  SmB6 has been predicted and verified as a prototype of topological Kondo
insulators (TKIs). Here we report longitudinal magnetoresistance and Hall
coefficient measurements on co-sputtered nanocrystalline SmB6 films and try to
find possible signatures of their topological properties. The magnetoresistance
(MR) at 2 K is positive and linear (LPMR) at low field and becomes negative and
quadratic at higher field. While the negative part is known from the reduction
of the hybridization gap due to Zeeman splitting, the positive dependence is
similar to what has been observed in other topological insulators (TI). We
conclude that the LPMR is a characteristic feature of TI and is related to the
linear dispersion near the Dirac cone. The Hall resistance shows a sign change
around 50 K. It peaks and becomes nonlinear at around 10 K then decreases below
10 K. This indicates that carriers with opposite signs emerge below 50 K. Two
films with different geometries (thickness and lateral dimension) show
contrasting behavior below and above 50K, which proves the surface origin of
the low temperature carriers in these films. The temperature dependence of
magnetoresistance and the Hall data indicates that the surface states are
likely non-trivial.
