Interchain Exchange Coupling Research Articles

Disorder free many-body localization transition in two quasiperiodically coupled Heisenberg spin chains

Disorder free many-body localization (MBL) can occur in interacting systems that can dynamically generate their own disorder. We address the thermal-MBL phase transition of two isotropic Heisenberg spin chains that are quasiperiodically coupled to each other. The spin chains are incommensurate and are coupled through a short-range exchange interaction of the XXZ type that decays exponentially with the distance. Using exact diagonalization, matrix product states, and a density matrix renormalization group, we calculate the time evolution of the entanglement entropy at long times and extract the inverse participation ratio in the thermodynamic limit. We show that this system has a robust MBL phase. We establish the phase diagram with the onset of MBL as a function of the interchain exchange coupling and of the incommensuration between the spin chains. The Ising limit of the interchain interaction optimizes the stability of the MBL phase over a broad range of incommensurations above a given critical exchange coupling. Incorporation of interchain spin flips significantly enhances entanglement between the spin chains and produces delocalization, favoring a prethermal phase whose entanglement entropy grows logarithmically with time. Published by the American Physical Society 2024

Ferrocenyl-substituted nitronyl nitroxide in the design of one-dimensional magnets.

By the reaction of M(hfac)2 (M = Mn(II), Co(II), Cu(II), and Zn(II); hfac is the hexafluoroacetylacetonate anion) and ferrocenyl-substituted nitronyl nitroxide (L), we succeeded in the synthesis of stable heterospin complexes: mononuclear [Zn(hfac)2L], trinuclear {[Cu(hfac)2]3L2} and chain polymer [Mn(hfac)2L]n and [Co(hfac)2L]n. The specific steric bulkiness of the ferrocenyl substituent leads to the formation of trans-type coordination polyhedra in the [Mn(hfac)2L]n and [Co(hfac)2L]n chains. The introduction of the ferrocene substituent leads to an effective weakening of intermolecular or interchain magnetic exchange coupling. Ferrimagnetic ordering was observed for one-dimensional complexes [M(hfac)2L]n (M = Mn(II), Co(II)). [Co(hfac)2L]n exhibits features of single-chain magnet behaviour: slow relaxation of magnetization below 13 K is associated with a high coercive field (54 kOe at 2 K).

Magnetocaloric effect manipulated through interchain exchange coupling in nanochain arrays

Magnetocaloric effect in nanochain arrays is numerically studied when interchain exchange couplings (Jinter) are taken into account. With increasing Jinter, moment-reorientation phase transition temperature driven by anisotropy is enhanced and magnetic ordering phase transitions governed by Jinter may happen independently at higher temperatures, resulting in temperature induced multiple phase transitions that separate distinct dynamic properties of magnetization. As a result, maximum values of positive and negative magnetic entropy change (ΔSM) are both close to 0.4 J kg−1 K−1, with their peak temperature 100–300 K and 250–550 K, depending on Jinter, and a large refrigeration capacity is obtained due to a wide working temperature range of ΔSM. In nanostructures, the proper magnetic viscosity arising from Jinter makes materials become semi-bulk, i.e., in which ΔSM maximum value and peak temperature are highly enhanced, associated with a considerably wide working temperature range.

Role of the spin anisotropy of the interchain interaction in weakly coupled antiferromagnetic Heisenberg chains**Project supported by the National Natural Science Foundation of China (Grant No. 11674392), the Ministry of Science and Technology of China, National Program on Key Research Project (Grant No. 2016YFA0300504), and the Research Funds of Remnin University of China (Grant No. 18XNLG24). R.Y. acknowledges the hospitality

In quasi-one-dimensional (q1D) quantum antiferromagnets, the complicated interplay of intrachain and interchain exchange couplings may give rise to rich phenomena. Motivated by recent progress on field-induced phase transitions in the q1D antiferromagnetic (AFM) compound YbAlO3, we study the phase diagram of spin-1/2 Heisenberg chains with Ising anisotropic interchain couplings under a longitudinal magnetic field via large-scale quantum Monte Carlo simulations, and investigate the role of the spin anisotropy of the interchain coupling on the ground state of the system. We find that the Ising anisotropy of the interchain coupling can significantly enhance the longitudinal spin correlations and drive the system to an incommensurate AFM phase at intermediate magnetic fields, which is understood as a longitudinal spin density wave (LSDW). With increasing field, the ground state changes to a canted AFM order with transverse spin correlations. We further provide a global phase diagram showing how the competition between the LSDW and the canted AFM states is tuned by the Ising anisotropy of the interchain coupling.

