부산대학교 도서관

RFeGe{sub 2}O{sub 7} (R = Ho, Er) have been prepared in polycrystalline form, and their crystal structures have been refined from room-temperature high-resolution neutron diffraction data by the Rietveld method. Both materials are isostructural, space group P2{sup 1}/m (no. 11), Z = 4. The most interesting feature of the structure is the existence of flattened chains of RO{sub 7} polyhedra along the b axis, which linked in the c direction through pairs of FeO{sub 6} octahedra form layers parallel to the bc crystal plane. Magnetic susceptibility measurements between 350 and 1.7 K reveal the existence of two anomalies for both compounds, at T{sub 1} and T{sub 2}, (T{sub 2} < T{sub 1}), 39 and 12 K, 40 and 8 K, for R = Ho and Er, respectively. From low-temperature neutron diffraction data, three-dimensional antiferromagnetic ordering in both compounds is established, with a simultaneous setting up of the order for R{sup 3+} and Fe{sup 3+} sublattices at T{sub N} = T{sub 1}. The propagation vector of the magnetic structure is k = [0, 0, 0]. In each case the magnetic structure consists of a ferromagnetic arrangement of all R{sup 3+} and Fe{sup 3+} magnetic moments within one ac plane, whereas the corresponding moments in up and down adjacent planes are oppositely aligned, leading to 3D AF coupling along the b direction. Kramers doublets splitting in the region of the {sup 4}I{sub 15/2}{r{underscore}arrow}{sup 4}I{sub 13/2} optical transitions of the Er compound have been observed in high-resolution optical absorption spectra. From these spectral measurements the temperature found for the magnetic ordering coincides with that T{sub N} determined by neutron diffraction data. Moreover optical data also show that T{sub 2} in {chi}{sub m}(T) does not correspond to any phase transition but it is most probably caused by the population changes within the ground Er{sup 3+} Kramers doublet split by the exchange interaction with the ordered Fe{sup 3+} subsystem.