On spin relaxation

Abstract

A rigorous formulation of spin relaxation which allows physical insight into the nature of the relaxation process, allows higher-order approximations than hitherto made to be easily formulated and which gives a starting point for a discussion of long correlation times is given. Two approximations are considered in turn, both based on the shortness of the correlation time for the heat bath. One is shown to lead to the usual density matrix formulation, the other to the method of Argyres and Kelley. The explicit solutions of the resulting equations are found in the case of a constant magnetic field plus a perpendicular rotating field when the heat bath displays two-dimensional rotational symmetry. The differences between the two approximations are noted, giving a limit on the validity of both. The effect of initial correlation between the heat bath and spin is incorporated into the theory.