Thermodynamic Properties of Weakly Anisotropic Disordered Magnetic Chains in the Large-S Limit

we investigate the thermodynamic properties of weakly anisotropic disordered magnetic chains where the nearest-neighbor Heisenberg exchange coupling is the dominant spin-spin interaction. In addition to the exchange interaction, there is single-ion anisotropy with the direction of the easy axis being the same for all spins. The analysis is carried out in the limit S >> 1, where S denotes the ionic spin, and in the temperature range T << JaveS, where Jave is the average magnitude of the exchange interaction. It is assumed that the independent boson picture is appropriate so that the thermodynamic properties of the chain are those of a gas of weakly interacting magnons whose frequencies are obtained from linearized equations of motion for the spins. The =+/-J model is studied in detail with both random and non-random anisotropy. Particular emphasis is placed on the existence