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

Abstract

The hydriding behaviour of the solid-solution series of compounds, U(Fe1−xNix)Al, has been investigated. In the parent pseudoternary compounds, as Ni is gradually substituted for Fe, the magnetic correlations grow. As a result, the magnetic properties change from exchange enhanced Pauli-paramagnetic and spin fluctuating (x=0), via weakly magnetic with no long range magnetic ordering down to 4 K (0<x≤0.3) to ferromagnetic (0.35≤x≤0.75) and eventually to antiferromagnetic for x≥0.9. The present hydriding report covers compositions up to the ferromagnetic regime. It is found that hydrogen absorption does not take place for x below ≅0.7. The lowest nickel containing composition, which forms a well defined hydride phase, viz., U(Fe0.3Ni0.7)Al, absorbs y=0.8 H atoms per formula unit. This matches exactly with the lower hydride phase of pure UNiAl. No other hydride phase is formed either above or below y=0.8. The magnetization studies show that U(Fe0.3Ni0.7)AlH0.8 has much higher values of the magnetic ordering temperature (TC), paramagnetic Curie temperature (θP) and the uranium magnetic moment, relative to the unhydrided composition. These findings are in consonance with the large increase in the 57Fe Mössbauer isomer-shift value, on hydriding. It is suggested that the electron charge transfer from H to the Fe 3d band (inferred from the Mössbauer studies) weakens the 5f–3d hybridization, thus enhancing the ferromagnetic correlations. The observed large increase in the a-axis cell parameter also implies a reduction in U–U hybridization, further justifying the observed increase in TC, θP and U moment values.