Interchain Exchange Interaction Research Articles

Effect of magnetic order on longitudinal Tomonaga-Luttinger liquid spin dynamics in weakly coupled spin- 12 chains

The quantum many-body interactions in one-dimensional spin-$\frac{1}{2}$ systems are subject to Tomonaga-Luttinger liquid (TLL) physics, which predict an array of multiparticle excitations that form continua in momentum-energy space. Here we use inelastic neutron spectroscopy to study the TLL spin dynamics in ${\mathrm{SrCo}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$, a compound which contains weakly coupled spin-$\frac{1}{2}$ chains of Co atoms, at 0.05 K and in a longitudinal magnetic field up to 9.0 T. The measurements were performed above 3.9 T, where the ground-state N\'eel antiferromagnetic (AFM) order is completely suppressed and the multiparticle excitations are exclusively of the TLL type. In this region and below 7.0 T, the longitudinal TLL mode---psinon/antipsinon (P/AP)---is unexpectedly well described by a damped harmonic oscillator (DHO) while approaching the zone center defining the static spin-spin correlations. A non-DHO-type, continuumlike signal is seen at higher fields, but deviations from the ideal one-dimensional TLL still remain. This change in the P/AP mode coincides with the phase transition between the longitudinal spin density wave (LSDW) and transverse AFM order. Inside the LSDW state, the DHO-type P/AP spectral weight increases and the linewidth broadens as the magnetic order parameter decreases. These results reveal the impact of three-dimensional magnetic order on the TLL spin dynamics; they call for beyond-mean-field treatment for the interchain exchange interactions.

Study of Interacting Heisenberg Antiferromagnet Spin-1/2 and 1 Chains

Haldane conjectures the fundamental difference in the energy spectrum of the Heisenberg antiferromagnetic (HAF) of the spin S chain is that the half-integer and the integer S chain have gapless and gapped energy spectrums, respectively. The ground state (gs) of the HAF spin-1/2 and spin-1 chains have a quasi-long-range and short-range correlation, respectively. We study the effect of the exchange interaction between an HAF spin-1/2 and an HAF spin-1 chain forming a normal ladder system and its gs properties. The inter-chain exchange interaction J⊥ can be either ferromagnetic (FM) or antiferromagnetic (AFM). Using the density matrix renormalization group method, we show that in the weak AFM/FM coupling limit of J⊥, the system behaves like two decoupled chains. However, in the large AFM J⊥ limit, the whole system can be visualized as weakly coupled spin-1/2 and spin-1 pairs which behave like an effective spin-1/2 HAF chain. In the large FM J⊥ limit, coupled spin-1/2 and spin-1 pairs can form pseudo spin-3/2 and the whole system behaves like an effective spin-3/2 HAF chain. We also derive the effective model Hamiltonian in both strong FM and AFM rung exchange coupling limits.

One-dimensional quantum magnetism in the S=12 Mo(V) system KMoOP2O7

We present a comprehensive experimental and ab-initio study of the $S=1/2$ Mo$^{5+}$ system, KMoOP$_2$O$_7$, and show that it realizes the $S = 1/2$ Heisenberg chain antiferromagnet model. Powder neutron diffraction reveals that KMoOP$_2$O$_7$ forms a magnetic network comprised of pairs of Mo$^{5+}$ chains within its monoclinic $P2_1/n$ structure. Antiferromagnetic interactions within the Mo$^{5+}$ chains are identified through magnetometry measurements and confirmed by analysis of the magnetic specific heat. The latter reveals a broad feature centred on $T_\textrm{N} = 0.54$ K, which we ascribe to the onset of long-range antiferromagnetic order. No magnetic Bragg scattering is observed in powder neutron diffraction data collected at 0.05 K, however, which is consistent with a strongly suppressed ordered moment with an upper limit $\mu_\textrm{ord} < 0.15 \mu_\textrm{B}$. The one-dimensional character of the magnetic correlations in KMoOP$_2$O$_7$ is verified through analysis of inelastic neutron scattering data, resulting in a model with $J_\textrm{1} \approx 34$ K and $J_\textrm{2} \approx -2$ K for the intrachain and interchain exchange interactions, respectively. The origin of these experimental findings are addressed through density-functional theory calculations.

