Neutron diffraction refinement and characterization of (R = La, Pr, Nd, Gd)

From stoichiometric mixtures of analytical grade , or and , polycrystalline samples of four iron rare-earth germanates (R = La, Pr, Nd, Gd) have been prepared. They are monoclinic, S.G. (No 14) and Z = 4, isotypic with AlR. Results 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 (A) = 7.308(1), b (A) = 6.667(1), c (A) = 13.065(2), and for R = La to a (A) = 7.141(1), b (A) = 6.5903(7), c (A) = 12.833(2), and for R = Gd. Magnetic susceptibility measurements between 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, respectively. IR spectra up to are included and briefly discussed.

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