Critical phenomena in superlattices: Reentrant dimensional crossover and anomalous critical amplitudes

Abstract

A crossover from $d$ to $d-1$, and then back to $d$-dimensional critical behavior is argued to be a generic feature characterizing ordering in a $d$-dimensional superlattice composed of atomically {\em thick} films of two ferromagnets. The crossover leads to anomalous changes in the amplitudes of critical singularities. In $d=3$ Heisenberg and $XY$ superlattices large scale critical fluctuations persist over a wide temperature range.