NEUTRON-DIFFRACTION REFINEMENT AND CHARACTERIZATION OF FERGE(2)O(7) (R=LA, PR, ND, GD)

From stoichiometric mixtures of analytical grade Fe3O4, R(2)O(3) or Pr 6O11 and GeO2, polycrystalline samples of four iron rare-earth germana tes FeRGe(2)O(7) (R = La, Pr, Nd, Gd) have been prepared. They are mon oclinic, S.G. P2(1)/c (No 14) and Z = 4, isotypic with AlRGe(2)O(7). R esults of the refinements from neutron (R = La, Pr) powder diffraction data by the Rietveld method of profile analysis as well as x-ray (R = Nd, Gd) powder diffraction data are given. The four x-ray diffraction powder patterns are included together with lattice dimensions, which decrease from a (Angstrom) = 7.308(1), b (Angstrom) = 6.667(1), c (Ang strom) = 13.065(2), beta (degrees) = 117.18(1) and V (Angstrom(3)) = 5 66.3(1) for R = La to a (Angstrom) = 7.141(1), b (Angstrom) = 6.5903(7 ), c (Angstrom) = 12.833(2), beta (degrees) = 117.08(2) and V (Angstro m(3))= 537.73(9) for R = Gd. Magnetic susceptibility measurements betw een 350 and 1.7 K confirm the existence of antiferro-magnetic ordering and Neel temperatures of 4.3, 3.7 and 5.8 K for R = Pr, Nd and Gd, re spectively. IR spectra up to 100 cm(-1) are included and briefly discu ssed.