Proton relaxation and the dynamics of the S=1/2 antiferromagnetic Heisenberg chain

In this thesis a proton relaxation study of the dynamics of the S=1/2 antiferromagnetic Heisenberg chain is presented for a large range of temperatures and fields. In particular the spin dynamics has been investigated in the region with strong short range ordering. Most attention has been given to the longitudinal proton relaxation rate which gives the most direct information about the electron spin dynamics. Measurements on single resonance lines as a function of the field direction have been performed, in order to distinguish contributions to the relaxation rate from fluctuations of electron spin components along and perpendicular to the field direction. The presence in CuSO4.5H2O and CuSeO4.5H2O of a second electron spin system, the paramagnetic system, has facilitated these measurements by providing at low temperatures a well splitted NMR spectrum. Finally, transverse proton relaxation is studied, to clarify the relation between the proton relaxation results obtained and previous NMR line shape measurements. (Auth.)