Strong Valence Fluctuation Effects in Sm$T{r}_2$Al${}_{20}$($Tr=$Ti, V, Cr)

We present a single crystal study of low temperature magnetism and transport in Sm$T{r}_2$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 $T_{\mathrm{N}}$ and induces the valence fluctuations and moreover field insensitive heavy fermion states.