Unusual Field-Insensitive Phase Transition and Kondo Behavior in SmTi2Al20

Magnetization, electrical resistivity and specific heat measurements were performed on high-quality single crystalline SmTi2Al20 (residual resistivity ratio \sim 40) grown by Al self-flux method. A Kondo-like \log T dependence in the resistivity is observed below 50 K. We discovered a field-insensitive phase transition at T_{x} = 6.5 K and a field-insensitive heavy fermion behavior with the electronic specific heat coefficient \gamma = 150 mJ/(K2 mol). Specific heat analysis reveals that the ground state is a \Gamma_{8} quartet state and the Sm magnetic dipole moment m_{\text{Sm}} (\sim 0.5\mu_{\text{B}} at T \simeq 0) orders below T_{x} in spite of the field-insensitive behavior. Possible reasons for the field insensitiveness will be discussed.