The hydriding behaviour of U(Fe1-xNix)Al system (0 <= x <= 0.75) and magnetic studies on U(Fe1-xNix)AlH0.8

The hydriding behaviour of the solid-solution series of compounds, U(Fe1-xN ix)Al, has been investigated. In the parent pseudoternary compounds, as Ni is gradually substituted for Fe, the magnetic correlations grow. As a resul t, the magnetic properties change from exchange enhanced Pauli-paramagnetic and spin fluctuating (x=0), via weakly magnetic with no long range magneti c ordering down to 4 K (0<x less than or equal to 0.3) to ferromagnetic (0. 35 less than or equal to x less than or equal to 0.75) and eventually to an tiferromagnetic for x greater than or equal to 0.9. The present hydriding r eport covers compositions up to the ferromagnetic regime. It is found that hydrogen absorption does not take place for x below congruent to 0.7. The l owest nickel containing composition, which forms a well defined hydride pha se, viz., U(Fe0.3Ni0.7)Al, absorbs y=0.8 H atoms per formula unit. This mat ches exactly with the lower hydride phase of pure UNiAl. No other hydride p hase is formed either above or below y=0.8. The magnetization studies show that U(Fe0.3Ni0.7)AIH(0.8) has much higher values of the magnetic ordering temperature (T-C), paramagnetic Curie temperature (theta(p)) and the uraniu m magnetic moment, relative to the unhydrided composition. These findings a re in consonance with the large increase in the Fe-57 Mossbauer isomer-shif t value, on hydriding. It is suggested that the electron charge transfer fr om H to the Fe 3d band (inferred from the Mossbauer studies) weakens the 5f -3d hybridization, thus enhancing the ferromagnetic correlations. The obser ved large increase in the a-axis cell parameter also implies a reduction in U-U hybridization, further justifying the observed increase in T-C, theta( p) and U moment values. (C) 2000 Published by Elsevier Science S.A. All rig hts reserved.