IRREVERSIBILITY IN HEISENBERG SPIN SYSTEMS .4. TIME-DEPENDENT FLUCTUATIONS AT CURIE POINT

We propose an approximate solution of the kinetic equations, recently derived by the authors, for the spin autocorrelation function q(t) of ferromagnets at the critical point. It is shown that, even for small wave numbers and long times, q(t) never reaches a diffusion regime, but decays to zero through damped oscillations. We also compare this theory with previous work on the subject. © 1969 The American Physical Society.