Calculation of Neel temperature for S=1/2 quasi-one-dimensional Heisenberg antiferromagnets

We study the Neel temperature of quasi one-dimensional S=1/2 antiferromagnets containing non-magnetic impurities. We first consider the temperature dependence of the staggered susceptibility of finite chains with open boundary conditions, which shows an interesting difference for even and odd length chains. We then use a mean field theory treatment to incorporate the three dimensional inter-chain couplings. The resulting Neel temperature shows a pronounced drop as a function ...

In a recent comment by A.A. Zvyagin to our Letter [Phys. Rev. Lett. 89, 47202 (2002)] it was pointed out that the bosonization treatment of the antiferromagnetic Heisenberg chain is only valid in the low temperature and long length limit. We support this statement and quantify the limits of validity by explicitly showing the crossover to the high temperature and/or short length limit using a combination of bosonization formulas and numerical results.

The N\'eel temperature, $T_{\rm N}$, of quasi-one- and quasi-two-dimensional antiferromagnetic Heisenberg models on a cubic lattice is calculated by Monte Carlo simulations as a function of inter-chain (inter-layer) to intra-chain (intra-layer) coupling $J'/J$ down to $J'/J\simeq 10^{-3}$. We find that $T_{\rm N}$ obeys a modified random-phase approximation-like relation for small $J'/J$ with an effective universal renormalized coordination number, independent of the size of ...

A novel mean-field approximation for quasi-one-dimensional (Q1D) quantum magnets is formulated. Our new mean-field approach is based on the Bethe-type effective-field theory, where thermal and quantum fluctuations between the nearest-neighbor chains as well as those in each chain are taken into account exactly. The self-consistent equation for the critical temperature contains the boundary-field magnetic susceptibilities of a multichain cluster, which can be evaluated accurat...

Thermodynamic properties of the quantum Heisenberg spin chains with S = 1/2, 1, and 3/2 are investigated using the transfer-matrix renormalization-group method. The temperature dependence of the magnetization, susceptibility, specific heat, spin-spin correlation length, and several other physical quantities in a zero or finite applied field are calculated and compared. Our data agree well with the Bethe ansatz, exact diagonalization, and quantum Monte Carlo results and provid...

The T=0 dynamical properties of the one-dimensional (1D) $s=1/2$ Heisenberg antiferromagnet in a uniform magnetic field are studied via Bethe ansatz for cyclic chains of $N$ sites. The ground state at magnetization $0<M_z<N/2$, which can be interpreted as a state with $2M_z$ spinons or as a state of $M_z$ magnons, is reconfigured here as the vacuum for a different species of quasiparticles, the {\em psinons} and {\em antipsinons}. We investigate three kinds of quantum fluct...

We develop a finite-temperature perturbation theory for quasi-one-dimensional quantum spin systems, in the manner suggested by H.J. Schulz (1996) and use this formalism to study their dynamical response. The corrections to the random-phase approximation formula for the dynamical magnetic susceptibility obtained with this method involve multi-point correlation functions of the one-dimensional theory on which the random-phase approximation expansion is built. This ``anisotropic...

We study the ground state properties of the Heisenberg spin-1/2 chain with ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions using two approximate methods. One of them is the Jordan-Wigner mean-field theory and another approach based on the transformation of spin operators to bose-ones and on the variational treatment of bosonic Hamiltonian. Both approaches give close results for the ground state energy and the T=0 magnetization curve. It...

The new antiferromagnetic (AF) compound BaCu_2Si_2O_7 is studied by magnetic susceptibility and neutron scattering techniques. The observed behavior is dominated by the presence of loosely coupled S=1/2 chains with the intrachain AF exchange constant J = 24.1 meV. Long-range Neel ordering is observed below Tn = 9.2 K. The results are discussed within the framework of the Mean Field-RPA model for weakly interacting quantum spin chains.

We calculate the N\'eel temperature $T_N$ for two-dimensional isotropic dipolar Heisenberg antiferromagnets via linear spin-wave theory and a high temperature expansion, employing the method of Callen. The theoretical predictions for $T_N$ for K$_2$MnF$_4$, Rb$_2$MnF$_4$, Rb$_2$MnCl$_4$ and (CH$_3$NH$_3$)$_2$MnCl$_4$ are in good agreement with the measured values.