  We have synthesized a new ferromagnetic topological insulator by doping Cr to
the ternary topological-insulator material TlSbTe2. Single crystals of
Tl_{1-x}Cr_{x}SbTe2 were grown by a melting method and it was found that Cr can
be incorporated into the TlSbTe2 matrix only within the solubility limit of
about 1%. The Curie temperature \theta_c was found to increase with the Cr
content but remained relatively low, with the maximum value of about 4 K. The
easy axis was identified to be the c-axis and the saturation moment was 2.8
\mu_B (Bohr magneton) at 1.8 K. The in-plane resistivity of all the samples
studied showed metallic behavior with p-type carriers. Shubnikov-de Hass (SdH)
oscillations were observed in samples with the Cr-doping level of up to 0.76%.
We also tried to induce ferromagnetism in TlBiTe2 by doping Cr, but no
ferromagnetism was observed in Cr-doped TlBiTe2 crystals within the solubility
limit of Cr which turned out to be also about 1%.
