The various phases in Sm 1−x Eu x B 6 are investigated based on magnetic susceptibility, resistivity, and Hall effect measurements. The end compounds are a Kondo insulator (SmB 6 ) and a polaronic ferromagnet (EuB 6 ). For x ≈ 0.2, the ground state undergoes a transition from a Kondo insulator to an antiferromagnetic (AF) insulator phase. Further doping induces a transition to an AF metal at x ≈ 0.4. The spin gap is reduced rapidly with the Eu substitution, while there is a charge gap up to x ≈ 0.4. The Hall effect indicates a dramatic decrease in the carrier density at low temperatures (T ) for the Kondo insulator regime, whereas, the carrier density is almost independent of T in the AF metallic phase.

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