One-dimensional Magnets Research Articles

Experimental observation of Bethe strings

Almost a century ago, string states-complex bound states of magnetic excitations-were predicted to exist in one-dimensional quantum magnets. However, despite many theoretical studies, the experimental realization and identification of string states in a condensed-matter system have yet to be achieved. Here we use high-resolution terahertz spectroscopy to resolve string states in the antiferromagnetic Heisenberg-Ising chain SrCo2V2O8 in strong longitudinal magnetic fields. In the field-induced quantum-critical regime, we identify strings and fractional magnetic excitations that are accurately described by the Bethe ansatz. Close to quantum criticality, the string excitations govern the quantum spin dynamics, whereas the fractional excitations, which are dominant at low energies, reflect the antiferromagnetic quantum fluctuations. Today, Bethe's result is important not only in the field of quantum magnetism but also more broadly, including in the study of cold atoms and in string theory; hence, we anticipate that our work will shed light on the study of complex many-body systems in general.

Possible quadrupolar nematic phase in the frustrated spin chain LiCuSbO4 : An NMR investigation

The frustrated one-dimensional (1D) quantum magnet LiCuSbO$_4$ is one rare realization of the $J_1-J_2$ spin chain model with an easily accessible saturation field, formerly estimated to 12~T. Exotic multipolar nematic phases were theoretically predicted in such compounds just below the saturation field, but without unambiguous experimental observation so far. In this paper we present extensive experimental research of the compound in the wide temperature (30mK$-$300K) and field (0$-$13.3T) range by muon spin rotation ($\mu$SR), $^7$Li nuclear magnetic resonance (NMR) and magnetic susceptibility (SQUID). $\mu$SR experiments in zero magnetic field demonstrate the absence of long range 3D ordering down to 30mK. Together with former heat capacity data [S.E. Dutton \emph{et al}, Phys. Rev. Lett. 108, 187206 (2012)], magnetic susceptibility measurements suggest short range correlated vector chiral phase in the field range $0-4$T. In the intermediate field values (5$-$12T), the system enters in a 3D ordered spin density wave phase with 0.75$\mu_B$ per copper site at lowest temperatures (125mK), estimated by NMR. At still higher field, the magnetization is found to be saturated above 13T where the spin lattice $T_1^{-1}$ relaxation reveals a spin gap estimated to 3.2(2)K. We narrow down the possibility of observing a multipolar nematic phase to the range 12.5$-$13T.

Spin-orbit interaction driven dimerization in one-dimensional frustrated magnets

We study the effect of spin-orbit interaction on one-dimensional U(1)-invariant frustrated magnets with dominant critical nematic fluctuations. The spin-orbit coupling explicitly breaks the U(1) symmetry of arbitrary global spin rotations about the high-symmetry axis down to $Z_2$ (invariance under a $\pi$-rotation). Given that the nematic order parameter is invariant under a $\pi$-rotation, it is relevant to ask if other discrete symmetries can be spontaneously broken. Here we demonstrate that the spin-orbit coupling induces a bond density wave that spontaneously breaks the translational symmetry and opens a gap in the excitation spectrum.

Efficient spin-filtering, magnetoresistance and negative differential resistance effects of a one-dimensional single-molecule magnet Mn(dmit)2-based device with graphene nanoribbon electrodes

We present first-principle spin-dependent quantum transport calculations in a molecular device constructed by one single-molecule magnet Mn(dmit)2 and two graphene nanoribbon electrodes. Our results show that the device could generate perfect spin-filtering performance in a certain bias range both in the parallel configuration (PC) and the antiparallel configuration (APC). At the same time, a magnetoresistance effect, up to a high value of 103%, can be realized. Moreover, visible negative differential resistance phenomenon is obtained for the spin-up current of the PC. These results suggest that our one-dimensional molecular device is a promising candidate for multi-functional spintronics devices.

