Reentrant spin-glass behavior in $TlFe_{2-x}Se_2$ with the $ThCr_2Si_2$-type structure

We investigated the physical properties of $TlFe_{2-x}Se_2$ single crystals. The resistivity of $TlFe_{2-x}Se_2$ shows typical semiconductor behavior with an activation energy of 25 meV. DC susceptibility indicates an antiferromagnetic transition at about 450 K. Reentrant spin-glass (RSG) behavior was found at about 130 K through DC and AC magnetic measurements. The RSG behavior suggests the existence of a strong competition between ferromagnetic (FM) and antiferromagnetic (AFM) interactions due to Fe deficiencies. Strong electron-electron correlation may exist in this material and it is possibly a candidate of parent compound for high $T_c$ superconductors.