The hydriding behaviour of U(Fe_(1-x)Ni_x)Al system (0<=x<=0.75) and magnetic studies on U(Fe_(1- x)Ni_x)AlH_(0.8)

摘要

The hydriding behaviour of the solid-solution seriesof compounds, U(Fe_(1-x)Ni_x)Al, has been investigated. In theparent pseudoternary compounds, as Ni is gradually substituted forFe, the magnetic correlations grow. As a result, the magneticproperties change from exchange enhanced Pauli-paramagnetic andspin fluctuating (x=0), via weakly magnetic with no long rangemagnetic ordering down to 4 K (0=0.9.The present hydriding report covers compositions up to theferromagnetic regime. It is found that hydrogen absorption doesnot take place for x below ? 0.7. The lowest nickel containingcomposition, which forms a well defined hydride phase, viz.,U(Fe_(0.3)Ni_(0.7))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. Themagnetization studies show that U(Fe_(0.3)Ni_(0.7))A1H_(0.8)has much higher values of the magnetic ordering temperature(T_C), paramagnetic Curie temperature (#theta#_p) and theuranium magnetic moment, relative to the unhydrided composition.These findings are in consonance with the large increase in the~(57)Fe M?ssbauer isomer-shift value, on hydriding. It issuggested that the electron charge transfer from H to the Fe 3dband (inferred from the M?ssbauer studies) weakens the 5f-3dhybridization, thus enhancing the ferromagnetic correlations. Theobserved large increase in the a-axis cell parameter also implies areduction in U-U hybridization, further justifying the observedincrease in T_C, #theta#_p and U moment values.