Abstract
The hydrogen storage compound LaNi5 is an exchange-enhanced Pauli paramagnet with susceptibility chi (LaNi5)=4.6*10-6 EMU g-1. Hydrogen absorption leads to a decrease of the susceptibility of chi (LaNi5H6.0)=1.3*10-6 EMU g-1. This decrease is usually covered by a strong irreversible increase of surface magnetism, where, through surface segregation and decomposition, superparamagnetic Ni precipitations are formed. The two effects explain the controversial results about the magnetic properties of the LaNi5 hydride. The implication of this decomposition on the cyclic lifetime is discussed.