Synthesis, magnetic properties and electronic structure of the S = ½ uniform spin chain system InCuPO5

We have studied the structural and magnetic properties and electronic structure of the compound InCuPO5 synthesized by a solid state reaction method. The structure of InCuPO5 comprises S = ½ uniform spin chains formed by corner-shared CuO4 units. Magnetic susceptibility (χ(T)) data show a broad maximum at about 65 K, a characteristic feature of one-dimensional (1D) magnetism. The χ(T) data are fitted to the coupled S = ½ Heisenberg antiferromagnetic (HAFM) uniform chain model that gives the intra-chain coupling (J/kB) between nearest-neighbor Cu2+ ions as −100 K and the ratio of inter-chain to intra-chain coupling (J′/J) as about 0.07. The exchange couplings estimated from the magnetic data analysis are in good agreement with the values computed from the electronic structure calculations based on the density functional theory + Hubbard U (DFT + U) approach. The combination of theoretical and experimental analysis confirms that InCuPO5 is a candidate material for weakly coupled S = ½ uniform chains. A detailed theoretical analysis of the electronic structure further reveals that the system is insulating with a gap of 2.4 eV and a local moment of 0.70 µB/Cu.

Dynamic Correlations in One-Dimensional Quantum Magnets at Finite Temperature

Dynamic Correlations in One-Dimensional Quantum Magnets at Finite Temperature

Room temperature ferroelectricity in one-dimensional single chain molecular magnets [{M(Δ)M(Λ)}(ox)2(phen)2]n (M = Fe and Mn)

The ferroelectric materials are mainly focused on pure inorganic oxides; however, the organic molecule based materials have recently attracted great attention because of their multifunctional properties. The mixing of oxalate and phenanthroline ligands with metal ions (Fe or Mn) at room temperature followed by hydrothermal treatment results in the formation of one–dimensional single chain molecular magnets which exhibit room temperature dielectric and ferroelectric behavior. The compounds are chiral in nature, and exhibit a ferroelectric behavior, attributed to the polar point group C2, in which they crystallized. The compounds are also associated with a dielectric loss and thus a relaxation process. The observed electric dipole moment, essential for a ferroelectricity, has been understood quantitatively in terms of lattice distortions at two different lattice sites within the crystal structure. The studied single chain molecular magnetic materials with room temperature ferroelectric and dielectric properties could be of great technological importance in non–volatile memory elements, and high-performance insulators.

Выполнение гипотез динамического и статического скейлинга для изинговского наномагнетика

The paper presents the results of computer simulation of the generalized Ising model of a quasi-onedimensional nanomagnet by the Monte Carlo method. The simulation is performed for antiferromagnetferromagnet phase transition with periodic boundary conditions. The dynamic scaling ratio Y = v* z and the static scaling relation dv = 2 – α have been verified for the Ising nanomagnet using values of the critical temperature, as well as values of the critical exponents. Temperature dependences of the kinetic critical index and the product of the dynamic critical index Y(T) on the correlation length index of the v* z(T) are constructed for a linear system (cluster) of finite size. The influence of interaction energy of the second, third neighbors, and four-particle interaction on the fulfillment of dynamic and static scaling hypotheses is described. Parameters are found for the dynamic scaling ratio near the critical region to be within the errors. It is shown that the static scaling hypothesis within the framework of the one-dimensional Ising magnet model near the critical region is violated for any type of interaction. However, the relation v + α = 2 is satisfied within the errors for some temperatures. The obtained results are compared with the values for the Ising model with the «dangling ends» boundary conditions.DOI 10.14258/izvasu(2017)4-04

Chirality-induced spin current through spiral magnets

Spin-polarized current through helimagnets and the conductance modulation due to the chirality mismatch are studied numerically. The one-dimensional spiral magnet structure is obtained by taking into account the Dzyaloshinskii-Moriya interaction and the ferromagnetic interaction. Although the spiral magnetic structure consists of the $y\text{\ensuremath{-}}z$ components of the magnetization, the conduction electron through the spiral magnet is polarized in the $x$ direction, and its sign depends on the chirality of the spiral structure. We also investigate charge transport through the junction system consisting of two helimagnets. Similar to the giant magnetoresistance in the uniform ferromagnet, the conductance is reduced significantly by attaching the helimagnets with different chiralities. It is possible that our proposed mechanism can make use of the chirality measuring method by using electron transport and an alternative type of magnetoresistance using a topological property.

