Abstract
Systematic magnetic and specific-heat studies of hydrides of ternary compounds on the basis of rare earths or actinides help to unravel different roles of f-states in these two classes of materials. In rare earths, the H absorption tends to suppress magnetism by weakening the exchange interaction mediated by conduction electrons.
Light actinides exhibit 5f band of variable width at the Fermi level and the hydrogenation makes magnetic features typically stronger. 5f band narrowing due to the volume expansion is responsible for this net tendency, but the effects of H bonding cannot be neglected.