Neutron diffraction and ac-susceptibility studies of U(Ni0.1Cu0.9)2Ge2

Polycrystalline samples of the solid solution U(${\mathrm{Ni}}_{0.1}$ ${\mathrm{Cu}}_{0.9}$ ${)}_2$ ${\mathrm{Ge}}_2$ have been investigated by neutron diffraction and ac susceptibility. This material exhibits the tetragonal ${\mathrm{ThCr}}_2$ ${\mathrm{Si}}_2$-type crystallographic structure. It orders ferromagnetically at ${\mathit{T}}_{\mathit{C}}$=115±5 K, undergoing another transition at ${\mathit{T}}_0$=100±5 K to a ferrimagnetic phase with a wave vector k=(0,0,2/3) and with (++-) stacking of ferromagnetic planes of uranium magnetic moments [(1.9±0.2)${\mathrm{\mu }}_{\mathit{B}}$ at 10 K] along the tetragonal axis. The magnetic properties of U(${\mathrm{Ni}}_{0.1}$ ${\mathrm{Cu}}_{0.9}$ ${)}_2$ ${\mathrm{Ge}}_2$ are discussed in reference to the tentative magnetic phase diagram (temperature versus composition) of the U(${\mathrm{Ni}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Cu}}_{\mathit{x}}$ ${)}_2$ ${\mathrm{Ge}}_2$ system.