1D Antiferromagnets Research Articles

Spin gap in quasi-one-dimensional S = 3/2 antiferromagnet CoTi2O5

Quasi-one-dimensional (1D) antiferromagnets are known to display intriguing phenomena especially when there is a spin gap in their spin-excitation spectra. Here we demonstrate that a spin gap exists in the quasi-1D Heisenberg antiferromagnet CoTi2O5 with highly ordered Co2+/Ti4+ occupation, in which the Co2+ ions with S = 3/2 form a 1D spin chain along the a-axis. CoTi2O5 undergoes an antiferromagnetic transition at T N ∼ 24 K and exhibits obvious anisotropic magnetic susceptibility even in the paramagnetic region. Although a gapless magnetic ground state is usually expected in a quasi-1D Heisenberg antiferromagnet with half-integer spins, by analyzing the specific heat, the thermal conductivity, and the spin-lattice relaxation rate (1/T 1) as a function of temperature, we found that a spin gap is opened in the spin-excitation spectrum of CoTi2O5 around T N, manifested by the rapid decrease of magnetic specific heat to zero, the double-peak characteristic in thermal conductivity, and the exponential decay of 1/T 1 below T N. Both the magnetic measurements and the first-principles calculations results indicate that there is spin-orbit coupling in CoTi2O5, which induces the magnetic anisotropy in CoTi2O5, and then opens the spin gap at low temperature.

Electric‐Field‐Tunable Bipolar Linear Magnetoelectric Effect in Zigzag Graphene Nanoribbon‐Based Antiferromagnet

Modern electronic devices are moving toward miniaturization and integration. Therefore, achieving electrical control of magnetization effectively in 1D materials represents a promising field for the practical applications in memory elements. Herein, it is discovered, from first‐principles calculations, that an electric‐field‐tunable bipolar linear magnetoelectric effect can be realized in 1D antiferromagnets based on double‐Gd‐adsorbed graphene nanoribbon with four zigzag carbon chains (2Gd‐4ZGNR). It is found that, compared with the bare 4ZGNR, the adsorption of two Gd atoms on the 4ZGNR reduces the bandgap. As a result, 2Gd‐4ZGNR transits from antiferromagnetic semiconductor to ferrimagnetic metal at a relatively low critical external transverse (perpendicular) electric field, where the net magnetic moment can be induced. The antiferromagnetism and inversion‐symmetrical crystal structure further allow to realize a bipolar linear magnetoelectric effect, where the 2Gd‐4ZGNR forms two groups of independent linear magnetic response states, acting as a magnetoelectric memory element.

Experimental Studies of Dzyaloshinskii–Moriya Interaction in Quantum Spin Systems: High-frequency High-field Electron Spin Resonance (ESR) Measurements

In this review, the importance of the Dzyaloshinskii–Moriya Interaction (DMI) to the magnetic properties of quantum spin systems is discussed mainly focusing on the determination of or understanding the role of DMI extracted from high-frequency high-field electron spin resonance (ESR) measurements. This review includes the ESR theories of the S = 1/2 one-dimensional (1D) antiferromagnet with the staggered field (Oshikawa–Affleck theory) and with the uniform DMI, and several related experimental results are shown. Then, the proposed mechanisms of the singlet–triplet transition in quantum spin systems together with the ESR selection rules are introduced in connection with various experimental results. Finally, the role of DMI in the ground state of kagome lattice antiferromagnets and the honeycomb lattice antiferromagnet is discussed with some experimental results.

Curvilinear One-Dimensional Antiferromagnets.

Antiferromagnets host exotic quasiparticles, support high frequency excitations and are key enablers of the prospective spintronic and spin-orbitronic technologies. Here, we propose a concept of a curvilinear antiferromagnetism where material responses can be tailored by a geometrical curvature without the need to adjust material parameters. We show that an intrinsically achiral one-dimensional (1D) curvilinear antiferromagnet behaves as a chiral helimagnet with geometrically tunable Dzyaloshinskii-Moriya interaction (DMI) and orientation of the Néel vector. The curvature-induced DMI results in the hybridization of spin wave modes and enables a geometrically driven local minimum of the low-frequency branch. This positions curvilinear 1D antiferromagnets as a novel platform for the realization of geometrically tunable chiral antiferromagnets for antiferromagnetic spin-orbitronics and fundamental discoveries in the formation of coherent magnon condensates in the momentum space.