Competing magnetic phases in the frustrated spin-1/2 chain compound β−TeVO4 probed by NMR

In frustrated spin-1/2 chains the competition between the nearest- and next-nearest-neighbor exchange interactions leads to a rich phase diagram that becomes even richer in the presence of perturbations in their material realizations. These effects are still largely unexplored, so that new insight into static and dynamic magnetism, in particular by sensitive local probes, is highly desired. Here we present a comprehensive $^{17}$O nuclear magnetic resonance study of $\beta$-TeVO$_4$, where the anisotropy of the main exchange interactions and additional weak interchain exchange interactions complement the theoretical phase diagram. Our results confirm the dynamical nature of the intriguing spin-stripe phase that has been reported in previous studies. In addition, we find that the magnetic order in the high-field phase, which develops just below the magnetization saturation, is consistent with an unusual type of spin-density-wave (SDW) order with different alignments of the magnetic moments on the neighboring chains. This is reminiscent of the ordering in the SDW phase, realized in the absence of the magnetic field, and is thus most likely stabilized by magnetic anisotropy.

Spin dynamics of the spin-chain antiferromagnet RbFeS2

We report transport and inelastic neutron scattering studies on electronic properties and spin dynamics of the quasi-one-dimensional spin-chain antiferromagnet ${\mathrm{RbFeS}}_{2}$. An antiferromagnetic phase transition at ${T}_{N}\ensuremath{\approx}195$ K and dispersive spin waves with a spin gap of 5 meV are observed. By modeling the spin excitation spectra using linear spin wave theory, intra and interchain exchange interactions are found to be $S{J}_{1}=100(5)$ meV and $S{J}_{3}=0.9(3)$ meV, respectively, together with a small single-ion anisotropy of $S{D}_{zz}=0.04(1)$ meV. Comparison with previous results for other materials in the same class of ${\mathrm{Fe}}^{3+}$ spin-chain systems reveals that although the magnetic order sizes show significant variation from 1.8 to $3.0\phantom{\rule{4pt}{0ex}}{\ensuremath{\mu}}_{B}$ within the family of materials, the exchange interactions $SJ$ are nevertheless quite similar, analogous to the iron pnictide superconductors where both localized and delocalized electrons contribute to the spin dynamics.

Epitaxial stabilization of thin films of the frustrated Ge-based spinels

Frustrated magnets can host numerous exotic many-body quantum and topological phenomena. ${\mathrm{GeNi}}_{2}{\mathrm{O}}_{4}$ is a three-dimensional $S=1$ frustrated magnet with an unusual two-stage transition to the two-dimensional antiferromagnetic ground state, while ${\mathrm{GeCu}}_{2}{\mathrm{O}}_{4}$ is a high-pressure phase with a strongly tetragonally elongated spinel structure and magnetic lattice formed by $S=1/2 {\mathrm{CuO}}_{2}$ linear chains with frustrated interchain exchange interactions and exotic magnetic behavior. Here, we report on the thin-film epitaxial stabilization of these two compounds. The developed growth mode, surface morphology, crystal structure, and copper valence state were characterized by in situ reflection high-energy electron diffraction, atomic force microscopy, x-ray reflectivity, x-ray diffraction, x-ray photoelectron spectroscopy, and resonant x-ray absorption spectroscopy. Our results pave an alternative route to the comprehensive investigation of the puzzling magnetic properties of these compounds and the exploration of emergent features driven by strain.

