Comparison between experiments and numerical calculations on S = 1/2 Heisenberg-XY ferromagnetic chains

Heat capacity measurements in fields 0 = B = 3 T were performed on [C6H11NH3] CuBr3 (CHAB), an excellent ferromagnetic S = 1/2 chain system with 5 % XY anisotropy. A comparison of the data on ¿C = C (B) - C (0) with extrapolations of numerical results for finite chains reveals systematic deviations at low temperatures, which are attributed to the limited chain lengths (up to 11 spins) used in the computations