Time-dependent fluctuations in spin systems in d dimensions

The time-dependent spin-correlation function is investigated near Tc in d dimensions, by a microscopic kinetic theory in a model with long-range forces. For the isotropic ferromagnet it is shown that there exists at least a large precritical region where, in the absence of a magnetic field and for T > Tc, dynamic scaling holds up to d = 6. In the range 4 6 the results agree with the conventional (Van Hove) theory. Conjectures are made about the true critical behavior, and a detailed comparison is presented between the kinetic theory and the phenomenological theory of dynamic scaling. For the anti-ferromagnet the conventional theory is recovered for d ≥ -4. © 1973.SCOPUS: ar.j