The magnetic properties of the LaCr3(BO3)4 crystal

This article investigates the magnetic susceptibility, χ(T), of the two-phase (R32 + C2/c) crystal LaCr3(BO3)4 in the temperature range 2–300 K for two orientations of an external magnetic field. It has been established that both structural modifications of lanthanum chromium borate are ordered antiferromagnetically, with each of them having its own Néel temperature (6.5 and 8.5 K). It has been shown that at T &amp;gt; 60 K, the magnetic susceptibility is well described by the Curie–Weiss law with an effective magnetic moment of μeff = 3.86 μB/Cr3+ and a Curie–Weiss temperature of θ = –23 K. Within the Heisenberg spin chain model, taking into account the interchain exchange interaction, the authors have obtained the following exchange-interaction constants: an antiferromagnetic intrachain exchange (J/k = 4.8 K) and a ferromagnetic interchain exchange (J'/k = –0.28 K).

Features of magnetic and magnetoelectric properties, H-T phase diagram of GdCr3(BO3)4

Comprehensive studies of magnetic properties of GdCr3(BO3)4 single crystal have been carried out. The integrals of intrachain (J/k = 4 ± 1 K) and interchain (J΄/k ≈ −0.7 K) exchange interactions in the Cr subsystem have been determined and the strength of Cr-Gd exchange interaction (JCr-Gd/k ~ −0.2 K) has been estimated. The values of the exchange field 2HE ≈ 17 T and the effective magnetic anisotropy field HA ≈ 0.05 T of GdCr3(BO3)4 have been estimated. The electric polarization ΔPa along the a axis in the longitudinal geometry of the experiment has been detected. Correlations between the electric polarization and the magnetization of the studied compound have been found. The spin-reorientation phase transition in the magnetically ordered state has been found. This transition exists for the external magnetic field applied along any crystallographic direction and the transition field depends weakly on the direction of the field. Nature of the spin-reorientation phase transition has been discussed. Magnetic phase diagram has been constructed and spin configurations for the low-field and high-field phases have been proposed.

Self‐Consistent Four‐Particle Cluster Model of Fe3+ Heisenberg Chains: Spectral and Magnetic Properties of YFe3(BO3)4 Crystals

The magnetic properties of antiferromagnetic quasi‐1D YFe3(BO3)4 crystals are studied based on the analysis of the measured optical spectra of the Fe3+ ions in different rare‐earth (RE) iron borates and a self‐consistent four‐particle cluster approach to helical iron chains. The parameters of crystal fields affecting the Fe3+ ions are calculated in the framework of the exchange charge model. The parameters of the isotropic intrachain and interchain exchange interactions between the Fe3+ ions are determined from modeling the temperature dependences of magnetic susceptibilities, the phase transition temperature, and spontaneous magnetic moments. The magnetic easy‐plane anisotropy is explained as the result of dipolar interactions between the Fe3+ ions in the trigonal crystal lattice. The developed model can be used to analyze and predict the properties of multiferroic multifunctional RE iron borates and highlight contributions of the iron subsystem into the magnetoelectric and magnetoelastic effects in these compounds.

Interchain interaction effect on the magnetic properties of azurite material

Considering the interchain exchange interaction through dimer and monomer in the azurite, a two-dimensional Ising–Heisenberg model with dimer and monomer interlacing arrangement is established, and the magnetic and thermodynamic properties are calculated by Monte Carlo method. In the ground state, as the magnetic field increases from zero, the system changes from quantum antiferromagnetic (QAF) state with monomer in antiferromagnetic state and dimer in spin singlet to the quantum ferrimagnetism (QFI) state with monomer in saturated state and dimer in spin singlet, and finally reaches the saturated spin state (SP). In the QFI state, system shows 1/3 magnetization plateau. Starting from the QAF phase closing to the boundary with QFI phase, the specific heat and magnetic susceptibility of the system with temperature show beaks in the low temperature region, corresponding phase change, and in the whole range of temperature they may present double peak structure. Starting from the two phases of QFI and SP near the boundary between them, the magnetic susceptibility and specific heat with temperature also show peak, and the corresponding phase transition temperature is symmetry with respect to the phase boundary. Comparing with the specific heat data in the experiment, we conjecture the strength of the interchain interaction of azurite material is about half of the dimer interaction.

