An antiferromagnetic (AF) superlattice of $\mathrm{F}\mathrm{e}/\mathrm{C}\mathrm{r}(211)$ is used as a model system to study magnetic transitions in a finite-size geometry. With polarization neutron reflectometry the magnetic structure at the surface spin-flop transition and its evolution with field is determined. A domain wall created near the surface penetrates the superlattice with increasing field, splitting it into two antiphase, AF domains. After reaching the center the spin-flopped phase spreads throughout the superlattice. The experimental results are in substantial agreement with theoretical and numerical predictions.

• Received 7 May 2002

DOI:https://doi.org/10.1103/PhysRevLett.89.127203