Universality of Heisenberg–Ising chain in external fields

Motivated by the recent surge of transverse-field experiments on quasi-one-dimensional (1D) antiferromagnets Sr(Ba)Co2V2O8, we investigate the quantum phase transition (QPT) in a Heisenberg–Ising chain under a combination of two in-plane inter-perpendicular transverse fields and a four-period longitudinal field, where the in-plane transverse field is either uniform or staggered. We show that the model can be unitary mapped to the 1D transverse-field Ising model (1DTFIM) when the x and y components of the spin interaction and the four-period field are absent. When these two terms are present, following both analytical and numerical efforts, we demonstrate that the system undergoes a second-order QPT with increasing transverse fields, where the critical exponents as well as the central charge fall into the universality of 1DTFIM. Our results naturally identify the 1DTFIM universality of 1D quantum phase transitions observed in the existed experiments in Sr(Ba)Co2V2O8 with transverse field applied along either [] or [] direction. Upon varying the tuning parameters, a critical surface with 1DTFIM universality is determined and silhouetted to exhibit the general presence of the universality in a much wider scope of models than conventional understanding. Our results provide a broad guiding framework to facilitate the experimental realization of 1DTFIM universality in real materials.

Spin gap in the quasi-one-dimensional S=12 antiferromagnet K2CuSO4Cl2

Electron spin resonance experiments in the quasi-1D S=1/2 antiferromagnet K$_2$CuSO$_4$Cl$_2$ reveal opening of a gap in absence of magnetic ordering, as well as an anisotropic shift of the resonance magnetic field. These features of magnetic excitation spectrum are explained by a crossover between a gapped spinon-type doublet ESR formed in a 1D antiferromagnet with uniform Dzyaloshinskii-Moriya interaction and a Larmor-type resonance of a quasi-1D Heisenberg system

Magnetism and High-magnetic Field Magnetization in Alkali Superoxide CsO2

Alkali superoxide CsO2 is one of candidates for the spin-1/2 one-dimensional (1D) antiferromagnet, which may be sequentially caused by an ordering of the pi-orbital of O2- molecule below TS ~ 70 K. Here, we report on the magnetism in powder CsO2 and high-magnetic field magnetization measurements in pulsed-magnetic fields of up to 60 T. We obtained the low temperature phase diagram around the antiferromagnetic ordering temperature TN = 9.6 K under the magnetic field. At 1.3 K, remarkable up-turn curvature in the magnetization around a saturation field of ~ 60 T is found, which corresponds to the spin-1/2. We will compare it with the theoretical calculation.

Low-lying Photoexcited States of a One-Dimensional Ionic Extended Hubbard Model

We investigate the properties of low-lying photoexcited states of a one-dimensional (1D) ionic extended Hubbard model at half-filling. Numerical analysis by using the full and Lanczos diagonalization methods shows that, in the ionic phase, there exist low-lying photoexcited states below the charge transfer gap. As a result of comparison with numerical data for the 1D antiferromagnetic (AF) Heisenberg model, it was found that, for a small alternating potential Δ, these low-lying photoexcited states are spin excitations, which is consistent with a previous analytical study [Katsura et al., Phys. Rev. Lett. 103, 177402 (2009)]. As Δ increases, the spectral intensity of the 1D ionic extended Hubbard model rapidly deviates from that of the 1D AF Heisenberg model and it is clarified that this deviation is due to the neutral-ionic domain wall, an elementary excitation near the neutral-ionic transition point.

Breaking of 1D magnetism in a spin-1 chain antiferromagnet Ni2V2O7: ESR and first-principles studies

We report the breaking of one-dimensional (1D) magnetism in a spin-1 chain antiferromagnet Ni2V2O7. First, basic structure and magnetization data are presented, showing that the compound is ordered at $ T_{N}=7$ K and a field-induced spin-flop transition occurs at $ H_{sf}=2.8$ T. Second, high-field electronic spin resonance (ESR) data demonstrate antiferromagnetic (AFM) resonance modes below T N, which can be well understood by conventional AFM resonance theory with uniaxial anisotropy. Third, the first-principles calculations based on density function theory reveal a much larger interchain AFM interaction than the intrachain couplings. Combining with all these results, we can see that Ni2V2O7 is not a 1D antiferromagnet, although it is a skew chain from the viewpoint of crystallographic structure.