Exchange constants in molecule-based magnets derived from density functional methods

Cu(pyz)(NO3)2 is a quasi one-dimensional molecular antiferromagnet that exhibits three dimensional long-range magnetic order below TN=110 mK due to the presence of weak inter-chain exchange couplings. Here we compare calculations of the three largest exchange coupling constants in this system using two techniques based on plane-wave basis-set density functional theory: (i) a dimer fragment approach and (ii) an approach using periodic boundary conditions. The calculated values of the large intrachain coupling constant are found to be consistent with experiment, showing the expected level of variation between different techniques and implementations. However, the interchain coupling constants are found to be smaller than the current limits on the resolution of the calculations. This is due to the computational limitations on convergence of absolute energy differences with respect to basis set, which are larger than the inter-chain couplings themselves. Our results imply that errors resulting from such limitations are inherent in the evaluation of small exchange constants in systems of this sort, and that many previously reported results should therefore be treated with caution.

DM-induced frustration of the weakly coupled Heisenberg chains

We present theoretical procedure for estimating interchain exchange coupling J′ between antiferromagnetic spin-1/2 Heisenberg chains with frustration due to Dzyaloshinskii-Moriya (DM) interaction characterized by DM vectors Dy which are uniform within each chain y, but staggered between adjacent chains, Dy ∼ (-1)yD. Under a magnetic field h ‖ D we obtain a field-temperature phase diagram which favorably agrees with the one experimentally observed. We then apply chain mean-field (CMF) technique to calculate interchain exchange J′ from the critical field hc at which the transition between the collinear spin-density wave and the cone states takes place. The CMF calculations are found to provide good physical description of the experimental measurements for the wide range of D/J′.

Crossover from one- to three-dimensional behavior in the S = 1/2 Heisenberg antiferromagnet Cu(N2H5)2(SO4)2

From experimental and theoretical analyses of magnetic and specific-heat properties, we present the complete magnetic phase diagram of the quasi-1D antiferromagnet Cu(N2H5)2(SO4)2. On cooling and at zero magnetic field this compound enters a 1D regime with short-range magnetic correlations, marked by a broad maximum in the specific heat and magnetic susceptibility at K, followed by a tridimensional antiferromagnetically ordered phase below K induced by small interchain couplings. The intermediate-temperature 1D regime can be modeled using exact quantum-transfer-matrix calculations, which offer a compatible description of the nonmonotonic behavior of as a function of the magnetic field, giving K for the intrachain exchange parameter. The analysis of magnetic specific-heat and susceptibility data at low temperature indicates that the interchain exchange couplings are an order of magnitude smaller than the coupling inside the chains.

Spin gap in the single spin-12chain cuprateSr1.9Ca0.1CuO3

We report $^{63}$Cu nuclear magnetic resonance and muon spin rotation measurements on the S=1/2 antiferromagnetic Heisenberg spin chain compound Sr$_{1.9}$Ca$_{0.1}$CuO$_3$. An exponentially decreasing spin-lattice relaxation rate 1/T$_1$ indicates the opening of a spin gap. This behavior is very similar to what has been observed for the cognate zigzag spin chain compound Sr$_{0.9}$Ca$_{0.1}$CuO$_2$, and confirms that the occurrence of a spin gap upon Ca doping is independent of the interchain exchange coupling $J'$. Our results therefore generally prove the appearance of a spin gap in an antiferromagnetic Heisenberg spin chain induced by a local bond disorder of the intrachain exchange coupling $J$. A low temperature upturn of 1/T$_1$ evidences growing magnetic correlations. However, zero field muon spin rotation measurements down to 1.5 K confirm the absence of magnetic order in this compound which is most likely suppressed by the opening of the spin gap.

