Antiferromagnetism, Ferromagnetism, and Phase Separation in the GMR System Sr_2-xLa_1+xMn₂O₇

Neutron and synchrotron X-ray powder diffraction techniques have been used to refine the crystal and magnetic structures of the n = 2 Ruddlesden−Popper (RP) system Sr 2 LaMn 2 O 7 . The sample is shown to be biphasic, although both phases are of the RP type and have similar structural parameters. The majority phase (81%) adopts a collinear antiferromagnetic structure below ∼210 K whereas the minority phase is ferromagnetically ordered below ∼125 K. The ordered magnetic moments lie in the xy plane in both phases. The behavior observed is discussed in terms of the interplay between structural and electronic factors. Comparison with data obtained previously by other workers leads to the conclusion that our results have some general significance in the study of n = 2 RP systems.