Short-Range and Long-Range Order in AFM–FM Exchange Coupled Compound LiCu2(VO4)(OH)2

The presence of both strong interchain and intrachain interactions of an antiferromagnetic as well as an ferromagnetic nature may lead to the appearance of a gap in the magnetic excitation spectrum of LiCu2(VO4)(OH)2 as evidenced by the hump in magnetic susceptibility χ at T* ≈ 30 K. The temperature range of short-range magnetic order is terminated by the onset of long-range magnetic order at TN = 10 K, which is triggered by substantial interchain exchange interactions. This observation is corroborated by the specific heat, Cp, singularity, electron spin resonance, and nuclear magnetic resonance measurements. The latter reveals a broad distribution of the resonance fields ascribed to the formation of a helix magnetic structure. First-principles calculations allow estimations of both intrachain and interchain exchange interaction parameters, suggesting the implementation of a strongly coupled scenario with competing inter- and intrachain interactions.

Composition dependence of magnetic properties in the mixed magnet Co1−xNixCl2·H2O

Abstract Effects of disorder, frustration and low dimensional character occur in mixed magnetic Co1−xNixCl2·H2O, examined by dc magnetization and susceptibility measurements across the composition range. The pure components are quasi-one-dimensional antiferromagnets ordering at 15.0 K (Co) and 5.65 K (Ni), with susceptibility maxima at 16.2 and 8.4 K respectively; a spin glass transition also appears in the cobalt system near 8 K. In each compound weaker antiferromagnetic interchain exchange interactions supplement dominant ferromagnetic exchange along MCl2MCl2M… chemical and structural chains. High temperature magnetic susceptibilities are analyzed to yield Curie and Weiss constants in χM = C/(T − θ). Regular but not mean-field composition dependences appear for C and θ. The former is not linear and the latter displays a minimum near x = 0.30. Notable is a susceptibility maxima varying in location only weakly from x = 0.10 to x = 0.70, decreasing markedly only for higher x. Magnetization isotherms evolve regularly as x varies, with systematic composition dependences of a metamagnetic transition field and hysteresis through x = 0.70. A qualitative change in the isotherms occurs for x = 0.90, but substantial curvature still appears with smaller but definite hysteresis. A thermoremanent magnetization is seen in all mixtures, and is largest for the composition extremes. Thus, nonequilibrium magnetic behavior characteristic of the cobalt component, in contrast to the more conventional nickel component, occurs even when the latter is present in strong majority.

Spin-wave dynamics and exchange interactions in multiferroic NdFe3(BO3)4 explored by inelastic neutron scattering

Magnetic excitations and exchange interactions in multiferroic NdFe3(BO3)4 were studied by inelastic neutron scattering in the phase with commensurate antiferromagnetic structure. The observed spectra were analyzed in the frame of the linear spin-wave theory. It was shown that only the model, which includes the exchange interactions within eight coordination spheres, describes satisfactorily all observed dispersion curves. The calculation showed that the spin-wave dynamics is governed by the strongest antiferromagnetic intra-chain interaction and three almost the same inter-chain interactions. Other interactions, including ferromagnetic exchange, appeared to be insignificant. The overall energy balance of the antiferromagnetic inter-chain exchange interactions, which couple the moments from the adjacent ferromagnetic layers as well as within a layer, stabilizes ferromagnetic arrangement in the latter. It demonstrates that the pathway geometry plays a crucial role in forming of the magnetic structure.

Synthesis and structural, magnetic, and resonance properties of the LiCuFe2(VO4)3 compound

Complex studies have been performed for the structural, static magnetic, and resonance properties of a new magnet LiCuFe2(VO4)3 prepared by solid-phase synthesis. The temperature dependence of the susceptibility has an anomaly at temperature T max = 9.6 K. At high temperatures, the LiCuFe2(VO4)3 sample is in the paramagnetic state described by the Curie–Weiss law at T > 50 K and mainly determined by iron ions with effective magnetic moment μeff(exp) = 8.6μB per formula unit. At low temperatures, a long-range magnetic order is observed in the magnetic subsystem of the sample; the order is predominantly characterized by the antiferromagnetic exchange interaction and high frustration level. The exchange interaction parameters are estimated in a six-sublattice representation of the LiCuFe2(VO4)3 magnet. It is shown that the LiCuFe2(VO4)3 compound is an antiferromagnet with strong intrachain and frustrating interchain exchange interactions.

