MAGNETIC-ORDERING IN U2PD2IN AND U2PD2SN

The tetragonal intermetallic compounds U2Pd2In and U2Pd2Sn have been studied by means of magnetic susceptibility, magnetization, specific heat, electrical resistivity, and x-ray- and neutron-diffraction techniques. The compounds order antiferromagnetically at 36 and 41 K, respectively, and have enhanced electronic specific-heat coefficients gamma of 393 and 203 mJ/mol f.u. K2, respectively. At low temperature, the nearest-neighbor U-U spacing is along the c axis in both compounds, though in U2Pd2Sn the in-plane U-U distance is shorter at room temperature. This crossover is due to motion of the U atoms within the cell rather than anisotropy of the thermal contraction. It is now well established in several classes of (1:1:1) uranium ternary intermetallic compounds that the strong magnetic anisotropy is correlated with the direction of nearest-neighbor U-U links; the moments are almost invariably oriented perpendicular to such links. This is also the case for U2Pd2In and U2Pd2Sn, where the moments lie in the tetragonal basal plane in a canted arrangement along [110] and [11BAR0] directions. Of four such Shubnikov subgroups of P4/mbm, one is clearly preferred by the data. At 10 K, the magnetic moments extracted are (1.6 +/- 0.2)mu(B) and (2.0 +/- 0.1)mu(B) per U atom in U2Pd2In and U2Pd2Sn, respectively.