Magnetotransport of compounds in the U–Ge system

Abstract

The recent more thorough reinvestigation of the U–Ge system has finally established the existence of five compounds with the chemical formulae U₅Ge₄, UGe, U₃Ge₅, UGe₂ and UGe₃. Here we add another compound UGe_2-x, existing in a homogeneity range of 0.30 < x > 0.35, and crystallizing in the defect tetragonal ThSi₂-type structure. This compound is a ferromagnet with T _c = 47 K. For all these compounds we have revised earlier measured magnetic properties and measured (often for the first time) the magnetotransport properties such as the electrical resistivity at 0T and in applied magnetic fields up to 8 T. We have found no superconducting properties for U₅Ge₄ down to 20 mK, which was claimed earlier. The most striking features found for both ferromagnets UGe_2-x (ThSi₂-type phase) and UGe₂ (ZrGa₂-type phase) are their temperature dependences of the magnetoresistivity (MR). At low temperatures the MRs for both these phases are large and positive which, above 10 and 15 K respectively, change sign to negative. The largest negative values of MR were found not at the corresponding T_c values but at the characteristic temperature T', which is an inflection point T _iof the ρ(T) curve; this is attributed to be a measure of the spin fluctuation temperature T_sf.