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.

Влияние взаимодействия неближайших соседей на стабильность фаз одномерных изинговских магнетиков

Влияние взаимодействия неближайших соседей на стабильность фаз одномерных изинговских магнетиков

NMR study on the quasi one-dimensional quantum spin magnet with ladder structure

The two-legged spin ladder Cu(CO3)0.5(ClO4)(H2O)0.5(NH3)2.5 consists of a rung formed by two Cu(II)’s and of a spacing molecule CO $_{3}^{2-}$ between each two rungs. The non-centrosymmetric shape of CO $_{3}^{2-}$ molecule brings a slight bond alternation along the leg, and hence the system can be considered as an alternating spin chain, which is confirmed so far by the temperature dependence of magnetic susceptibility. In order to investigate its spin state at low temperatures, we have performed experiments of 1H-NMR, magnetization and specific heat under wide range of magnetic field, and have found the critical diverging of longitudinal relaxation rate 1/T 1, the spectral broadening and the lambda-type anomaly in specific heat at T N≃ 3.4 K, indicating the existence of long range magnetic order. In paramagnetic state well above T N, 1/T 1 showed a power-law temperature dependence, suggesting the realization of Tomonaga Luttinger liquid state.

The Effect of Spin-Peierls Instability Suppression in Nanometer-Scale-Sized CuGeO3 Crystals

In this work, we study the influence of size effects on magnetic properties of quasi-one-dimensional spin-Peierls magnet CuGeO3. It was found that the reduction of the crystallite’s size to nanometer scale (~300 × 30 nm) leads to full suppression of spin-Peierls transition, which takes place in the bulk material at \(T\approx 14\) K. Combined analysis of electron spin resonance (ESR) and magnetic susceptibility measurements allowed separating of the dynamic magnetization of Cu chains \(\chi _{ESR}\). Its temperature dependence is found to be typical for one-dimensional magnets with quantum critical (QC) behavior and is described by Curie–Weiss law \(\chi \sim \frac{1}{T+\Theta }\) at high temperatures, turning into power law asymptotic \(\chi \sim T^{-\alpha }\)\((\alpha <1)\) with temperature decrease. The data for two samples with different synthesis times (24 and 96 h) are analyzed in the framework of the QC behavior model. Although the values of magnetic parameters strongly depend on the synthesis time, the qualitative behavior is similar for both samples, which is shown by a comparative study of QC behavior of CuGeO3 doped with 1 % of Fe. We argue that the reason for the observed behavior is the competition between the onset of the staggered magnetic field and dimerization effects.

One-dimensional quantum magnetism in the anhydrous alum KTi(SO4)2

The anhydrous alum KTi(SO4)2, where the Ti3+ (d1, S = 1/2) ions form an anisotropic triangular lattice, has been prepared by a new hydrothermal route and characterized by magnetic susceptibility and neutron scattering measurements. Contrary to expectations, fits to the magnetic susceptibility indicate that the spins are isotropic (i.e. Heisenberg) and that the frustrating couplings are weak; indeed, the system is well modelled by nearly isolated chains. The inelastic neutron scattering data furthermore shows excellent agreement with an exact theoretical calculation for the one-dimensional spinon continuum. The unexpected magnetic properties of KTi(SO4)2 are explained in the light of density functional calculations, which reveal an unusual orbital ground state for the Ti3 + ion.

