Structural and magnetic properties of RSr2Fe3O9 (R = La, Y, Pr, and Gd)

We have investigated the RSr2Fe3O9 (R=La, Y, Pr, and Gd) materials by sever al experimental techniques, including x-ray and neutron diffraction, magnet ic susceptibility, and Mossbauer spectroscopy measurements. All materials s tudied are single phase and crystallize in the hexagonal perovskite structu re. Magnetic susceptibility studies reveal that, for R=La and Pr, the Fe io ns order antiferromagnetically at about T-N =190 K. Short range magnetic co rrelations are observed up to 250 K. For R = La and Pr, Fe-57 Mossbauer stu dies reveal two inequivalent magnetic sextets below 190 K, with the area ra tio 2:1. Above T-N, one singlet is observed with an isomer shift value typi cal to Fe4+ For R = Y and Gd, the magnetization curves do not lend themselv es to easy determination of the magnetic transition due to an extra magneti c phase which exists up to 350 K. This phase is a result of deficiency of o xygen. The (57)Mossbauer spectra at 300 K indicate two superimposed singlet lines, and contain a small magnetic sextet. There is no indication that th e R sublattice in RSr2Fe3O9 (R=Pr and Gd) orders magnetically down to 1.5 K . (C) 1998 American Institute of Physics.