The search for magnetic order in δ-Pu metal using muon spin relaxation

We review results from previous muon spin relaxation (mu SR) measurements in applied fields of H-0 = 0 and 0.25 T which established an upper limit for the ordered or disordered frozen spin moment above T = 4 K in delta-Pu (4.3 at.% Ga) of mu(ord) <= 10(-3) mu(B). In addition, we present new data in H-0 = 0.25 and 2 T applied field on a highly annealed delta-Pu (4.3 at.% Ga) sample. Neither the muon Knight shift (H-0 = 2 T) nor the inhomogeneous linewidths in the new sample show appreciable temperature dependence below about T = 60 K, also consistent with no spin freezing. Recent theoretical arguments advanced to explain these results are mentioned. (C) 2006 Elsevier B.V. All rights reserved.