Nuclear and magnetic structure of U{sub 3}Ga{sub 2}Ge{sub 3}: A neutron powder diffraction study
- CEA-CEN, Saclay (France)
- Universitaet Wien (Austria); and others
The crystal structure of U{sub 3}Ga{sub 2}Ge{sub 3} has been investigated by means of neutron powder diffractometry in the range from 1.5 to 100 K. Full matrix full profile refinements of the nuclear structure at 100 K revealed a new structure type with almost fully ordered distribution of Ga and Ge atoms in the 8c sites of space group I4. The new U{sub 3}Ga{sub 2}Ge{sub 3} type is a low symmetry derivative of the ordered antitype-Cr{sub 5}B{sub 3} (I4/mcm), R{sub 1} = 0.032, R{sub F} = 0.030. From model refinements, eventual interstitial nonmetal occupation in the metal octahedra U{sub 1}Ge{sub 1}Ge{sub 2}Ga{sub 2} or U{sub 2}Ge{sub 2}Ga{sub 2} or in metal tetrahedra Ge{sub 2}Ga{sub 2} is ruled out. At temperatures lower than T{sub c} = 90 K uranium atoms order ferromagnetically as monitored by the intensity of the magnetic reflection {sup M}I{sub (011)}. Due to the observation of the {sup M}(011) reflection, the magnetic spin structure is consistent with the symmetry of the noncentrosymmetric space group I422. The lower symmetry invokes a splitting of the 4a sites of the parent Cr{sub 5}B{sub 3} type (I4/mcm) into two twofold uranium sites 2a and 2b of I422. Besides the uranium atoms in 8j ({mu}{sub U} = 2.57{mu}{sub B}), only the uranium atoms in 2a were found to carry a magnetic moment {mu}{sub U} = 2.45{mu}{sub B}. All moments are parallel to the crystallographic a axis. To comply with the symmetry of the Ge/Ga atoms, magnetic and nuclear structure have to be described in space group I4. The reliability values for :the 1.5 K diffractogram were: R{sub I} = 0.024, R{sub F} = 0.019, and R{sub mag} = 0.033.
- OSTI ID:
- 589023
- Journal Information:
- Journal of Solid State Chemistry, Vol. 131, Issue 1; Other Information: PBD: Jun 1997
- Country of Publication:
- United States
- Language:
- English
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