Structure and magnetic studies on UNiAlD2.2

Heavy fermion itinerant antiferromagnetic UNiAl is one of the very few U-co ntaining compounds which absorbs H-2/D-2 without disproportionation. The pr esent neutron diffraction studies on UNiAlDy (y = 2.2) are directed towards resolving controversies with regard to the occupancy of Ni atoms and the a ssociated interstitial sites for (H/D) atoms, as well as the nature of magn etic ordering in the higher hydride phase with y greater than or equal to 2 . The fit to the neutron diffraction data is found to improve considerably if the Ni atoms originally lying in the U-atoms' plane in UNiAl get shifted to the Ni-Al atoms' plane in the deuteride. This is in agreement with an e arlier neutron diffraction report on a deuteride sample of similar composit ion [T. Yamamoto , J. Alloys Compd. 269, 162 (1998)] and our x-ray structur al studies on UNiAlH2.3 [P. Raj , Phys. Rev. B 63, 94414 (2001)], but diffe rs from those of Bordallo , [H. N. Bordallo , Physica B 276-278, 706 (2000) ] and of Kolomiets [A. V. Kolomiets , J. Appl. Phys. 87, 6815 (2000)]. Our values of the structural parameters including the D-site occupancies are br oadly in agreement with the results of Yamamoto The magnetization studies o n UNiAlD2.2 show a single antiferromagnetic transition with Neel temperatur e, T-N = 95 K. (C) 2001 American Institute of Physics.