Proton spin lattice relaxation by ising spin excitation in CoCl2 2H2O

The nuclear relaxation of proton has been studied in an antiferromagnet CoCl 2 2H 2 O ( T N =17.2 K) which is characterized by ferromagnetic linear chain of Ising-like spin S =1/2. With the external magnetic field applied along the spin axis, the field and temperature dependences of the nuclear relaxation time ( T 1 ) were measured in the three metamagnetic (antiferro-, ferri- and ferro-magnetic) states. The experimental analysis was made by using a simple phenomenological model for the spin fluctuation in onedimensional Ising spin system. It was found that the proton nuclear relaxation in CoCl 2 2H 2 O is closely related to the Ising spin excitation in its ferromagnetic linear chains.