We report on inelastic neutron scattering (INS) measurements on the molecular spin ring CsFe8, in which eight spin-5/2 Fe(III) ions are coupled by nearest-neighbor antiferromagnetic Heisenberg interaction. We have recorded INS data on a non-deuterated powder sample up to high energies at the time-of-flight spectrometers FOCUS at PSI and MARI at ISIS, which clearly show the excitation of spin waves in the ring. Due to the small number of spin sites, the spin-wave dispersion relation is not continuous but quantized. Furthermore, the system exhibits a gap between the ground state and the first excited state. We have modeled our data using exact diagonalization of a Heisenberg-exchange Hamiltonian together with a small single-ion anisotropy term. Due to the molecule's symmetry, only two parameters J and D are needed to obtain excellent agreement with the data. The results can be well described within the framework of the rotational-band model as well as antiferromagnetic spin-wave theories.
@article{arxiv.1001.3755,
title = {Quantized antiferromagnetic spin waves in the molecular Heisenberg ring CsFe$_8$},
author = {J. Dreiser and O. Waldmann and C. Dobe and G. Carver and S. T. Ochsenbein and A. Sieber and H. U. Güdel and J. van Duijn and J. Taylor and A. Podlesnyak},
journal= {arXiv preprint arXiv:1001.3755},
year = {2010}
}