NOVEL MAGNETIC PHASE-TRANSITION BEHAVIOR IN SHORT-PERIOD EUTE/PBTE SUPERLATTICE

[EuTe(xi)/PbTe(eta)]n short period superlattices were grown by molecular beam epitaxy along the [111] growth direction, with xi denoting the number of monolayers of EuTe separated by eta monolayers of diamagnetic PbTe, and 2 less-than-or-equal-to xi less-than-or-equal-to 5 alternated with 6 less-than-or-equal-to eta less-than-or-equal-to 15. We find that superlattices with even xi numbers show antiferromagnetic phase transitions; those with odd xi show ferromagnetic phase transitions; while bulk EuTe is a simple two-sublattice antiferromagnet. The transition temperatures T(c) observed for these short period superlattices are all below or close to the bulk phase Neel temperature and T(c) increases as xi increases. An antiferromagnetic interlayer correlation along the direction perpendicular-to to the superlattice planes is found for superlattices with eta less-than-or-equal-to 12. In the paramagnetic regime, the Curie-Weiss law fits well for all superlattices. Positive paramagnetic Curie-Weiss temperatures theta are obtained for superlattices with odd xi numbers while negative theta are obtained for even xi.