  We present a single crystal study of low temperature magnetism and transport
in Sm$Tr_2$Al$_{20}$ ($Tr =$ Ti, V and Cr). Strong valence fluctuation is
manifested as Kondo effects including a large Sommerfeld coefficient $\gamma$,
a weak temperature dependence of magnetic susceptibility and a $-\ln T$
dependent resistivity. All the systems order antiferromagnetically at $T_{\rm
N}=$ 6.4 K (Ti), 2.3 K (V) and 1.8 K (Cr). Systematic change in the
susceptibility, specific heat, and resistivity indicates that stronger $c$-$f$
hybridization in SmV$_2$Al$_{20}$ and SmCr$_2$Al$_{20}$ than in
SmTi$_2$Al$_{20}$ suppresses $T_{\rm N}$ and induces the valence fluctuations
and moreover field insensitive heavy fermion states.
