound 1 is a mononuclear complex that crystallizes as discrete units. Conversely, compound 2 is a single equatorial-axial end-to-end thiocyanato bridged polymeric chain of Cu(II) with the oxime as a co-ligand. The coordination geometry around the Cu(II) centers is distorted square pyramidal for 1 and 2. The magnetic susceptibility data for 2 reveal weak intrachain antiferromagnetic coupling, with J value −0.74(3) cm−1 and g = 2.10(1). The application of computational tools to a binuclear model of 2 allowed us to unveil the structural basis that modulates the magnetic behavior of this type of thiocyanato-bridged Cu(II) chains. The results suggest that although small values of J are expected, the strongest ferromagnetic interactions can be obtained by including co-ligands that trigger a squared-based pyramidal-to-trigonal bipyramidal distortion of the coordination polyhedra.

Intrachain collinear magnetism and interchain magnetic phases in Cr3As3−K -based materials

We perform a comparative study of the KCr3As3 and the K2Cr3As3 quasi 1D compounds, and show that the strong interplay between the lattice and the spin degrees of freedom promotes a new collinear ferrimagnetic ground state within the chains in presence of intrachain antiferromagnetic couplings. We propose that the interchain antiferromagnetic coupling in KCr3As3 plays a crucial role for the experimentally observed spin-glass phase with low critical temperature. In the same region of the parameter space, we predict K2Cr3As3 to be non-magnetic but on the verge of the magnetism, sustaining interchain ferromagnetic spin fluctuations while the intrachain spin fluctuations are antiferromagnetic.

Low-dimensional magnetism of BaCuTe2O6

X-ray diffraction, thermodynamic measurements, and density-functional band-structure calculations are used to study the magnetic behavior of BaCuTe$_{2}$O$_{6}$, a member of the $A$CuTe$_2$O$_6$ structural family that hosts complex three-dimensional frustrated spin networks with possible spin-liquid physics. Temperature-dependent magnetic susceptibility and heat capacity of the Ba compound are well described by the one-dimensional spin-$\frac12$ Heisenberg chain model reminiscent of the Sr analog SrCuTe$_2$O$_6$. While the intrachain coupling $J/k_{\rm B}\simeq 37$ K is reduced compared to 49 K in the Sr compound, the N\'eel temperature increases from 5.5 K (Sr) to 6.1 K (Ba). Unlike the Sr compound, BaCuTe$_2$O$_6$ undergoes only one magnetic transition as a function of temperature and shows signatures of weak spin canting. We elucidate the microscopic difference between the Sr and Ba compounds and suggest that one of the interchain couplings changes sign as a result of negative pressure caused by the Sr/Ba substitution. The N\'eel temperature of BaCuTe$_2$O$_6$ is remarkably insensitive to the magnetic dilution with Zn$^{2+}$ up to the highest reachable level of about 20%.

Quasi-one-dimensional magnetism in the spin- 12 antiferromagnet BaNa2Cu(VO4)2

We report synthesis and magnetic properties of quasi-one-dimensional spin-$\frac{1}{2}$ Heisenberg antiferromagnetic chain compound BaNa$_2$Cu(VO$_4$)$_2$. This orthovanadate has a centrosymmetric crystal structure, $C2/c$, where the magnetic Cu$^{2+}$ ions form spin chains. These chains are arranged in layers, with the chain direction changing by 62$^0$ between the two successive layers. Alternatively, the spin lattice can be viewed as anisotropic triangular layers upon taking the inter-chain interactions into consideration. Despite this potential structural complexity, temperature-dependent magnetic susceptibility, heat capacity, ESR intensity, and NMR shift agree well with the uniform spin-$1/2$ Heisenberg chain model with an intrachain coupling of $J/k_{\rm B} \simeq 5.6$ K. The saturation field obtained from the magnetic isotherm measurement consistently reproduces the value of $J/k_{\rm B}$. Further, the $^{51}$V NMR spin-lattice relaxation rate mimics the 1D character in the intermediate temperature range, whereas magnetic long-range order sets in below $T_{\rm N} \simeq 0.25$ K. The effective interchain coupling is estimated to be $J_{\perp}/k_{\rm B} \simeq 0.1$ K. The theoretical estimation of exchange couplings using band-structure calculations reciprocate our experimental findings and unambiguously establish the 1D character of the compound. Finally, the spin lattice of BaNa$_2$Cu(VO$_4$)$_2$ is compared with the chemically similar but not isostructural compound BaAg$_2$Cu(VO$_4)_2$.

An investigation of two copper(ii) complexes with a triazole derivative as a ligand: magnetic and catalytic properties.

Two new copper(ii) complexes [Cu2(L)2(OAc)2(H2O)2] (1) (L = 3-methyl-5-pyridin-2-yl-1,2,4-triazole) and [CuL2] (2) were prerared and thoroughly studied. The complexes are able to selectively catalyze the oxidation of styrene towards benzaldehyde and of cyclohexane to KA oil. The 2D coordination polymer 1 showed an antiferromagnetic behaviour attributed to the intrachain magnetic coupling.

Synthesis, structure and magnetic properties of two new spin-chain compounds Ca2Ni(HSeO3)2(SeO3)2 and Na2Cu(SeO3)2·2H2O.

Two new selenite compounds Ca2Ni(HSeO3)2(SeO3)2 (CaNi) and Na2Cu(SeO3)2·2H2O (NaCu) were obtained by a hydrothermal method. Both compounds crystallize in the triclinic system of space group P1̄, featuring a selenite-bridged one-dimensional (1D) spin-chain structure running along the a-axis. Magnetic measurements indicate that CaNi undergoes a long-range antiferromagnetic order (LRO) at TN = ∼3.8 K, while NaCu does not exhibit a LRO down to 2 K but the onset of a short-range correlation at TM = ∼30 K. The intrachain exchange coupling J/kB = -2.59 K for CaNi and J/kB = -47.13 K for NaCu can be estimated by a fit using the 1D spin-chain model. The thermogravimetric analyses show that both compounds are stable below 130 °C. The UV-vis diffuse reflectance spectra indicate that the band gaps of CaNi and NaCu are 4.38 eV and 3.18 eV, respectively.