  We report low-temperature muon spin relaxation/rotation (muSR) measurements
on single crystals of the actinide superconductor UTe2. Below 5 K we observe a
continuous slowing down of magnetic fluctuations that persists through the
superconducting (SC) transition temperature (Tc = 1.6 K), but we find no
evidence of long-range or local magnetic order down to 0.025 K. The temperature
dependence of the dynamic relaxation rate down to 0.4 K agrees with the
self-consistent renormalization theory of spin fluctuations for a
three-dimensional weak itinerant ferromagnetic metal. Our muSR measurements
also indicate that the superconductivity coexists with the magnetic
fluctuations.