A Nearly Ideal One-Dimensional S = 5/2 Antiferromagnet FeF3(4,4'-bpy) (4,4'-bpy =4,4'-bipyridyl) with Strong Intrachain Interactions.

An ideal one-dimensional (1D) magnet is expected to show exotic quantum phenomena. For compounds with larger S (S = 3/2, 2, 5/2, ...), however, a small interchain interaction J' tends to drive a conventional long-range ordered (LRO) state. Here, a new layered structure of FeF3(4,4'-bpy) (4,4'-bpy = 4,4'-bipyridyl) with novel S = 5/2 (Fe(3+)) chains has been hydrothermally synthesized by using 4,4'-bpy to separate chains. The temperature-dependent susceptibility exhibits a broad maximum at high as 164 K, suggesting a fairly strong Fe-F-Fe intrachain interaction J. However, no anomaly associated with a LRO is seen in both magnetic susceptibility and specific heat even down to 2 K. This indicates an extremely small J' with J'/J < 3.2 × 10(-5), making this new material a nearly ideal 1D antiferromagnet. Mössbauer spectroscopy at 2.7 K reveals a critical slowing down of the 1D fluctuations toward a possible LRO at lower temperatures.

Observation of the Thermal Conductivity due to Spins in the One-Dimensional Antiferromagnetic Ising-Like Spin System ACoX3 (A = Rb, Cs; X = Cl, Br)

Thermal conductivity measurements have been carried out for single crystals of the onedimensional (1D) antiferromagnetic (AF) Ising-like spin system ACoX3 (A = Rb, Cs; X = Cl, Br). A shoulder originating from the thermal conductivity due to spin excitations, \k{appa}?spin, has been observed around 60 K in the temperature dependence of the thermal conductivity along the c-axis parallel to spin chains for every ACoX3. To our knowledge, this is the first observation of ?\k{appa}spin in 1D AF Ising-like spin systems. It has been found that the magnitude of ?\k{appa}spin in ACoX3 is a little smaller than those in 1D AF Heisenberg spin systems. The reason is discussed in terms of the Heisenberg-like character in ACoX3.

Dimethylammonium copper formate [(CH3)2NH2]Cu(HCOO)3: A metal-organic framework with quasi-one-dimensional antiferromagnetism and magnetostriction

Metal-organic frameworks (MOFs) can exhibit many interesting properties such as multiferroic behavior, dipolar glass, gas storage, and protonic conductivity. Here we report that dimethylammonium copper formate (DMACuF) [(CH${}_{3}$)${}_{2}$NH${}_{2}$]Cu(HCOO)${}_{3}$, a cation templated nonporous MOF with perovskite topology, exhibits strong one-dimensional (1D) antiferromagnetism with a N\'eel temperature, ${T}_{N}$, of 5.2 K. These conclusions are derived from detailed magnetic susceptibility, heat capacity, dielectric constant, and high-frequency electron paramagnetic resonance measurements as well as density functional theory (DFT) calculations. The magnetic susceptibility exhibits a broad maximum at \ensuremath{\sim}50 K, suggesting low-dimensional magnetism; heat capacity measurements show a N\'eel temperature of 5.2 K. The magnetization versus field data at 1.8 K shows a spin-flop transition at ${H}_{sf}$ \ensuremath{\sim} 1.7 T. The ratio ${T}_{N}$/$J=6.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$, where $J$ is the near-neighbor exchange constant (77.4 K), and the small value (2 K) of the interchain coupling suggests that DMACuF is close to an ideal 1D magnet. In this three-dimensional crystal lattice, the 1D magnetic behavior is made possible by the Jahn-Teller distortion of the 3${d}^{9}$ Cu${}^{2+}$ ions. Temperature dependence of the electron paramagnetic resonance field and the linewidth exhibits critical broadening for temperatures below 50 K, following a behavior quite characteristic of 1D spin systems. DFT calculations show that [(CH${}_{3}$)${}_{2}$NH${}_{2}$]Cu(HCOO)${}_{3}$ has a magnetic structure in which 1D antiferromagnetic chains parallel to the $c$ direction are weakly coupled ferromagnetically, supporting the thermomagnetic and EPR results. Dielectric measurements under applied magnetic fields of 0\ensuremath{-}7 T reveal a kink at the ${T}_{N}$, a clear indication of magnetostriction behavior.