Quantum renormalizations in anisotropic multisublattice magnets and the modification of magnetic susceptibility under irradiation

The dispersion equation of a strongly anisotropic one-dimensional magnet catena-[FeII(ClO4)2{FeIII(bpca)2}]ClO4 containing alternating high-spin (HS) (S = 2) and low-spin (LS) (S = 1/2) iron ions is obtained by the diagram technique for Hubbard operators. The analysis of this equation yields six branches in the excitation spectrum of this magnet. It is important that the crystal field for ions with spin S = 2 is described by the Hamiltonian of single-ion easy-plane anisotropy, whose orientation is changed by 90° when passing from one HS iron ion to another. The U(N) transformation technique in the atomic representation is applied to diagonalize a single-ion Hamiltonian with a large number of levels. It is shown that the modulation of the orientation of easy magnetization planes leads to a model of a ferrimagnet with easy-axis anisotropy and to the formation of energy spectrum with a large gap. For HS iron ions, a decrease in the mean value of the spin projection due to quantum fluctuations is calculated. The analysis of the specific features of the spectrum of elementary excitations allows one to establish a correspondence to a generalized Ising model for which the magnetic susceptibility is calculated in a wide range of temperatures by the transfer-matrix method. The introduction of a statistical ensemble that takes into account the presence of chains of different lengths and the presence of iron ions with different spins allows one to describe the experimentally observed modification of the magnetic susceptibility of the magnet under optical irradiation.

Theoretical investigation of the behavior of CuSe2O5 compound in high magnetic fields

Based on the analytical and numerical approaches, we investigate thermodynamic properties of CuSe2O5 compound at high magnetic fields which is a candidate for the strong intra-chain interaction in quasi one-dimensional (1D) quantum magnets. Magnetic behavior of the system can be described by the 1D spin-1/2 XXZ model in the presence of the Dzyaloshinskii–Moriya (DM) interaction. Under these circumstances, there is one quantum critical field in this compound. Below the quantum critical field the spin chain system is in the gapless Luttinger liquid (LL) regime, whereas above it one observes a crossover to the gapped saturation magnetic phase. Indications on the thermodynamic curves confirm the occurrence of such a phase transition. The main characteristics of the LL phase are gapless and spin–spin correlation functions decay algebraic. The effects of zero-temperature quantum phase transition are observed even at rather high temperatures in comparison with the counterpart compounds. In addition, we calculate the Wilson ratio in the model. The Wilson ratio at a fixed temperature remains almost independent of the field in the LL region. In the vicinity of the quantum critical field, the Wilson ratio increases and exhibits anomalous enhancement.

Matrix Representation of Constants of Motion for One-Dimensional Heisenberg Magnet

Matrix Representation of Constants of Motion for One-Dimensional Heisenberg Magnet

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.

Localization and topology protected quantum coherence at the edge of hot matter.

Topological phases are characterized by edge states confined near the boundaries by a bulk energy gap. On raising temperature, these edge states are typically lost due to mobile thermal excitations. However, disorder can localize an isolated many-body system, potentially allowing for a sharply defined topological phase even in a highly excited state. We explicitly demonstrate this in a model of a disordered, one-dimensional magnet with spin one-half edge excitations. Furthermore, we show that the time evolution of a simple, highly excited state reveals quantum coherent edge spins. In particular, we demonstrate the coherent revival of an edge spin over a time scale that grows exponentially with system size. This is in sharp contrast to the general expectation that quantum bits strongly coupled with a hot many-body system will rapidly lose coherence. This result opens new directions in the study of topologically protected quantum dynamics.

Magnetocaloric Effect and Frustrations in One-Dimensional Magnets

In this paper, we investigated the magnetocaloric effect (MCE) in one-dimensional magnets with different types of ordering in the Ising model, Heisenberg, XY-model, the standard, planar, and modified Potts models. Exact analytical solutions to MCE as functions of exchange parameters, temperature, values and directions of an external magnetic field are obtained. The temperature and magnetic field dependences of MCE in the presence of frustrations in the system in a magnetic field are numerically computed in detail.