Inhomogeneous magnetic order in Th-doped UPt3 detected by μSR

We report on a mu SR study of U1-xThxPt3 (0 <= X <= 0.05) conducted to investigate the onset of "large-moment antiferromagnetism" (LMAF). At low Th content (x <= 0.002) magnetic ordering on the time scale of the mu SR experiment (10(-8)s) is not detected. For x = 0.005 a weak magnetic signal appears below T=2K, while for 0.006 <= x <= 0.05, spontaneous oscillations in the mu SR spectra signal the presence of the LMAF phase. Analysis of the mu SR spectra with a three-component depolarization function reveals that the magnetic phase transition is quite broad. The broadening may be the effect of disorder on the fluctuation spectrum of the small-moment antiferromagnetic state reported for UPt3 below T(N)similar to 6K. (c) 2005 Elsevier B.V. All rights reserved.