New limits on the ordered moments in α-Pu and Ga-stabilized δ-Pu

We present the first μSR measurements ever performed on elemental Pu, and set the most stringent upper limits to date on the magnitude of the ordered moment μord in α-Pu and δ-stabilized Pu (alloyed with 4.3 at% Ga). Assuming a nominal hyperfine coupling field of 1 kOe/μB we find μord⩽10-3μB at T ≅4K.