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

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

Strong H···F Hydrogen Bonds as Synthons in Polymeric Quantum Magnets: Structural, Magnetic, and Theoretical Characterization of [Cu(HF2)(pyrazine)2]SbF6, [Cu2F(HF)(HF2)(pyrazine)4](SbF6)2, and [CuAg(H3F4)(pyrazine)5](SbF6)2

Three Cu(2+)-containing coordination polymers were synthesized and characterized by experimental (X-ray diffraction, magnetic susceptibility, pulsed-field magnetization, heat capacity, and muon-spin relaxation) and electronic structure studies (quantum Monte Carlo simulations and density functional theory calculations). [Cu(HF(2))(pyz)(2)]SbF(6) (pyz = pyrazine) (1a), [Cu(2)F(HF)(HF(2))(pyz)(4)](SbF(6))(2) (1b), and [CuAg(H(3)F(4))(pyz)(5)](SbF(6))(2) (2) crystallize in either tetragonal or orthorhombic space groups; their structures consist of 2D square layers of [M(pyz)(2)](n+) that are linked in the third dimension by either HF(2)(-) (1a and 1b) or H(3)F(4)(-) (2). The resulting 3D frameworks contain charge-balancing SbF(6)(-) anions in every void. Compound 1b is a defective polymorph of 1a, with the difference being that 50% of the HF(2)(-) links are broken in the former, which leads to a cooperative Jahn-Teller distortion and d(x(2))(-y(2)) orbital ordering. Magnetic data for 1a and 1b reveal broad maxima in chi at 12.5 and 2.6 K and long-range magnetic order below 4.3 and 1.7 K, respectively, while 2 displays negligible spin interactions owing to long and disrupted superexchange pathways. The isothermal magnetization, M(B), for 1a and 1b measured at 0.5 K reveals contrasting behaviors: 1a exhibits a concave shape as B increases to a saturation field, B(c), of 37.6 T, whereas 1b presents an unusual two-step saturation in which M(B) is convex until it reaches a step near 10.8 T and then becomes concave until saturation is reached at 15.8 T. The step occurs at two-thirds of M(sat), suggesting the presence of a ferrimagnetic structure. Compound 2 shows unusual hysteresis in M(B) at low temperature, although chi vs T does not reveal the presence of a magnetic phase transition. Quantum Monte Carlo simulations based on an anisotropic cubic lattice were applied to the magnetic data of 1a to afford g = 2.14, J = -13.4 K (Cu-pyz-Cu), and J(perpendicular) = -0.20 K (Cu-F...H...F-Cu), while chi vs T for 1b could be well reproduced by a spin-1/2 Heisenberg uniform chain model for g = 2.127(1), J(1) = -3.81(1), and zJ(2) = -0.48(1) K, where J(1) and J(2) are the intra- and interchain exchange couplings, respectively, which considers the number of magnetic nearest-neighbors (z). The M(B) data for 1b could not be satisfactorily explained by the chain model, suggesting a more complex magnetic structure in the ordered state and the need for additional terms in the spin Hamiltonian. The observed variation in magnetic behaviors is driven by differences in the H...F hydrogen-bonding motifs.

Magnetic Properties of Ferromagnetic Quasi-1D Copper-Peptide Compounds: Exchange Interactions and Very Low Temperature Phase Transitions

The magnetic properties of the Cu(II)-peptide compounds (L-tyrosyl-L-leucinato)Cu(II) and (L-tryptophyl-glycinato)Cu(II), to be identified as Cu(II)Tyr-Leu and Cu(II)Trp-Gly, respectively, have been investigated by specific heat (0.08 < T < 28 K), dc magnetization (2 < T < 80 K, with B(0) = mu(o)H < or = 9 T), and ac magnetic susceptibility (with B(0) = 0 for 0.03 < T < 3 K and B(0) up to 9 T for 2 < T < 80 K) measurements. Above approximately 1 K, the specific heat and magnetization of both compounds display a ferromagnetic (FM) spin chain behavior sustained by syn-anti carboxylate bridges connecting equatorially Cu(II) ions at about 5 A. To model this behavior, we calculated the eigenvalues of Heisenberg chains with up to 20 spins 1/2 and used the method of Bonner and Fisher. A global fit of the model to the specific heat and magnetization data gives 2J(0)/k(B) = 3.60(5) K and 2.59(5) K for the intrachain exchange interactions in Cu(II)Tyr-Leu and Cu(II)Trp-Gly, respectively (H(ex)(i,j) = -2J(0) S(i).S(j)). These values of 2J(0) are discussed in terms of structural properties of the carboxylate bridges in the two compounds. Using the parameters obtained from the global fit, we calculated isothermal susceptibilities in agreement with the ac susceptibilities measured with small applied dc magnetic fields. However, the ac susceptibility measured with applied dc fields larger than 1 T lie between the values calculated for the isothermal and adiabatic susceptibilities. At 0.16 K for Cu(II)Tyr-Leu and 0.53 K for Cu(II)Trp-Gly, the observed specific heat and magnetic susceptibility display peaks associated to three-dimensional magnetic phase transitions. The interchain exchange couplings 2J(1) producing the 3D magnetic order are ferromagnetic and have magnitudes 2J(1)/k(B) approximately 0.015 and 0.073 K for Cu(II)Tyr-Leu and Cu(II)Trp-Gly, respectively.

