共查询到20条相似文献,搜索用时 15 毫秒
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We study a frustrated 3D antiferromagnet of stacked J(1)-J(2) layers. The intermediate 'quantum spin liquid' phase, present in the 2D case, narrows with increasing interlayer coupling and vanishes at a triple point. Beyond this, there is a direct first-order transition from Néel to columnar order. Possible applications to real materials are discussed. 相似文献
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We study the ground-state phase diagram of the frustrated spin-[Formula: see text] antiferromagnet with J(2) = xJ(1) > 0 (J(1) > 0) on the honeycomb lattice, using the coupled-cluster method. We present results for the ground-state energy, magnetic order parameter and plaquette valence-bond crystal (PVBC) susceptibility. We find a paramagnetic PVBC phase for x(c(1)) < x < x(c(2)), where x(c(1)) ≈ 0.207 ± 0.003 and x(c(2)) ≈ 0.385 ± 0.010. The transition at x(c(1)) to the Néel phase seems to be a continuous deconfined transition (although we cannot exclude a very narrow intermediate phase in the range 0.21 ? x ? 0.24), while that at x(c(2)) is of first-order type to another quasiclassical antiferromagnetic phase that occurs in the classical version of the model only at the isolated and highly degenerate critical point [Formula: see text]. The spiral phases that are present classically for all values x > 1/6 are absent for all x ? 1. 相似文献
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《Physics letters. A》2020,384(27):126687
We investigate the phase transitions in the Ising model on a layered square lattice with first-() and second-() neighbor intralayer interactions and interlayer couplings (J). The thermodynamics of the system is evaluated within a cluster mean-field approximation, which allows us to identify the nature of the thermally driven phase transitions hosted by the model. As a result, we find that interlayer couplings reduce the region of first-order phase transitions between paramagnetic and superantiferromagnetic states. We also find that the interlayer couplings reduce the frustration effects by reducing the entropy content of the low-temperature phases. Our results suggest that tricriticality is present in the special case , which is in qualitative agreement with recent Monte Carlo simulations for the model. 相似文献
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Kato K Todo S Harada K Kawashima N Miyashita S Takayama H 《Physical review letters》2000,84(18):4204-4207
Ground-state magnetic properties of the diluted Heisenberg antiferromagnet on a square lattice are investigated by means of the quantum Monte Carlo method with the continuous-time loop algorithm. It is found that the critical concentration of magnetic sites is independent of the spin size S, and equal to the two-dimensional percolation threshold. However, the existence of quantum fluctuations makes the critical exponents deviate from those of the classical percolation transition. Furthermore, we found that the transition is not universal, i.e., the critical exponents significantly depend on S. 相似文献
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M. Marcellini B. Hjörvarsson G. Nowak 《Journal of magnetism and magnetic materials》2009,321(9):1214-1220
The relation between the interlayer exchange coupling and magnetic order is addressed, using Fe/V(0 0 1) superlattices as a model system. Large decrease in the ordering temperature (Tc) is observed with decreasing interlayer exchange coupling. The effective exponents of the magnetization were determined to be larger than 0.5 for all the samples, which is strongly deviating from the classical values of both two- and three-dimensional systems. This effect can partially be ascribed to the presence of boundaries, invoked by the finite number of magnetic layers. 相似文献
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H. Niggemann A. Klümper J. Zittartz 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):15-19
We use the vertex state model approach to construct optimum ground states for a large class of quantum spin-2 antiferromagnets
on the square lattice. Optimum ground states are exact ground states of the model which minimize all local interaction operators.
The ground state contains two continuous parameters and exhibits a second order phase transition from a disordered phase with
exponentially decaying correlation functions to a Néel ordered phase. The behaviour is very similar to that of the corresponding
ground state of a quantum spin-3/2 model on the hexagonal lattice, which has been investigated in an earlier paper.
Received 8 April 1999 相似文献
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Bombardi A Rodriguez-Carvajal J Di Matteo S de Bergevin F Paolasini L Carretta P Millet P Caciuffo R 《Physical review letters》2004,93(2):027202
Powder neutron diffraction and resonant x-ray scattering measurements from a single crystal have been performed to study the low-temperature state of the 2D frustrated, quantum-Heisenberg system Li2VOSiO4. Both techniques indicate a collinear antiferromagnetic ground state, with propagation vector k=(1 / 2 1 / 2 0), and magnetic moments in the a-b plane. Contrary to previous reports, the ordered moment at 1.44 K, m=0.63(3)micro(B), is very close to the value expected for the square lattice Heisenberg model ( approximately 0.6micro(B)). The magnetic order is three dimensional, with antiferromagnetic a-b layers stacked ferromagnetically along the c axis. Neither x-ray nor neutron diffraction shows evidence for a structural distortion between 1.6 and 10 K. 相似文献
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A.S.T. Pires 《Journal of magnetism and magnetic materials》2011,323(15):1977-1979
In this paper we study the low temperature behavior of the quantum S=1 Heisenberg antiferromagnet with exchange and single-site anisotropies on the square lattice. The properties of the model change drastically as the single-site anisotropy D varies from very small to very large values. A quantum phase transition takes place at a critical value D=DC. We study the low D phase using a self-consistent harmonic approximation and a schematic phase diagram is proposed. 相似文献
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The ground state and the lowest excited states of the spin 1/2-Heisenberg model are investigated by exact diagonalization and variational Monte Carlo techniques. Our trial state represents a generalization of a wave function introduced by Hulthen, Kasteleijn and Marshall. The long range character of the spin-correlation function is in excellent agreement with exact diagonalization and also with recent neutron scattering results for La2CuO4. The asymptotic behavior of the spin-correlation function is found to differ from spin-wave theory. From the exact (N<=20 spins) and variational (N<=400) ground state energies we determine as asymptotic values 1.3025 and 1.288, respectively. We calculate the dispersion for the spin-wave excitations and identify an excited triplet which becomes degenerate with the ground state in the thermodynamic limit. This triplet state allows spontaneous symmetry breaking to occur atT=0 K. Quantum fluctuations reduce the sublattice magnetization to an effective value of 0.195 (3) as compared to the Néel-state value of 1/2. 相似文献
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The quantum anisotropic antiferromagnetic Heisenberg model with single ion anisotropy, spin S=1 and up to the next-next-nearest neighbor coupling (the J1–J2–J3 model) on a square lattice, is studied using the bond-operator formalism in a mean field approximation. The quantum phase transitions at zero temperature are obtained. The model features a complex T=0 phase diagram, whose ordering vector is subject to quantum corrections with respect to the classical limit. The phase diagram shows a quantum paramagnetic phase situated among Neél, spiral and collinear states. 相似文献
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A. K. Murtazaev M. K. Ramazanov M. K. Badiev 《Journal of Experimental and Theoretical Physics》2007,105(5):1011-1017
Several Monte Carlo algorithms are used to examine the critical behavior of the 3D frustrated Heisenberg model on stacked triangular lattice with variable interlayer exchange coupling for values of the interlayer-to-intralayer exchange ratio R = |′/J| in the interval between 0.01 and 1.0. A finite-size scaling technique is used to calculate the static magnetic and chiral critical exponents α (specific heat), γ and γk (susceptibility), β and βk(magnetization), ν and νk(correlation length), and the Fisher exponent η. It is shown that 3D frustrated Heisenberg models on stacked triangular lattice with R > 0.05 constitute a new universality class of critical behavior. At lower R, a crossover from 3D to 2D critical behavior is observed. 相似文献