| dc.description |
The heavy-fermion compound UCu<sub>5</sub>Sn has been studied by means of neutron powder diffraction. This compound exhibits the hexagonal CeNi<sub>5</sub>Sn-type structure with space group P6<sub>3</sub>/mmc. We have determined the lattice parameters and atomic positions at room temperature, using a high-resolution diffractometer. The neutron diffraction diagrams were also measured at various temperatures between 1.4 and 61 K, using an 800-cell position-sensitive diffractometer. The observed minimum in the unit-cell volume at temperature of 30 K, being rather far below the magnetic ordering one (T<sub>C</sub> = 53 K), may suggest a change in the strength of the 5f-conduction electron hybridization which probably takes place at low temperatures. It was found that the magnetic phase transition at T<sub>C</sub> corresponds to the onset of a ferrimagnetic order. The magnetic structure is characterized by forming the ferromagnetic planes (001) with the (+ - + -) stacking sequence, where the U moments are oriented parallel to the hexagonal c-axis. However, the size of the U moments arranged in the z = 0 plane (M<sub>U1</sub>), and formed by the sites 2(a), is substantially larger than these arranged in the adjacent z = ¼ plane (M<sub>U2</sub>), and formed by the sites 2(c). At 1.4 K, they are M<sub>U1</sub> = 2.14(2) µ<sub>B</sub>/atom U and M<sub>U2</sub> = 0.18(4) µ<sub>B</sub>/atom U. We discuss several mechanisms leading to a reduction of the magnetic moment at the one site compared to the other one. |