One-Dimensional Transition Metal−Benzene Sandwich Polymers: Possible Ideal Conductors for Spin Transport

We investigate the electronic and magnetic properties of the proposed one-dimensional transition metal (TM = Sc, Ti, V, Cr, and Mn) -benzene (Bz) sandwich polymers by means of density functional calculations. [V(Bz)](infinity) is found to be a quasi-half-metallic ferromagnet, and half-metallic ferromagnetism is predicted for [Mn(Bz)](infinity). Moreover, we show that stretching the [TM(Bz)](infinity) polymers could have dramatic effects on their electronic and magnetic properties. The elongated [V(Bz)](infinity) displays half-metallic behavior, and [Mn(Bz)](infinity) stretched to a certain degree becomes an antiferromagnetic insulator. The possibilities to stabilize the ferromagnetic order in [V(Bz)](infinity) and [Mn(Bz)](infinity) polymers at finite temperatures are discussed. We suggest that the hexagonal bundles composed by these polymers might display intrachain ferromagnetic order at finite temperatures by introducing interchain exchange coupling.

Landau model for the elastic properties of the quasi-one-dimensional antiferromagnetic compoundCsNiCl3

We present a Landau model that accounts for the unusual elastic properties of the quasi-one-dimensional antiferromagnetic compound $\mathrm{Cs}\mathrm{Ni}{\mathrm{Cl}}_{3}$. The model's predictions are tested using published strain measurements and recent high resolution sound velocity measurements realized as a function of temperature and pressure. In particular, we derive an analytical expression which indicates how the low temperature dependence of the elastic constants is related to the critical order parameters. A close inspection of the temperature dependence of ${C}_{33}$ indicates that the value of the critical exponent $\ensuremath{\beta}$ associated with the order parameter of the elliptical state below $T=4.10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is $\ensuremath{\beta}=0.33$. The obtained value agrees with the expected critical behavior of $\mathrm{Cs}\mathrm{Ni}{\mathrm{Cl}}_{3}$ in the absence of an external magnetic field (conventional three-dimensional $XY$ criticality). Using sound velocity measurements under hydrostatic pressures up to $7.0\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$, we also derive the pressure-temperature phase diagram of $\mathrm{Cs}\mathrm{Ni}{\mathrm{Cl}}_{3}$. With increasing pressure, we observe that the critical temperatures ${T}_{{N}_{1}}$ and ${T}_{{N}_{2}}$ increase at a rate of $d{T}_{{N}_{1}}∕dP=0.17\phantom{\rule{0.3em}{0ex}}\mathrm{K}∕\mathrm{kbar}$ and $d{T}_{{N}_{2}}∕dP=0.065\phantom{\rule{0.3em}{0ex}}\mathrm{K}∕\mathrm{kbar}$, respectively. Finally, taking advantage of the magnetoelastic coupling in the paramagnetic state, we could estimate the pressure dependence of the interchain exchange coupling along the $c$ axis, $d{J}_{\ensuremath{\Vert}}∕dP=0.45\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$. All these results seem to indicate that the Ising-type anisotropy and the quasi-one-dimensional character of $\mathrm{Cs}\mathrm{Ni}{\mathrm{Cl}}_{3}$ are both enhanced with pressure.

Reentrant behavior and gigantic response in a disordered spin-Peierls system

Effects of disorder and external field on the competing spin-Peierls and antiferromagnetic states are studied theoretically in terms of the numerical transfer matrix method applied to a quasi one-dimensional spin 1/2 Heisenberg model coupled to the lattice degree of freedom. We show that, at temperatures above the impurity-induced antiferromagnetic phase, inhomogeneous spin-Peierls lattice distortions remain to exist showing a re-entrant behavior. This feature can be drastically altered by very weak perturbations, e.g., the staggered magnetic field or the change in interchain exchange coupling $J_\perp$, leading to a huge response, which is analogous to the colossal magnetoresistance phenomenon in perovskite manganese oxides.

