Structure, magnetization and heat capacity of U(Ni0.85Co0.15)AlH2.1 system

Abstract The structural and magnetic properties of the intermetallic compound U(Ni 0.85 Co 0.15 )Al and its hydride have been studied by means of X-ray diffraction, magnetization and heat capacity measurements. Like the parent compound UNiAl, the Co-substituted U(Ni 0.85 Co 0.15 )Al forms a hydride with a composition U(Ni 0.85 Co 0.15 )AlH 2.1 . Structural studies show that the hydride retains the hexagonal structure of the parent compound, but with a shifting of transition metal atoms from 1b to 1a site of the unit cell. The magnetic susceptibility and heat capacity measurements indicate paramagnetic, spin fluctuation behavior at low temperatures in U(Ni 0.85 Co 0.15 )Al. In contrast the hydride, U(Ni 0.85 Co 0.15 )AlH 2.1 , is found to order antiferromagnetically at T N  ≅ 90 K. The electronic specific heat coefficient, γ , decreases from ∼237 mJ mol −1  K −2 in U(Ni 0.85 Co 0.15 )Al to ∼39 mJ mol −1  K −2 in U(Ni 0.85 Co 0.15 )AlH 2.1 , which implies a more localized U-5f derived band induced by hydrogenation.