  The intermediate-valence compound SmB6 is a well-known Kondo insulator, in
which hybridization of itinerant 5d electrons with localized 4f electrons leads
to a transition from metallic to insulating behavior at low temperatures.
Recent studies suggest that SmB6 is a topological insulator, with topological
metallic surface states emerging from a fully insulating hybridized bulk band
structure. Here we locally probe the bulk magnetic properties of pure and 0.5 %
Fe-doped SmB6 by muon spin rotation/relaxation methods. Below 6 K the Fe
impurity induces simultaneous changes in the bulk local magnetism and the
electrical conductivity. In the low-temperature insulating bulk state we
observe a temperature-independent dynamic relaxation rate indicative of
low-lying magnetic excitations driven primarily by quantum fluctuations.
