Magnetic fluctuations in frustrated Laves hydrides R ( Mn 1 − x Al x ) 2 H y ( R = Y , Tb )

By neutron scattering, we have studied the spin correlations and spin fluctuations in frustrated Laves hydrides, where magnetic disorder sets in the topologically frustrated Mn lattice. Below the transition towards short-range magnetic order, static spin clusters coexist with fluctuating and almost uncorrelated spins. The magnetic response shows a complex line shape, connected with the presence of the magnetic inhomogeneities. Its analysis shows the existence of two different processes, relaxation and local excitations, for the spin fluctuations below the transition.