Magnetic study of the polymeric chain in Cu(II) (1,4-C 4H 4N 2)(C 4O 4)(H 2O) 4

The magnetic properties of the one dimensional Cu(II)(1,4-C 4H 4N 2)(C 4O 4)(H 2O) 4 have been studied. This compound is a typical linear chain. Susceptibility measurements show strong antiferromagnetic intrachain exchange of the order of −8.72 K with poor interchain exchange coupling.

Pressure Effect on Mn Complexes of Bisaminoxyl Radicals

The pressure effects on magnetic properties of one-dimensional Mn complexes with 1,3-bis(N-tert-butylaminoxyl)benzene and 5-chloro-1,3-bis(N-tert-butylaminoxyl)benzene have been studied. These complexes have weak interchain interactions with different signs and the former is a metamagnet and the latter is a ferrimagnet at ambient pressure. The interchain interactions of the former is enhanced by pressurization. The transition temperature becomes higher and the critical field becomes larger with applying pressure. The closer spacing of each chains caused by pressurization, yields larger antiferromagnetic interchain interactions in this compound. On the other hand, the response to the pressure of the latter ferrimagnet, is rather complicated. The transition temperature becomes higher and the antiferromagnetic interchain interactions are induced by pressurization. The interchain exchange coupling in this compound should be sensitive to the relative orientation of the chain structure The decrease of the ferromagnetic contribution and/or the increase of the antiferromagnetic one in the interchain interactions is brought about by pressurization.

Onsager reaction field theory for the three-dimensional anisotropicXYmodel

We discuss coupled $\mathrm{XY}$ spin chains in three dimensions and calculate the transition temperature and spin correlation lengths as functions of the ratio of the interchain exchange coupling ${J}^{\ensuremath{'}}$ to the intrachain coupling $J,$ for chainlike spatial anisotropy ${J}^{\ensuremath{'}}&lt;J.$ We use two different approaches of the Onsager reaction-field (ORF) formalism. First we use the standard ORF theory, in which both the intrachain and interchain couplings are treated equally. Second, we treat one chain exactly and consider it in the effective field caused by the other chains, with the ORF formalism applied to the interchain interaction. The transition temperatures obtained are compared with results from Monte Carlo simulations.

Study of spin-Peierls CuGeO 3 by high-field ESR

An inorganic spin-Peierls compound CuGeO 3 has been studied by high-field ESR combining pulsed magnetic fields and far-infrared lasers. In EPR measurements under megagauss fields, an exchange splitting is observed and the interchain exchange coupling is evaluated. In the dimerized spin-Peierls phase, a direct transition between the singlet ground and the triplet excited states is observed. This result supports the existence of the second gap between the triplet state and the continuum. Collective spin wave modes in the field-induced magnetic phase and in the antiferromagnetic phase of the impurity-doped system have been also studied.

Role of Dipole-Dipole Interaction in Phase Transition of Organic Antiferromagnet Motmp

The role of the dipole-dipole (DD) interaction in organic molecular antiferromagnet MOTMP is elucidated. The anisotropy energy due to the DD interaction ca.n explain well the experimental values of the spin-flop field and the saturation field along each crystal axis if we use the nearest neighbor (n.n.) interchain exchange coupling Jc = -0.0087 K and if we introduce small anisotropy for the intrachain exchange coupling. The uniform magnetic susceptibility in the paramagnetic state has been calculated by taking into account the DD interaction on the basis of the dynamical correlated-effective-field approximation. The observed susceptibility are well reproduced by assuming the n.n. intrachain exchange coupling Ja =0.45 K and the next n.n. interchain exchange coupling Jb =0 K. The Néel temperature T N is determined to be 0.15 K, which agrees with the observation.

Effect of magnetic dipolar interactions on the interchain spin-wave dispersion in CsNiF3.

Inelastic neutron scattering measurements were performed on the ferromagnetic chain system CsNiF_3 in the collinear antiferromagnetic ordered state below T_N = 2.67K. The measured spin wave dispersion was found to be in good agreement with linear spin wave theory including dipolar interactions. The additional dipole tensor in the Hamiltonian was essential to explain some striking phenomena in the measured spin wave spectrum: a peculiar feature of the dispersion relation is a jump at the zone center, caused by strong dipolar interactions in this system. The interchain exchange coupling constant and the planar anisotropy energy were determined within the present model to be J'/k_B = -0.0247(12)K and A/k_B = 3.3(1)K. This gives a ratio J/J' \approx 500, using the previously determined intrachain coupling constant J/k_B = 11.8$. The small exchange energy J' is of the same order as the dipolar energy, which implies a strong competition between the both interactions.