Spin nematic states in spin-1 antiferromagnets with easy-axis anisotropy

It is well known that spin nematic phases can appear in either frustrated magnets or in those described by Hamiltonians with large exotic non-Heisenberg terms like biquadratic exchange. We show in the present study that non-frustrated spin-1 1D, 2D and 3D antiferromagnets with single-ion easy-axis anisotropy can show nematic phases in strong magnetic field. For 1D case we support our analytical results by numerical ones.

Theory of Raman Scattering in One-Dimensional Quantum Spin-12Antiferromagnets

We study theoretically the Raman-scattering spectra in the one-dimensional (1D) quantum spin-1/2 antiferromagnets. The analysis reveals that their low-energy dynamics is exquisitely sensitive to various perturbations to the Heisenberg chain with nearest-neighbor exchange interactions, such as magnetic anisotropy, longer-range exchange interactions, and bond dimerization. These weak interactions are mainly responsible for the Raman scattering and give rise to different types of spectra as functions of frequency, temperature, and external field. In contrast to the Raman spectra in higher dimensions in which the two-magnon process is dominant, those in 1D antiferromagnets provide much richer information on these perturbations.

Metamagnetism and weak ferromagnetism in nickel (II) oxalate crystals

Microcrystals of orthorhombic nickel (II) oxalate dihydrate were synthesized through a precipitation reaction of aqueous solutions of nickel chloride and oxalic acid. Magnetic susceptibility exhibits a sharp peak at 3.3 K and a broad rounded maximum near 43 K. We associated the lower maximum with a metamagnetic transition that occurs when the magnetic field is about ≥ 3.5 T. The maximum at 43 K is typical of 1D antiferromagnets, whereas weak ferromagnetism behavior was observed in the range of 3.3–43 K.

Structure and Physical Properties of Molecule-Based Magnets Including Transition Metal Complexes of Crown Thioethers

Abstract A new series of molecule-based magnets, including crown thioether (9S3 = 1,4,7-trithiacyclononane) complexes of transition metals (Ni, Co, Cu), are presented. TCNQ salts [M(9S3)2](TCNQ)2 (M = Ni, Co) are one-dimensional (1D), antiferromagnetic (AF) complexes with an intra-chain interaction J = −3.9 K and −1.3 K for M = Ni and Co, respectively, despite its long intermolecular distance, for which the large spin density on the sulfur atom in the magnetic [M(9S3)2]2+ cation is responsible. The mixed valence salt [M(9S3)2](TCNQ)3 (M = Ni, Co) is a paramagnetic semiconductor. 1D AF magnet [Cu(9S3)Br2] does not undergo any magnetic transition because of the weak inter-chain interaction. Substituting a very small amount (∼5%) of Cu with Ni causes a structural change. The change decreases the distances of inter-chain S–S contacts, resulting in the generation of an AF transition at TN = 4.5 K. [M(9S3)2][Ni(bdt)2]2 (M = Ni, Co; bdt = 1,2-benzenedithiolato) are weak-ferromagnets with TN = 6.2 K and 2.6 K for M = Ni and Co, respectively. In the crystals, [M(9S3)2]2+–[Ni(bdt)2]− alternate chains and [Ni(bdt)2]− uniform chains coexist. The appearance of weak-ferromagnetism is associated with a competition between two kinds of inter-chain AF interactions between [M(9S3)2]2+–[Ni(bdt)2]− alternate chains, where the stronger one is an indirect inter-chain interaction through [Ni(bdt)2]− uniform chains, while the weaker is a direct inter-chain interaction.

