Spin-Spin Relaxation and Spin Temperatures

Abstract

The equilibrium and nonequilibrium properties of an assembly of interacting spins are analyzed in the case of paramagnetism (nuclear). The evolution towards equilibrium is described by a generalized Pauli equation. This equation contains two relaxation times: a first one characterizing the evolution of the dipole-dipole system to equilibrium and a second one describing the energy exchange between the dipole-dipole and the Zeeman system. The real temperature of the system is the dipole-dipole one whereas the state of the Zeeman system is given by a "chemical potential" fixing the mean magnetic moment. It is shown that the Zeeman dipole-dipole relaxatin may also be considered as a kind of Brownian motion problem of a collective Zeeman coordinate in the "dipole-dipole heat bath."