Uniform susceptibility of classical antiferromagnets in one and two dimensions in a magnetic field

The thermodynamics of low dimensional spin-1/2 Heisenberg ferromagnets (HFM) in an external magnetic field is investigated within a second-order two-time Green function formalism in the wide temperature and field range. A crucial point of the proposed scheme is a proper account of the analytical properties for the approximate transverse commutator Green function obtained as a result of the decoupling procedure. A good quantitative description of the correlation functions, mag...

We present results of large scale simulations of the spin-1 Heisenberg antiferromagnet on a tetragonal lattice. The stochastic series expansion quantum Monte Carlo method is used to calculate equilibrium thermodynamic variables in the presence of an external magnetic field. In particular, the low temperature magnetization curve is investigated in the quasi-one-dimensional (Q1D), quasi-two-dimensional (Q2D), and three-dimensional (3D) limits. Starting from the 3D limit, the Q1...

Predictions of the anisotropic magnetic susceptibility chi below the antiferromagnetic (AFM) ordering temperatures TN of local moment Heisenberg AFMs have been made previously using molecular field theory (MFT) but are very limited in their applicability. Here a MFT calculation of chi(T<=TN) is presented for a wide variety of collinear and noncollinear Heisenberg AFMs containing identical crystallographically equivalent spins without recourse to magnetic sublattices. The resu...

The magnetic properties of the one dimensional (1D) monatomic chain of Co reported in a previous experimental work are investigated by a classical Monte Carlo simulation based on the anisotropic Heisenberg model. In our simulation, the effect of the on-site uniaxial anisotropy, Ku, on each individual Co atom and the nearest neighbour exchange interaction, J, are accounted for. The normalized coercivity HC(T)/HC(TCL) is found to show a universal behaviour, HC(T)/HC(TCL) = h0(e...

A computer aided high temperature expansion of the magnetic susceptibility and the magnetic specific heat is presented and demonstrated for frustrated and unfrustrated spin chains. The results are analytic in nature since the calculations are performed in the integer domain. They are provided in the form of polynomials allowing quick and easy fits. Various representations of the results are discussed. Combining high temperature expansion coefficients and dispersion data yield...

The numerical value of a universal quantity associated with the quantum critical regime, namely $\chi_u c^2/T$, for a two-dimensional (2D) dimerized spin-1/2 antiferromagnet is calculated using the quantum Monte Carlo simulations (QMC). Here $\chi_u$, $c$, and $T$ are the uniform susceptibility, the spin-wave velocity, and the temperature, respectively. By simulating large lattices at moderately low temperatures, we find $\chi_u c^2/T \sim 0.32$. Our estimation of $\chi_u c^2...

The temperature dependence of the uniform susceptibility and the ground state energy of antiferromagnetic Heisenberg ladders with up to 6 legs has been calculated, using the Monte Carlo loop algorithm. The susceptibilities of even-leg-ladders show spin gaps while these of odd-leg-ladders remain finite in the zero temperature limit. For small ratios of intra- to inter-leg couplings, odd-leg-ladders can be mapped at low temperatures to single chains. For equal couplings, the lo...

We compute the magnetic susceptibilities of interacting electrons in the presence of disorder on a two-dimensional square lattice by means of quantum Monte Carlo simulations. Clear evidence is found that at sufficiently low temperatures disorder can lead to an enhancement of the ferromagnetic susceptibility. We show that it is not related to the transition from a metal to an Anderson insulator in two dimensions, but is a rather general low temperature property of interacting,...

Using conformal field theory methods Eggert and Affleck have shown that the semi-infinite S=1/2 Heisenberg antiferromagnetic chain exhibits a remarkable alternation in its local response to a uniform field at low temperatures. Such alternation is not an essentially quantum effect: similar, and sometimes stronger, susceptibility alternation is a feature of classical Heisenberg-Ising chains at T=0. In S=1/2 chains, susceptibility alternation is not unique to the Heisenberg mode...

By means of the density matrix renormalization group (DMRG) method, the magnetic properties of the J-J-J$^{\prime}$ quantum Heisenberg chains with spin $S=1/2$, 1, 3/2 and 2 in the ground states are investigated in the presence of a magnetic field. Two different cases are considered: (a) when $J$ is antiferromagnetic and $J^{\prime}$ is ferromagnetic (i.e. the AF-AF-F chain), the system is a ferrimagnet. The plateaus of the magnetization are observed. It is found that the wid...