Magnetic structures of the ternary stannide U2(Ni0.70Pd0.30)2Sn

The Neel temperature T-N in the tetragonal (P4/mbm space group) antiferromagnetic U-2(Ni1-xPdx)(2)Sn solid solution exhibits a minimum (T-N=12(1) K) at x approximate to 0.30-0.35; the end values being respectively equal to T-N=25 K (x=0) and T-N=42 K (x=1). In order to understand this T-N vs. x dependence, we have investigated the U-2(Ni0.70Pd0.30)(2)Sn stannide by neutron powder diffraction. This alloy exhibits two magnetic transitions, at T-N=11.5(5) K and T-N'=8.0(5) K. Between T-N' and T-N, the magnetic peaks are associated to k=(001/2) propagation vector; below T-N', two propagation vectors are present, k=(0 0 1/2) and k'=(1/21/21/2), which are associated to different volumes of the sample. We discuss this complex magnetic behaviour, in connection with the U2Ni2Sn (k=(0 0 1/2)) and U2Pd2Sn (k"=(0 0 0)) magnetic structures. (C) 1998 Elsevier Science S.A.