Strong Valence Fluctuation Effects in Sm$Tr_2$Al$_{20}$($Tr=$Ti, V, Cr)

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.