Tunable crossover between one- and three-dimensional magnetic dynamics inCoIIsingle-chain magnets organized by halogen bonding

Low-temperature magnetometry, ac susceptibility, and calorimetry have been employed to study Co-based single-chain magnets (SCMs) organized through halogen bonding. Magnetic hysteresis and maxima in the dc and ac susceptibilities, respectively, confirm the SCM behavior of the system. Several characteristic magnetic relaxation regimes are observed at different temperatures, which can be associated with both intra- and interchain exchange interactions. Remarkably, tweaking the rate at which an external magnetic field is swept along the axis of the chains enables a controlled transition between the one- and three-dimensional dynamics. Experiments on an isostructural Co-based SCM system crystallized with different halogens do not show three-dimensional dynamics, illustrating the importance of halogen bonding on the control of interchain interactions.

A multifrequency EPR study of poly(PADPA) synthesized with Trametes versicolor laccase from the aniline dimer p-aminodiphenylamine (PADPA) in the presence of anionic vesicles

Poly(PADPA) synthesized with the enzyme Trametes versicolor laccase (TvL) at pH = 3.5 in aqueous solution from the aniline dimer p-aminodiphenylamine (PADPA) was studied by EPR spectrometry at X-band and W-band frequencies. For the synthesis of poly(PADPA), vesicles formed from AOT (sodium bis-(2-ethylhexyl)sulfosuccinate) were used as structure-directing templates, and TvL/O2 as catalyst and oxidant. The isolated product is abbreviated as “poly(PADPA)-TvL-AOT” to distinguish it from poly(PADPA) obtained by other means. The EPR spectrum of poly(PADPA)-TvL-AOT recorded at room temperature is complex. It can be decomposed into two separate Dyson–type spectral components. Furthermore, the spectra measured at high frequency exhibit a line broadening behavior in comparison to the spectra recorded at low frequency where there is no line broadening. This behavior was used to estimate the effective inter-chain spin exchange interaction for each monitored spectral component. The obtained effective distances between the polymer (or oligomer) chains in both identified components of poly(PADPA)-TvL-AOT can be explained by considering slightly different interactions between the chains and the AOT molecules present in the sample. Additionally, due to different average g tensor values, gav, of these components, it seems that each spectral component originates from one of two different molecular subunits (or local structural motifs) within the polymer (or oligomer) chains.

Spin-stripe phase in a frustrated zigzag spin-1/2 chain.

Motifs of periodic modulations are encountered in a variety of natural systems, where at least two rival states are present. In strongly correlated electron systems, such behaviour has typically been associated with competition between short- and long-range interactions, for example, between exchange and dipole–dipole interactions in the case of ferromagnetic thin films. Here we show that spin-stripe textures may develop also in antiferromagnets, where long-range dipole–dipole magnetic interactions are absent. A comprehensive analysis of magnetic susceptibility, high-field magnetization, specific heat and neutron diffraction measurements unveils β-TeVO4 as a nearly perfect realization of a frustrated (zigzag) ferromagnetic spin-1/2 chain. Notably, a narrow spin-stripe phase develops at elevated magnetic fields due to weak frustrated short-range interchain exchange interactions, possibly assisted by the symmetry-allowed electric polarization. This concept provides an alternative route for the stripe formation in strongly correlated electron systems and may help understanding of other widespread, yet still elusive, stripe-related phenomena.

