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 several experimental techniques, including x-ray and neutron diffraction, magnetic susceptibility, and Mossbauer spectroscopy measurements. All materials studied are single phase and crystallize in the hexagonal perovskite structure. Magnetic susceptibility studies reveal that, for R=La and Pr, the Fe ions order antiferromagnetically at about TN=190 K. Short range magnetic correlations are observed up to 250 K. For R=La and Pr, 57Fe Mossbauer studies reveal two inequivalent magnetic sextets below 190 K, with the area ratio 2:1. Above TN, one singlet is observed with an isomer shift value typical to Fe4+. For R=Y and Gd, the magnetization curves do not lend themselves to easy determination of the magnetic transition due to an extra magnetic phase which exists up to 350 K. This phase is a result of deficiency of oxygen. The 57Mossbauer spectra at 300 K indicate two superimposed singlet lines, and contain a small magnetic sextet. There is no indication that the R sublattice in RSr2Fe3O9 (R=Pr and Gd) orders magnetically down to 1.5 K