Recent high field ESR studies of low-dimensional quantum spin systems in Kobe

Recent advances in the high-field ESR studies of low-dimensional quantum spin systems in Kobe are presented. Among many systems studied, the results of S= 1 2 quasi-one-dimensional (1D) antiferromagnet BaCu 2(Si 1− x Ge x ) 2O 7 with the staggered field and S= 1 2 diamond chain system Cu 3OH 2(CO 3) 2 are discussed. As the interchain interaction is almost canceled in the BaCu 2(Si 1− x Ge x ) 2O 7 ( x=0.65) system, we have found that the field and temperature dependences of the linewidth and the resonance field obey the Oshikawa–Affleck (OA) ESR theory of 1D antiferromagnet. The effect of the interchain interaction from the x dependence measurement and the existence of the breather mode at low temperature are also discussed. On the other hand, the high-field ESR measurements at 1.8 K revealed the direct transition in Cu 3OH 2(CO 3) 2. The direct transition turned out to be anisotropic and it will be discussed in connection with the 1 3 magnetization plateau which is also anisotropic.

From achiral ligands to chiral coordination polymers: spontaneous resolution, weak ferromagnetism, and topological ferrimagnetism.

Using the achiral diazine ligands bearing two bidentate pyridylimino groups as sources of conformational chirality, five azido-bridged coordination polymers are prepared and characterized crystallographically and magnetically. The chirality of the molecular units is induced by the coordination of the diazine ligands in a twisted chiral conformation. The use of L(1) (1,4-bis(2-pyridyl)-1-amino-2,3-diaza-1,3-butadiene) and L(2) (1,4-bis(2-pyridyl)-1,4-diamino-2,3-diaza-1,3-butadiene) induces spontaneous resolution, yielding conglomerates of chiral compounds [Mn(3)(L(1))(2)(N(3))(6)](n) (1) and [Mn(2)(L(2))(2)(N(3))(3)](n)(ClO(4))(n).nH(2)O (2), respectively, where triangular (1) or double helical (2) chiral units are connected into homochiral one-dimensional (1D) chains via single end-to-end (EE) azido bridges. The chains are stacked via hydrogen bonds in a homochiral fashion to yield chiral crystals. When L(3) (2,5-bis(2-pyridyl)-3,4-diaza-2,4-hexadiene) is employed, a partial spontaneous resolution occurs, where binuclear chiral units are interlinked into fish-scale-like homochiral two-dimensional (2D) layers via single EE azido bridges. The layers are stacked in a heterochiral or homochiral fashion to yield simultaneously a racemic compound, [Mn(2)(L(3))(N(3))(4)](n) (3a), and a conglomerate, [Mn(2)(L(3))(N(3))(4)](n).nMeOH (3b). On the other hand, the ligand without amino and methyl substituents (L(4), 1,4-bis(2-pyridyl)-2,3-diaza-1,3-butadiene) does not induce spontaneous resolution. The resulting compound, [Mn(2)(L(4))(N(3))(4)](n) (4), consists of centrosymmetric 2D layers with alternating single diazine, single EE azido, and double end-on (EO) azido bridges, where the chirality is destroyed by the centrosymmetric double EO bridges. These compounds exhibit very different magnetic behaviors. In particular, 1 behaves as a metamagnet built of homometallic ferrimagnetic chains with a unique "fused-triangles" topology, 2 behaves as a 1D antiferromagnet with alternating antiferromagnetic interactions, 3a and 3b behave as spin-canted weak ferromagnets with different critical temperatures, and 4 also behaves as a spin-canted weak ferromagnet but exhibits two-step magnetic transitions.

Magnetic order and moment distribution in doped spin-chain systems

We consider the effect of doping on the magnetic order in quasi one-dimensional (1D) antiferromagnets. First the detailed magnetic response of finite spin-1/2 chains in the presence of a staggered field is determined, which by itself shows an interesting crossover as function of length and field strength. We can then understand the ordering by including an effective coupling between the chains, which results in a Neel ordered phase at low temperatures, but with a broad distribution of magnetic moments that has to be determined self-consistently.

Magnetic Dimensionality of the Antiferromagnet CuO

We present evidence for the quasi one-dimensional (1D) antiferromagnetism of CuO in the framework of the Heisenberg model. Our result supports the speculations and conclusions made by earlier authors. We also present experimental evidence which explains the reason for CuO to be a quasi 1D antiferromagnet in spite of appearing to have a 3D structure.