Suitability of chromium phthalocyanines to test Haldane's conjecture: First-principles calculations

We have studied the intrachain magnetic interactions in chromium phthalocyanine (CrPc, spin 2) for a wide range of chain structural parameters using hybrid exchange density functional theory. A comparison of the computed interchain and intrachain exchange interactions and zero-field splitting shows that many of the chain structures including those in the α and η phases are suitable one-dimensional antiferromagnetic chains of integer spins for testing Haldane’s conjecture. In addition, the exchange interaction in CrPc is strongly dependent on the stacking angle and weakly on the sliding angle. The peak value of the exchange interactions is 120 K when the molecules are face on, which is much larger than those in copper phthalocynines. The prediction of the relationship between the computed magnetic properties and geometrical parameters can provide guidance to experimentalists for the applications of CrPc structures in spintronics.

Crystal and Magnetic Structures and Physical Properties of a New Pyroxene NaMnGe2O6 Synthesized under High Pressure

A new pyroxene compound, NaMnGe(2)O(6), has been synthesized at 3 GPa and 800 °C and fully characterized by X-ray single-crystal diffraction, neutron powder diffraction, and measurements of magnetization and specific heat. NaMnGe(2)O(6) crystallizes into a monoclinic C2/c structure with unit-cell parameters a = 9.859(2) Å, b = 8.7507(18) Å, c = 5.5724(11) Å, and β = 105.64(3)° at 153 K. A cooperative Jahn-Teller distortion is formed by an ordering of the longest Mn-O bonds between two neighboring octahedra along the chain direction. This feature distinguishes NaMnGe(2)O(6) from other pyroxene compounds without Jahn-Teller active cations and suggests that the Jahn-Teller distortion competes with the intrinsic local distortion in the pyroxene structure. No orbital order-disorder transition has been found up to 750 K. Like other alkali-metal pyroxenes with S > (1)/(2), NaMnGe(2)O(6) (S = 2) was found to undergo a long-range antiferromagnetic (AF) ordering at T(N) = 7 K due to intrachain and interchain exchange interactions. Due to the peculiar structural features and the corresponding magnetic coupling, the weak AF spin ordering gives way to a ferromagnetic-like state at a sufficiently high magnetic field. Specific-heat measurements demonstrated that a large portion of the magnetic entropy, >60%, has been removed above T(N) as a result of strong spin correlations within the quasi-one-dimensional Mn(3+)-spin chains. The Reitveld refinement of neutron powder diffraction data gives a commensurate magnetic structure defined by k = [0 0 0.5] with Mn moments aligned mainly along the c-axis with a small component along both a- and b-axes.

ChemInform Abstract: Synthesis and Magnetic Properties of One-Dimensional Ferro- and Ferrimagnetic Chains Made up of an Alternating Array of 1,3-Bis(N-tert-butyl-N-oxyamino)benzene Derivatives and Mn(II)(hfac)2

Abstract Bis(hexafluoroacetylacetonato) manganese(II), Mn(hfac) 2 , reacts with the bisnitroxide radicals, 5- R -1,3-bis( N - tert -butyl- N -oxyamino)benzene ( 1 R ) (R=H, Cl and Br), yielding one-dimensional (1-D) polymeric complexes of formula [Mn(hfac) 2 1 R ] n . X-ray analysis of the complexes has shown that they crystallize in the monoclinic space group P 2 1 / n . In this structure, the manganese(II) ions and 1 R molecules make up one-dimensional chains with the bisnitroxide radical serving as a bidentate ligand to Mn(II)(hfac) 2 . The 1 H complex orders antiferromagnetically at 5.5 K, while the 1 Cl and 1 Br complexes show ferrimagnetic order at 4.8 and 5.3 K, respectively. The intrachain exchange interaction parameters for a model of S =3/2 ferromagnetic chains were found to be, 2 J eff / k =23±2 K in all the compounds. J eff is the effective magnetic exchange interaction between units of NOMnNO. A change in the sign of the interchain exchange interaction is referred to as the change of the shortest exchange path, from the MnFN( tert -Bu)O ( 1 Cl and 1 Br ) to N( tert -Bu)O FN( tert -Bu)O ( 1 H )