FINITE-SIZE-SCALING IN FEF2 ZNF2 SUPERLATTICES/

Thermal-expansion measurements of (FeF2)n(ZnF2)m magnetic/nonmagnetic superlattices high-resolution x-ray diffraction have been made through out the antiferromagnetic phase-transition region. Using the proportio nality of the magnetically induced thermal expansion to the magnetic s pecific heat, the experimental results are compared with detailed Mont e Carlo simulations. Both the experimental and Monte Carlo data are an alyzed in terms of finite-size scaling theory. From this combined anal ysis, we are able to show that the observed shifts in the phase-transi tion temperature with respect to bulk FeF2 arise from three-dimensiona l to two-dimensional Ising-model crossover behavior. To our knowledge, this is the first time that dimensional crossover in a real Ising-lik e magnetic system has been experimentally observed.