On the susceptibility of the one-dimensional Ising chain

The elements of the tensor of the susceptibility and the staggered susceptibility of a one-dimensional I Ising chain, with xx couplings between the spins are investigated in the presence of a magnetic field b parallel with or perpendicular to the x direction. Exact expressions are given for all susceptibilities, apart from the parallel susceptibilities in a transverse field which are evaluated by perturbation calculation. Special attention is paid to the conditions under which a susceptibility can have a minimum for b = 0. Furthermore, a system with weakly coupled Ising chains is considered on the basis of a model hamiltonian with separable interchain interactions.