We study the one-dimensional isotropic spin-1 Heisenberg magnet with antiferromagnetic nearest-neighbor (nn) and next-nearest-neighbor (nnn) interactions by using the modified spin wave theory (MSWT). The ground state energy and the singlet-triplet energy gap are obtained for several values of...

We investigate the ground-state magnetic long-range order of quasi-one-dimensional quantum Heisenberg antiferromagnets for spin quantum numbers s=1/2 and s=1. We use the coupled cluster method to calculate the sublattice magnetization and its dependence on the inter-chain coupling J<Subscript>⊥</Subscript>. We find...</subscript>

We compute the magnetic susceptibility and specific heat of the spin-<InlineEquation ID="Equ2"> <EquationSource Format="TEX">$\frac{1}{2}$</EquationSource> </InlineEquation> Heisenberg model on the kagome lattice with high-temperature expansions and exact diagonalizations. We compare the results with the experimental data on ZnCu<Subscript>3</Subscript>(OH)<Subscript>6</Subscript>Cl<Subscript>2</Su bscript> obtained by Helton et al. [Phys. Rev. Lett....<//su></subscript></subscript></subscript></equationsource></inlineequation>

Using analytical series expansion by continuous unitary transformations we study the magnetic properties of a frustrated tetrahedral spin-<InlineEquation ID="Equ1"> <EquationSource Format="TEX">$\frac{1}{2}$</EquationSource> </InlineEquation> chain. Starting from the limit of isolated tetrahedra we analyze the evolution of the ground state energy and the elementary triplet...</equationsource></inlineequation>