GROUND-STATE OF ANTIFERROMAGNETIC SYSTEMS IN A MAGNETIC-FIELD AND IN THE PRESENCE OF SURFACES

We determine the ground state of semi-infinite uniaxial antiferromagne ts and films, in terms of a two-dimensional area-preserving map, where the surfaces are introduced as appropriate boundary conditions. For t he film, the ground state is calculated in a very rapid and accurate w ay for any value of N, the number of planes. For the semi-infinite sys tem, we show that the so-called surface spin-flop state does not exist , while a non-homogeneous ground state is found in the bulk spin-flop phase.