Proton Spin Lattice Relaxation by Ising Spin Excitation in CoCl₂ 2H₂O

Abstract

The nuclear relaxation of proton has been studied in an antiferromagnet CoCl₂ 2H₂O (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 (T₁) 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 CoCl₂ 2H₂O is closely related to the Ising spin excitation in its ferromagnetic linear chains.