Influence of linear and nonlinear excitations in the ferromagnetic S = 1/2 chain system [C6H11NH3]CuBr3 (CHAB)

The magnetic properties of the title compound have been studied by measurements of the nuclear spin-lattice relaxation time T1, the uniform magnetization M, and by quasielastic and inelastic neutron scattering. The field and temperature dependence of T1 and the wave-number dependence of the magnon excitation energy can be satisfactorily described by linear spin-wave theory. A good description of M, however, requires a contribution from kink solitons. The available evidence suggests that, in contrast to the linear excitations, the nonlinear excitations in CHAB for B¿c can be described very well by a classical model, which is consistent with the interpretation of earlier heat-capacity measurements.