mu SR magnetic properties of stoichiometric and under-stoichiometric PrP

Stoichiometric PrP has a crystal electric field (CEF) singlet ground state and no magnetic ordering down to 1 K. In contrast, non-stoichiometric PrP1- x (0.05 < x < 0.15) has been called an "induced-moment spin glass". In our samples of PrP and PrP0.9, the ZF muon spin relaxation rate increased smoot hly with cooling, giving no indication of spin freezing, in accord with sus ceptibility measurements on these samples. They are thus Van Vleck paramagn ets, not spin glasses. Good fits to the mu SR data could be obtained using strong-collision-dynamic Lorentzian Kubo-Toyabe relaxation in zero and long itudinal field. This means that in PrP1.0 and PrP0.9 each muon sees the ful l Lorentzian field distribution in the spin-dynamical regime. The results w ill be discussed in terms of a singlet ground-state CEF fluctuation model. Published by Elsevier Science B.V. All rights reserved.