Charge ordering and structural transitions in Pr0.5Sr0.41Ca0.09MnO3

The structural and magnetic transitions in Pr0.5Sr0.41Ca0.09MnO3 have been investigated by neutron diffraction and electron microscopy. Two structural transitions, Imma to I4/mcm and I4/mcm to Pmmn, are observed by decreasing the temperature. Two magnetic transitions, from a paramagnetic insulating to a ferromagnetic metallic and from a ferromagnetic metallic to an antifer romagnetic insulating states at T-C = 250 K and T-N = 180 K, respectively, are also observed. The structures of these three forms have been determined from neutron powder diffraction data. The first important result concerns the low temperature antiferromagnetic CE type and charge ordered structure, which has been refined in the Pmmn space group, without any constraint. Th is structure is completely long range ordered, with two Mn-sites, Mn3+ in t etragonally elongated octahedra, and Mn4+, off-centered in nearly regular o ctahedra. The second important point concerns the abrupt character of the s tructural transition from the I4/mcm to the Pmmn structure, without any app earance of incommensurability. The magnetic and transport properties of thi s compound are compared with those of Pr0.5Sr0.5MnO3. (C) 1998 Elsevier Sci ence B.V. All rights reserved.