Static properties of an easy-plane ferromagnetic S=1/2 chain: Comparison of numerical results and experimental data on [C6H11NH3]CuBr3

New results of a variant of the numerically exact transfer matrix method have been compared with the experimentally determined static properties of [C6H11NH3]CuBr3 (CHAB). Above T=3.5 K, the available data on the zero-field heat capacity, the excess heat capacity C=C(B) -C(B=0) for B=1, 2, and 3 T, and the magnetization up to 5 T are described with an accuracy that is comparable to the experimental error. Calculations of the spin-spin correlation functions by this method reveal that the fair description of the experimental correlation length in CHAB by a classical spin model is largely accidental. The zero-field susceptibility deduced from these correlation functions is in satisfactory agreement with the reported data.